Defence Standard 02-0617

Design Guide and Requirements for Equipment to Achieve a Low Magnetic

Signature

Ministry of Defence Defence Standard 02-617

Issue 3 Publication Date 11 October 2004

Category 2

AMENDMENTS ISSUED SINCE PUBLICATION

AMD NO DATE OF ISSUE

TEXT AFFECTED SIGNATURE & DATE

Revision Note The Issue of this Standard has been prepared to reflect the change from Interim to Extant Standard and to reflect minor changes to text and presentation. Historical Record DEF STAN 07-242 Issue 2 11 May 2001 DEF STAN 07-242 Issue 1 1 April 2000 DEF STAN 02-617 Issue 1 1 April 2000 NES 617 Issue 3 July 1989 NES 617 Issue 2 December 1988 NES 617 Issue 1 May 1983

1

DEFENCE STANDARD 02–617 (NES 617)

DESIGN GUIDE AND REQUIREMENTS FOR EQUIPMENT

TO ACHIEVE A LOW MAGNETIC SIGNATURE

ISSUE 3

This Defence Standard is

authorized for use in MOD contracts

by the Defence Procurement Agency and

the Defence Logistics Organisation

Published by:

Defence Procurement AgencyAn Executive Agency of The Ministry of DefenceUK Defence StandardizationKentigern House65 Brown StreetGlasgow G2 8EX

DEF STAN 02–617 / ISSUE 3

2

SCOPE

1. This Defence Standard (DEF STAN) provides guidance for designers and suppliers of LowMagnetic Signature equipment, Mine Countermeasures Vessels (MCMV). It includes specificrequirements for the HUNT and Single Role Minehunter (SRMH).

2. The guidance and requirements cover magnetic fields due to ferromagnetic, eddy current and straymagnetic field sources. A general syetem description is given in Clauses 4.1.1a to 4.1.1f whichoutlines the system design principles.

3. The ferromagnetic design guide and requirements contain practical working rules which must beused only as a guide. The verification processes for equipment acceptance are described.

FOREWORD

Sponsorship

4. This Defence Standard is sponsored by the WSA, MLSIPT, Defence Logistics Organisation(DLO), Ministry of Defence (MOD).

5. Any user of this Standard either within MOD or in industry may propose an amendment to it.Proposals for amendments that are not directly applicable to a particular contract are to be madeto the publishing authority identified on Page 1, and those directly applicable to a particularcontract are to be dealt with using existing departmental procedures.

6. If it is found to be unsuitable for any particular requirement, MOD is to be informed in writingof the circumstances.

7. No alteration is to be made to this Standard except by the issue of an authorized amendment.

8. Unless otherwise stated, reference in this Standard to approval, approved, authorized and similarterms means by the MOD in writing.

9. Any significant amendments that may be made to this Standard at a later date will be indicatedby a vertical sideline. Deletions will be indicated by 000 appearing at the end of the line interval.

10. Extracts from British Standards quoted within this Standard have been included with thepermission of the British Standards Institution.

11. This Standard has been reissued at Issue 3, dated October 2004 to reflect the status changes fromInterim to Extant and to reflect the minor editorial changes.

Conditions of Release

General

12. This Standard has been devised solely for the use of the MOD, and its contractors in the executionof contracts for the MOD. To the extent permitted by law, the MOD hereby excludes all liabilitywhatsoever and howsoever arising (including but without limitation, liability resulting fromnegligence) for any loss or damage however caused when the Standard is used for any otherpurpose.

13. This document is Crown Copyright and the information herein may be subject to Crown or thirdparty rights. It is not to be released, reproduced or published without written permission of theMOD.

14. The Crown reserves the right to amend or modify the contents of this Standard without consultingor informing any holder.


3

MOD Tender or Contract Process

15. This Standard is the property of the Crown. Unless otherwise authorized in writing by the MODit must be returned on completion of the contract, or submission of the tender, in connection withwhich it is issued.

16. When this Standard is used in connection with a MOD tender or contract, the user is to ensure thathe is in possession of the appropriate version of each document, including related documents,relevant to each particular tender or contract. Enquiries in this connection may be made to theauthority named in the tender or contract.

17. When Defence Standards are incorporated into MOD contracts, users are responsible for theircorrect application and for complying with contractual and any other statutory requirements.Compliance with an Defence Standard does not of itself confer immunity from legal obligations.

Categories of Defence Standard

18. The Category of this Standard has been determined using the following criteria:

a. Category 1. If not applied may have a Critical affect on the following:

Safety of the vessel, its complement or third parties.

Operational performance of the vessel, its systems or equipment.

b. Category 2. If not applied may have a Significant affect on the following:

Safety of the vessel, its complement or third parties.

Operational performance of the vessel, its systems or equipment.

Through life costs and support.

c. Category 3. If not applied may have a Minor affect on the following:

MOD best practice and fleet commonality.

Corporate Experience and Knowledge.

Current support practice.

Related Documents

19. In the tender and procurement processes the related documents listed in each section and AnnexA can be obtained as follows:

a. British Standards British Standards Institution,389 Chiswick High Road,London, W4 4AL.

b. Defence Standards Defence Procurement Agency,An Executive Agency of the Ministry of Defence,UK Defence Standardization,Kentigern House,65 Brown Street,Glasgow, G2 8EX.

c. Other documents Tender or Contract Sponsor to advise.

20. All applications to Ministry Establishments for related documents are to quote the relevant MODInvitation to Tender or Contract number and date, together with the sponsoring Directorate andthe Tender or Contract Sponsor.

21. Prime Contractors are responsible for supplying their subcontractors with relevantdocumentation, including specifications, standards and drawings.


4

Health and Safety

Warning

22. This Standard may call for the use of processes, substances and/or procedures that may be injuriousto health if adequate precautions are not taken. It refers only to technical suitability and in no wayabsolves either the supplier or the user from statutory obligations relating to health and safety atany stage of manufacture or use. Where attention is drawn to hazards, those quoted may notnecessarily be exhaustive.

23. This Standard has been written, and is to be used, taking into account the policy stipulated inJSP 430: MOD Ship Safety Management System Handbook.

Additional Information

Terminology

24. The terminology used in this Defence Standard follows the NATO convention for magneticsilencing defined in NATO document AMP–14. Terms and Symbols used in this Standard aredefined in Annex B.

System of Units

25. The system of units used in this specification is the International System of Units (SI) complyingwith BS 5555 with the Sommerfeld convention for magnetic measurements. This system is theNATO standard in degaussing and magnetic silencing.

26. For consistency with DEF STAN 02–617 Issue 3, imperial units have been retained for certainHUNT design parameters.


5

CONTENTS

Page No

TITLE PAGE 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SCOPE 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

FOREWORD 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Sponsorship 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Conditions of Release 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Categories of Defence Standards 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Related Documents 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Health and Safety 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Additional Information 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

CONTENTS 5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SECTION 1. PERFORMANCE SPECIFICATION 10. . . . . . . . . . . . . . . . . . 1.1 Verification 10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Table 1 Verification Stages 10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 System Validation 10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SECTION 2. NATIONAL/INTERNATIONAL REGULATIONS 10. . . . . . .

SECTION 3. MILITARY STANDARDS/REQUIREMENTS 10. . . . . . . . . . .

SECTION 4. DESIGN REQUIREMENTS/GUIDANCE 11. . . . . . . . . . . . . . 4.1 General System Description 11. . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.1 Introduction 11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.2 Magnetic Signature Requirement 11. . . . . . . . . . . . . . . . . . . . . . 4.1.3 Magnetic Signature Apportionment 12. . . . . . . . . . . . . . . . . . . . 4.1.3.1 General 12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.3.2 Ferromagnetic Field 12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.3.3 Eddy Current Field 13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.3.4 Stray Field 13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2 Magnetic Signature Control 13. . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.1 General 13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.2 Contractor’s Average Relative Permeability Checks 14. . . . . . 4.2.3 Contractor’s Magnetic Field Measurements 14. . . . . . . . . . . . . 4.2.4 Magnetic Land Ranging 14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.5 Position and Orientation on the Vessel of

Equipment Containing Magnetic Sources 14. . . . . . . . . . . . . . . 4.2.6 Magnetic Sea Ranging 14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.7 Magnetic Signature Tracking 15. . . . . . . . . . . . . . . . . . . . . . . . . 4.3 Extra Low Frequency Electromagnetic and

Underwater Electric Potential Fields 15. . . . . . . . . . . . . . . . . . .


6

Page No4.4 Design Guide 15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.1 Introduction 15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5 Design Guide – Ferromagnetic Field Source 16. . . . . . . . . . . . . . 4.5.1 General 16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5.2 Materials having an Electromagnetic Function 16. . . . . . . . . . . 4.5.3 Materials Requiring Mechanical Strength 16. . . . . . . . . . . . . . . . 4.5.4 Materials where there is no Practicable Alternative 16. . . . . . . . 4.6 Design Guide – Eddy Current Field Sources 17. . . . . . . . . . . . . . 4.7 Design Guide – Stray Field Sources 17. . . . . . . . . . . . . . . . . . . . . 4.7.1 General 17. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.7.2 Detailed Principles 17. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.7.3 Stray Field Design Guide for the Arrangement of Cables 18. . . 4.7.4 Stray Field Design Guide for the Arrangement of Batteries 18. 4.7.5 Stray Field Design Guide for Motor Generators 18. . . . . . . . . . . 4.7.6 Stray Field Design Guide for Induction Clutches 18. . . . . . . . . . 4.7.7 Stray Field Design Guide for Solenoid and Resistors 18. . . . . . . 4.7.8 Stray Field Design Guide for Switch and Contactor Panels 18. 4.8 Design Guide – Working, Handling, Stowage, Packaging

and Transport of Materials 19. . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.8.1 General Principles 19. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.8.2 Detailed Principles and Guidelines – Magnetic Fields 19. . . . . . 4.8.3 Detailed Principles and Guidelines – Mechanical Stress 20. . . 4.8.4 Detailed Principles and Guidelines – Temperature 21. . . . . . . . 4.9 Detailed Principles and Guidelines – Contamination 21. . . . . . 4.10 Design Guides – Compensation Methods 22. . . . . . . . . . . . . . . . 4.11 Design Requirements for HUNT and SRMH 22. . . . . . . . . . . . 4.11.1 Introduction 22. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.12 Design Requirement – Ferromagnetic Field Sources 22. . . . . . 4.12.1 General 22. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.12.2 To Calculate Average Relative Magnetic Permeability 23. . . . . Figure 1 Relationship between Materials with Permeabilities of less

than 2.5, their Volume and Magnetic Field Factor. (SRMH) 25Figure 2 Relationship between materials with Permeabilities less

than 1.4 (Volume 0.1 cubic feet to 1000 cubic feet) and Magnetic Field Factor (HUNT) 26. . . . . . . . . . . . . . . . . . . .

Figure 3 Relationship between material with Permeabilities less than 2.5 (Volume 0.1 cubic feet to 10 cubic feet) and Magnetic Field Factor (HUNT) 27. . . . . . . . . . . . . . . . . . . .

Figure 4 Relationship between Materials with Permeabilities of 2.5 and above, their Volume and Magnetic Field Factor (SRMH) 28. . . . . . . . . . . . . . . . . . . . . . .

Figure 5 Relationship between Materials with Permeabilities of 2.5 and above (Volume 0.001 cubic feet to 10 cubic feet) and Magnetic Field Factor (HUNT) 29. . . . . . . . . . . . . . . . . . . . . . . .

4.13 Design Requirements – Eddy Current Field Sources 30. . . . . . 4.13.1 General 30. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Table 2 Equivalent Values, Conductivity and Resistivity 30. . . . . . . . . . 4.13.2 Sheet Materials (Figures 6 and 7) 30. . . . . . . . . . . . . . . . . . . . . .


7

Page NoTable 3 Sheet Material – Conductivity Calculation 31. . . . . . . . . . . . . . Table 4 Frames and Pipes – Conductivity Calculation 31. . . . . . . . . . . 4.13.3 Frames and Pipes (Figures 8 and 9) 31. . . . . . . . . . . . . . . . . . . . Figure 6 Relationship between Area, Thickness and Conductivity

of Sheet Material (SRMH). 32. . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 7 Relationship between Area, Thickness and Conductivity

of Sheet Material (HUNT) 33. . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 8 Relationship between Area, Cross Section and Conductivity

of any Frame or Pipe (SRMH) 34. . . . . . . . . . . . . . . . . . . . . . . . 4.14 Design Requirements – Stray Field Sources 35. . . . . . . . . . . . . Figure 9 Relationship between Area, Cross Section and Conductivity

of any Frame or Pipe (HUNT) 35. . . . . . . . . . . . . . . . . . . . . . . . 4.15 Sources of Guidance 35. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SECTION 5. CORPORATE KNOWLEDGE AND EXPERIENCE 36. . . . . .

ANNEX A. RELATED DOCUMENTS A.1. . . . . . . . . . . . . . . . . . . . . . . . . . . .

ANNEX B. ABBREVIATIONS AND DEFINITIONS B.1. . . . . . . . . . . . . . . .

