Cupula - Gran Telescopio Canarias Referencia...check and illustrate their applicability. A final trade-off analysis was developed to evaluate the pros and cons of each solution. All

Gran Telescopio de Canarias, S.A.

Instituto de Astrofísica de Canarias Centro Común de Astrofísica de La Palma Vía Láctea s/n Cuesta de San José s/n 38200 - LA LAGUNA, TENERIFE, Islas Canarias 38712 BREÑA BAJA, LA PALMA, Islas Canarias Tfno +34 922 315 031 Fax +34 922 315 032 Tfno +34 922 425 720 Fax +34 922 425 701

http://www.gtc.iac.es E-Mail: [email protected]

Código : EXT/IDOM/2015-R Edición : 1.A Fecha: 2014-05-19

GTC Dome Shutters Upgrade. Preliminary Reliability Analysis

Cupula

Control de aprobación

Recibido por:

Lluís Cavaller Marques Ingeniero de Desarrollos

Autorizado por: Pedro Álvarez Martín

Director

Fecha:2014-05-19

GTC Dome Shutters Upgrade Reliability Analysis

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GTC Dome Shutters Upgrade

PHASE II: RELIABILITY ANALYSIS

TECHNICAL REPORT

Doc. Number: 18242-TRE-012 Issue: 2 Date: 11/04/2014 Revision: - Date: - Contract No: -

Name Signature Date

Written Nigel Bilbao 11/04/2014

Revised Asier Larringan 11/04/2014

Project Manager Celia Gómez 11/04/2014

Principal Gaizka Murga 11/04/2014

File: 18242-TRE-012-01_Reliability-Analysis.docx Pages: 42


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RECORD OF CHANGES

Issue Date Author Description

1.D 26/02/2014 Nigel Bilbao Draft version

1 28/02/2014 Nigel Bilbao First version

2 11/04/2014 Nigel Bilbao Version after Review Meeting with

GRANTECAN


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ABBREVIATIONS AD Applicable Document GTC Gran Telescopio de Canarias HPU Hydraulic Power Unit MTTF Mean Time To Failure MTBF Mean Time Between Failures MTTR Mean Time To Repair N/A Not Applicable NC Not Compliant ORM Observatorio de Roque de los Muchachos PA Product Assurance PHA Preliminary Hazards Analysis RAMS Reliability, Availability, Maintainability and Safety RBD Reliability Block Diagram RD Reference Document ROM Rough Order of Magnitude SOW Statement of Work TBC To Be Confirmed TBD To Be Determined TBR To Be Revised UPS Uninterrupted Power System VSD Variable Speed Drives


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TABLE OF CONTENTS

1 SCOPE OF THE DOCUMENT ................................................................................................. 7

2 APPLICABLE AND REFERENCE DOCUMENTS ................................................................. 8

2.1 APPLICABLE DOCUMENTS .............................................................................................................................. 8

2.2 REFERENCE DOCUMENTS .............................................................................................................................. 8

3 INTRODUCTION ...................................................................................................................... 9

3.1 BACKGROUND .................................................................................................................................................. 9

3.2 OVERVIEW OF THE PROPOSED DESIGN ..................................................................................................... 10

3.3 DOCUMENT STRUCTURE ............................................................................................................................... 11

4 RELIABILITY ANALYSIS PROCEDURE ............................................................................... 12

4.1 INTRODUCTION .............................................................................................................................................. 12

4.2 RELIABILITY BLOCK DIAGRAMS ................................................................................................................. 12

4.3 DEFINITION OF FAILURE RATE .................................................................................................................... 13

4.4 REPAIRABLE AND NON-REPAIRABLE SYSTEMS ......................................................................................... 14

5 UPPER SHUTTER SYSTEM .................................................................................................... 16

5.1 INTRODUCTION .............................................................................................................................................. 16

5.2 CURRENT STATUS ........................................................................................................................................... 17

5.2.1 System representation ..................................................................................................................................... 17 5.2.2 Results ........................................................................................................................................................... 19

5.3 NEW STATUS ................................................................................................................................................... 21


5.4 RELIABILITY AND AVAILABILITY DIAGRAMS ............................................................................................. 25

6 LOWER SHUTTER SYSTEM .................................................................................................. 27

6.1 INTRODUCTION .............................................................................................................................................. 27

6.2 CURRENT STATUS ........................................................................................................................................... 28


6.3 NEW STATUS ................................................................................................................................................... 31


6.4 RELIABILITY AND AVAILABILITY DIAGRAMS ............................................................................................. 35

7 CONCLUSIONS ....................................................................................................................... 37

8 ADDITIONAL ANALYSES ...................................................................................................... 38

8.1 UPPER SHUTTER UPDATED NEW STATUS ................................................................................................... 38

8.2 LOWER SHUTTER UPDATED NEW STATUS ................................................................................................. 40


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1 S C O P E O F T H E D O C U M E N T

This document describes the Reliability Analysis performed for the proposed GTC Dome Shutters Upgrade as compared to the current situation. The results from this analysis determine the current and upgraded system availability and can be used for the definition of a preventive maintenance plan. Together with the Preliminary Design Report (18242-TRE-011-01), the Implementation Plan (18242-PLA-013-01) and the Preliminary Cost Estimation (18242-LIS-014-01), this report constitutes the Final Delivery Package for the Definition of the GTC Dome Shutters Upgrade project.


