Section 2

Section 2System One-Line Diagram

PageINTRODUCTION ................................................................................................ 2-2

DEVELOPING A ONE-LINE DIAGRAM .............................................................. 2-2

PRELIMINARY ONE-LINE DIAGRAM................................................................. 2-4

PARTIALLY DEVELOPED ONE-LINE DIAGRAM .............................................. 2-5

DEVELOPED ONE-LINE DIAGRAM ................................................................. 2-6

ADAPTING ONE-LINE DIAGRAM TO EQUIPMENT........................................... 2-8

REFERENCES............................................................................................... 2-10

2-1

Contents

System One-Line Diagram

INTRODUCTION

The first step in preparing a specification formetalclad switchgear is to develop a one-line dia-gram. A one-line diagram (single line) is “a dia-gram that shows, by means of single line andgraphic symbols, the course of an electric circuitor system of circuits and the component devicesor parts used therein.” (See Ref. 1 on Page 2-10.)

When preparing switchgear one-line diagrams,use graphic symbols in accordance with IEEE andANSI standards listed in References 2 and 3 onpage 2-10.

One-line diagrams employ device functionnumbers which, with appropriate suffix letters, areused to identify the function of each device in alltypes of partially automatic, fully automatic, andin many types of manual switchgear. A completelist of such device function numbers is publishedin C37.2.1996 and shown in Table 2-2.

DEVELOPING A ONE-LINE DIAGRAM

To illustrate the development of a one-line dia-gram, a typical resistance grounded system hasbeen chosen. The same general procedures wouldapply to solidly grounded distribution systems.

Three steps are used in producing a one-linediagram: the preliminary diagram, followed by thepartially developed diagram, and finishing with thedeveloped diagram.

The abbreviations used for principal meters,instruments, and other devices (not including re-laying, which is listed in Table 2-2), as found inthe application guide, are listed in Table 2-1.

Each device in an automatic switching equip-ment has a device function number which is placedadjacent to or within the device symbol on all wir-ing diagrams and arrangement drawings so thatits function and operation may be readily identi-fied.

These numbers are based on a system whichwas adopted as standard for Automatic Switchgearby the American National Standards Institute andappear in ANSI C37.2-1996. (See Ref. 4 on page2-10.)

Table 2-2 is a list of device numbers andfunctions as taken from this standard.

Table 2-1. Abbreviations

2-2

AM Ammeter S Synchronous motorAS Ammeter switch S/A Surge arresterAux Auxiliary SS Synchronizing switchBkr Breaker SYN SynchroscopeCO Cut off switch SYN BR Synchronizing bracketCPT Control power transformer TD Test deviceCS Control switch VAR Varmeter (one-line)CT Current transformer VARM Varmeter (device list)FA Field ammeter VM VoltmeterFM Frequency meter VR Voltage regulatorG Generator VS Voltmeter switchGS Governor switch WHM Watthour meterI Induction motor WHDM Watthour demand centerVT Voltage transformer WM Wattmeter

Abbr. Description Abbr.

Section 2

Dev.No. Function1 Master Element2 Time-Delay Starting or Closing Relay3 Checking or Interlocking Relay4 Master Contactor5 Stopping Device6 Starting Circuit Breaker7 Anode Circuit Breaker8 Control Power Disconnecting Device9 Reversing Device10 Unit Sequence Switch11 Multifunction Relay12 Over-Speed Device13 Synchronous-Speed Device14 Under-Speed Device15 Speed or Frequency Matching Device16 Reserved for future application17 Shunting or Discharge Switch18 Accelerating or Decelerating Device19 Starting-to-Running Transition Contactor20 Electrically Operated Valve21 Distance Relay22 Equalizer Circuit Breaker23 Temperature Control Device24 Reserved for future application25 Synchronizing or Synchronism-Check Device26 Apparatus Thermal Device27 Undervoltage Relay28 Flame Detector29 Isolating Contactor30 Annunciator Relay31 Separate Excitation Device32 Directional Power Relay33 Position Switch/Cell Switch34 Master Sequence Device35 Brush-Operating or Slip-Ring Short-Circuiting Device36 Polarity or Polarizing Voltage Device37 Undercurrent or Underpower Relay38 Bearing Protective Device39 Mechanical Condition Monitor40 Field Relay41 Field Circuit Breaker42 Running Circuit Breaker43 Manual Transfer or Selector Device44 Unit Sequence Starting Relay45 Atmospheric Condition Monitor46 Reverse-Phase or Phase-Balance Current Relay47 Phase-Sequence Voltage Relay48 Incomplete Sequence Relay49 Machine or Transformer Thermal Relay50 Instantaneous Overcurrent or Rate-of-Rise Relay