ANNEX C. PROCUREMENT CHECK LIST C.1. . . . . . . . . . . . . . . . . . . . . . .

ANNEX D. AVERAGE RELATIVE MAGNETIC PERMEABILITY D.1. . D.1 Introduction D.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D.2 Definition D.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure D1 Plot showing Induced Magnetic Moment D.2. . . . . . . . . . . . . . . . D.3 Assumptions and Approximations D.4. . . . . . . . . . . . . . . . . . . . . D.4 Relationship Between Average Magnetic Permeability, Land

Range Measurements and Ship’s Magnetic Signatures D.4. . . . Figure D2 Relationship Between Magnetic Dipole Moment and

Magnetic Flux Density D.5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ANNEX E. AVERAGE RELATIVE MAGNETIC PERMEABILITY E.1. . E.1 General E.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E.2 When to Measure Relative Magnetic Permeability E.1. . . . . . . . E.3 Measuring Relative Magnetic Permeability E.1. . . . . . . . . . . . . . E.4 Measuring Relative Magnetic Permeability –

Comments and Problems E.2. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ANNEX F. CALCULATION OF AVERAGE MAGNETIC PERMEABILITY (HUNT) F.1. . . . . . . . . . . . . . . . . . . . . . . . . . .

F.1 Example 1 F.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F.2 Example 2 F.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ANNEX G. CALCULATION OF AVERAGE MAGNETIC PERMEABILITY (SRMH) G.1. . . . . . . . . . . . . . . . . . . . . . . . . . .

G.1 Example 1 G.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G.2 Example 2 G.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .


8

Page No

ANNEX H. STRAY FIELD – GUIDE FOR THE ARRANGEMENT OF CABLES H.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

H.1 Direct Current Power Cables H.1. . . . . . . . . . . . . . . . . . . . . . . . . . H.1.1 Four Conductor Quadded Cables H.1. . . . . . . . . . . . . . . . . . . . . . . H.1.2 Double Conductor Cables H.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . H.1.3 Single Conductor Cables H.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . H.2 Alternating Current Power Cables H.2. . . . . . . . . . . . . . . . . . . . . . H.2.1 Phase Conductors in a Common Core H.2. . . . . . . . . . . . . . . . . . . H.2.2 Phase Conductors in a Separate Cables H.2. . . . . . . . . . . . . . . . . . H.3 Cable Terminal Connections H.2. . . . . . . . . . . . . . . . . . . . . . . . . . . H.3.1 Compatibility of Cable Runs and Terminals H.2. . . . . . . . . . . . . . H.3.2 Arrangement of Terminals and Approach by Cable Run H.2. . . H.3.3 Three Terminal Arrangements H.2. . . . . . . . . . . . . . . . . . . . . . . . . H.3.4 Connecting Four Single Conductor Cables

to Three Terminals H.2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . H.3.5 Connecting Eight Single Conductor Cables

to Three Terminals H.2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . H.3.6 Connecting Six Single Conductor Cables

to Three Terminals H.2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure H1 Arrangement of Single Conductor dc Cables

for Opposing Current Loops H.3. . . . . . . . . . . . . . . . . . . . . . . . . . . Figure H2 Unequal Current Division Among Cables

Connected in Parallel H.4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure H3 Edgewise and Flat Three Terminal Arrangements H.5. . . . . . . . . Figure H4 Connection of an Endways Cable Run with Four Cables

to Edgewise Terminals H.6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure H5 Connection of a Crossways Cable Run with Four Cables

to Edgewise Terminals H.7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure H6 Connection of Endways Cable Run with Four Cables

to Flat Terminals H.8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure H7 Connection of a Crossways Cable Run with Four Cables

to Flat Terminals H.9. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure H8 Connection to an Endways Cable Run with Eight Cables

to Flat Terminals H.9. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure H9 Connection to a Crossways Cable Run with Eight Cables

to Flat Terminals H.10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure H10 Connection to a Sideways Cable Run with Eight Cables

to Flat Terminals H.10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure H11 Connection to an Endways and Crossways Cable Run

with Six Cables H.11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ANNEX I. STRAY FIELD – GUIDE FOR THE ARRANGEMENT OF BATTERIES I.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

I.1 Definitions and General Principles I.1. . . . . . . . . . . . . . . . . . . . . I.2 Series and Parallel Compensation I.1. . . . . . . . . . . . . . . . . . . . . I.3 Positioning of Battery Connecting Bus Bars I.1. . . . . . . . . . . . . I.4 Positioning of Connecting Bus Bars I.1. . . . . . . . . . . . . . . . . . . . I.5 Preferred Storage Battery Arrangements I.1. . . . . . . . . . . . . . . I.6 Battery Arrangement Warning Plates I.1. . . . . . . . . . . . . . . . . .


9

Page No

ANNEX J. STRAY FIELD – GUIDE FOR MOTORS AND GENERATORS J.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

J.1 Frame Design J.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J.1.1 Frame Type J.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J.1.2 Frame Material J.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J.1.3 Frame Outside Shape J.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J.1.4 Current Carrying Leads J.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . J.2 Poles J.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J.2.1 Number of Poles J.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J.2.2 Orientation of Field poles J.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . J.2.3 Magnetic Contact J.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J.3 Symmetry and Uniformity J.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . J.3.1 Air Gaps J.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J.3.2 Commutating Poles (Interpoles) J.2. . . . . . . . . . . . . . . . . . . . . . . J.3.3 Number of Turns J.2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J.3.4 Equalizer Connections J.2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J.4 Wiring Around the Frame J.2. . . . . . . . . . . . . . . . . . . . . . . . . . . . J.4.1 Field Coils J.2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J.4.2 Commutating Coils and Compensating Windings J.2. . . . . . . . J.5 Brush Collector Rings J.2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J.5.1 Construction J.2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J.5.2 Arrangement J.2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J.5.3 Current Take–off Point J.2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J.5.4 Connections from Brush Collector Rings J.3. . . . . . . . . . . . . . . . J.5.5 Position of Brush Collector Rings J.3. . . . . . . . . . . . . . . . . . . . . . J.5.6 Brush Rigging J.3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J.5.7 Number of Commutator Bars J.3. . . . . . . . . . . . . . . . . . . . . . . . . J.5.8 Double Armature Machines J.3. . . . . . . . . . . . . . . . . . . . . . . . . .

ANNEX K. STRAY FIELD – GUIDE FOR INDUCTION CLUTCHES K.1K.1 Field Pole Requirements K.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . K.2 Field Coil Requirements K.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . K.3 Number of Field Poles K.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ANNEX L. STRAY FIELD – GUIDE FOR SWITCH AND CONTACTOR PANELS L.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

L.1 Basic Conductor Arrangement L.1. . . . . . . . . . . . . . . . . . . . . . . . L.2 Conductor Bends L.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L.2.1 Conductors Lying in Different Planes on Each Side

of the Bend L.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L.2.2 Conductors Lying in the Same Plane on Each Side

of the Bend L.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L.3 Devices in Power Circuits L.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . L.3.1 Power Circuit Arrangements L.1. . . . . . . . . . . . . . . . . . . . . . . . . Figure L1 Bend for Conductors Lying in Different Planes on

Each Side of the Bend L.2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure L2 Bend for Conductors Lying in the Same Plane on

Each Side of the Bend L.3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .


10

1. PERFORMANCE SPECIFICATION

Related Documents: There are no related documents in this section.

1.1 Verification

a . The magnetic performance of low magnetic signature equipment shall be verifiedas required by the Procurement Authority at the following stages:

Programme Stage Verifying Action Location

Design Approval Check average relative permeability (seeClause 4.12.2).

Approve drawings.

Contractor

ProcurementAuthority

Manufacture:Inspect raw material

Check relative permeability(see Annex E.).

Contractor

Manufacture:Check finished items

Check relative permeability of fabricatedparts (see Annex E.).

Check relative permeability of finishedassemblies (see Clause 4.12.2).

Contractor’s magnetic field measurements(see Clause 4.2.3).

Contractor

Contractor

Contractor

Measure equipmentsignature on Land Range

Ferromagnetic signature (seeClause 4.2.4).

Stray field signature (seeClause 4.2.4).

Land Range

Land Range

Ship Magnetic Ranging Measure ship’s ferromagnetic signature.Set degaussing controls (see Clause 4.2.6).

Measure ship’s eddy current signature.Set the degaussing controls.

Open Sea Range

Roll Range

Table 1 – Verification Stages

1.2 System Validation

a . The ship’s magnetic signature performance is validated by an open sea magneticmeasuring range (see Clause 4.2.6).

2. NATIONAL/INTERNATIONAL REGULATIONS

This Defence Standard contains no National/International Regulations information.

3. MILITARY STANDARDS/REQUIREMENTS

This Defence Standard contains no Military Standards/Requirements information.


11

4. DESIGN REQUIREMENTS/GUIDANCE

Related Documents: DEF STAN 02–612; AMP–14; see also Annex A.

4.1 General System Description

4.1.1 Introduction

a . This section provides general background to assist in understanding the DesignGuide (see Clause 4.4) and the Design Requirements for the HUNT and Single RoleMinehunters (SRMH) (see Clause 4.11).

b . A ship’s ferromagnetic fields are exploited by mine designers because the shortrange influence maximises the chances of serious damage to the ship. It is essentialtherefore that the magnetic fields of Mine Countermeasure Vessel (MCMV) arereduced to the lowest practical level.

c . Since the hull is made from non–magnetic material (GRP, wood, or special steel),the magnetic effect of an MCMV is due mainly to the on–board equipments.

d . This section outlines the basis of the guidelines and requirements for designing lowmagnetic signature equipments. The process was developed for the HUNT andSRMH, but may be applied to other vessels by following the Design Guide (seeClause 4.4) and developing different design requirement limits (seeClause 4.11 Design Requirement for HUNT and SRMH) as required.

e . This section also outlines the overall process for designing low magnetic signaturevessels and ensuring the requirement is met.

f . The magnetic effect of an MCMV depends on:

(1) Ferromagnetic Field Sources;

(2) Eddy Current Field Sources;

(3) dc Stray Field Sources (ship’s power systems);

(4) ac Stray Field Sources (ship’s power systems);

(5) Extra Low Frequency Electromagnetic (ELFE) and Underwater ElectricPotential (UEP) sources;

(6) Position and orientation of magnetic equipment on the vessel;

(7) The form of magnetic compensation and degaussing;

(8) This Defence Standard gives detailed design guidance for minimising (1),(2), (3) and (4). Items (5), (6) and (7) are discussed briefly.

4.1.2 Magnetic Signature Requirement

a . A vessel’s magnetic signature requirement is defined by operational assessmentstudies and is based on the vessel’s role, the perceived threat and the budgetconstraints.

b . The recommended NATO magnetic signature requirement for MCMV is defined indocument AMP–14. Individual navies may choose alternative limits to suit theirparticular requirements. In the United Kingdom, ADNA/SR on behalf ofDOR(SEA) define the Signature Target Level (STL) through the committeestructure for input into the appropriate Staff Requirement (SR).


12

4.1.3 Magnetic Signature Apportionment

4.1.3.1 General

a . The signature requirement is apportioned into detailed ferromagnetic, eddycurrent, and stray field requirements for each equipment. These requirements arethe basis of the Design Guide (see Clause 4.4) and the Design Requirements forHUNT and SRMH (see Clause 4.11).

b . Initially, the magnetic signature requirement is translated into vessel magneticmoments assuming the vessel is represented as a three–axis dipole source. Whilstthis is not strictly accurate, it has been found sufficient in practice for system designpurposes. These moments are apportioned into total allowable magnetic momentsfor the ferromagnetic, eddy current and stray field contributions. Theferromagnetic portion takes account of the expected improvement due todegaussing. The apportionment depends on features of construction andequipment fit, and may typically be 70:20:10 for ferro:eddy:stray.

4.1.3.2 Ferromagnetic Field

a . The allowable ferromagnetic moment is split into an allowance for each equipmentby taking a fraction of the total allowable ferromagnetic moment using the ratio,(volume of a specific equipment)/(sum of volumes of all equipments).

b . Individual equipment moments are then split into permanent and induced momentsby assuming:

(1) Vertical magnetic equilibrium where PVM = IVM

(2) Randomly orientated horizontal permanent moments and accounting forthem by assuming PLM = 1/3ILM and PAM = 1/3IAM.

c . A major assumption in apportioning ferromagnetic moments and in modelling formagnetic signature tracking (see Clause 4.2.7), is that the magnetic interactionbetween equipments with a low ferromagnetic content is not significant, i.e. theprinciple of superposition is valid. This has been found correct to an acceptableextent for typical equipment and machinery distributions on board an MCMV.Care must be taken in applying this principle to close proximity ferromagneticcomponents.

d . The resulting magnetic moments are the foundation for the Ferromagnetic DesignGuide (see Clause 4.5) and the Ferromagnetic Design Requirements (see Clause4.12). The latter uses a set of practical rules based on the concept of average relativemagnetic permeability. Since these rules are derived by making certainassumptions and approximations, they must be used only as a general guide.Average relative magnetic permeability is defined in Annex B.

e . The ultimate acceptance of an equipment for MCMV service is determined bymagnetic land range measurements (see Clause 4.2.4) or contractor’s certifiedmagnetic field measurements (see Clause 4.2.3) supported, if necessary, by asignature tracking acceptance (see Clause 4.2.7)

f . The bench marks for magnetic land range acceptance and signature trackingacceptance are the apportioned magnetic moments for each equipment. These maybe modified by the magnetic signature design authority as designs evolve and thevessel programme proceeds. The overall aim is to meet the vessel’s magneticsignature requirement.