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2 A P P LI C A B LE A N D R E F E R E N C E D O C U M E N T S

2.1 APPLICABLE DOCUMENTS

Title Reference Iss. Date

AD 1 Statement of Work for the definition of GTC Dome Shutters Upgrade

ESP/EDIF/0200-R 1.A 20/03/2013

AD 2 Current Status of the Dome Shutters RPT/EDIF/0386-R 1.A 18/03/2013

2.2 REFERENCE DOCUMENTS

Title Reference Iss. Date

RD 1 1st Progress Meeting Presentation 18242-PRE-001 1 11/10/2013

RD 2 1st Progress Report 18242-TRE-002 1 9/10/2013

RD 3 1st Progress Meeting Minutes 18242-MIN-003 1 16/10/2013

RD 4 Phase I: Analysis of Alternatives Report 18242-TRE-004 1 25/11/2013

RD 5 End of Phase I Meeting Presentation 18242-PRE-005 1 29/11/2013

RD 6 End of Phase I Meeting Minutes 18242-MIN-006 2 02/12/2013

RD 7 Phase II: Preliminary Cost Estimation 18242-LIS-014 2 11/04/2014

RD 8 Phase II: Implementation Plan 18242-PLA-013 2 11/04/2014

RD 9 Phase II: Preliminary Design Report 18242-TRE-011 2 11/04/2014

RD 10 The Complete Guide to Chain (http://chain-guide.com)

RD 11 Michael Hess – Replacing the K1 Dome Shutter drive system

Proc. SPIE 6273-17

RD 12 “Reliability, Maintainability and Risk”, D. J. Smith

RD 13 “Reliability, Availability and Optimization”, Reliasoft System Analysis Reference


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3 I N T RO D U C T I O N

3.1 BACKGROUND

The current shutter system of the GTC dome does not fully comply with the expected requirements. The problems detected are essentially: a) a restricted range on main shutter opening, which limits the telescope observation angle to 70 deg. above horizon; b) premature damage on shutter bogies; c) the impossibility of deploying the windscreen, which has not been commissioned yet; d) damages (cracks, corrosion, deformations) in the dome arch beams. These problems are described by GRANTECAN in document AD 2. GRANTECAN has launched this project consisting of: a) an analysis of alternatives aimed to finding solutions to the current problems of the GTC dome shutters; b) selecting the best solution in terms of performance, cost and implementation time and developing it up to a preliminary design. During the Phase I of this project the diagnostics developed by GRANTECAN was analysed and completed and individual actions were identified aimed to solve each problem detected. In order to evaluate the feasibility of these actions, they were combined into 3 particular packages, intended to configure 3 potential solutions that were physically developed up to a conceptual design stage to check and illustrate their applicability. A final trade-off analysis was developed to evaluate the pros and cons of each solution. All this work is compiled in RD 4. At the end of Phase I, GRANTECAN reviewed the delivered documentation and decided on the solution out of the 3 proposed options which will be further developed up to a preliminary design stage. The solution selected was the first alternative proposed (Option A), but modified to include some additional actions:

• Bogies design upgrade

• Possibility of excluding the counterweight system

• Prevision of emergency systems for the lower shutter operation Option A consists in basically keeping the existing drive system typology but introducing a set of incremental actions aimed to improve the current performance and solve the main problems. The safety and reliability of each of the components (chains, motors, gearboxes) is increased as their demanding loads will be lower than the allowable values. The actions include: – Replace current upper shutter chains by others with higher strength – Implement a counterweight system to reduce load at the last part of upper shutter travel – Improve load sharing between drives by a proper control system strategy. – Install a take-up system in chains to reduce the required preload – Install axial supplements in the guiding rails to reduce the rail runout – Replace motors and gearboxes of Lower shutter by others with higher power – Move the location of windscreen latching system to avoid overlapping – Reduce the windscreen weight – Replace current windscreen rollers cam followers for friction reduction – Modify the bottom profile of the windscreen guides – Monitor crack propagation, register a crack inventory and take actions according to the

propagation speed (grind-repair, crack arrest drilling, structural reinforcement…)


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3.2 OVERVIEW OF THE PROPOSED DESIGN

The GTC Dome Shutters proposed modifications relevant to the present reliability analysis affect to the drive system, control system and guiding system of both upper shutter and lower shutter.

• Regarding the drive system, the upgraded design includes:

- Replacement of current roller chains by higher capacity chains, in both upper and lower shutter

- In addition, for the lower shutter:

o replacement of main motors for higher power motors

o replacement of current gearboxes for double input gearboxes to include an auxiliary gearmotor for redundancy, which will enable emergency operation in case of failure of main motor.

Fig 3-1 Actions in shutters drive systems

The proposed redesign also includes an optional counterweight system, which would contribute to reduce the loads in the last stage of the upper shutter travel.

• For the guiding system, an improved bogie design is proposed with capability to absorb the rail radial misalignment by means of a hydraulic equalization system. For each shutter, four hydraulic equalization groups (each one including 5 bogies for the upper shutter and 2 bogies for the lower shutter) have been defined.

Fig 3-2 Guiding system upgrade


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Apart from the hydraulic actuator and the eccentric shaft for radial adjustment, the new bogie design includes two radial wheels instead of one, for additional strength under the acting loads.

The shutters lateral guidance is also improved by means of axial correction supplements welded to the rails.

• For the control system, an optimized control strategy (“Speed Trim Follower”) is proposed aimed to provide a better load sharing between drives. This configuration consists of:

– the master drive is operated in speed regulation

– the slave drives are operated in speed regulation with a speed trim that is function of the difference between the master drive and each slave drive torque.

The equal load distribution between drives achieved with this new control strategy, together with the replacement of drive chains and the improvement on shutter lateral guidance provided by the axial correction supplements, can enable the operation of the upper shutter with only three out of the four drives in emergency conditions.

More information about the Preliminary Design can be found in RD 9.