Dev.No. Function51 AC Time Overcurrent Relay52 AC Circuit Breaker53 Exciter or DC Generator Relay54 Reserved for future application55 Power Factor Relay56 Field Application Relay57 Short-Circuiting or Grounding Device58 Rectification Failure Relay59 Overvoltage Relay60 Voltage or Current Balance Relay61 Reserved for future application62 Time-Delay Stopping or Opening Relay63 Pressure Switch64 Ground Protective Relay65 Governor66 Notching or Jogging Device67 AC Directional Overcurrent Relay68 Blocking Relay69 Permissive Control Device70 Rheostat71 Level Switch72 DC Circuit Breaker73 Load-Resistor Contactor74 Alarm Relay75 Position Changing Mechanism76 DC Overcurrent Relay77 Pulse Transmitter78 Phase-Angle Measuring or Out-of-Step Protective Relay79 AC Reclosing Relay80 Flow Switch81 Frequency Relay82 DC Reclosing Relay83 Automatic Selective Control or Transfer Relay84 Operating Mechanism85 Carrier or Pilot-Wire Receiver Relay86 Locking-Out Relay87 Differential Protective Relay88 Auxiliary Motor or Motor Generator89 Line Switch90 Regulating Device91 Voltage Directional Relay92 Voltage and Power Directional Relay93 Field-Changing Contactor94 Tripping or Trip-Free Relay95 Used only for specific applications96 in individual installations97 where none of the98 assigned numbered functions99 from 1-94 are suitable.

}

2-3

Table 2-2. ANSI Standard Device Function Numbers

System One-Line Diagram

PRELIMINARY ONE-LINE DIAGRAM

On this diagram (Figure 2-1) show:

• System voltage and major component ratings.

• Major medium-voltage cable lengths,sizes,and construction. (Not shown inexample.)

• Approximate number and ratings of allmotors.

• Supply system available short-circuitcapabilityin symmetrical MVA (plus X/R ra-tio) or per unit R+jX (on a given basis).

Using data on the one-line diagram, perform shortcircuit calculations:

• Compare the calculated “first cycle” (Momen-tary) asymmetrical current duty with the closeand latch circuit breaker capability.

• Compare the calculated “1-1/2 to 4-cycle”(interrupting) current duty with the circuitbreaker symmetrical interrupting capability.(See Ref. 5 on page 2-10.)

• Determine the applicable circuit breakerratings.

• Compare the feeder cable short-circuit heat-ing limit with the maximum available short-circuit current time Kt times Ko.(See Ref. 10 and 11 on page 2-10.)

Note that the calculations performed in accor-dance with Reference 5 (on page 2-10) determineonly medium and high-voltage circuit breaker rat-ings. Perform short-circuit studies to determinerelay operating currents in accordance with pro-cedures outlined in Reference 6 (on page 2-10).For other than power circuit breakers, refer to theappropriate ANSI standard for short-circuit calcu-lation procedure.2-4

Figure 2-1. Preliminary one-line diagram

Section 2

PARTIALLY DEVELOPED ONE-LINE DIAGRAM

Using the sample system, a partially devel-oped one-line diagram is shown in Figure 2-2. Onthis diagram, the specifier should:

• Show the results of the short-circuit cal-culations performed, using the preliminaryone-line diagram and selected circuitbreaker ratings.

• Show ratings selected for external de-vices, such as grounding resistors, con-trol power transformers, considering thetype of protective relaying instrumentationand metering required.