13

g . The residual magnetic effect of equipments which, by the nature of their function,cannot be made low magnetic are compensated with degaussing if required (see Clause 4.10).

4.1.3.3 Eddy Current Field

a . The allowable eddy current magnetic moments are split into an allowance for eachequipment by using the ratio of equipment volumes as in the ferromagnetic case.The allocated moments are transformed into Design Requirements for suppliers ofequipment for the HUNT and SRMH (see Clause 4.13). The requirements take theform of limits for the areas of electrically conducting sheets and loops.

b . The allocated equipment moments are also used as bench marks for magnetic landrange acceptance tests, roll range acceptance tests and magnetic signature trackingacceptance.

c . Eddy current magnetic field sources are reduced by design (Design Guide, seeClause 4.6; Design Requirements, see Clause 4.13). Degaussing compensation canbe applied if necessary and has been used on the HUNT.

4.1.3.4 Stray Field

a . The dc and ac stray magnetic fields are reduced by the design measures described inClause 4.7.

4.2 Magnetic Signature Control

4.2.1 General

a . A ship’s ferromagnetic, eddy current and stray magnetic fields are controlled by asequence of steps:

(1) Equipment design and production controls. These controls are applied bycontractors and are based on the Design Guide (see Clause 4.4) and theDesign Requirements (see Clause 4.11) in this specification. Proposedequipment designs are approved by the appointed design authority. Existingstandard designs could be submitted to the Magnetic Land Range forapproval.

(2) Equipment–final verification. The magnetic effect of individual equipmentsis verified in three ways:

(a) Contractor’s average relative permeability checks (see Clause 4.2.2)

(b) Contractor’s magnetic field measurements (see Clause 4.2.3)

(c) Magnetic land range measurements. (see Clause 4.2.4)

(3) Ship magnetic design. The position and orientation of equipments on–boardthe ship is controlled (see Clause 4.2.5).

(4) Degaussing. An appropriate degaussing system is fitted to compensateresidual ferromagnetic and eddy current fields (see Clause 4.10)

(5) Validation. The measurement and optimisation of the ship’ s magneticsignature is carried out on a magnetic sea range (see Clause 4.2.6)

(6) Magnetic signature tracking. This activity co–ordinates the overall process(see Clause 4.2.7).

b . Verification and validation stages are described in Clauses 1.1 and 1.2.


14

4.2.2 Contractor’s Average Relative Permeability Checks

a . The method of carrying out these checks is described in Clause 4.12.2.

b . The checks are carried out by the contractor to confirm that a proposed design or amanufactured item meets the requirement. The process is strictly a guide and maybe confirmed by a contractor’s accredited magnetic field measurements (see Clause4.2.3) or by magnetic land ranging (see Clause 4.2.4).

4.2.3 Contractor’s Magnetic Field Measurements

a . These checks are carried out by accredited contractors in accordance withprocedures in documents DGUW(N) Pub 84282 and 84281. They are intended togive contractors increased control, reduce programme delays and reduce the landrange work load.

b . They use magnetic field measurements to determine if an equipment meets themagnetic signature requirement.

4.2.4 Magnetic Land Ranging

a . A magnetic land range is used to measure the ferromagnetic effect of equipmentsprior to on–board installation to confirm they meet the allocated magnetic signaturerequirements.

b . A land range may also be used for:

(1) Calibrating the built in degaussing coils on individual equipments;

(2) Measuring Stray Fields;

(3) Measuring Eddy Current Fields. (This function is carried out on the rollrange for the HUNT and SRMH equipments);

(4) Carrying out PVM stabilisation.

4.2.5 Position and Orientation on the Vessel of Equipment Containing Magnetic Sources

a . Equipments containing unavoidable magnetic sources are preferably located ashigh in the ship as is practicable and are evenly dispersed through the ship to avoidproducing peaks in the ship’s magnetic signature.

b . Equipment orientation is chosen to minimise the magnetic signature. Where thechoice exists, long thin objects shall be oriented horizontally to minimise theirmagnetic fields beneath the ship.

c . The vessel’s magnetic signature must be measured with the vessel in a defined“reference” condition. Movable equipments having magnetic sources musttherefore have designated stowage spaces.

4.2.6 Magnetic Sea Ranging

a . A magnetic sea range is used to measure the ship’s magnetic signature and set thevessel’s degaussing system controls to obtain the minimum magnetic signature. Anopen sea range is used to measure the ferromagnetic signature and a roll range tomeasure the eddy current signature.

b . Degaussing current values are accurately determined for individual equipmentcoils on the land range. These settings must be applied on the ship prior to searanging.


15

4.2.7 Magnetic Signature Tracking

a . Magnetic signature tracking is a computer based magnetic modelling processwhich is used to build and maintain a magnetic model of the ship. The model isconstructed in the early stages of design and is used to monitor the vessel’spredicted magnetic signature as the design evolves and as a vessel is built.

b . Magnetic signature tracking may be used to help decide whether a manufacturedequipment which exceeds the design criteria is acceptable for MCMV service.

c . Magnetic signature tracking is controlled by the vessel’s magnetic signature designauthority.

4.3 Extra Low Frequency Electromagnetic and Underwater Electric Potential Fields

a . Signature Target Levels (STL) are set for Static Magnetic (SM), Static Electric(SE), Alternating Magnetic (AM) and Alternating Electric (AE) for vessels whereappropriate. The SE term is sometimes referred to as Underwater Electric Potential(UEP). The main source of UEP is through the use of dissimilar metals, such asNAB and steel. The Impressed Current Cathodic Protection (ICCP) System is usedto counter the corrosion currents from the dissimilar metals and also contributes tothe SE signature. AE and AM contributions are usually defined in terms of shaftrelated (usually referred to as Extra Low Frequency Electromagnetic (ELFE)), andpower related.

b . The electromagnetic fields originating from a ship’s ac power system arecontrolled by this specification (stray field design).

c . Corrosion related ELFE and UEP signature control is described briefly inDEF STAN 02–612.

4.4 Design Guide

4.4.1 Introduction

a . This section provides guidance for suppliers and designers of low magneticsignature equipment.

b . Materials and their fabrication shall be selected in accordance with Clause 4.5 tominimise the ferromagnetic field.

c . Electrically conducting materials shall obey the size and construction constraintsdefined in Clause 4.6 to minimise eddy current fields.

d . dc (and also ac at power frequencies) electrical systems shall be designed inaccordance with Clause 4.7 minimise stray magnetic fields.

e . Handling, stowage, packaging, and transport of materials shall be in accordancewith Clause 4.8.

f . Residual magnetic fields shall be compensated using the methods inClause 4.10.

g . Verification steps specified in Clause 1.1 shall be applied.


16

4.5 Design Guide – Ferromagnetic Field Source

4.5.1 General

a . The materials used in low magnetic equipments shall, as far as is reasonablypracticable, be non–magnetic. Some materials will necessarily be magnetic andguidance on them is given in Clauses 4.5.2 to 4.5.4. The net magnetic effect of allthe materials in an equipment shall be such that the equipment’s average relativemagnetic permeability shall not be greater than the vessel’s design requirement.

b . The ferromagnetic design requirements for the HUNT and SRMH are specified inClause 4.12. The design requirements for other vessels will be specified by themagnetic signature design authority for those vessels and they will be applied in thesame way as those for the HUNT and SRMH.

c . Average relative magnetic permeability is defined in Annex B.

d . Low magnetic requirements are difficult to meet. The best chance of meeting them,with the lowest risk, is to use non–magnetic material to the greatest practicableextent.

4.5.2 Materials having an Electromagnetic Function

a . Such materials will be magnetic, but the volume of the material and features whichenhance its magnetic effect shall be minimised.

b . These items shall be included in the calculation of average magnetic permeability.(see Clause 4.12.2).

4.5.3 Materials Requiring Mechanical Strength

a . Where materials require special mechanical strength properties which cannot bemet with a non–magnetic material, then a magnetic material may be used. Itsvolume and features which enhance its magnetic effect shall be minimised.

b . These items shall be included in the calculation of average magnetic permeability.(see Clause 4.12.2).

c . Magnetic remanence (permanent magnetism) shall be minimised by:

(1) Selecting appropriate materials during design;

(2) Taking care in handling materials and parts during manufacture (see Clause4.8);

(3) Carrying out appropriate magnetic treatment on parts or the whole equipmentafter manufacture.

4.5.4 Materials where there is no Practicable Alternative

a . Standard components having some of their parts made from magnetic material willbe allowable provided there is no practicable alternative. The number of suchitems, the volume of magnetic material and the features which enhance theirmagnetic effect shall be minimised. Examples of items in this category aresemiconductor cases, parts of other standard electronic components and parts ofother proprietary items.

b . These items shall be included in the calculation of average magnetic permeability.(see Clause 4.12.2 ).


17

4.6 Design Guide – Eddy Current Field Sources

a . Eddy current field sources shall be controlled during design by selecting suitablematerials and limiting the size of electrically conducting sheets, frames and pipes.

b . The magnitude of an eddy current field source depends on:

(1) The velocity of movement of the vessel (roll, pitch);

(2) The magnitude of the earth’s magnetic field;

(3) The square of the effective area of the sheet, frame or pipe;

(4) The cross sectional area of the sheet, frame or pipe;

(5) The electrical conductivity of the sheet, frame or pipe.

Items (3), (4) and (5) are controlled by design.

c . The enclosed areas of sheets, frames and pipes for equipments intended for theHUNT or SRMH shall comply with the design requirements inClause 4.13.3. The design requirements for other vessels will be specified by themagnetic signature design authority for those vessels. If the design requirementareas cannot be met, the areas shall be split as indicated inClause 4.13.3. Since the magnitude of the eddy current field is proportional to thesquare of the enclosed area, then splitting an area into two equal halves will halvethe total magnitude.

d . All conductors used for electrical grounding shall not form any electricallycontinuous loops.

e . The peak magnetic moments, and hence the peak magnetic fields, for simple loopsand sheets can readily be calculated using standard text book formulae. Computermethods are normally used for more complex shapes and real vessel motions.

4.7 Design Guide – Stray Field Sources

4.7.1 General

a . The stray field sources shall be controlled during design by minimising themagnetic fields produced by current carrying conductors within an equipment.This applies to dc and low frequency ac currents.

b . These principles shall be followed for all vessels. There are no specific designrequirement parameters for the HUNT and SRMH.

c . The general principle is to always arrange current carrying circuits so that theirmagnetic fields are compensated by equal and opposite circuits. For example, flowand return conductors are run together as quads and where there are current loops,their areas must be minimised and their magnetic effects compensated by equal andopposite closely adjacent loops.

4.7.2 Detailed Principles

a . Simplicity: Use simple solutions. Arrange heavy current cables in quads. Usefour or more poles in dc machines.


18

b . Current Loops: The net magnetic field from two equal and opposite current loopsis proportional to the current, the loop area, and their distance apart. Minimise eachof these by design.

c . Series or Parallel Compensation: A current carrying circuit shall preferably haveits compensation circuit connected in series to ensure the currents are equal. Ifparallel compensation is unavoidable, steps must be taken to ensure currentsremain equal.

d . Self Compensation: An item of equipment is compensated within itself. Thecompensation shall not be dependent on the equipment’s orientation (in the vessel).

e . Mutual Compensation: Two or more similar equipments or components arepositioned so that their stray fields cancel each other.

f . Magnetic Material: Magnetic material must never form the core of a current loopunless it is essential for the design.

4.7.3 Stray Field Design Guide for the Arrangement of Cables

a . Cables shall be arranged in accordance with ANNEX H.

4.7.4 Stray Field Design Guide for the Arrangement of Batteries

a . Batteries shall be arranged in accordance with ANNEX I. Any battery arrangementwhose centre is separated from its associated equipment by more than 1.5 metresshall be considered a separate stray field source and not as part of the its associatedequipment. Any battery arrangement whose centre is within 0.3 metres of itsassociated equipment shall be considered part of the equipment as a stray fieldsource.

4.7.5 Stray Field Design Guide for Motor Generators

a . Motors and generators shall conform to the requirements of ANNEX J.

4.7.6 Stray Field Design Guide for Induction Clutches

a . Standard commercial forms of induction clutch design can usually be modified tominimise the stray magnetic field. The design of induction clutches shall conformwith the requirements of ANNEX K.

4.7.7 Stray Field Design Guide for Solenoid and Resistors

a . Solenoids shall be mutually compensated. Additional compensating coils shall beused where appropriate.

b . Tubular resistors shall be wound non–inductively. Heavy duty ones for motorstarting shall also be mutually compensated.