3.3 DOCUMENT STRUCTURE

The contents of this document are structured as follows:

• The next chapter (Chapter 4) describes the general reliability analysis procedure: the concepts of Mean Time Between Failures (MTBF) and Mean Time to Repair (MTTR), the assumptions and exclusions of the present analysis, the representation in Reliability Block Diagrams (RBD), the definition of the Failure rate and the classification of systems in Repairable and Non-Repairable.

• Chapter 5 and Chapter 6 contain the reliability assessment for the Upper Shutter and the Lower Shutter respectively, applied to current status and new status (upgraded system). It includes the system representation and the obtained results, together with final plots comparing the availability and reliability in current and new status.

• Finally, Chapter 7 summarizes the conclusions of this analysis.


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4 R E LI A B I LI T Y A NA LY S I S P RO C E D U R E

4.1 INTRODUCTION

The aim of this analysis is to study the reliability of the GTC Dome Shutters proposed upgrade and quantify the improvement with respect to the current. As part of this assessment, the mean time between failures (MTBF) is obtained for the Upper and Lower Shutter Once obtained the MTBF and determined the MTTR, the availability of each shutter, defined as the probability that a repairable system will fulfil its specified function at a certain time, can be determined as,

MTTRMTBF

MTBFAI

+=

The down time (= 1-Availability) gives an idea of how much time the system is stopped comparing to the total time. A reliability analysis provides a quantitative measure of how close a proposed design comes to meeting the design objectives and allows comparisons to be made between different designs (in this case, current system and proposed redesign). The assessment has been performed at a high level, i.e. potential failures of easily replaceable components, such as electric elements of electric cabinets (relays, current supply, etc.) have not been considered. This reliability analysis refers only to components whose MTTR is more than 4 hours. Also, it is assumed an uninterrupted power supply to the GTC dome in the Observatory (an UPS would provide power in case of failure of the electrical supply)

4.2 RELIABILITY BLOCK DIAGRAMS

In order to determine the reliability of the systems, the different failure modes have been identified and the system reliability as a function of component reliability has been studied, by means of Reliability Block Diagrams.

Fig 4-1 Reliability Block Diagram (RBD) for a given system


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In order to form a system reliability block diagram, the reliability-wise configuration of the components must be determined. The RBD of a complex system can be formed by different combinations of the following simple configurations:

- Series configuration: in a series configuration a failure of any component results in the failure of the entire system

- Simple parallel configuration: in a simple parallel system, at least one of the units must succeed for the system to succeed.

- K-out-of-n configuration: this type of configuration requires that at least k components succeed out of the total n parallel components for the system to succeed.

Fig 4-2 Series, parallel and k-out-of-n configuration examples

4.3 DEFINITION OF FAILURE RATE

For the different components involved in the system the failure rate λ(t) - defined as the probability of an item failing in the interval t to t+dt, given that it has survived until time t- is assigned.

)(

)()(

tR

tft =λ

where, f(t) is the failure probability density function R(t) is the reliability or probability of survival until a time t Many mechanical and electrical components failure rate can be adjusted to a “bathtub” failure rate function, which establishes that,

- the failures exhibited in the first part of the curve, where failure rate is decreasing, are called early or infant mortality failures

- the middle portion is referred to as the useful life and it is assumed that failures exhibit a constant failure rate

- the latter part of the curve describes the wear-out failures and it is assumed that failure rate increases as the wear-out mechanisms accelerate


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Fig 4-3 Bathtub failure rate distribution, typical of many mechanical components

A constant value of λ (failure rate) has been considered for each component of the system. This assumption involves that early failures would be mostly corrected during the commissioning of the systems and wear-out failures would be minimized with an appropriate preventive maintenance policy. Thus, reliability (R(t)) can be expressed as,

td

eetR

t

λττλ

−−

=∫

= 0)(

)(

The failure rate data for the different components have been obtained from the FARADIP.THREE data bank [RD 12].

4.4 REPAIRABLE AND NON-REPAIRABLE SYSTEMS

Systems can be generally classified into non-repairable and repairable systems. Non-repairable systems are those that do not get repaired when they fail. On the other hand, repairable systems are those that get repaired when fail. This is done by repairing or replacing the failed components in the system. Considering a system as a non-repairable one, analytical methods can be applied, obtaining parameters such as the followings:

- system failure probability density function (pdf) - warranty periods - system failure rate - mean time to failure (MTTF)

If the systems are treated as repairable ones and a maintenance policy is established, similar results can be determined by means of simulation, obtaining the following parameters:

- system availability - mean time between failure (MTBF)

Depending on the preliminary results of the reliability analysis, actions on the most critical component of each system in order to improve system reliability can be considered. This action is focused following two approaches,


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- fault avoidance, e.g. increase components reliability - fault tolerance, e.g. consider component redundancy or ‘k-out-of-n’ parallel configurations


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5 U P P E R S H UT T E R S Y S T E M

5.1 INTRODUCTION

The aim of this chapter 5 is to make a comparison between the current status and the new status of the dome upper shutter system. For this purpose, taking into account the failure rates of the different components that compose the upper shutter, the MTBF, the MTTR and the availability will be obtained. In the new status analysis, the optional counterweight system has not been considered. If this system is finally installed, it will increase the reliability associated to the upgraded upper shutter. The following figures show some of the different components and subsystems that have been taken into account for the reliability analysis:

Fig 5-1 Upper shutter current status guiding system and drive mechanism

Fig 5-2 Upper shutter new status guiding system and drive mechanism


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5.2 CURRENT STATUS

The following figure represents the RBD of the current status of the upper shutter system:

Fig 5-3 Upper shutter system current status reliability block diagram

5.2.1 System representation

For the correct operation of the upper shutter mechanism, the control system, the drive system and the guiding system must work correctly. Therefore the RBD for the dome upper shutter mechanism is as follows:

Fig 5-4 Upper shutter mechanism representation


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The control system controls the upper shutter drive system and is composed of a PLC (which includes communication cards, power supplies, etc.) and a rectifier.

