2011 International Conference on Electrical Engineering and Informatics
17-19 July 2011, Bandung, Indonesia
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Through Fault Current Monitoring System to
Predict the Degradation of Transformer
Withstand Capability
H. Maryono#1, H.I. Septiyani#2, M. Muhlis #3, M.N. Nugraha#4
#
PT PLN (Persero) P3B Jawa Bali West Jawa Regional Offices - Maintenance Department
Jl. M. Toha km 04 Cigereleng, Bandung – Indonesia 40255
1
hendrik.m@pln-jawa-bali.co.id
henny.ika@pln-jawa-bali.co.id
3
muhlis@pln-jawa-bali.co.id
4
n.nugraha@pln-jawa-bali.co.id
2
Abstract— PLN P3B Jawa Bali is a unit that responsible for
managing and operating the transmission system in Jawa and
Bali area. For this utility, power transformer is one of the
equipments that has important role in the transmission system,
therefore various efforts have been done to prevent transformer
failures. To prevent unexpected transformer failure, the condition assessment of distribution transformers is done. Distribution
transformer failure analysis has been done as the early stage of
the assessment. The results of the analysis indicate that faults on
20 kV feeders are the main root cause of the damage on
distribution transformer (150/20 kV and 70/20 kV). Some
references also mentioned that the transformer failures caused
by 20 kV feeder faults are highly affected by the fault currents
and duration. Therefore, this paper will presents about the
development of the through fault current (TFC) monitoring
system to predict the degradation of transformer withstand
capability and its application on distribution transformers 150/20
kV 60 MVA. This system consists of TFC logger, PC concentrator and web based database system. TFC logger will record
the fault current and duration that exceed the normal current on
the transformer and then send the data to the server. The
cumulative TFC data will be used to predict the degradation of
transformer withstand capability.
Keywords— Through fault current, transformer withstand capability, TFC monitoring system
I. INTRODUCTION
PLN P3B Jawa Bali is a unit that responsible for managing
and operating the transmission system in Jawa and Bali area.
For this utility, power transformer is one of the equipment that
has important role in transmission system. Therefore, various
efforts have been done to prevent transformer failures.
Distribution transformer failure analysis has been
conducted as a part of transformer condition assessment. The
results showed that the faults on 20 kV feeders are the main
root cause of transformer failures in P3B Jawa Bali [1].
References [2,3,4] also mention that through fault currents
produce mechanical and electrical stress which can cause a
weakening of winding clamping pressure, movement of
conductors, insulation damage and changes in winding
structure. These stresses are strongly affected by the fault
current and duration.
Therefore, this paper presents a TFC monitoring system to
predict the degradation of transformer withstand capability
and its application on the distribution transformers 150/20 kV
60 MVA. TFC monitoring system is used to record the fault
current and duration which exceed the overload current. This
data is sent to the server and used to predict the transformer
withstand capability. TFC data on transformers 150/20 kV 60
MVA in Cigereleng and Fajarsurya substations will also be
presented. Some assumptions are needed for predicting the
remaining withstand capability of the transformer, therefore it
is difficult to get the accurate value. However, by using the
TFC monitoring system, fault current and duration can be
monitored and used as a basis for possible corrective actions.
II. TRANSFORMER WITHSTAND CAPABILITY
When the fault occurs, current which flows through the
transformer exceeds the transformer overload current (see Fig.
1). This current causes electrical and mechanical stress on the
transformer. These stresses can cause a weakening of winding
clamping pressure, movement of conductors, insulation
damage and changes in winding structure.
20 kV
Fig. 1, Through fault current
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Based on the IEC 60076-5, distribution transformers should
be able to withstand maximum short circuit current for 2
seconds. Reference [3] mention that the degradation of
transformer withstand capability can be predicted using
equation (1).
………………………………………..(1)
transformer remaining withstand capability and as a basis to
conduct the possible corrective actions.
A. The Architecture of TFC Monitoring System
The architecture of TFC monitoring system can be seen in
Fig. 4. This system consists of three main components. There
are TFC logger, PC concentrator and server.
Where:
I = Short circuit current
t = Duration
k = Constant
During the operation, transformer withstand capability
always be decreased as shown in Fig. 2. This degradation can
be caused by thermal and chemical stress, etc.
Fig 4, Architecture of TFC monitoring system
TFC Logger
TFC logger is a device mounted on the secondary side of
distribution transformer to monitor the current flowing
through that transformer. When the current exceeds the setting
value (transformer overload current) the logger will record the
fault current and duration, and then transmit them to the PC
concentrator via wireless communication.
Fig.2, Stress withstand capability over transformer lifetime
Transformer withstand capability will be decreased quickly
if exposed to through fault current (see Fig. 3). This figure
shows that the first two faults reduce the withstand capability
significantly, and then the transformer could not withstand the
force of the third fault.
Fig. 3, Stress withstand capability with through fault current
III. TFC MONITORING SYSTEM
TFC monitoring system can be used as one
detection of transformer condition. The system
current and duration and then store the data into
server. The cumulative of t are used to
of the early
record fault
the database
predict the
PC Concentrator
PC concentrator is used to collect and pass the data to the
server. By using TFC driver installed on the PC concentrator,
the users can change the instrument settings and access the
data in TFC logger.