4.7.8 Stray Field Design Guide for Switch and Contactor Panels

a . Switch and contactor panels shall conform to the requirements of ANNEX L.

b .


19

4.8 Design Guide – Working, Handling, Stowage, Packaging and Transport ofMaterials

4.8.1 General Principles

a . The magnetic performance of materials can be altered by:

(1) Exposure to external magnetic fields;

(2) Imposition of Mechanical stress;

(3) Temperature changes;

(4) Contamination by other magnetic materials.

b . External magnetic fields will magnetise ferromagnetic materials. Stress willenhance the magnetising effect and can cause a permanent change in permeability ifthe material is taken beyond its elastic limit.

c . The general principal of handling is to avoid or minimise exposure to these factors.

d . It is recommended that parts and materials which unavoidably become magnetisedduring manufacture are demagnetised.

4.8.2 Detailed Principles and Guidelines – Magnetic Fields

a . All parts and materials intended for MCMV must not be exposed, even forextremely brief times, to ambient magnetic fields greater than 100 µT. Thisincludes dc fields and peak ac fields up to 400 Hz. This guideline applies totransport, storage, assembly and working of parts and materials. As a guide, theearth’s magnetic field is approximately 50 µT in the United Kingdom.

b . Magnetic fields are produced by:

(1) Electric current carrying conductors, dc or ac;

(2) Permanent magnets, electromagnets, electromagnetic machines;

(3) Ferromagnetic materials used in buildings, jetties, foundations, vehicles,lifting equipment, pallets, workbenches, storage bins, etc., will becomemagnetised in the earth’s magnetic field and act as magnetic sources.

c . Requirement of Clause 4.8.2b (1) implies that parts and materials must not beplaced any closer to current carrying conductors than the distance given by:

distance r = 0.002∗I metres

Where I = Net current in amperes (dc or ac peak) carriedby one or more conductors running together.Net current = current x number of turns.

This rule is derived from:

B =

µπoI

r2 Teslas


20

d . In certain buildings, areas close to steel support girders or steel foundations may beunsuitable and items must not be placed near them. The following clearancedistances shall be used as a guide:

(1) Within 1 m of external walls, pillars, or electric lights;

(2) Within 2 m of any pillar of an overhead gantry crane;

(3) Within 1 m of overhead gantry cranes or wires;

(4) Within 2 m of overhead gantry crane racks, electric motors or any pillarloaded with this type of equipment.

e . Non magnetic shelving systems, storage containers and pallets must be used.

f . Parts and materials placed on steel floors shall be isolated with non–magneticpallets. Similarly, they shall be isolated from steel benches by at least 20 mm ofnon–magnetic material.

g . Parts and materials must not be lifted or handled with electromagnets or grippedwith magnetic clamps.

h . Permanent magnets must not be used for checking if materials are magnetic.Magnetic permeability must be checked with a permeability tester as described inANNEX E.

i . Certain types of electric fork lift trucks may be unsuitable because of their largestray magnetic field. Those with the motors away from the lifting forks cangenerally be used. Certain types of mechanical fork lift trucks may also beunsuitable owing to the transient stray magnetic field from the starter motor currentsurge. If available, non–ferrous lifting forks are recommended, steel ones canbecome magnetised with use.

4.8.3 Detailed Principles and Guidelines – Mechanical Stress

a . All forms of mechanical stress, e.g. cold working, machining, vibration and shock,can affect the magnetic properties of materials. Stress alone can increase amaterial’s magnetisation to the extent that a non–magnetic material with no coldworking, may become magnetic after cold working. Stress combined with amagnetic field can also increase the magnetisation. The general principle is toavoid mechanically stressing all parts and materials, especially those which havebeen demagnetised after working.

b . Working stresses at room temperature can transform low magnetic, austenitic,stainless steels into ferromagnetic ferrite or martensitic steels through plasticdeformation. Pipe bending and sheet folding must only be carried out whenessential for certain types of stainless steel.

c . Screws and bolts made from nominally non–magnetic material can becomemagnetic because of stresses during manufacture or through over–tightening inuse.

d . Austenitic stainless steels can be obtained with a range of “stability” of theaustenitic phase. For example, the 316LN, 254SMO varieties are very stable andunlikely to be transformed to magnetic phases under normal working conditions.


21

e . The 301, 302, 304 and 308 series of stainless materials are often referred to as“metastable”. These are most likely to be transformed to magnetic phases byplastic deformation at room temperature. They can also suffer a transformation atcryogenic temperatures.

f . Most care must be taken when working with these metastable stainless steels.Heating during fabrication can be tolerated, but care must be exercised over themethod of cooling. A material quench to sub–zero temperatures must be avoided.Slow cooling to room temperature is more likely to allow unwanted growth of theequilibrium phase (ferrite), although this is unlikely unless the material is workedduring the cooling process.

g . The storage and carriage of parts and materials shall be effected such that items arenot unduly stressed. Sheets shall be laid horizontally or stood vertically on flatsurfaces rather than “bridged” across supports. Stressing caused by the weight ofitems stacked in layers shall be avoided. Parts and materials must be carried andplaced carefully. They must not be dropped (shock).

h . Machining shall be effected using good workshop practices. Undue stressing bytaking deep cuts in milling or turning shall be avoided.

4.8.4 Detailed Principles and Guidelines – Temperature

a . Temperature affects the magnetic properties of materials in several ways:

(1) Causes small reversible magnetisation changes for changes in temperaturearound the normal ambient. This is not significant in the present context;

(2) High temperatures (several hundred degrees centigrade) can causepermanent changes in magnetic properties, e.g. an increase in permeability.This is most noticeable in metastable austenitic stainless steels, particularlynear welds;

(3) Local heating (e.g. soldering, welding, brazing) can set up mechanicalstresses.

b . The general principle is to avoid unnecessary exposure to high temperatures.

c . For notes on stainless steels see Clauses 4.8.3b to 4.8.3f .

4.9 Detailed Principles and Guidelines – Contamination

a . Welding Filler – The correct consistency of weld electrode or filler must be used toensure minimal magnetic content in welded joints. Guidance on welding processescan be provided by The Welding Institute, Abington Hall, Abington, Cambridge,CB1 6AL.

b . Machining – For very stringent low magnetic requirements, ferrous particlecontamination from normal machine tools can cause permeabilitynon–compliance. This is frequently observed in non–metallic materials such asnylons and plastics.


22

4.10 Design Guides – Compensation Methods

a . Residual ferromagnetic sources are compensated with degaussing. An MCMVnormally requires a three axis coiling system and the coils may enclose sections ofthe vessel, specific compartments or selected equipments. Degaussingcompensates for the induced and permanent magnetisation residuals.

b . The optimum equipment degaussing coil currents are determined by the magneticland range (see Clause 4.2.4). These values must be applied during the vessel’smagnetic ranging (see Clause 4.2.6) when the compartment degaussing coilcurrents are determined.

c . Dipole compensation with permanent magnets must not be carried out owing to therisk of signature contamination by lost magnets, and lost magnets being free tomagnetise other materials.

d . Eddy current field sources are minimised by design in the first instance. Residualeffects may then be compensated with degaussing. The degaussing current settingsare determined on the degaussing roll range.

e . Stray field sources must always be minimised by design. Compensation is part ofthe design process and is described in Clause 4.7. Degaussing compensation is notappropriate.

4.11 Design Requirements for HUNT and SRMH

4.11.1 Introduction

a . The following Clause 4.12 defines the requirements for equipments intended forthe HUNT and SRMH vessels. It covers ferromagnetic and eddy current fields.The stray field requirements are the same as those in the design guide, see Clause4.7.

4.12 Design Requirement – Ferromagnetic Field Sources

4.12.1 General

a . The average relative magnetic permeability of all materials and components usedin an equipment shall not be greater than 1.05 (HUNT) and 1.35 (SRMH). Averagerelative magnetic permeability shall be calculated as shown inClause 4.12.2.

b . To assist understanding, average relative magnetic permeability is defined inAnnex B. It is a concept which provides practical rules for the design of lowmagnetic signature equipments. Since the rules are derived by making certainassumptions and approximations, they must only be used as a guide.

c . The ultimate acceptance of an equipment for MCMV service is determined bymagnetic land range measurements (see Clause 4.2.4) or contractor’s certifiedmagnetic field measurements (see Clause 4.2.3) supported, if necessary, by asignature tracking acceptance (see Clause 4.2.7).

d . The average relative magnetic permeability limits for other future vessels shall beapplied in the same way. Different limits may be necessary depending on othervessels’ magnetic signature requirements. They will be determined by the vessel’smagnetic signature design authority by the process outlined in Clause 4.1.3.


23

4.12.2 To Calculate Average Relative Magnetic Permeability

a . The average relative magnetic permeability is calculated as follows:

(1) Estimate the volume of the equipment;

(2) Estimate the volume of all its ferromagnetic parts;

(3) Measure the relative magnetic permeability, µr, of all its ferromagnetic partsafter fabrication. Guidance on measuring relative permeability is given inAnnex E. (During design, data sheet relative permeability values are used);

(4) Apply the permeability acceptance criteria in Figure 1 to Figure 3(µr less than 2.5) and Figure 4 and Figure 5 (µr greater than 2.5);

(5) Example calculations are given in Annex F. (HUNT), and Annex G.(SRMH).

b . Materials with µr less than 2.5. Figure 1 to Figure 3:

(1) Estimate and record the total volume (in cubic metres or cubic feet) of eachmaterial used in the construction of the equipment;

(2) Erect a perpendicular from the volume value to intersect the associatedpermeability line and note the corresponding magnetic field factor, X1, foreach material;

(3) Calculate the total volume, V, and the sum of all the magnetic field factors,Σ(X1).

c . Materials with µr equal to, or greater than 2.5. Figure 4 and Figure 5:

(1) Estimate and record the volume of each item used in the construction of theequipment;

(2) Measure the major axis and estimate the mean value of the two minor axes ofthe item;

(3) Divide the major axis by the mean value of the two minor axes and obtain theshape factor, S. If the shape factor is not an integer, take the next higher value;

(4) Erect a perpendicular from the volume value to intersect the associated shapefactor line, and note the corresponding magnetic field factor, X2;

(5) Repeat for each item and finally calculate the total volume, V, and the sum ofthe magnetic field factors, Σ(X2).

d . Determine the average relative magnetic permeability:

(1) Obtain the total volume of all the items used in the equipment , Σ(V), and thetotal summation of all the magnetic field factors, Σ(X1) + Σ(X2);

(2) If Σ(X1) + Σ(X2) is equal to Σ(V), the average relative magnetic permeabilityis 1.05 (HUNT) or 1.35 (SRMH) and the equipment as a whole is acceptable;

(3) If Σ(X1) + Σ(X2) is less than Σ(V), the average relative magneticpermeability is less than 1.05 (HUNT) or 1.35 (SRMH) and the equipment asa whole is acceptable;

(4) If Σ(X1) + Σ(X2) is greater than Σ(V), the average relative magneticpermeability is greater than 1.05 (HUNT) or 1.35 (SRMH) and theequipment as a whole is not acceptable.


24

e . If an equipment is shown to be unacceptable, each item is to be consideredindividually to determine which, if any, could be made of a lower permeabilitymaterial. Examples are given for the HUNT in Annex F. and for the SRMH inAnnex G.


25

Figure 1 – Relationship between Materials with Permeabilities of less than 2.5, their Volume andMagnetic Field Factor. (SRMH)


26

Figure 2 – Relationship between Materials with Permeabilities less than 1.4, (Volume 0.1 cubic feetto 1000 cubic feet) and Magnetic Field Factor. (HUNT)


27

Figure 3 – Relationship between Materials with Permeabilities less than 2.5, (Volume 0.1 cubic feetto 10 cubic feet) and Magnetic Field Factor. (HUNT)


28

Figure 4 – Relationship between Materials with Permeabilities of 2.5 and above, their Volume andMagnetic Field Factor. (SRMH)


29

Figure 5 – Relationship between Materials with Permeabilities of 2.5 and above,(Volume 0.001cubic feet to 10 cubic feet) and Magnetic Field Factor. (HUNT)


30

4.13 Design Requirements – Eddy Current Field Sources

4.13.1 General

a . The sizes of electrically conducting sheets, frames and pipes, in equipmentsintended for the HUNT or SRMH, shall comply with the limits specified in Clauses4.13.2 and 4.13.3.

b . The limits for other vessels may be different but shall be applied in the same way.

c . Electrical conductivity is expressed as percentage International Annealed CopperStandard (% IACS).

% IACS = (1.7 x 100 )/(resistivity in microhm–cms)

The equivalent resistivity values are given in Table 1.

Conductivity %IACS

Resistivitymicrohm – cms

100 1.7

90 1.9

80 2.2

70 2.5

60 2.9

50 3.4

40 4.3

30 5.7

20 8.6

10 17.2

5 34.5

Table 2 – Equivalent Values, Conductivity and Resistivity

d . Electrical conductivity in siemens per metre is the reciprocal of electrical resistivityin ohm–metres.

