01_power transformer saudi arbia

8/19/2019 01_power Transformer Saudi Arbia

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1

A STUDY TO DETERMINE THE ROOT

CAUSES OF REPEATED FAILURES ON MV

CABLE

TERMINATIONS

AT

NATIONAL

GRID SA SYSTEM12 May 2013

Jeddah ‐ Saudi Arabia

Hussain Mueidh Al Yami

Lines Maintenance Department Manager


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The

Main

Goal

of

the

Electric

Utilities

isThe world Illumination!

But there is an aggressive Enemy

Which is

Electrical

Equipment

Failures!


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Table

of

Contents

Introduction

Data Collection

Brain Storming

Data Analysis

Samples Investigations and Site Visit

Conclusion and Recommendations

Substations with High Failure Rate


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4

• National Grid

SA

has

more

than

two

thousand

transformers

(2012

transformers

up

to

mid of March 2013) in its system.

• MV Cross‐linked Polyethylene (XLPE) insulated cables cables are used to connect

these step down transformers to MV switchgears.

• National Grid SA network were interrupted by several MV cable failures.

• MV cable terminations were the source of these cable failures.

• In addition

to

the

high

cost

of

repairing

these

failures,

they

cause

a negative

effect

on

the availability and reliability of National Grid SA network.

• It was decided to study this problem to find out the root cause of these failures and

recommend the solution.

Introduction


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5

Before starting the study, the problem size must be identified

by collecting the statistical data of the MV cable termination

failures from all Operating Areas. The failures numbers were

collected from the following areas:

Data

Collection

• Central Operating Area (COA)

• Eastern Operating Area (EOA)

• Western Operating

Area

(WOA)

• Southern Operating Area (SOA)


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6

Data

Collection

The collected data were covering the last 5 years.In terms of the number of failures, the following chart shows a comparison

between these different working areas.

The great deal of termination failures were concentrated in COA.

As a result, the study focused on that Area.


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7

Data

Collection

The COA consists of three sub‐areas, namely Riyadh, Qassim and Hail.

The following chart shows a comparison between these three sub‐areas.

All Sub Areas have significant failures . As a result, all sub areas will be studied .


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8

Brain

Storming

A brain storming for the main possible root causes that may affect the service

lifetime of the MV cable terminations and may lead to the MV cable termination

failure was done. The possible causes were as follow:

• Bad workmanship.

• Overheat ( overloaded )

• Overvoltage.

• Termination Design problems..

• Manufacturer Installation Instruction problem.

• Wrong selection for the termination size.• Wrong Grounding and /or high grounding resistance.

• Cable lug design.

• Improper design of transformer's LV cable box.


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9

Brain

Storming

Since these terminations were manufactured by the same manufacturer

in all areas and the failures were concentrated in COA only, so all causes

related to termination materials and design were eliminated. The study

focused on the following root causes:

• Bad workmanship.

• Overheat ( overloaded )

• Overvoltage.

• Manufacturer Installation Instruction problem.• Improper design of transformer's LV cable box.


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10

Data

Analysis

• The data were collected for both 33 kV and 13.8 kV. 13.8 kV terminationfailures present only (approx. 6%). The design principle and operational

conditions are the same, the two voltage levels can be considered together

neglecting the factor of voltage level.

• The concern was taken about dimensions of transformer LV cable boxeswhich might introduce electrical stress on cable terminations. Drawings of

cable boxes were selected randomly for reviewed and they were found

complying with the specifications.

• The data of transformers loads and voltage profiles of 33kV & 13.8kV bus

bars were requested in order to use them in the study. The available data

was not comprehensive and not sufficient as it was expected to be.

However, the available data gives some hints about where to look.


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11

• The entire failures in COA for the last five years ( 112 failures ) were

concentrated at 39 substations out of 227 substations (100 % of Faults

occurred at 17.2% of Sub. ) .

