Define Electrical Bushing Be familiar with the reasons for transformer failure Be Familiar with Online Bushing Monitoring Identify the future failing bushing. Detect the condition of electrical bushing. Benefits of online monitoring

1. EE 476/576
High Voltage Engineering
1
On Line HV Bushing Monitoring
Instructor: Dr. K. M. Burke
Energy Systems Institute
Department of Electrical Engineering
University at Buffalo
Aljuboori Ahmed
Email:ahmedalj@buffalo.edu
Aljuboori Ahmed

2.  Define Electrical Bushing
 Be familiar with the reasons for transformer failure
 Be Familiar with Online Bushing Monitoring
 Identify the future failing bushing.
 Detect the condition of electrical bushing.
 Benefits of online monitoring
Objectives
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3. The conductive materials can be classified into
three groups:
Bus bar
Isolator Bus bar
Electrical Bushing
Introduction
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Figure 1: Bushings on 380 kV transformer
From Wikipedia, the free encyclopedia [1]
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4. Electrical Bushing
 conductive material with insulation and it is
passes through any earthed material[1].
Figure 2: Electrical Bushing
http://www.myfactoryrep.com/infosheets/eci/Electrical_Bushings.aspx
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5. Capacitor of Electrical Bushing
 C1 Capacitance is the capacitance between the
center conductor and the tap. As shown in
figure 3.[2]
 C2 Capacitance is the capacitance from tap to
ground.
Figure 3: Capacitor of Electrical Bushing[]
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6. Electrical Bushing Failure
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 The voltage can be attracted towards earth point. When
the electric field becomes of sufficient strength, this can
generator a leakage path. This lead to the failure of
electrical bushing[3].
Figure 3: Electrical Bushing Failure[3]

7. The Reason of Bushing Failure
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 About 90 percent of bushing failure are caused by moisture
failure entering the bushing through leaky gaskets or other
openings[4].
 Improper maintenance for electrical bushing was a major
cause of transformer failure.

8. The Reason of Bushing Failure
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 Also, overloading can be caused the failure.
 Line surge such as voltage spikes and line faults.
 Lightning

9. Power Transformer Aging
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It is aging of insulation system which
reduces both the mechanical and dielectric-
withstand strength of the transformer .
Figure 4 displays the distribution of
transformer failures by age. The average
age at failure was 18 years[5].

10. Power Transformer Aging
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Figure 4: Distribution of losses by Age of Transformer[5]
http://www.bplglobal.net/eng/knowledge-center/download.aspx?id=191

11. The increasing number of failures in the power
transformer, causing
Increase the cost of maintenance
Reduce transformer life span
Increase outage time
New transformer might cost millions of dollars
It might take time to fix the fault
Problem Description
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12. There are many reasons for transformer failure[6]
Problem Description
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Figure 4: Electrical Bushing Failure[6]
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13. How to know the condition of electrical
bushing of transformer to detect impending
failures in a timely manner.
Figure 5: Transformer Fire
http://www.nttworldwide.com/xfmrfail2.htm
What is the Solution?
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14. Faults of HV Bushing for transformer can be detected
by using different technology.
One method is to take a sample of oil transformer
and sent it to lab. The negative of this method that a
fault may develop over shorter time.
 Inappropriate storage and bad sampling
techniques may lead to errors in the results.
What is the Solution?
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15. Online Bushing Monitoring is active method to detect
and replace failing bushing to supporting asset
management. Run the test without outage so it is
continuous monitoring while the bushing in service
Figure 6: Advance Monitoring of transformer
http://www.ldic.de
Proposed Solution?
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16. It is Continuous method to collect of
parameter data from power transformer and
the analysis it to determine the risk of
unexpected.
What is Online Monitoring?
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17. Online Bushing theory is based on the
relationship between detection of insulation
deterioration and measure minimal partial
discharge. By applying a test voltage while
observing the waveform on an oscilloscope.
What is Online Monitoring?
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18.  Incorrect design
 Manufacturing errors
 Electrical and Thermal stress due to aging
 Increase the risk of failures due to transformer age
Figure: 7 Typical Power Transformer
http://www.cst.com/Content/Applications/Article/Siemens+Energy+optimises+power+transformers+with+the+aid+of+3
D+EM+Simulation
Why Online Monitoring is required for
Transformer ?
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19. The results of monitoring are recorded by
different methods and compared with previous
result in order to predict the life service of the
equipment.
Thermal Imaging Transformer Oil Transformer
Types of Technology Monitoring
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20.  Transformer Oil Analysis
 Thermography
 Ultrasonic
 Vibration
 Lube Oil Analysis
 Battery Testing
 Motor Testing
Types of Technology Monitoring
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21. It is based to measure the sum of current method
according to the formula below[2]
Where
Sum of Currents
Tangent delta change
Relative Change in bushing capacitance
Initial Capacitance Reading
Initial Sum of Current value
Online Bushing monitoring Procedure
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22.  In normal situation , the sum of three current is
equal to zero as shown in figure 8a[7].
 If any defect develops, the sum of three current is
not equal to zero due to unbalance system as
shown in figure 8b[7].
Online Bushing monitoring Procedure
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Figure 8: Phase Diagram A, B &C [7]