σ (S/m) = 1/ρ (ohm–metres)

4.13.2 Sheet Materials (Figures 6 and 7)

a . For the largest sheet (of Area A) in an equipment, erect a perpendicular from thesheet thickness value in Figure 6 (SRMH) or Figure 7 (HUNT) to intersect theassociated % IACS line. Read off the maximum allowable area, Area B. Followthe guidance in Table 2. Repeat for other sheets as required.


31

Sheet Size Guidance

B � A Not Acceptable

1.4B � A > B Not Acceptable Form by two sheets of equal size insulated from eachother by at least 1 ohm

or

Halve the thickness

or

Use another material of lower conductivity

1.7B � A > B Not Acceptable Form by three sheets of equal size insulated from eachother by at least 1 ohm

or

Use a sheet of one third thickness

or


2B � A > B Not Acceptable Form by four sheets of equal size insulated from eachother by at least 1 ohm

or

Use a sheet of one quarter the thickness

or


A > 2B Not Acceptable Use another material

Table 3 – Sheet Material – Conductivity Calculations

4.13.3 Frames and Pipes (Figures 8 and 9)

a . For the largest frame or pipe (enclosing an Area A) in an equipment, erect aperpendicular from the cross sectional area value in Figure 8 (SRMH) or Figure 9 (HUNT) to intersect the associated % IACS line. Read off themaximum allowable enclosed area, Area B. Follow the guidance in Table 3.Repeat for other frames or pipes as required.

Enclosed Area Guidance

B � A Acceptable

A > B Not Acceptable Break the continuous loop and insert two insulatingsections of at least 1 ohm resistance. The sections shallbe approximately 180 degrees apart.

NOTE: Special care is to be taken to ensure that whenbreaking continuous loop, the break cannot bebypassed by another loop member.

Table 4 – Frames and Pipes – Conductivity Calculations


32

Figure 6 – Relationship between Area, Thickness and Conductivity of Sheet material (SRMH)


33

Figure 7 – Relationship between Area, Thickness and Conductivity of Sheet Material (HUNT)


34

Figure 8 – Relationship between Area,Cross Section and Conductivity of any Frame or Pipe(SRMH)


35

Figure 9 – Relationship between Area, Cross Section and Conductivity of any Frameor Pipe (HUNT)

4.14 Design Requirements – Stray Field Sources

a . There are no special design requirement parameters for the HUNT and SRMH. Theguidance given in Clause 4.7 shall be followed.

4.15 Sources of Guidance

a . The equipment Design Authority or the equipment Sponsor are the source ofguidance for all queries.


36

5. CORPORATE KNOWLEDGE AND EXPERIENCE

This Defence Standard contains no Corporate Knowledge and Experience information.


ANNEX AA.1

ANNEX A.

RELATED DOCUMENTS

A1. The following documents and publications are referred to in this DEF STAN:

BS 5555 Specification for SI Units and Recommendations for the use of theirmultiples and of certain other units

JSP 430 Ships Safety Management Systems Handbook:

Volume 1: Policy and Guidance on MOD Ship and Equipment SafetyManagement

BR 6506 (111) Impressed Current Cathodic Protection System - Active ShaftGrounding System - Nuclear Submarines

BR 6619 Signature Controls and Special Features - HUNT Class MCMV

BR 825/4 Manual of Degaussing:

Part 4: Degaussing by Magnetic Treatment

DEF STAN02-612(NES 612)

Guide to the Design of Ferromagnetic Signature Control Systemsand Degaussing

DGUW(N)Pub 84281

Mine Countermeasures (MCM) Division Magnetic Field Testing byContractors and Guidelines for MOD(N) Project Manager

DGUW(N)Pub 84282

Mine Countermeasures (MCM) Division Magnetic Field Testing byContractors

AMP-14 Protection of Vessels from Electromagnetic Mines(or Electromagnetic Silencing)


ANNEX A A.2

Containing System (Ship)

Electromagnetic SignatureControl Systems

Ferromagnetic SignatureControl Systems

NES 612

Corrosion RelatedElectromagnetic

Signature Control Systems

Active ShaftGrounding

(ASG)BR 6506 (111)

ImpressedCathodic

Protection(ICCP)

MagneticTreatmentBR825/4

Low MagneticConstruction

On–boardDegaussing

Ship’s PowerSystems SignatureControl Systems

SignatureReductionthroughSystemDesign

SteelShips

MCMVDesign

NES 617

Figure A.1 – Electromagnetic Signature Control Systems Related NES and Defence Manuals

Eddy CurrentSignature

Control Systems

Signature Control Systems

MCMVControl

BR 6619

EddyCurrent

ReductionMCMV

NES 617

StrayField

ReductionMCMV

NES 617

Other Systems

Other SignatureControl Systems


ANNEX BB.1

ANNEX B.

ABBREVIATIONS AND DEFINITIONS

B1. For the purpose of this DEF STAN the following abbreviations apply:

ac Alternating Current

ADNA/SR Assistant Director Naval Architecture/Signature Reduction

AE Alternating Electric

AM Alternating Magnetic

DEF STAN Defence Standard

dc Direct Current

DG Degaussing

DLO Defence Logistics Organisation

DOR(Sea) Director Operation Requirements (Sea)

DPA Defence Procurement Agency

ELFE Extra Low Frequency Electromagnetic

GRP Glass Reinforced Plastic

IACS International Annealed Copper Standard

ICCP Impressed Current Cathodic Protection

IAM Induced Athwartships Magnetisation

ILM Induced Longitudinal Magnetisation

IVM Induced Vertical Magnetisation

MCMV Mine Countermeasures Vessel

MHSC Mine Hunter Sweeper Coastal

MOD Ministry of Defence

NATO North Atlantic Treaty Organisation

NES Naval Engineering Standard

PAM Permanent Athwartships Magnetisation

PLM Permanent Longitudinal Magnetisation

PVM Permanent Vertical Magnetisation

SE Static Electric

SM Static Magnetic

SRMH Single Role Minehunter

STL Signature Target Level

UEP Underwater Electric Potential


ANNEX B B.2

B2. For the purpose of the DEF STAN the following definitions apply:

Degaussing Degaussing is the compensation of a magnetic field using currentcarrying coils.

Degaussing Coil A current carrying coil whose magnetic field is used to compensatethe ferromagnetic or eddy current magnetic field of an equipment orpart of a ship.

Demagnetising Factor (N) A ferromagnetic body which is magnetised by an appliedmagnetising force, Ho, generates an internal demagnetising force, HD, which opposes Ho and gives a net internal magnetising force, Hin.HD is caused by the formation of poles and is a function of bodyshape. HD is related to magnetisation M and other parameters by thedemagnetising factor, N.

HD = NMHin = Ho – HD = Ho – NMN has a value between 0 and 1 depending on shape.

Approximate Demagnetising Factors for Common Shapes

Body Shape Aspect Ratio N

Toroid 0Very long cylinder 0Cylinder 20 0.006Cylinder 10 0.016Cylinder 5 0.04Cylinder 1 0.27Sphere 1 0.33Thin disc 1.0

Reference: D.C.Jiles, Introduction to Magnetism and MagneticMaterials, Chapman and Hall, 1991.

Eddy Current Magnetic Field The magnetic field generated by eddy currents induced in electricallyconducting materials or structures by the ship’s motion in the earth’smagnetic field.

Ferromagnetic Field The magnetic field generated by a magnetised ferromagneticmaterial.

Induced Magnetisation See Magnetisation.

Magnetic Equilibrium A body is in magnetic equilibrium when its permanentmagnetisation has attained its maximum possible value in thepresence of magnetic shaking or mechanical stress for a constantapplied magnetising force, Ho. In this condition, known asequilibrium permanent magnetisation, the body’s internalmagnetising force, Hin, is very small.

Magnetic Flux Density (B) Primary magnetic vector quantity. It is a measure of the mechanicalforce experienced by an element of electric current at a point in amagnetic field. Units are Teslas (T). NanoTeslas (nT) andmicroTeslas (µT) are normally used in ship’s magnetic silencingwork. It is the unit commonly used to describe magnetic fieldstrength in air. (See Magnetising Force).


ANNEX BB.3

Magnetic Moment (m) Magnetic moment is a measure of the strength of a magnetic dipole,i.e. a measure of the strength of the magnetising force, H, producinga field at points in space by a single plane current loop or amagnetised body. The term “moment” derives from the mechanicalforce or moment experienced by a current carrying loop situated in amagnetic field. Magnetic moment is a vector quantity whosemagnitude, for a plane current loop, is equal to the product of looparea (in square metres) and the total loop current in amperes. (Totalloop current = current x number of turns). The vector direction isnormal to the plane of the loop in a sense which the current isclockwise when looking along the direction of the vector. Units areampere metres squared (Am2).

m = current x area Am2

Magnetisation (M) Magnetisation is the magnetic moment per unit volume of a solid. Itis a vector quantity and is the property of a magnetic material whichcauses the ferromagnetic field. For engineering convenience, it issub–divided into induced and permanent magnetisations. Forpractical purposes, the induced magnetisation is directly proportionalto the applied magnetising force, H, it lies in the same sense as Hand changes immediately with H. The permanent magnetisation(due to magnetic remanence) is changed only by magnetic treatment,or by mechanical stress. See Magnetic Equilibrium. Magnetisationis related to magnetising force, H, flux density, B, and thepermeability of free space, µo, by:

B = µo(H + M)

Magnetising Force (H) Secondary magnetic vector quantity. It is a measure of the ability ofan element of current to produce a magnetic flux density at a point inspace. Units are Amperes per metre (A/m).

B and H are related in free space by: B = µ0H

Where µ0 is the permeability of free space. µ0 = 4p*10–7 Henries permetre.

Permanent Magnetisation See Magnetisation.

PVM Stabilisation PVM stabilisation is where a body is magnetically treated to achieveequilibrium permanent vertical magnetisation for an earth’s magneticfield greater than that in the vessel’s proposed operating area. (seeMagnetic Equilibrium).

Relative MagneticPermeability (mr)

This defines the relationship between B and H at a point within amagnetic material.

B = µ0 µr H where µr is a dimensionless ratio and describes therelationship between B and µ0H.

Shape Factor (S) The shape factor is the aspect ratio of a component derived bydividing the overall length by the mean diameter.

Stray Magnetic Field The unwanted magnetic field generated by dc and low frequency accurrent carrying conductors within shipborne equipments andmachinery under normal operation.


ANNEX B B.4

B3. The following are Conversion Factors used within this DEF STAN:

1 Oersted (Oe) = 103/4π Amperes per metre (A/m)

1 Gauss (G) = 10–4 Teslas (T)

1 Gamma (γ) = 10–5 Oersted (Oe)

A magnetising force of 1 Gamma is equivalent to a flux density of 1 nT in free space.

B4. The following are Symbols used within this DEF STAN:

A/m Amperes per metre. Units of H

Am2 Ampere metres squared. Unit of magnetic moment

B magnetic flux density in Teslas

H magnetising force in A/m

Ho applied magnetising force in A/m

Hin magnetising force inside a material in A/m

m magnetic moment; or metres

nT nanoTesla

N demagnetising factor

S shape factor (aspect ratio)

V volume in cubic metres

x1 magnetic field factor

x2 magnetic field factor

µ absolute permeability. µ = µ0µr

µ0 permeability of free space

µr relative magnetic permeability

µT microTesla

σ electrical conductivity in siemens per metre

ρ electrical resistivity in ohm–meters


ANNEX CC.1

ANNEX C.

PROCUREMENT CHECK LIST

C1. No revelant information included.


ANNEX C C.2


ANNEX DD.1

ANNEX D.

AVERAGE RELATIVE MAGNETIC PERMEABILITY

D.1 Introduction

a. This Annex defines Average Relative Magnetic Permeability and shows how it isused to create practical pass/fail acceptance criteria for equipment designs.Assumptions and approximations are stated. The relationship to land rangemeasurements and a vessel’s magnetic signature is described.

b. Average relative magnetic permeability is a design and acceptance criteria forequipments having a low magnetic signature. It is applied by following the set ofrules in Clause 4.12. The purpose of the rules is to provide design and inspectionguide–lines which people without magnetics knowledge can apply.

c. This Annex describes the basis of the rules in order to:

(1) Understand the limitations of the rules because of the inherent assumptionsand approximations;

(2) Provide additional information to make pass/fail judgements more easily inmarginal cases;

(3) Understand the relationship between the rules, land range magnetic fieldmeasurements and ship’s magnetic signatures;

(4) Enable the rules to be amended to suit the requirements of new vessels.

D.2 Definition

a. The induced magnetic moment, m, for a ferromagnetic ellipsoid is given by:

mH V

Nr

=

−+

0

1

1µ

Am2 (1)

Where m = magnetic moment in Am2

H0 = applied magnetising force in A/m

V = volume of solid, m3

µr = relative magnetic permeability

N = demagnetising factor (value between 0 and 1, Annex B)

b. Eq (1), without H0V, is plotted in Figure D1 for a range of µr and N.

c. In the region µr >> 2.5, Eq (1) can be approximated as:

m H V N= 0 (2) for µr >> 2.5

because m largely depends on N.

d. In the region µr just > 2.5, to µr >> 2.5, Eq (2) does not hold. The error is thedifference between the curves and the dashed lines on the graph. The consequencesof using Eq (2) to describe all the region µr > 2.5 is a pessimistic acceptancecriterion for µr just > 2.5. i.e. the limit set by the rules is tighter in this region thanis really required.