• About 68% of these interruptions occurred in 11 substations out of these

227 substations (68 % of Faults occurred at 4.85 % of Sub. )

• These substations with high failure rate were reviewed, case by case.

Data

Analysis


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12

Substations

with

High

Failure

Rate

Riyadh

Area• In Riyadh area, the entire 34 interruptions in the last five years occurred in 19

substations out of 162 substations ( 100 % of Faults at 11.7% of Sub.).

• 47% of these interruptions occurred in 3 substations out of all ( 47 % of Faults at

less than 2% of Sub.).

• These substations are 8508, 8505 and 8034.

6 6

4

2 2

1 1 1 1 1 1 1 1 1 1 1 1 1 1

0

1

2

3

45

6

7

8 5 0 5

8 5 0 8

8 0 3 4

8 0 2 7

8 0 3 8

8 0 2 1

8 0 1 4

8 0 2 6

8 0 9 6

8 0 1 0

8 7 0 5

8 6 0 5

9 0 1 3

8 0 1 9

8 0 7 5

8 0 3 6

8 0 4 7

8 1 2 9

8 0 3 3

47 %

2 %


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13

Substation:

8508 2

0 0

2

0

1

0

1

0 0 0 00

0.5

1

1.5

2

2.5

JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC

Bar Chart showing the Number of Failures on a Monthly Basis during

the last Five Years

Substations

with

High

Failure

Rate

Riyadh

Area

5

0

1

0 00

2

4

6

2008 2009 2010 2011 2012

0 0 0 0 0

2

0 0

2

0 0 0 0 0

1

0 0 0 0 0 0

1

0 00

0.5

1

1.5

2

2.5

66% of Failures occur in the winter and spring

66% of Failures occur in (AM)

Bar Chart showing the Number of Failures on an Incident Time Basis

during the last Five Years

Bar Chart showing the Number of Failures on a Yearly Basis during

the last Five Years

• It was having a very light load ( 2001 to 2007).

• Rapid increasing in the infra‐structure development.

• The load of the substation was also on the rise.

• Late 2010, all terminations were replaced.

• As a result, no failures occurred after that.


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14

Substation: 8505

0

1

0 0 0 0 0 0 0 0 0 0

2

0 0 0

1 1

0 0

1

0 0 00

0.5

1

1.5

2

2.5

2 2

1

0

1

0

0.5

1

1.5

2

2.5

2008 2009 2010 2011 2012

1

0

3

0 0

1

0 0 0 0 0

1

0

1

2

3

4


Substations

with

High

Failure

Rate

Riyadh

AreaBar Chart showing the Number of Failures on a Monthly Basis during

the last Five Years




the last Five Years

83.3 % of Failures occur in the winter

83% of

Failures

occur

in

(PM)

• Radial Substation• All MV cables were replaced at late 2010.

• But it is still showing interruptions.

• More investigation is needed.


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Substation: 8034

0 0 0 0 0 0 0 0 0 0

3

1

0

1

2

3

4


Substations

with

High

Failure

Rate

Riyadh Area

0

1

0

3

00

1

2

3

4

2008 2009 2010 2011 2012

0 0 0 0 0 0 0 0 0

2

0

1

0 0 0 0 0 0 0 0

1

0 0 00

0.5

1

1.5

2

2.5


the last Five Years




the last Five Years

100 % of Failures occur in the autumn & winter ( just after summer)

75% of Failures occur in (AM)

• Was subjected to a fire incident mid of 2006.

• MV cables were affected and replaced in 2006.

• Heavily loaded in the last three years.• Out of firm capacity in the last year.

• This situation leads to accelerate the failure.



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16

Substations

with

High

Failure

Rate

Qassim Area

• In Qassim area, the entire 37 interruptions in the last five years occurred in 14

substations out of 37 substations. (100 % of Faults at 37.8% of Sub. )

• 57% of these interruptions occurred in 4 substations out of all. (57 % of Faults

at 11 % of Sub. )

• These substations are 8818, 8606, 8811 and 8802.