Fig 5-5 Upper shutter control system representation

As shown in Fig 5-1, the drive system is composed of four drives that two of them are in the upper motor stations (upper part of the dome) and the other two are in the lower motor stations (at the lower part of the dome). These drives are composed by some subsystems such as the frequency converter (VSD), the motor, the brake, the encoder, the gearbox and the chain (see Fig 5-6). As it can be seen in Table 5-1, some drive’s components have two MTTR (Mean Time To Repair) values depending if the component belongs to an upper or a lower drive.

Fig 5-6 Upper shutter drive system representation

The guiding system, shown in Fig 5-1, is composed of twenty six bogies, which need to be working for the correct movement of the dome upper shutter. In the same way, every wheel of the bogie together with its corresponding bearing has to be working for its correct operation.


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Fig 5-7 Upper shutter guiding system representation

As it has been explained before, the system has been studied as a repairable system. The failure data for each component, used as input for the system analysis, has been obtained from the FARADIP.THREE data bank [RD 12], and are shown as follows:

Table 5-1. Component failure rate and MTTR used in the Upper Shutter System Current Status analysis

5.2.2 Results

The whole GTC Dome Shutters lifetime (50 years) has been considered. Up to 10000 different failure scenarios have been simulated (with different combination of components failure along the time). For each component, a MTTR (mean time to repair) value has been considered. The MTBF for each subsystem has been obtained, as well as the MTBF of the whole system. Applying the formula explained in chapter 4.1, with the selected MTTR, the availability and MTTR of every subsystem and the whole system have been obtained. These results are shown in the following table:

Failure Rate

(per million hours)

λ

(1/hours)

Component MTTF

(hours)

Component MTTF

(years)

Component MTTR

(hours)

Wheels 2 0.000002 5.00E+05 119.05 168Bearings 2 0.000002 5.00E+05 119.05 168VSD 5 0.000005 2.00E+05 47.62 4Motor a.c. 5 0.000005 2.00E+05 47.62 Upper: 36 / Lower: 24Brake 10 0.00001 1.00E+05 23.81 Upper: 12 / Lower: 8Encoder 7 0.000007 1.43E+05 34.01 Upper: 36 / Lower: 24Gearbox 20 0.00002 5.00E+04 11.90 Upper: 72 / Lower: 48Chain 0.5 0.0000005 2.00E+06 476.19 24PLC 40 0.00004 2.50E+04 5.95 4Rectifier 4 0.000004 2.50E+05 59.52 24


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Table 5-2. Upper Shutter System Current Status Reliability, Availability & MTTR analysis results.

MTBF

(hours)

MTBF

(years)

MTTR

(hours)

Availability

(%)

Bogie 2.49031E+05 59.29 167.99 99.93Guiding System 9.59461E+03 2.28 167.93 98.28Upper Drive 2.09829E+04 5.00 42.72 99.80Lower Drive 2.09847E+04 5.00 28.73 99.86Drive System 5.26684E+03 1.25 35.63 99.33Control System 2.26503E+04 5.39 5.82 99.97System 2.95969E+03 0.70 72.40 97.61


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5.3 NEW STATUS

The following figure represents the RBD of the new status of the upper shutter system:

Fig 5-8 Upper shutter system new status reliability block diagram


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For the correct operation of the upper shutter mechanism, the control system, the drive system and the guiding system must work correctly. Therefore the RBD for the dome upper shutter mechanism is as follows:

Fig 5-9 Upper shutter mechanism representation

The control system controls the upper shutter drive system and is composed of a PLC (which includes communication cards, power supplies, etc.) and a rectifier.

Fig 5-10 Upper shutter control system representation

As shown in Fig 5-2, the drive system is composed of four drives that two of them are at the top of the shutter and the other two are at the lower part of the shutter. These drives are composed by some subsystems such as the frequency converter (VSD), the motor, the brake, the encoder, the gearbox and the chain (see Fig 5-11). As it can be seen in Table 5-3, some drive’s components have two MTTR (Mean Time To Repair) values depending if the component belongs to an upper or a lower drive. Considering the actions taken for the drive system upgrade (higher resistance chains, improved control strategy) together with the lateral guidance correction, the new design enables the operation with 3 out of 4 drives

Fig 5-11 Upper shutter drive system representation

DRIVE 1

DRIVE 2

DRIVE 3

DRIVE 4

3/4


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The updated guiding system, shown in Fig 5-2, is composed of four hydraulic groups (5 bogies per group). All hydraulic groups need to be properly working for the correct support of the dome upper shutter. It has been assumed that inside each hydraulic group, a failure of one of the new supporting bogies can be admitted. The new bogie system is composed of a hydraulic actuator and a new bogie. Each bogie has two radial wheels with each corresponding bearing. None of them can be damaged for a proper working of this bogie.

NEW BOGIE

SYSTEM 1

NEW BOGIE

SYSTEM 2

NEW BOGIE

SYSTEM 3

NEW BOGIE

SYSTEM 4

4/5

NEW BOGIE

SYSTEM 5

HYDRAULIC BOGIE GROUP’S COMPOSITION


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Fig 5-12 Upper shutter guiding system representation


Table 5-3. Component failure rate and MTTR used in the Upper Shutter System New Status analysis

5.3.2 Results


Table 5-4. Upper Shutter System New Status Reliability, Availability & MTTR analysis results.