ANNEX D D.2

1/(1/(u–1)+N) versus u(u = relative permeability: N = demagnetising factor)

(1/(1/(u–1)+N) is proportional to the par unit induced magnetic moment)

u, relative permeability (Log Scale)KEY:

1/(1

/(u–

1)+

N)

Figure D1 – Plot showing Induced Magnetic Moment

e. In the region µr < 2.5, Eq (1) can be approximated to Eq (3) below because m isnot significantly dependent on N.

m H V r= −0 1( )µ (3) for µr < 2.5

f. Consider firstly Eq (3), where µr < 2.5

Letx

k m

Hk V r1

1

01 1= = −( )µ

(4)

where x1 is called the magnetic field factor. (It is proportional to the per unitinduced moment, m/H0).

Thenk1

1

135 12 857=

−=

( . ).

(5) for µr = 1.35, V = 1, x1 = 1

Andx

V r1

1

135 1= −

-

( )( . )

µ

(6) for a single body


ANNEX DD.3

g. For several bodies, of volumes Va, Vb, etc, the combined magnetic field factor, x1’,assuming superposition is:

xV Va ra b rb

11

135 1

1135 1

’( )

( . )

( )( . )

= −-

+ −-

+µ µ

(7)

h. If the magnetic effect, x1’, of several bodies is equivalent to that of a single bodyoccupying the same total volume, i.e. x1=x1’, then, from (6) and (7):

V V Vr a ra b rb( )

( . )

( )

( . )

( )

( . )

µ µ µ−−

= −−

+ −−

+1

135 1

1

135 1

1

135 1 (8)

And x x xa b1 1 1= + +( ...) (9)

i. From (8), the permeability µr is described as the average relative magneticpermeability because the volume V with permeability µr has an equivalentmagnetic effect to several bodies of volumes Va, Vb, etc, with permeabilities µra,µrb, etc.

j. From (6), x V1 = for µr = 1.35 (10)

And x V1 < for µr < 1.35 (11)

k. From (9) and (11), the average relative magnetic permeability of an assembly ofitems is equal to or less than the target of 1.35 or 1.05 provided:

( ...) ( ...)x x Va Vba b1 1+ + ≤ + + (12)

l. From (6), a family of permeability curves can be drawn (Figure 1, SRMH; Figure2 and Figure 3, HUNT) and used to infer values of x1a, x1b, etc.

m. The case where µrr > 2.5, from Eq (2), is now considered:

m H V N= 0 (2) for µr > 2.5

Letx

k m

H

k V

N2

2

0

2= =(13)

n. By lettingx

k m

Hx

k m

H1

1

02

2

0= = =

from (4) and (10):

Then k1 = k2 = 2.857

Andx

k V

N2

2 2 857

0 3338 658= = =

.

..

(14) for V = 1

o. The value of the demagnetising factor, N, lies between 0 and 1 depending on theitem’s aspect ratio, (or shape factor), S. For a sphere or a cube, S = 1 andN = 0.333. (Demagnetising Factor, Annex B).


ANNEX D D.4

p. By similar reasoning to that in Clauses D.2g. and D.2h. magnetic field factors x2ae,x2bf,, etc, can be assigned to each item in an equipment such that:

x x xe f2 2 2= + +( ...) (15)

And ( ...) ...)x x V Ve f e f2 2+ + ≤ + + (16)

q. From (14), a family of aspect ratio curves can be drawn (Figure 4, SRMH; andFigure 5, HUNT) and used to infer values of x2ae, x2f, etc. These values are addedto x1a, x1b, etc, so that the average relative magnetic permeability of an equipmentis less than 1.35 or 1.05 provided:

( ... ...) ( ... ...)x x x x V V V Va b e f a b e f1 1 2 2+ + + + ≤ + + + + (17)

i.e.x x V1 2+ ≤ �� (18)

r. The procedure for applying this process is described in Clause 4.12.

D.3 Assumptions and Approximations

a. The above process has been developed by making certain assumptions andapproximations which are listed below. Because of this, the process must be usedonly as a general working guide.

b. The method is based on ellipsoid shaped bodies and is only approximate for othershapes. It is only very approximate for a body consisting of an assembly of itemsrepresented by a single volume with an average relative magnetic permeability.

c. The method does not distinguish between a solid object and a shell where each havethe same weight of steel. A thin walled spherical shell has a much greater magneticmoment than a solid of the same weight.

d. It is assumed that the magnetic interaction between different ferromagnetic itemswithin an equipment is small and that superposition applies.

e. Magnetic behaviour is described for µr > 2.5 and µr < 2.5. It ignores the errors inthe transition region.

f. Individual items are assumed to have a uniform µr. In practice it will vary and anaverage will be used.

g. Predictions based on this method may not align with land range results. Thepredictions assume far field conditions and ignore the distribution of items withinan equipment. Land range measurements automatically include the distribution.This difference may mean that some items which are acceptable by the averagerelative magnetic permeability criteria are not acceptable by the land range criteriaand vice versa. Final acceptance is by the land range or by an authorisedcontractor’s magnetic field measurements.

D.4 Relationship Between Average Magnetic Permeability, Land Range Measurementsand Ship’s Magnetic Signatures

a. The magnetic moment, m, of an ellipsoid of volume V, permeability µr anddemagnetising factor N, can be calculated from equation (1). This can beapproximated by equation (2) or equation (3).


ANNEX DD.5

b. The magnetic field at a distance r metres from an ellipsoid of moment m, can becalculated from the simple dipole formulae in Figure D2 assuming far fieldconditions.

c. A vessel’s magnetic signature is the sum of the magnetic field contributions fromall the dipole sources on the vessel. Dipole sources are three axis.

d. Bearing in mind the assumptions and approximations in Clause D.3, theequipments in a vessel can be magnetically modelled as ellipsoids and the vessel’smagnetic signature calculated.

e. The process can be applied in a reverse sense. A vessel’s magnetic signature targetcan be translated into an allowable average magnetic moment per unit volume ofequipment within the vessel and this in turn can be translated into an allowableaverage relative magnetic permeability for equipments. The allowablepermeability values for the HUNT and SRMH are given inClause 4.12.

Radial component Br = (200 m Cos a)/r3 nT

Tangential component Bt = (100 m Sin a)/r3 nTz component Bz = 100 m (3 Cos2 a –1)/r3 nT

y component By = 100 m (1.5 Sin2 a)/r3 nT

moment, m, Am2

P

Bt

By

Br

Bz

Distance r, meters

–

+a Magnetic Flux Density, B, nT

Figure D2 – Relationship Between Magnetic Dipole Moment and Magnetic Flux Density


ANNEX D D.6


ANNEX EE.1

ANNEX E.

GUIDELINES FOR MEASURING RELATIVE MAGNETIC PERMEABILITY

E.1 General

a. This Annex gives guidance on:

(1) When to Measure Relative Magnetic Permeability;

(2) How to Measure Relative Magnetic Permeability;

(3) Comments and Problems;

(4) Sources of Advice and Guidance.

E.2 When to Measure Relative Magnetic Permeability

a. Relative magnetic permeability must be measured during the initial stages ofmanufacture shown in Section 1 to give confidence that an equipment will meet itsmagnetic signature target. They are detailed in Clauses E.2c. to E.2e. below andshall be applied as appropriate.

b. The acceptance of an equipment for MCMV service is determined by magneticland range measurements (see Clause 4.2.4) or an approved contractor’s magneticfield measurements (see Clause 4.2.3), supported if necessary, by signaturetracking acceptance (see Clause 4.2.7).

c. Received raw materials must be checked and accepted before use. Measurementson large pieces of material must be taken at several points to obtain a representativeaverage.

d. When materials have been cut, worked or machined the parts must be checked.Ideally readings shall be taken at several points to obtain a representative average.Gross non–compliance implies that the working or machining process is unsuitablefor this class of material and an alternative material or process must be considered.

e. Finished parts must be checked to ensure that assembly processes have not causedany permeability changes.

E.3 Measuring Relative Magnetic Permeability

a. Example of instrument: Forster Magnetoscope Type 1.068:

Supplier: Forster Instruments UK Limited,Wrens Court, 50 Victoria Road,Sutton Coalfield, West Midlands,B72 1SY

b. Permeability testing must be carried out in an area reasonably free from magneticfields. For bench tested items, the recommended position for a test bench is:

(1) Not less than 2 metres from external walls, pillars, electrical cables, inertmagnetic sources or ferromagnetic material which could become magnetic;

(2) Not less than 3.5 metres from any active sources including machines, powercables, etc.


ANNEX E E.2

c. Testing shall be carried out in accordance with the instrument instructions.

d. The instrument shall be calibrated and zeroed before use. Reference materials,supplied by an accredited supplier, should be used for calibration. Suitablemeasures must be taken to protect the materials.

e. The probe must be used in the orientation that it was calibrated. It must berecalibrated for a different orientation.

f. The probe tip must be kept clean of dirt and swarf.

g. The probe must not be placed on a sample which is known to be magnetised or hasa known high permeability (e.g. a steel work bench). It is recommended that initialchecks are made with a finger placed over the probe tip to prevent overloading theinstrument and the probe. Subsequent checks are then made directly.

h. Measurements shall be made at the following points:

(1) Round Bar. – Circumferentially at intervals not exceeding 150 mm along thebar. On the faces at each end of the bar;

(2) Sheet. – On both surfaces at intervals not exceeding 150 mm;

(3) Irregular shapes. – At intervals not exceeding 150 mm in two orthogonaldirections over the surface, in the most practical manner that the surface willpermit.

i. Sheet materials which are significantly thinner than the instrument’s calibrationsample will give low readings. If a thin sheet has a reading higher than therequirement, it can be ruled outside specification. The reading obtained fromstacked thin samples is not reliable.

j. The probe must not be used in a cavity where the walls are close to the probe.

k. Tiny parts may not give reliable readings and it may only be possible to indicatehigh or low permeability. Take measurements on the flattest surface. Checkthreaded or knurled parts on the end.

E.4 Measuring Relative Magnetic Permeability – Comments and Problems

a. Relative magnetic permeability does not indicate the magnetisation of a body, andconsequently does not indicate its magnetic signature. A highly magnetised, squarehysteresis loop material, e.g. a permanent magnet, could give a low relativepermeability reading, but still give a large magnetic signature.

b. A permeability probe contains a powerful magnet which could locally magnetisea material at the test point. A minimum number of test points shall be used toprevent excessive magnetisation over the surface of an item.

c. Materials must never be “tested” with a permanent magnet, the material maybecome permanently magnetised.


ANNEX FF.1

ANNEX F.

CALCULATION OF AVERAGE MAGNETIC PERMEABILITY (HUNT)

F.1 Example 1

a. Aluminium reel on stand with mild steel axle and ball races. Reel containingstainless steel wire.

NOTE The materials used in this example have been chosen to illustrate themethod and may not be otherwise compatible together.

b. Materials with permeabilities less than 2.5, using Figure 2 or Figure 3:

Item Material Volume(ft3)

Permeability(µr)

Magnetic FieldFactor (X1)

1. Drum Aluminium 0.5 1.01 )

2. Stand Aluminium 0.6

)1.01 ) 0.22

3. Wire on Drum Stainless Steel 0.35 2.00 7.00(EN58B)

4. Ball Race Cages Stainless Steel 0.01 1.01 0.0024. Ball Race Cages Stainless Steel(EN58A)

0.01 1.01 0.002(EN58A)Σ Volume = 1.46 ΣXI = 7.222

c. Materials with permeabilities 2.5 and above, using Figure 5:


Shape Factor(S)


5. Axle Mild Steel 0.005 10 4.25

6. Ball Race Balls Steel 0.01 1 0.5Σ Volume = 0.0015 Σ X2 = 4.75

Total Volume = 1.46 + 0.015 = 1.475 ft3

ΣXl + ΣX2 = 7.222 + 4.75 = 11.972

Total Magnetic Field Factor (ΣXl + ΣX2) is greater than Total Volume andtherefore the equipment is not acceptable without modification (see Clause F.2Example 2).


ANNEX F F.2

F.2 Example 2

a. Equipment as in Example 1, with the wire on drum (Item 3) and the axle(Item 5) considered to be of materials of lower permeability than before.

b. Materials with permeabilities less than 2.5, using Figure 2 and Figure 3.

Item Material Vol�ume (f

t 3)

Permeabil�ity(µr)

MagneticField

Factor (XI)

1. Drum Aluminium 0.5 1.01)

2. Stand Aluminium 0.6 1.01))0.22

3. Wire on Drum StainlessSteel(EN58A)

0.35 1.01))0.072

4. Ball RaceCages

StainlessSteel(EN58A)

0.01 1.01)

5. Axle K Monel 0.005 1.01 0.001Σ Volume = 1.465 ΣXI = 0.293

c. Materials with permeabilities 2.5 and above, using Figure 5.