8

54 4

2 2 2 2 2 21 1 1 1

0

2

4

68

10

57%

11%


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Substation: 8818

0 0 0 0 0

1

3

0

1

2

0

1

0

0.5

1

1.5

2

2.5

3

3.5


Substations

with

High

Failure

Rate

1

0

1

3 3

0

1

2

3

4

2008 2009 2010 2011 2012

0

1 1

0 0 0 0 0 0 0 0

1 1 1 1

0 0 0 0 0

1 1

0 00

0.2

0.4

0.6

0.8

1

1.2

Qassim Area


the last Five Years




the last Five Years

87.5% of Failures occur in the summer & early autumn

62%

of

Failures

occur

in

(PM)

• Heavily loaded.

• The tap changers were operated manually.

• From the failed terminations investigation and site visit , there were a clear

evidences of :

A. Bad workmanshipB. Overvoltage at the LV side of the transformer

C. Over heat inside the cable box.

• Examine all terminations physically and replace the defective.

• Notify the Dispatcher about the sign of overvoltage.

• Monitor the situation.


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Substation: 8606

0 0 0 0 0

2

0

1

2

0 0 00

0.5

1

1.5

2

2.5


Substations

with

High

Failure

Rate

0

1

3

1

00

1

2

3

4

2008 2009 2010 2011 2012

1

0 0 0 0

1

0 0

1

0 0 0 0 0 0

1

0 0 0

1

0 0 0 00

0.2

0.4

0.6

0.8

1

1.2

Qassim Area


the last Five Years

Bar Chart showing the Number of Failures on An Incident Time Basis



the last Five Years

100% of Failures occur in the summer

60% of

Failures

occur

in

(AM)

• All MV cables were replaced at late 2010.


• The dimensions of cable boxes at the auxiliary transformers were

not as per the standards.

• The manufacturer was called to study the case.

• The cable boxes of the auxiliary transformers were replaced.

• No fault occurred after this correction.


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19

Substation: 8811

1

2

0 0 0

1

0 0 0 0 0 00

0.5

1

1.5

2

2.5


Substations

with

High

Failure

Rate

Qassim Area

0

1 1

2

00

1

2

3

2008 2009 2010 2011 2012

0 0 0 0

1

0 0 0

1 1

0 0 0 0 0 0 0 0 0

1

0 0 0 00

0.2

0.4

0.6

0.8

1

1.2


the last Five Years




the last Five Years

75% of Failures occur in the Winter

75% of

Failures

occur

in

(AM)

• Radial Substation

• No failed terminations were available for investigation.



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Substation: 8802

0

1

0 0 0

2

0 0 0 0

1

00

0.5

1

1.5

2

2.5


Substations

with

High

Failure

Rate

Qassim Area

0

2

0

1 1

0

0.5

1

1.5

2

2.5

2008 2009 2010 2011 2012

0 0 0 0 0 0 0 0 0 0 0

1

0

2

0 0 0 0 0 0 0 0 0

1

0

0.5

1

1.5

2

2.5


the last Five Years




the last Five Years

75% of Failures occur in the summer & autumn

75% of Failures occur in (PM)• Heavily loaded in the last five years.

• Out of firm capacity in the last three years.




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21

Substations

with

High

Failure

Rate

• In Hail area, the entire 41 interruptions in the last five years occurred in 6 switching

substations out of 28 switching substations (100 % of Faults at 21.4% of Sub.).

• 95 % of these interruptions occurred in 4 substations out of all (95% of Faults at

14.3 % of Sub. ) .

• These substations are 8901, 8914 , 8915 and 8913.