• Select tentative current transformer (CT)ratios inconsidering the maximum trans-former rating, motor ratings, and ampacityof the circuits involved. (See Section 5.)

• Locate current transformers and voltagetransformers, considering the type of pro-tective relaying instrumentation andmetering required.

2-5

Figure 2-2. Partially developed one-line diagram

System One-Line Diagram

Figure 2-4. Typical Protective Relay Symbols

DEVELOPED ONE-LINE DIAGRAM

A developed one-line diagram for the systemis shown in Figure 2-3. In addition to the informa-tion shown on the partially developed one-line dia-gram, the specifier should:

• Show all relaying, instrumentation, andmetering.

• Select relaying, instrumentation, and meter-ing using the information given in Sections 5and 6 of this Application Guide.

• Confirm the selection of relay ratings andcharacteristics by performing a completesystem short-circuit and coordination study.(See Ref. 7 through 10 on page 2-10.)

• Include in the study an examination of allcircuits for compliance with applicable localand national codes.(See Ref. 11 on page 2-10.)

• Verify that all circuit conductors are appliedwithin the conductor short-circuit heating limit.(See Ref.10 on page 2-10.)

2-6

Time (Typical) 0.5 to 5 seconds

Phase Time & Instantaneous Relay

Residually Connected Time Overcurrent Relay

Ground Time Overcurrent Relay

Ground Sensor Instantaneous Overcurrent Relay

Phase Time Overcurrent Relay

Residually Connected Time Overcurrent Relay

High Speed Transformer Differential Relay

Motor Differential Relay

Motor Lockout Relay

Bus Differential Relay

Bus Differential Lockout Relay

5051

51N

51G

50GS

51B

51NB

87T

87TG

86T

87M

86M

87B

86

62

B

Transformer Ground Differential Relay

Transformer Differential Lockout Relay

Section 2

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Section 2

2-9

ADAPTING ONE-LINE DIAGRAMTO EQUIPMENT

Figure 2-5 shows two possible arrangements ofPower/Vac metalclad switchgear as developed fromthe one-line diagram in Figure2-3. Both save space when compared to one-high metalclad switchgear, and both permit theaddition of future units on either end.

The arrangements shown are not the only oneswhich can be developed to satisfy the conditionsof the one-line diagram. Use theinformation in Sections 6 and 7 to adapt the one-line diagram to the equipment and develop asuitable arrangement for the particular installation.

System One-Line Diagram

REFERENCES

Standards

ANSI IEEE Standard Standard Title

1. C42.100-1992 100-1977 IEEE Standard Dictionary of Electrical and Electrical Terms.

2. Y32.2-1975 315-1975 Graphic Symbols for Electrical and Electronic Diagrams.

3. Y14.15-1966 (R1973) Electrical and Electronics Diagram.

4. C37.2-1996 Electrical Power System Device Function.

5. C37.010-1999 Application Guide for AC High-Voltage Circuit BreakersRated on a Symmetrical Current Basis.

6. C37.95-1989 (R1994) 357-1973 IEEE Guide for Protective Relaying of Utility-ConsumerInterconnections.

7. 141-1969 Electric Power Distribution for Industrial Plants.

8. 142-1972 IEEE Recommended Practice for Grounding of Industrialand Commercial Power Systems.

9. 241-1974 IEEE Recommended Practice for Electrical Power Systemsin Commercial Buildings.

10. 242-1975 IEEE Recommended Practice for Protection andCoordination of Industrial and Commercial Power Systems.

2-10

Books11. Industrial Power Systems Handbook

D.L. Beeman, Editor McGraw-Hill BookCo., 1955.

Publications12. GEA-10049H Power/Vac® Metalclad Switchgear.

13. GET-6600F Power/Vac® Application Guide.

Standards may be purchased from:American National Standards Institute, Inc.

1430 BroadwayNew York, NY 10018

Institute of Electrical and Electronics Engineers, Inc.Service Center445 Hoes LanePiscataway, NJ 08854

National Electrical Manufacturers AssociationPublication Department2101 L St. N.W. Suite 300Washington, D.C. 20037

National Fire Protection Association470 Atlantic AvenueBoston, MA 02210