Failure Rate

(per million hours)

λ

(1/hours)

Component MTTF

(hours)

Component MTTF

(years)

Component MTTR

(hours)

Wheels 1 0.000001 1.00E+06 238.10 168Bearings 1 0.000001 1.00E+06 238.10 168Hydraulic Actuator 15 0.000015 6.67E+04 15.87 48Hydraulic System 10 0.00001 1.00E+05 23.81 168VSD 5 0.000005 2.00E+05 47.62 4Motor a.c. 5 0.000005 2.00E+05 47.62 Upper: 36 / Lower: 24Brake 10 0.00001 1.00E+05 23.81 Upper: 12 / Lower: 8Encoder 7 0.000007 1.43E+05 34.01 Upper: 36 / Lower: 24Gearbox 20 0.00002 5.00E+04 11.90 Upper: 72 / Lower: 48Chain 0.5 0.0000005 2.00E+06 476.19 24PLC 40 0.00004 2.50E+04 5.95 4Rectifier 4 0.000004 2.50E+05 59.52 24

MTBF

(hours)

MTBF

(years)

MTTR

(hours)

Availability

(%)

Bogie 2.48382E+05 59.14 167.88 99.93Bogie System 5.26788E+04 12.54 73.09 99.86Hydraulic Bogie Group 1.98860E+06 473.48 35.81 100.00Guiding System 8.27506E+04 19.70 145.20 99.82Upper Drive 2.09829E+04 5.00 42.72 99.80Lower Drive 2.09847E+04 5.00 28.73 99.86Drive System 1.05209E+06 250.50 17.37 100.00Control System 2.26503E+04 5.39 5.82 99.97System 1.74524E+04 4.16 35.32 99.80


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5.4 RELIABILITY AND AVAILABILITY DIAGRAMS

The next figures show the comparison of the reliability functions for current status and new status of the upper shutter. Fig 5-13 time scale refers to the lifetime of 50 years. Fig 5-14 shows the first part of the plots (ten initial years) for discernment of the difference in the curve shape.

Fig 5-13 Upper shutter current and new status reliability diagrams (50 years)

Fig 5-14 Upper shutter current and new status reliability diagrams (10 years)

Next figure shows the system up/down periods along time for the upper shutter current status and new status. The system availability is increased from 97.61% to 99.80%.

Control System

Drive System

Guiding System

System

Control System

Drive System

Guiding System

System


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Fig 5-15 Upper shutter current and new status availability diagrams


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6 LOW E R S H U T T E R S Y S T E M

6.1 INTRODUCTION

The aim of this chapter 6 is to make a comparison between the current status and the new status of the dome lower shutter system. For this purpose, taking into account the failure rates of the different components that compose the upper shutter, the MTBF, the MTTR and the availability will be obtained. For the lower shutter system reliability analysis, the windscreen potential failures have not been considered for the analysis. The following figures show some of the different components and subsystems that have been taken into account for the reliability analysis:

Fig 6-1 Lower shutter current status guiding system and drive mechanism

Fig 6-2 Lower shutter new status guiding system and drive mechanism


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6.2 CURRENT STATUS

The following figure represents the RBD of the current status of the lower shutter system:

Fig 6-3 Lower shutter system current status reliability block diagram


For the correct operation of the lower shutter mechanism, the control system, the drive system and the guiding system must work correctly. Therefore the RBD for the dome lower shutter mechanism is as follows:

Fig 6-4 Lower shutter mechanism representation

The control system controls the lower shutter drive system and is composed of a PLC (which includes communication cards, power supplies, etc.) and a rectifier.

PLC

DRIVE 1

DRIVE 2

RECTIFIER

BOGIE 1

BOGIE 2

CONTROL SYSTEM

DRIVE SYSTEM

GUIDINGSYSTEM

VSD

MOTOR

GEARBOX

CHAIN 1

BRAKE

ENCODER

DRIVE’S

COMPOSITION

WHEEL 1

BEARING 1

BOGIE’S COMPOSITION

BOGIE 10

CHAIN 2


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Fig 6-5 Lower shutter control system representation

As shown in Fig 6-1, the drive system is composed of two drives that both of them are in the upper motor stations (upper part of the dome). These drives are composed by some subsystems such as the frequency converter (VSD), the motor, the brake, the encoder, the gearbox and two chains (as a single motor moves the two chains, see Fig 6-6).

Fig 6-6 Lower shutter drive system representation

The guiding system, shown in Fig 6-1, is composed of ten bogies (5 at each side), which need to be working for the correct support of the dome lower shutter. In the same way, every wheel of the bogie together with its corresponding bearing has to be working for its correct operation.

Fig 6-7 Lower shutter guiding system representation


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Table 6-1. Component failure rate and MTTR used in the Lower Shutter System Current Status analysis

6.2.2 Results


Table 6-2. Lower Shutter System Current Status Reliability, Availability & MTTR analysis results.

Failure Rate

(per million hours)

λ

(1/hours)

Component MTTF

(hours)

Component MTTF

(years)

Component MTTR

(hours)

Wheels 2 0.000002 5.00E+05 119.05 168Bearings 2 0.000002 5.00E+05 119.05 168VSD 5 0.000005 2.00E+05 47.62 4Motor a.c. 5 0.000005 2.00E+05 47.62 36Brake 10 0.00001 1.00E+05 23.81 12Encoder 7 0.000007 1.43E+05 34.01 36Gearbox 20 0.00002 5.00E+04 11.90 72Chain 1 0.5 0.0000005 2.00E+06 476.19 24Chain 2 0.5 0.0000005 2.00E+06 476.19 24PLC 40 0.00004 2.50E+04 5.95 4Rectifier 4 0.000004 2.50E+05 59.52 24

MTBF

(hours)

MTBF

(years)

MTTR

(hours)

Availability

(%)