23.  DGA is the best detector for any defect in power
transformer. The faults detect by DGA is based on
measuring of partial discharge in insulation system
of transformer.
 Partial Discharge (PD) may occur small arcs within
the insulation system and it destroys the insulation
and can lead to breakdown of insulation.
Dissolved Gas for Transformer Oil
Analysis
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24.  DGA can detect and give warning based on that
each faults produces different level of gases.
 The type of faults that detect by DGA as following:-
 Corona
Arcing
High Temperature
Dissolved Gas Analysis
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25. The gases may produce from bushing and
transformer as following[8]
Hydrocarbons and hydrogen gases: methane,
ethane,
Ethylene, acetylene and hydrogen.
Carbon oxide: carbon monoxide and carbon
dioxide.
Naturally occurring gases: nitrogen and oxygen.
Dissolved Gas Analysis
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26.  The hydrogen, methane, ethane, ethylene and
acetylene are produced this means the fault is oil
breakdown
 High levels of hydrogen this means the fault is
corona.
 High levels of acetylene this means the presence of
arcing at high temperatures.
 carbon monoxide this means high temperature.
Dissolved Gas Analysis Results[8]
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27. Figure 9: Typical output from on-line DGA monitoring system[9]
Dissolved Gas Analysis Results[9]
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28. Device accuracy
Noise
System voltage variations
Factors Affecting Online Accuracy
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29. Power transformer is the most expensive
equipment in substation.
 It can be raised the service life of transformer to 60
years.
 By using Online monitoring, it can be scheduled
outage and reduced the repair costs
Benefits: Online Monitoring
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30. Online HV Bushing monitoring can give a good
result to estimate the transformer aging and provide
details for transformer condition.
Online program can do testing and monitoring to
make sure the equipment is safe for personals and
operation.
Conclusion
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31. The results of online monitoring can be recorded
and compared with previous result in order to predict
the life.
DGA can detect and give warning of 70% of the
most common failure in transformer.
Online technology can produce alarm before
bushing failure has been occurred.
Conclusion
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32. 1.www.Wikipedia.com. Bushing (electrical) [cited 09/2013]; 1:
[Available
from:http://en.wikipedia.org/wiki/Bushing_(electrical)].
2. Kane, Claude, “ On-line Bushing Monitoring and Comparision
to Off- line Testing” Dynamic Rating ; 4:[Available from;
www.dynamicratings.com/US/Application/Transformers/...
/AppNote8.pd...
3. http://www.bplglobal.net/eng/knowledge-
center/download.aspx?id=229
4. http://www.usbr.gov/power/data/fist/fist3_2/vol3-2.pdf
References
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33. 5. http://www.bplglobal.net/eng/knowledge-
center/download.aspx?id=191
6. Maik Kock, Michael Kruger,” A new Method for On-line
Monitoring of Bushings and Partial Discharges of Power
Transformer”, 2012 IEEE International Conference on Condition
Monitoring and Diagnosis23-27 September 2012, Bali,Indonesia
7.http://www.eaton.com/ecm/groups/public/@pub/@electrical/doc
uments/content/1077779936326.pdf
8. S. M. Dhlamini and T. Marwala, "Using SVM, RBF and MLP for
bushings," in Proceedings of IEEE Africon, pp. 613 - 617, 2004.
References
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34. 10E. A. Mackenzie, J. Crossey, A. dePablo, W. Ferguson,”
On-line Monitoring and Diagnostics For Power Transformers”,
Transformer Services GE Energy
References
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