Hail Area

18

11

7

31 1

0

5

10

15

20

95%

14.3%


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22

Substation: 8901

0

3

2 2

1

3 3

0

1

2

0

1

0

0.5

1

1.5

2

2.5

3

3.5


Substations

with

High

Failure

Rate

Hail Area

1

8

0

7

2

0

2

4

6

8

10

2008 2009 2010 2011 2012

0

0

1

0

1 1

0 0

1 1 1

0

2

1

2

0 0

1

2

0 0

2

0

2

0

0.5

1

1.5

2

2.5


the last Five Years




the last Five Years

66.6% of Failures occur in the summer

66.6% of

Failures

occur

in

(PM)

• Radial Substation.

• The MV cables were replaced at late 2009.

• But it is still showing interruptions


• More Investigation is needed.


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Substation: 8913

0 0

1

0

1 1

0

1

0

2

1

00

0.5

1

1.5

2

2.5


Substations

with

High

Failure

Rate

Hail Area

2

3

0

2

00

0.5

1

1.5

2

2.5

3

3.5

2008 2009 2010 2011 2012

0

1

0 0 0 0

1

0 0 0

1

0

1

0 0 0

1

0

1

0 0

1

0 0

0

0.2

0.4

0.6

0.8

1

1.2


the last Five Years




the last Five Years

85.7% of Failures occur in the summer

57% of Failures occur in (PM)

• Radial Substation.

• The MV cables were replaced at late 2009.• But it is still showing interruptions.




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Substation: 8915

0 0 0

1

0

1 1

0 0 0 0 00

0.2

0.4

0.6

0.8

1

1.2


Substations

with

High

Failure

Rate

Hail Area

1

0 0 0

2

0

0.5

1

1.5

2

2.5

2008 2009 2010 2011 2012

0 0

0 0 0 0 0 0 0 0 0 0

0

1

0 0 0 0

0 0

1

0 0

1

0

0.2

0.4

0.6

0.8

1

1.2


the last Five Years




the last Five Years

66 % of Failures occur in the summer

100% of

Failures

occur

in

(PM)

• The cables were newly energized (2012).

• Failed terminations were investigated.

• There were a clear sign of Bad workmanship.

• All cables and cable terminations were replaced.

• No fault recorded since the time of replacement.


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Substation: 8914

0 0 0

1

0

1 1

3

0 0

4

1

0

1

2

3

4

5


Substations

with

High

Failure

Rate

Hail Area

4

2 2 2

1

0

1

2

3

4

5

2008 2009 2010 2011 2012

0 0 0 0 0

1

2

0 0

1

0

1

0 0 0 0

1

0

2

0

1

0

1 1

0

0.5

1

1.5

2

2.5


the last Five Years




the last Five Years

90% of Failures occur in the summer & autumn

54.5% of Failures occur in (PM)• The MV cables were replaced in 2008.





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Samples

Investigations

and

Site

Visit

A site visit was made to Substation 8818 which is one of the substations that has high

failure concentration, in order to have a close look to the operational environment and

try to find some clues about possible root causes.

It was noticed that the tap changers of the transformers were operated manuallywhich affects the accuracy of voltage control at the low voltage side.


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Samples

Investigations

and

Site

Visit

Flashovers on the cable box wall

indicates overvoltage that breaks

the gap between connecting bar and box's walls.

The edges of the connecting bar

were melted because of arcs.

Voltage stresses were suspected on the terminations of that substation since there were a clearspark between connection bar and cable box’s wall. This evidence was obtained from some previous

pictures.

Substation 8818


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Samples

Investigations

and

Site

Visit

Healthy termination removed from Substation 8818 for investigation . It shows non‐

compliance of installation instructions and effect of overheating or improper

application of stress control tube

Brown color due to loose stress control tube (SCT).

Improper application of SCT or overheating of

cables affects termination's mechanical integrity.

Failure due to bad workmanship. Non

compliance of the installation instruction

led to failures

Substation 8818


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Samples

Investigations

and

Site

Visit

Failed termination removed from Substation 8915 in Hail area, shows the use of thewrong tool to cut the semiconducting layer.

Failure due to bad workmanship.

The use of wrong tools led to

failure.