Shape Factor(S)


6. Ball Race Balls Steel 0.01 1 0.5

Total Volume = 1.465 + 0.01 = 1.475 ft3

ΣXI + ΣX2 = 0.293 + 0.5 = 0.793

Total Magnetic Field Factor (ΣXI + ΣX2) is now less than Total Volume andtherefore the equipment is acceptable.


ANNEX GG.1

ANNEX G.

CALCULATION OF AVERAGE MAGNETIC PERMEABILITY (SRMH)

G.1 Example 1

a. Aluminium reel on stand with mild steel axle and ball races. Reel containingstainless steel wire.

NOTE The materials used in this example have been chosen to illustrate themethod and may not be otherwise compatible together.

b. Materials with permeabilities less than 2.5, using Figure 1:

Item Material Volume(m3)

Permeability(µr)

Magnetic FieldFactor (XI)

1. Drum Aluminium 0.014 1.01 0.000435

2. Stand Aluminium 0.017 1.01 0.00053

3. Wire on Drum Stainless Steel(EN58B)

0.01 2.00 0.0315

4. Ball Race Cages Stainless Steel(EN58A)

0.00028 1.01 0.000008(EN58A)ΣVolume = 0.04128 ΣXl = 0.032473

c. Materials with permeabilities 2.5 and above, using Figure 4:


Shape Factor(S)


5. Axle Mild Steel 0.00014 10 0.019

6. Ball Race Balls Steel 0.00028 1 0.0022Σ Volume 0.00042 ΣX2 = 0.0212

Total Volume = 0.04128 + 0.00042 = 0.0417 m3

ΣXI + ΣX2 = 0.0325 + 0.0212 = 0.0537

Total Magnetic Field Factor (ΣXl + ΣX2) is greater than Total Volume andtherefore the equipment is not acceptable without modification (see Clause G.2Example 2).


ANNEX G G.2

G.2 Example 2

a. Equipment as in Example 1, with the wire on drum (Item 3) and the axle(Item 5) considered to be of materials of lower permeability than before.

b. Materials with permeabilities less than 2.5, using Figure 1.


Permeability(µr)


1. Drum Aluminium 0.014 1.01 0.000435

2. Stand Aluminium 0.017 1.01 0.00053

3. Wire on Drum Stainless Steel(EN58A)

0.01 1.01 0.00031

4.Ball Race Cages Stainless Steel

(EN58A)0.00028 1.01 0.000008

5. Axle K MonelΣ Volume =

0.000140.04142

1.01ΣXI =

0.0000040.001287

c. Materials with permeabilities 2.5 and above, using Figure 4.


Shape Factor(S)


6.Ball Race Balls Steel 0.00028 1 0.0022

Total Volume = 0.0414 + 0.0003 = 0.0417 m3

ΣXI + ΣX2 + 0.00129 + 0.0022 = 0.0035

Total Magnetic Field Factor (ΣXI + ΣX2) is now less than Total Volume andtherefore the equipment is acceptable.


ANNEX HH.1

ANNEX H.

STRAY FIELD – GUIDE FOR THE ARRANGEMENT OF CABLES

H.1 Direct Current Power Cables

H.1.1 Four Conductor Quadded Cables

a. Four conductor quadded cables shall be used for dc power cables whereverpracticable.

H.1.2 Double Conductor Cables

a. Where four conductor quadded cable is not available or not practicable, one doubleconductor cable may be utilised in a dc cable run if it is twisted such that the cable’sconductors are transposed at regular intervals by the twist of the conductors to formthe lay of the cable or the conductors are concentric and the size of the cable is smallenough to handle conveniently for the selected application. Two or more doubleconductor cables connected in parallel shall only be utilised with care in dc cableruns since unequal division of current between conductors connected in parallel cangive rise to a magnetic field of objectionable magnitude.

H.1.3 Single Conductor Cables

a. An even multiple of single conductor cables in the positive and negative branchesof a dc cable run shall be utilised. The cables shall be arranged in accordance withClauses H.1.3b. to H.1.3e. Cable runs consisting of only one or an odd multipleof single conductor cables in the positive and negative branches of a dc circuit shallnot be utilised since an odd number of current loops makes magnetic fieldcompensation by arrangement impracticable and results in large magnetic fields.

b. Arrangement of Cables for Opposing Current Loops: Parallel, singleconductor cables in the positive and negative branches of a dc cable run shall bearranged in a manner that gives opposing current loops, so that their magnetic fieldsare self compensating. Figure H.1 illustrates several preferred and non–preferredarrangements and their resulting fields.

c. Equal Current Division Among Cables Connected in Parallel: Parallel, singleconductor cables in the positive and negative branches of a dc cable run shall beselected and installed so that the resistance in each branch is equal to ensure equalcurrent sharing. Figure H.2 gives several examples of unequal current division.

d. Spiralling the Cable to Minimise the Effects of Unequal Currents: A dc circuitcable run array consisting of multiple, single conductor cables shall be spiralledfrom one cable hanger to the next so that any magnetic field created by unequalcurrent divisions in parallel circuits shall be minimised. Cable runs less than 1.5metres need not be spiralled. Spiralling will aid in minimising the separationbetween adjacent conductors of the cable.

e. Cable Spacing: Multiple, single conductor dc cables in a cable run shall be spacedequally to each other along their entire run to effect a balanced compensation.Cables in a quad shall be pressed tightly together all along the run with their centresat the corners of a square. Equal spacing of cables in a circular array shall beaccomplished by utilising cables of the same diameter, tightly clamped around asuitably sized central core.


ANNEX H H.2

H.2 Alternating Current Power Cables

H.2.1 Phase Conductors in a Common Core

a. Special cable arrangement is not necessary when all phase conductors of an accircuit are in the same cable.

H.2.2 Phase Conductors in a Separate Cables

a. Where this is necessary, the cables shall not be grouped on the same cable hangerswith dc power cables and shall be as close together as practicable throughout theentire length of the cable run. Closed loops of magnetic material around a phaseconductor and the placing of magnetic material between the phase conductor cablesshall be avoided.

H.3 Cable Terminal Connections

H.3.1 Compatibility of Cable Runs and Terminals

a. The terminals on equipment shall be arranged for ready connection to the cable runswhich take current to and from the equipment. In the absence of a terminalarrangement to which the cable run can be conveniently connected, an adapterbetween the cable run and the equipment shall be utilised.

H.3.2 Arrangement of Terminals and Approach by Cable Run

a. Terminals for cable runs shall be equally spaced, parallel terminals in the sameplane arranged edgeways or flat, with the cable run approaching the terminalsendways, crossways, or sideways. Edgewise terminals are preferred since thecentre to centre distance between terminals can be made smaller than for flatterminals, which results in smaller current loops. Edgewise terminals can utilisethe same type of cable lugs for endways and crossways connections.

H.3.3 Three Terminal Arrangements

a. Three terminal arrangements are preferred and shall be in accordance with FigureH.3. The figure also shows endways, crossways and sideways orientation of thecable run approach.

H.3.4 Connecting Four Single Conductor Cables to Three Terminals

a. Connections shall be made in accordance with Figure H.4 to Figure H.7. Asideways approach to edgewise or flat terminals shall be avoided since special busbar adapters are required to make a connection giving minimum stray field.

H.3.5 Connecting Eight Single Conductor Cables to Three Terminals

a. Connections shall be made in accordance with Figure H.8 to Figure H.10. In eachcase the positive cables shall be located symmetrically about the cable run axis; thisapplies to negative cables similarly.


ANNEX HH.3

H.3.6 Connecting Six Single Conductor Cables to Three Terminals

a. Connections shall be generally in accordance with Figure H.11 and as follows:

(1) Draw in every other cable and connect it to a single conductor which liesalong the axis of the cable group. Connect the single conductor to the centreterminal.

(2) Connect the remaining three cables to a conducting ring which is concentricwith the axis of the cable group.

(3) Connect two diametrically opposite points on this ring to the two outsideterminals.

b. This arrangement creates current loops of equal area and opposite polarity, andreduces the stray magnetic field.


ANNEX H H.4

A. Typical preferred cable arrangements.

Cable Arrangement Max. magnetic flux density – NanoTesla

2.0

1.0

B. Typical non–preferred cable arrangements.

Cable Arrangement Max. magnetic flux density – NanoTesla90

570

280

280

150

850

280

50

150

NOTE

1. Cable arrangement figures illustrate the cross–sectional views of thesingle conductor cables in a cable run. “+” indicates positive conductorcables connected in parallel. “–” indicates negative conductor cablesconnected in parallel. For a given arrangement, if all “+” are changedto “–” and all “–” changed to “+”, the same indicated maximum fluxdensity will result.

2. The indicated maximum flux density is the vertical componentcalculated on a plane 7.5 metres above or below the cable run basedupon cables with an outside diameter of 40 mm that are touching eachother so that the centre–to–centre distance between adjacent cables is40 mm. The length of the cable run is 18 metres and the direct currentmagnitude is 2000 amperes (A) (1000 A per cable for cable runs withtwo cables in each branch and 667 A per cable for cable runs with threecables in each branch). No magnetic materials are assumed to bepresent anywhere in the region around the cable run and the totalcurrent is assumed to be equally divided between conductorsconnected in parallel.

Figure H.1 – Arrangement of Single Conductor dc Cables for Opposing Current Loops


ANNEX HH.5

Cable 1

Cable 2

Cable 3

Cable 4

Current Division Among Conductors (Amperes) Maximum MagneticFlux Density

Cable 1 Cable 2 Cable 3 Cable 4Flux Density(NanoTesla)

1000 1000 1000 1000 1

2000 2000 0 0 280

0 1000 1000 2000 150

900 900 1100 1100 30

NOTE1. Cable arrangement figures illustrate the cross–sectional views of the

single conductor cables in a cable run. “+” indicates positive conductorcables connected in parallel. “–” indicates negative conductor cablesconnected in parallel. For a given arrangement, if all “+” are changedto “–” and all “–” changed to “+”, the same indicated maximum fluxdensity will result.

2. The indicated maximum flux density is the vertical componentcalculated on a plane 7.5 metres above or below the cable run basedupon cables with an outside diameter of 40 mm that are touching eachother so that the centre–to–centre distance between adjacent cables in40 mm. The length of the cable run is 18 metres and the direct currentmagnitude is 2000 amperes (A) (1000 A per cable for cable runs withtwo cables in each branch and 667 A per cable for cable runs with threecables in each branch). No magnetic materials are assumed to bepresent anywhere in the region around the cable run and the totalcurrent is assumed to be equally divided between conductorsconnected in parallel.

Figure H.2 – Unequal Current Division Among Cables Connected in Parallel


ANNEX H H.6

Terminals

Sideways cable approach

Endways cable approach

Crossways cable approach

A - Edgewise Arrangement

Terminals

Sideways cable approach

Endways cable approach

Crossways cable approach

B - Flat Arrangement

Figure H.3 – Edgewise and Flat Three Terminal Arrangements


ANNEX HH.7

T1

T2

T3

Direction of current

1

2

3

4

2

341

NOTE1. The cable run shall approach the terminals with its axis in line with the

horizontal axis of the centre terminal T2.2. The two Cables 1 and 3, which lie in a horizontal plane, shall be bolted

to the opposite sides of terminal T2.3. Cable 2 is bent to the left and slightly down to connect to terminal T1.

Cable 4 is bent to the right and slightly up to connect to terminal T3.4. The area outlined by cables 1 and 4 equals the area of the cable run

outlined by Cables 2 and 3.5. The polarity of the current in the loop made by Cables 1 and 4 is

opposite to the polarity of the current in the loop made by Cables 2 and3.

Figure H.4 – Connection of an Endways Cable Run with Four Cables to Edgewise Terminals


ANNEX H H.8

1 234

1

23

4


T1

T2

T3

NOTE

1. This figure can be obtained from Figure H.4 by rotating through 90degrees the cable run (or terminals) about an axis through the points ofattachment of the cables to the terminals, when these points are on a lineperpendicular to the terminals.

2. The cable run shall approach the terminals with its axis in line with thevertical axis of the centre terminal T2.

3. The two Cables 1 and 3, which lie in a vertical plane, shall be bolted tothe opposite sides of terminal T2.

4. Cable 2 is bent to the left and slightly forward to connect to terminal T1.Cable 4 is bent to the right and slightly back to connect to terminal T3.

5. The area outlined by cables 1 and 4 equals the area outlined by Cables 2and 3.

6. The polarity of the current in the loop made by Cables 1 and 4 isopposite to the polarity of the current in the loop made by Cables 2 and3.

Figure H.5 – Connection of a Crossways Cable Run with Four Cables to Edgewise Terminals


ANNEX HH.9

1

2 3

4

4

3

2

1

T1

T2

T3


NOTE1. The cable run shall approach the terminals with its axis in line with the

horizontal axis of the centre terminal T2.2. The two Cables 2 and 4 which lie in a vertical plane, shall be bolted to

the upper and lower sides of the terminal T2.3. Cable 1 is bent to the left and slightly down to be bolted to the under

side of terminal T1. Cable 3 is bent to the right and slightly up to theupper side of terminal T3.

4. The area outlined by cables 1 and 4 equals the area outlined by Cables 2and 3.

5. The polarity of the current in the loop made by Cables 1 and 4 isopposite to the polarity of the current in the loop made by Cables 2 and3.