Server
On the server, there is a web-based database application.
This server collects all data TFC and then predict the
transformer remaining withstand capability. This server is
equipped with an early warning system that can send a short
message when the cumulative TFC reach a limit value. This
setting limit is adjustable.
B. Transformer 150/20 kV 60 MVA in Fajarsurya S/S
The failure of distribution transformer 150/20 kV 60 MVA
at Fajarsurya substation occurred in 2010. This transformer
failed when the short circuit occurred on the 20 kV feeder.
Sudden pressure relay initiated CBs to open and localize the
fault. Based on the disturbance recorder, the fault currents that
flow through RST windings were 1267.5 A, 3990A and T
3325 A respectively.
Electrical tests have been done to investigate the failed
transformer. The results of SFRA and dc resistance tests
showed that S phase winding is open. Further investigation
has been done to inspect internal condition of the transformer.
The results of internal inspection showed that S phase winding
elongated as shown in Fig. 5. It was supposed that the S-phase
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winding was no longer able to resist axial force
f
caused by the
last fault.
transformer since 2009. The through fault currents and
can be seen inn Fig. 7 ~ 8 respectively.
cumulative of
Fig 7, Through faault currents data
Cumulative TFC on Tran
nsformer 150/20 kV 60
MVA Cigereleng S/S
S in 2009 - 2010
80
Cumulative I2t (kA2.s)
70
Fig 5, Failed transformer
Based on the operation record book, it was
w known that the
failed transformer experienced high numbeer of 20 kV feeder
faults. The cumulative of t during 2009-22010 can be seen in
Fig. 6 as follow.
Cumulative TFC on Trx 150/20 kV
V 60 MVA
Fajarsurya S/S in 2009-201
10
70
Cumulative I2t (kA2.s)
60
50
40
30
60
50
40
30
20
10
0
I2t phase R
I2tt phase S
I2t phase T
Fig 8, Cumulative TFC on Transformer 150/20 kV 60 MVA in Cigereleng
substaation
By using the cumulative of
, remaining withstand
capability of the transformer caan be predicted as shown in Fig
9. These curves are calculateed under assumption that the
initial withstand capability of thhe transformer in 2009 is 0.9 x
k, where
2
. The through fault currents
will reduce the initial withstannd capability. Figure 9 shows
that the R-phase winding suffeer a higher stress than another
phases.
20
Remaining withstand capability
10
0
I2t phase R
I2t phase S
I phase T
I2t
Fig 6, Cumulative TFC on Transformer 150/20 kV 60
6 MVA in Fajarsurya
substation
Based on the inspection result and cumuulative TFC, it is
supposed that mechanical stress on the S-phase
S
winding is
higher than the other phases during the 20099-2010.
Remaining withstand capability
375
365
355
345
335
325
315
305
295
285
275
R-phase winding
C. Transformer 150/20 kV 60 MVA in Cigeereleng S/S
Transformer 60 MVA 150/20 kV in Ciggereleng substation
operated since 1994. This transformer is one
o of transformers
which experience high number of faults on 20 kV feeder.
Therefore, TFC monitoring system has been installed in this
S-phaase winding
T-phase winding
Fig. 9, Remaining withstand capability
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Authorized licensed use limited to: Universidad Nacional de Colombia (UNAL). Downloaded on February 17,2021 at 20:30:13 UTC from IEEE Xplore. Restrictions apply.
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IV. CONCLUSIONS
Transformer failure at Fajarsurya substation show that the
TFCs can cause the changes in winding structure and open
circuit. By using TFC Monitoring System, the fault current
and duration can be recorded for predicting the remaining
withstand capability of transformer. Some assumptions are
needed to predict the remaining withstand capability, so it is
difficult to obtain the accurate withstand capability. However,
by using this system, the fault current and duration can
monitored as a basis for taking possible corrective actions.
ACKNOWLEDGMENT
We would like to thanks to the Management of PLN P3B
Jawa Bali and all contributors who have supported us for
developing this TFC Monitoring System.
REFERENCES
[1]
[2]
[3]
[4]
[5]
[6]
N. Ukhita A. W., A.P. Purnomoadi, A. Susilo, E. Yuliastuti dan A.
Pharmatrisanti, Failure Analysis on Power Transformers 60 MVA
150/20 kV, Proceedings of the International Conference on Electrical
Engineering and Informatics, Institut Teknologi Bandung, Indonesia
June 17-19, 2007.
Anita Oommen, A Case Study Evaluation of the Causes for the
Premature Failure of Transformer on the Escom Transmission Network,
Study Committee B5 Colloquium CIGRE, Canada, 14-16 September
2005.
Roy Moxley and Armando Guzman, Transformer Maintenance Interval
Management, Schweitzer Engineering Laboratories, Inc., 2005.
R.P.P smeets, L.H.te Paske, T. Fogelberg, Short Circuit Withstand
Capability of Large Power Transformers.
IEC, Power Transformer – Ability to withstand short circuit, IEC
60076-5, 2000.
IEEE Guide for Transformer Through Fault Current Duration, IEEE
C57.109-1995.
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