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Conclusion

and

Recommendations

• It can be inferred that the termination is most likely to fail if it is operated in

an environment that has one the following characteristics:A. Radial Substation.

B. Heavily loaded Substation .

C. Lightly loaded Substation.

• Because of lack of data, identifying an exact contribution of each factor on the

failures was difficult. Thus, informative database must be built starting from 2013.

• However, it was obvious that the installation instructions were not followed exactly

and human errors is the greatest among other factors in all investigated

terminations.


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Conclusion

and

Recommendations

• Confirmation that all terminations were brought from the correct source is needed.The Batch No. of each termination must be provided and recorded in the As‐Built

Drawing.

• The installation of each termination must be performed by a Certified Jointer.

• The installation of each termination must be supervised by the COMPANY personal.

• Each termination must have a name plate.

• The name plate should consist (Contract Information, Name of jointer, SECSupervisor Name, Installation Date, Manufacture Date and Enegization Date).


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Conclusion

and

Recommendations

More investigation is needed in the following Substations :

• Riyadh Area ( 8505 , 8034 )

• Qassim Area ( 8802 , 8811 , 8818 ( Monitor Only after the correction ) )

• Hail Area ( 8901 , 8913 , 8914 )

In term of the following aspects :

• Does it subjected to Over loading? Record from Jan 2013 to Dec 2013

• Does it subjected to Over voltage? Record from Jan 2013 to Dec 2013

• Does the actual cables ampacity within the rated value ?• Does the terminations import from the main source?

• Investigate each single faulty termination and record the result.

• Cable and Substation earthing system.


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Thanks For your Kind Attention

Q&A


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34

Conclusion

and

Recommendations

In order to contain the failures by building an informative database and enhancinginstallation and maintenance procedures, the following recommendations are to be

followed:

1. The contractor must provide proof that all terminations were brought from the

correct source. The Batch No. of each termination must be provided and recorded inthe As‐Built Drawing.

2. The installation of each termination must be performed by a Certified Jointer and

the contractor must comply with this. The contractor must submit a name plate for

each termination. The name plate should consist (Contract Information, Name of jointer, SEC Supervisor Name, Installation Date, Manufacture Date and Enegization

Date). This name plate must be provided and recorded in the As‐Built Drawing.


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Conclusion

and

Recommendations

3. The installation of each termination must be supervised by the COMPANY personal.

The COMPANY supervisor name must be added to the name plate of each termination.

4. Each sample is an evidence and therefore, samples should be preserved and

documented in a correct way that keeps the sample integrity as it was, whenremoved.

5. Accurate data about the incidents, events that happened at the same time and

weather and operational records are very important in the analysis stage. In

addition, terminations that are installed under the same contract or by the same

contractor should be stored together because they are more likely to have thesame failure cause.


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36

Conclusion

and

Recommendations

6. Installation instructions should be clear and easy to follow and read. Manufacturers

shall be called to conduct short courses about their products and installation

instructions. In the case of unclear or missing instruction, feedback should be sent to

the manufacturer to update their instructions and make them clearer.

7. After the samples are collected and documented properly, a group of experts shall

analyze the failure and identify the possible root cause. As a result, an informative

database will be built and recommendation shall be made to improve the service life of

terminations. In case of human errors, the most common human errors should be

presented to SEC personnel in order to consider them carefully in the new projects andmaintenance work. In addition, feedback should be sent to manufacturer in case of

design errors or unclear instructions.


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37

Conclusion

and

Recommendations

8. All findings should be reported and documented in order to build a strong

experience about this subject. By building the experience, we will gain many benefits

such as; training improvement, outages reduction, cost reduction and reduction of the

need of diagnostics. In addition, we will be able to predict failures and increase the

network reliability.

9. A database for the over voltage and the over load on the 33kV & 13.8 KV

transformers should be available and easy to access in order to have an idea about the

maximum voltage and maximum load that might affect the termination service life.

Moreover, all transformers with manual tap changer should be modified to be

automatic controlled tap changer.

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