Figure H.6 – Connection of Endways Cable Run with Four Cables to Flat Terminals


ANNEX H H.10

2

1

3

4

4

32

1

T1T2

T3


NOTE

1. The cable run shall approach the terminals with its axis in line with thevertical axis of the centre terminal T2.

2. The two Cables 2 and 4 which lie in a vertical plane, shall be bolted to theupper side of the terminal T2.

3. Cable 1 is bent to the left and slightly forward to be bolted to the upper side ofterminal T1. Cable 3 is bent to the right and slightly back to the upper side ofterminal T3.

4. The area outlined by Cables 1 and 4 equals the area outlined by Cables 2 and3.

5. The polarity of the current in the loop made by Cables 1 and 4 is opposite tothe polarity of the current in the loop made by Cables 2 and 3.

Figure H.7 – Connection of a Crossways Cable Run with Four Cables to Flat Terminals

Cable(typical – shown reduced size for clarity)

Terminal (typical)


Figure H.8 – Connection to an Endways Cable Run with Eight Cables to Flat Terminals


ANNEX HH.11

Cable(typical – shown reducedsize for clarity)

Terminal (typical)


Figure H.9 – Connection to a Crossways Cable Run with Eight Cables to Flat Terminals

Cable(typical – shown reduced size for clarity)

Terminal (typical)


Figure H.10 – Connection to a Sideways Cable Run with Eight Cables To Flat Terminals


ANNEX H H.12


Terminal (typical)


A. Crossways cable run

Terminal (typical)



B. Endways cable run

Figure H.11 – Connection to an Endways and Crossways Cable Run with Six Cables


ANNEX II.1

ANNEX I.

STRAY FIELD – GUIDE FOR THE ARRANGEMENT OF BATTERIES

I.1 Definitions and General Principles

a. A battery tray consists of one or more battery cells assembled in a single unit. Eachcell has one positive and one negative terminal. The cells are electrically linkedwith inter–cell connections. A battery circuit consists of one or more battery trayslinked together to a pair of output terminals which connect to an external circuit.Stray magnetic fields are minimised by choosing arrangements of inter–cellconnections and inter–tray bus bars which result in groups of equal and oppositeself cancelling current loops. The magnetic moments of equal and opposite loopsshall be as small as possible and the distance between loops shall be as small aspossible. The arrangements shall be made in the simplest manner possible.

I.2 Series and Parallel Compensation

a. Series compensation is preferred. Parallel compensation may be used if care istaken to minimise the effects of unequal current sharing.

I.3 Positioning of Battery Connecting Bus Bars

a. Except for cross–over points, the centrelines of the bus bars connected to thebattery shall be in the same horizontal plane as the centrelines of the inter–cellconnections. At cross–over points, the bus bars or cable links shall depart from thisplane only as much as needed for insulation clearance.

I.4 Positioning of Connecting Bus Bars

a. Bus bars shall be used for connecting battery trays together to facilitate fabricationand preserve equal area current loops.

I.5 Preferred Storage Battery Arrangements

a. The preferred arrangement is an even number of battery trays where half the trayshave an inter–cell connection pattern which is a mirror image of the other half. Thetrays shall be arranged so that the small current loops in the mirror image pairs areequal and opposite and result in a minimum stray magnetic field.

I.6 Battery Arrangement Warning Plates

a. Warning plates shall show the physical arrangement of and the connections to thebattery trays. The plates shall be fitted close to the batteries.


ANNEX I I.2


ANNEX JJ.1

ANNEX J.

STRAY FIELD – GUIDE FOR MOTORS AND GENERATORS

J.1 Frame Design

a. The frame design shall meet the following requirements.

J.1.1 Frame Type

a. The magnetic frame shall be either a one piece construction with no joints orlaminated. This avoids the non–symmetry at a split. The weld in the frame shallbe at the main pole.

J.1.2 Frame Cross Section

a. The frame shall have a uniform cross section. If necessary, the inside and outsidesurfaces shall be machined.

J.1.3 Frame Material

a. The frame material shall be magnetically homogeneous throughout.

J.1.4 Frame Outside Shape

a. The exterior of the frame shall be smooth and cylindrical in nature with its axiscoincident with the axis of the generator. Magnetic feet and other major projectionsshall be avoided. Pole boltheads shall be recessed (bolts with slotted round headswhich almost completely fill the recessed holes are preferable).

J.1.5 Current Carrying Leads

a. Current carrying leads shall not be passed through the frame or other magnetic partof the machine, although they may go through some part of the enclosure whichis non magnetic.

J.2 Poles

J.2.1 Number of Poles

a. Two pole machines must not be used for any application of 100 watts or more andeven for these small machines, four poles are to be employed wherever possible.In general, the largest number of poles possible shall be used for all applications.

J.2.2 Orientation of Field Poles

a. To minimise the vertical component of stray field, one pair of main field poles shallbe oriented in a vertical plane or oriented so that a vertical plane equally dividesthe angle between adjacent main field poles.

J.2.3 Magnetic Contact

a. Care shall be taken, if necessary by grinding, to ensure good magnetic contactbetween the poles and the inside of the frame.

J.3 Symmetry and Uniformity

J.3.1 Air Gaps

a. All air gaps are to be uniform and as equal as possible.


ANNEX J J.2

J.3.2 Commutating Poles (Interpoles)

a. In machines which have commutating poles, there shall be as many commutatingpoles as main poles.

J.3.3 Number of Turns

a. All coils of the same kind (shunt field coils, commutating field coils) shall be thesame size and shape and shall have exactly the same number of turns.

J.3.4 Equalizer Connections

a. If these are fitted to a lap wound armature, they shall be in the form of rings ofuniform cross section throughout.

J.4 Wiring Around the Frame

J.4.1 Field Coils

a. Connections to field coils shall have no net turns around the shaft and nouncompensated current loops. This shall be implemented by looping back the fieldcoil connections on themselves to effect a stray field cancellation between theforward and return conductors. Shunt field connections shall all be at the same endof the machine and as close together as possible.

J.4.2 Commutating Coils and Compensating Windings

a. The end connections to the commutating coils and the compensating winding shallhave no net turns around the shaft and no uncompensated current loops. It isessential that the conductors are as close together as possible.

J.5 Brush Collector Rings

J.5.1 Construction

a. The brush collector rings shall be complete rings, concentric with the axis of themachine and of uniform cross section throughout the entire circumference.

J.5.2 Arrangement

a. There shall be either:

(1) Three brush collector rings equally spaced in the direction parallel to the axisof the machine, with the centre ring carrying full positive (or negative)current and each of the two outer rings carrying one half of the negative (orpositive) current;or:

(2) Two concentric rings, one larger than the other, mounted in the same planeperpendicular to the axis of the machine.

J.5.3 Current Take–off Point

a. The current take–off points shall be either:

(1) in line with the axis of the machine for machines with three brush connectorrings,


ANNEX JJ.3

or:(2) in a plane passing through the axis of the machine for machines with two

concentric brush rings in the same plane.

b. The current take–off point from one brush collector ring shall be at the same pointwhere one set of brushes is connected to the ring.

J.5.4 Connections from Brush Collector Rings

a. The connections from brush collector rings of a machine and the associated circuitshall be arranged with a central conductor carrying the full current and the twosymmetrically placed flanking conductors, each carrying half current, all soarranged as to avoid unbalanced current loops.

J.5.5 Position of Brush Collector Rings

a. The axial distance from the brush collector rings to the commutator risers shall beselected in a manner to minimise the effect of unequal current division betweendifferent sets of brushes.

J.5.6 Brush Rigging

a. Brush rigging shall be designed in a manner to force a well defined current pathbetween a set of brushes and the brush collector ring. This current path shall be ina plane which passes through the axis of the machine.

J.5.7 Number of Commutator Bars

a. The number of commutator bars shall be equal to an integral multiple of the numberof field poles.

J.5.8 Double Armature Machines

a. Machines with two armatures on the same shaft shall be designed in accordancewith the principle of mutual compensation. The two armatures shall be as alike aspossible and have their connections so arranged that the magnetic field of one isin opposition to the other.


ANNEX J J.4

NES 617Issue 4

October 2000

ANNEX KK.1

ANNEX K.

STRAY FIELD – GUIDE FOR INDUCTION CLUTCHES

K.1 Field Pole Requirements

a. A series of long and narrow field poles, which are alternately North and South, shallbe utilised in the induction clutch design. Field poles shall be wound with fieldcoils. Pole pieces may be fixed on the outside of the inner member or the insideof the outer member.

K.2 Field Coil Requirements

a. Each field coil wound round a field pole piece shall be interconnected as for a dcmachine described in Clause J.1.4. Field coil connections shall be at the same endof the clutch assembly and arranged as close together as possible. The connectionsshall be arranged to prevent a single concentric turn from being formed around theshaft of the machine.

K.3 Number of Field Poles

a. The preferred induction clutch design shall have 16 or more field poles.

NES 617Issue 4October 2000

ANNEX K K.2


ANNEX LL.1

ANNEX L.

STRAY FIELD – GUIDE FOR SWITCH AND CONTACTOR PANELS

L.1 Basic Conductor Arrangement

a. The basic arrangement of conductors in switch and contactor panels shall be threeparallel and closely adjacent conductors in the same plane. The central conductorshall carry two units of current in the forward sense and the two symmetricallydisposed outer conductors shall each carry one unit of current in the return sense.This is the same principle as the three terminal arrangement for cable runs in AnnexF.

b. The distance between devices and conductors in compensation circuits shall be theminimum required by the electrical creepage and clearance distances of theapplicable specification for the switch boxes and contactor panels.

L.2 Conductor Bends

a. Conductor bends can be of two types:

(1) the conductors lie in different planes on each side of the bend;or(2) the conductors lie in the same plane on each side of the bend.

L.2.1 Conductors Lying in Different Planes on Each Side of the Bend

a. Three parallel and closely adjacent conductors in the same plane shall maintain thesame separation and turn through the same angle as they bend into another plane.This is shown in Figure L.1.

L.2.2 Conductors Lying in the Same Plane on Each Side of the Bend

a. Three parallel and closely adjacent conductors in the same plane which bend in thatplane shall alter the spacing between themselves on the bend such that the areabetween the outer and the centre one is equal to the area between the centre and theinner one during the bend. This is shown in Figure L.2.

L.3 Devices in Power Circuits

a. Two terminal, series connected devices in power circuits such as ammeter shuntsand overload relays, shall always be arranged as the centre limb in a three terminalarrangement. The limbs on either side shall be the conductors for the return pathand be symmetrically arranged to effect the best cancellation.

L.3.1 Power Circuit Arrangements

a. Power circuit arrangements shall be the folded or criss–cross type. Thestraight–through type, i.e. cables entering one side of the panel or box and leavingon the opposite side, shall not be used. The folded arrangement inherently requiresthe incoming and outgoing terminals to be on the same end of the panel or box.The arrangement of conductors within the box shall be for best stray fieldcompensation and the distances between ingoing and outgoing conductors shall bethe minimum needed for creepage and clearance requirements.


ANNEX L L.2

Angle of the bend (angle A) isthe same for all three conductors

Conductor

A

A

A

A. Conductor bent in two planes

If the currents in the twoouter conductors are equaland if Area W = Area X andArea Y = Area Z, then zeronet magnetic moment ofcurrent will result.

ConductorA

A

A

B. Resulting current loops

Z

X

W

Y

Figure L.1 – Bend for Conductors Lying in Different Planes on Each Side of the Bend


ANNEX LL.3

Conductors

A

X

BIf the currents in the twoouter conductors are equaland if Area Z = Area X, thenzero net magnetic momentof current will result.

C

D E F

Z

Figure L.2 – Bend for Conductors Lying in the Same Plane on Each Side of the Bend


ANNEX L L.4

Inside Rear Cover

© Crown Copyright 2004

Copying Only as Agreed with DStan

Defence Standards are Published by and Obtainable from:

Defence Procurement Agency An Executive Agency of The Ministry of Defence

UK Defence Standardization Kentigern House 65 Brown Street

GLASGOW G2 8EX

DStan Helpdesk

Tel 0141 224 2531/2 Fax 0141 224 2503

Internet e-mail [email protected]

File Reference The DStan file reference relating to work on this standard is D/DStan/69/02/617 Contract Requirements When Defence Standards are incorporated into contracts users are responsible for their correct application and for complying with contractual and statutory requirements. Compliance with a Defence Standard does not in itself confer immunity from legal obligations. Revision of Defence Standards Defence Standards are revised as necessary by up issue or amendment. It is important that users of Defence Standards should ascertain that they are in possession of the latest issue or amendment. Information on all Defence Standards is contained in Def Stan 00-00 Standards for Defence Part 3 , Index of Standards for Defence Procurement Section 4 ‘Index of Defence Standards and Defence Specifications’ published annually and supplemented regularly by Standards in Defence News (SID News). Any person who, when making use of a Defence Standard encounters an inaccuracy or ambiguity is requested to notify the Directorate of Standardization (DStan) without delay in order that the matter may be investigated and appropriate action taken.