01_power Transformer Saudi Arbia
Transcript of 01_power Transformer Saudi Arbia
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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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• 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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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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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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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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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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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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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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• 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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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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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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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
JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
Substations
with
High
Failure
Rate
Riyadh
AreaBar Chart showing the Number of Failures on a Monthly Basis during
the last Five Years
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
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
JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
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
Bar Chart showing the Number of Failures on a Monthly Basis during
the last Five Years
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
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.
• More investigation is needed.
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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
JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
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
Bar Chart showing the Number of Failures on a Monthly Basis during
the last Five Years
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
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
JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
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
Bar Chart showing the Number of Failures on a Monthly Basis during
the last Five Years
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
100% of Failures occur in the summer
60% of
Failures
occur
in
(AM)
• All MV cables were replaced at late 2010.
• But it is still showing interruptions.
• 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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Substation: 8811
1
2
0 0 0
1
0 0 0 0 0 00
0.5
1
1.5
2
2.5
JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
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
Bar Chart showing the Number of Failures on a Monthly Basis during
the last Five Years
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
75% of Failures occur in the Winter
75% of
Failures
occur
in
(AM)
• Radial Substation
• No failed terminations were available for investigation.
• More investigation is needed.
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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
JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
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
Bar Chart showing the Number of Failures on a Monthly Basis during
the last Five Years
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
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.
• No failed terminations were available for investigation.
• More investigation is needed.
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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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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
JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
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
Bar Chart showing the Number of Failures on a Monthly Basis during
the last Five Years
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
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
• No failed terminations were available for investigation.
• 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
JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
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
Bar Chart showing the Number of Failures on a Monthly Basis during
the last Five Years
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
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.
• No failed terminations were available for investigation.
• More Investigation is needed.
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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
JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
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
Bar Chart showing the Number of Failures on a Monthly Basis during
the last Five Years
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
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
JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
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
Bar Chart showing the Number of Failures on a Monthly Basis during
the last Five Years
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
90% of Failures occur in the summer & autumn
54.5% of Failures occur in (PM)• The MV cables were replaced in 2008.
• But it is still showing interruptions.
• No failed terminations were available for investigation.
• More Investigation is needed.
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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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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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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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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.