Bogie 2.49031E+05 59.29 167.99 99.93Guiding System 2.50204E+04 5.96 167.94 99.33Drive 2.08276E+04 4.96 42.54 99.80Drive System 1.03862E+04 2.47 42.42 99.59Control System 2.26503E+04 5.39 5.82 99.97System 5.54270E+03 1.32 61.34 98.91


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6.3 NEW STATUS

The following figure represents the RBD of the new status of the lower shutter system:

Fig 6-8 Lower shutter system new status reliability block diagram

PLC

DRIVE 1

DRIVE 2

HYDRAULIC

SYSTEM

RECTIFIER

CONTROL SYSTEM

DRIVE SYSTEM

GUIDINGSYSTEM

VSD

MAIN

MOTOR

MAIN

GEARBOX

CHAIN 2

BRAKE

ENCODER

DRIVE’S

COMPOSITION

NEW BOGIE

SYSTEM 1

NEW BOGIE

SYSTEM 2

NEW BOGIE

SYSTEM 1

NEW BOGIE

SYSTEM 2

HYDRAULIC BOGIE GROUP’S

COMPOSITION

VSD

AUXILIARY

MOTOR

BRAKE

ENCODER

AUXILIARY

GEARBOX

CHAIN 1

HYDRAULIC

ACTUATOR

WHEEL 1

BEARING 2

BEARING 1

WHEEL 2

NEW BOGIE SYSTEM’S

COMPOSITION

NEW BOGIE’S

COMPOSITION

HYDRAULIC BOGIE GROUP 1

NEW BOGIE

SYSTEM 3

NEW BOGIE

SYSTEM 4


NEW BOGIE

SYSTEM 5

NEW BOGIE

SYSTEM 6


NEW BOGIE

SYSTEM 7

NEW BOGIE

SYSTEM 8


7/8


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For the correct operation of the lower shutter mechanism, the control system, the drive system and the guiding system must work correctly. Therefore the RBD for the dome lower shutter mechanism is as follows:

Fig 6-9 Lower shutter mechanism representation

The control system controls the lower shutter drive system and is composed of a PLC (which includes communication cards, power supplies, etc.) and a rectifier.

Fig 6-10 Lower shutter control system representation

As shown in Fig 6-2, the drive system is composed of two drives located at the upper station. Each drive moves two chains and includes a redundant auxiliary motor apart from the main motor (see Fig 6-11)

Fig 6-11 Lower shutter drive system representation


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The guiding system, shown in Fig 6-2, is composed of eight bogies in four hydraulic groups (2 bogies per group). It has been assumed that one bogie out of the eight can fail without affecting to the guiding system operation. The new bogie system is composed of a hydraulic actuator and a new bogie. Each bogie has two radial wheels with each corresponding bearing

Fig 6-12 Lower shutter guiding system representation

HYDRAULIC

SYSTEM

NEW BOGIE

SYSTEM 1

NEW BOGIE

SYSTEM 2


NEW BOGIE

SYSTEM 3

NEW BOGIE

SYSTEM 4


NEW BOGIE

SYSTEM 5

NEW BOGIE

SYSTEM 6


NEW BOGIE

SYSTEM 7

NEW BOGIE

SYSTEM 8


7/8

NEW BOGIE

SYSTEM 1

NEW BOGIE

SYSTEM 2

HYDRAULIC BOGIE GROUP’S COMPOSITION


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Table 6-3. Component failure rate and MTTR used in the Lower Shutter System New Status analysis

6.3.2 Results


Table 6-4. Lower Shutter System New Status Reliability, Availability & MTTR analysis results.

Failure Rate

(per million hours)

λ

(1/hours)

Component MTTF

(hours)

Component MTTF

(years)

Component MTTR

(hours)

Wheels 1 0.000001 1.00E+06 238.10 168Bearings 1 0.000001 1.00E+06 238.10 168Hydraulic Actuator 15 0.000015 6.67E+04 15.87 48Hydraulic System 10 0.00001 1.00E+05 23.81 168VSD 5 0.000005 2.00E+05 47.62 4Motor a.c. 5 0.000005 2.00E+05 47.62 36Brake 10 0.00001 1.00E+05 23.81 12Encoder 7 0.000007 1.43E+05 34.01 36Gearbox (main) 20 0.00002 5.00E+04 11.90 72Gearbox (auxiliary) 20 0.00002 5.00E+04 11.90 72Chain 1 0.5 0.0000005 2.00E+06 476.19 24Chain 2 0.5 0.0000005 2.00E+06 476.19 24PLC 40 0.00004 2.50E+04 5.95 4Rectifier 4 0.000004 2.50E+05 59.52 24

MTBF

(hours)

MTBF

(years)

MTTR

(hours)

Availability

(%)

Bogie 2.48382E+05 59.14 167.88 99.93Bogie System 5.26788E+04 12.54 73.09 99.86Hydraulic Bogie Group 2.07920E+07 4950.48 36.96 100.00Guiding System 8.71346E+04 20.75 150.80 99.83Drive 4.75259E+04 11.32 69.44 99.85Drive System 2.37007E+04 5.64 69.48 99.71Control System 2.26503E+04 5.39 5.82 99.97System 1.02011E+04 2.43 50.34 99.51


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6.4 RELIABILITY AND AVAILABILITY DIAGRAMS

The next figures show the comparison of the reliability functions for current status and new status of the upper shutter. Fig 6-13time scale refers to the lifetime of 50 years. Fig 6-14shows the first part of the plots (ten initial years) for discernment of the difference in the curve shape.

Fig 6-13 Lower shutter current and new status reliability diagrams (50 years)

Fig 6-14 Lower shutter current and new status reliability diagrams (10 years)

Next figure shows the system up/down periods along time for the upper shutter current status and new status. The system availability is increased from 98.91% to 99.51%.

Control System

Drive System

Guiding System

System

Control System

Drive System

Guiding System

System


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Fig 6-15 Lower shutter current and new status availability diagrams


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7 C O N C LU S I O N S

The next tables summarize the final results obtained from the reliability assessment:

Table 7-1. Upper Shutter System comparison between current and new status

Table 7-2. Lower Shutter System comparison between current and new status

In both Upper and Lower Shutter systems, the improvement in the MTBF value is considerable when comparing the results obtained for the proposed redesign (new status) with the current installed system (current status). For the upper shutter, the MTBF of the overall system is increased by a factor of 6, from a current value of less than 1 year to a new value of more than 4 years. Especially relevant is the increase in the availability of the drive system, mainly achieved by the possibility of operating with 3 out of the 4 drives. Also, a significant improvement in the MTBF is achieved for the guiding system. In the case of the lower shutter, the current MTBF is higher than in the upper shutter (1.32 years instead of 0.7 years), basically because the drive system is currently capable of operating with a higher safety factor. However, this applies only to the lower shutter individual operation as currently the lower shutter drives (motors and chains) have not enough capacity to deploy the windscreen. The proposed actions for the drive system include higher capacity motors and chains in order to enable windscreen deployment. There would be also an emergency system to guarantee shutter operation in case of failure of one motor (auxiliary redundant motor in each drive), what contributes to increase the drive system reliability. Apart from that, and similarly to the upper shutter, the improved guiding system increases considerably the MTBF with respect to the current bogies. The combination of these factors increases the MTBF for the lower shutter overall system from 1.32 years to 2.43 years.

Current Status

MTBF (years)

New Status

MTBF (years)

Upper Shutter System 0.70 4.16

Guiding System 2.28 19.70Drive System 1.25 250.50Control System 5.39 5.39

Current Status

MTBF (years)

New Status

MTBF (years)

Lower Shutter System 1.32 2.43

Guiding System 5.96 20.75Drive System 2.47 5.64Control System 5.39 5.39


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8 A D D I T I O NA L A NA LY S E S

During the meeting with GRANTECAN on 6th March, 2014, the following actions were agreed:

1. The necessity of referring the reliability study in terms of failures that avoid closing the shutter system. In this sense, some malfunctions previously considered as failures (as in the case of the bogies hydraulic system) have been reviewed as they will not affect to the emergency closing of the shutter system.

2. The review of the drive system modelling: it was pointed out the necessity of representing

a gearbox and chain failure as critical failures which could entail to a stop of the system. The probability of occurrence of this kind of failures is lower than a simple failure of the gearbox which can or not bring to a stop of the system (example: the gearbox may not be able to transmit torque however it is capable to rotate, allowing to be dragged by the rest of the driving system). Therefore, the failure rate of the gearbox has been reduced down to 5 failures per million working hours.

3. Clarify if the MTBF refer to the operational time or real time. This issue is answered in the

next section. It refers to operational time, which for main components is around 1 hour/day. However, a few subsystems such as the power source of the control system has a longer operational period, so during this study the operational time has been maintained in 12 hours/day.

4. Indication of potential improvements in the control system aimed to increase its reliability.

The possibility of including some redundant components is outlined in next section. This chapter includes the response to the previous actions and corresponding update of the results of the reliability analysis.

8.1 UPPER SHUTTER UPDATED NEW STATUS

In order to account for the scenario stated in Action 2 of previous section, the Drive System has been changed from the study shown in chapter 5.3. An additional block called Transmission, which accounts for the chain and gearbox failure rates (set in series), has been added in series. Following the request by GRANTECAN, an increase in the reliability of the Control System (Action 4 of previous section) is proposed by duplicating the power source and the communication card obtaining an increase in the reliability of the PLC. The new failure rate has been defined as 20 failures per million working hours. The failure data for each component, used as input for the system analysis are shown as follows:


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Table 8-1. Component failure rate and MTTR used in the Upper Shutter System Updated New Status analysis


Table 8-2. Upper Shutter System Updated New Status Reliability, Availability & MTTR analysis results.

Even though the operational time of most of the components of the guiding system, transmission and driving system is around 1 hour/day, during this study the operational time per day has been maintain in 12 hours/day as it should keep in mind that few subsystems such as the power source of the control system has that operational period (Action 3 of previous section). Thus, in case of reading the MTBF of the guiding, transmission and driving system, it is most convenient to use the hours values and from them generate the corresponding number is years.

Failure Rate

(per million

hours)

λ

(1/hours)

Component

MTTF (hours)

Component

MTTF (years)

Component MTTR

(hours)

Wheels 1 0,000001 1,00E+06 238,10 168

Bearings 1 0,000001 1,00E+06 238,10 168

Hydraulic Actuator 15 0,000015 6,67E+04 15,87 48

Hydraulic System 10 0,00001 1,00E+05 23,81 168

VSD 5 0,000005 2,00E+05 47,62 4

Motor a.c. 5 0,000005 2,00E+05 47,62 Upper: 36 / Lower: 24

Brake 10 0,00001 1,00E+05 23,81 Upper: 12 / Lower: 8

Encoder 7 0,000007 1,43E+05 34,01 Upper: 36 / Lower: 24

Gearbox 5 0,000005 2,00E+05 47,62 Upper: 72 / Lower: 48

Chain 0,5 0,0000005 2,00E+06 476,19 24

PLC 20 0,00002 5,00E+04 11,90 4

Rectifier 4 0,000004 2,50E+05 59,52 24

MTBF

(hours)

MTBF

(years)

MTTR

(hours)

Availability

(%)

Bogie 2,48382E+05 59,14 167,88 99,93

Bogie System 5,26788E+04 12,54 73,09 99,86

Hydraulic Bogie Group1,98860E+06 473,48 35,81 100,00

Guiding System 8,27506E+04 19,70 145,20 99,82

Transmission 4,53367E+04 10,79 56,89 99,87

Upper Drive 3,68824E+04 8,78 21,21 99,94

Lower Drive 3,68601E+04 8,78 14,39 99,96

Drive System 4,50226E+04 10,72 56,28 99,88

Control System 4,13818E+04 9,85 7,32 99,98

System 1,71494E+04 4,08 54,71 99,68


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Finally, in order to obtain the system reliability in terms of unfeasibility to close the upper shutter system (Action 1), the simulation has been repeated by assuming that the failures of the hydraulic actuators and the hydraulic group (hydraulic system) do not cause system failure, i.e., by removing these components from the guiding system reliability blocks. The update results, including also the previous modifications, are included in the next table.

Table 8-3. Upper Shutter System Updated New Status, in terms of failures that avoid closing the shutter. Reliability,

Availability & MTTR analysis results.

The reliability of the guiding system in this case increases significantly, as a result of considering that it will be still operative in case of failure of the hydraulic system. It is important to remark that under these circumstances the guiding system performance will not be optimal and it should be avoided to operate it regularly in these conditions. However, an emergency closing of the dome shutters would be possible.

8.2 LOWER SHUTTER UPDATED NEW STATUS

Following the same criteria explained in the previous section (resulting from Actions 2 and 4), an updated study of the Lower shutter system has been carried out. The failure data for each component, used as input for the system analysis are shown as follows:

Table 8-4. Component failure rate and MTTR used in the Lower Shutter System Updated New Status analysis

MTBF

(hours)

MTBF

(years)

MTTR

(hours)

Availability

(%)

Bogie 2.48382E+05 59.14 167.88 99.93

Bogie System = Bogie 2.48382E+05 59.14 167.88 99.93

(Hydraulic)Bogie Group 1.84210E+07 4385.95 78.83 100.00

Guiding System 4.59510E+06 1094.07 85.80 100.00

Transmission 4.53367E+04 10.79 56.89 99.87

Upper Drive 3.68824E+04 8.78 21.21 99.94

Lower Drive 3.68601E+04 8.78 14.39 99.96

Drive System 4.50226E+04 10.72 56.28 99.88

Control System 4.13818E+04 9.85 7.32 99.98

System 2.15494E+04 5.13 31.11 99.86

Failure Rate

(per million

hours)

λ

(1/hours)

Component

MTTF (hours)

Component

MTTF (years)

Component MTTR

(hours)

Wheels 1 0,000001 1,00E+06 238,10 168

Bearings 1 0,000001 1,00E+06 238,10 168

Hydraulic Actuator 15 0,000015 6,67E+04 15,87 48

Hydraulic System 10 0,00001 1,00E+05 23,81 168

VSD 5 0,000005 2,00E+05 47,62 4

Motor a.c. 5 0,000005 2,00E+05 47,62 36

Brake 10 0,00001 1,00E+05 23,81 12

Encoder 7 0,000007 1,43E+05 34,01 36

Gearbox (main) 5 0,000005 2,00E+05 47,62 72

Gearbox (auxiliary) 5 0,000005 2,00E+05 47,62 72

Chain 1 0,5 0,0000005 2,00E+06 476,19 24

Chain 2 0,5 0,0000005 2,00E+06 476,19 24

PLC 20 0,00002 5,00E+04 11,90 4

Rectifier 4 0,000004 2,50E+05 59,52 24


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Table 8-5. Lower Shutter System Updated New Status Reliability, Availability & MTTR analysis results.

Even though the operational time of most of the components of the guiding system, transmission and driving system is around 1 hour/day, during this study the operational time per day has been maintain in 12 hours/day as it should keep in mind that few subsystems such as the power source of the control system has that operational period (Action 3). Thus, in case of reading the MTBF of the guiding, transmission and driving system, it is most convenient to use the hours values and from them generate the corresponding number is years. Analogously, the system reliability in terms of unfeasibility to close the lower shutter system (Action 1) has been obtained. The results are collected in the next table.

Table 8-6. Lower Shutter System Updated New Status, in terms of failures that avoid closing the shutter. Reliability,

Availability & MTTR analysis results.

Similarly to the upper shutter, the reliability of the guiding system increases significantly, as a result of considering that it will be still operative in case of failure of the hydraulic system. In this case the

MTBF

(hours)

MTBF

(years)

MTTR

(hours)

Availability

(%)

Bogie 2,48382E+05 59,14 167,88 99,93

Bogie System 5,26788E+04 12,54 73,09 99,86

Hydraulic Bogie Group2,07920E+07 4950,48 36,96 100,00

Guiding System 8,71346E+04 20,75 150,80 99,83

Drive 1,66339E+05 39,60 63,66 99,96

Drive System 8,37553E+04 19,94 63,66 99,92

Control System 4,13818E+04 9,85 7,32 99,98

System 2,09424E+04 4,99 56,29 99,73

MTBF

(hours)

MTBF

(years)

MTTR

(hours)

Availability

(%)

Bogie 2.48382E+05 59.14 167.88 99.93

Bogie System = Bogie 2.48382E+05 59.14 167.88 99.93

(Hydraulic)Bogie Group 3.00000E+08 71428.57 68.20 100.00

Guiding System 6.30622E+06 1501.48 84.64 100.00

Drive 1.66339E+05 39.60 63.66 99.96

Drive System 8.37553E+04 19.94 63.66 99.92

Control System 4.13818E+04 9.85 7.32 99.98

System 2.76513E+04 6.58 26.53 99.90


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guiding system performance will not be optimal and it should be avoided to operate it regularly in these conditions. However, an emergency closing of the lower shutter would be possible.

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