Aijun Wu

Liang Li

Yu Chen

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C I R E D 21st International Conference on Electricity Distribution Frankfurt, 6-9 June 2011
Paper 0574
Paper No 0574 1/3
USING AUXILIARY CONTACT FOR THE DISPOSITION
OF DROP-OUT FUSE FAULTS
---A NEW RESCUE MEASURES TO SHORTEN THE RESTORATION TIME AND
INCREASE THE POWER SUPPLY RELIABILITY IN FAULT RESCUE
Liang LI Yu CHEN Aijun WU
Songjiang Power Supply Company, Songjiang Power Supply Company, Songjiang Power Supply Company,
Shanghai Municipal Electric Power Shanghai Municipal Electric Power Shanghai Municipal Electric Power
Company– China Company– China Company– China
redcrusade@yahoo.cn cair_2000@163.com sindigar@163.com
ABSTRACT
Faults of the upper stationary contact on the commonly
used drop-out fuse in distribution network often happen.
The traditional method to repair the fault is to change the
fault drop-out fuse by using hot line works, but it also has
some problems in aspects of system reliability, schedule
and safety of hot line works. After analyzing the main
causes of the fuse faults on the PRW type drop-out fuse
widely used in Shanghai China (shown in Fig. 1), a new
rescue measures to dispose such faults are researched.
The new measures can increase the power supply
reliability and the safety of live working.
INTRODUCTION
Due to the improper installation or operation, product
quality, environmental factor and other reasons, the drop-
out fuse faults induced by high temperature on the
electrical contact often happen.
In this paper a new rescue measures to dispose faults of
the upper stationary contact of the drop-out fuse by using
an auxiliary contact is presented. Through the application
of the auxiliary contact, we can not only shorten the
outage duration and restore power supply immediately
caused by fuse faults thus improve the power supply
reliability, but also can change such un-planned hot line
rescue works into planned works to increase the safety of
hot line works.
Fig. 1: PRW type drop-out fuse and its upper stationary
contact
ANALYSIS OF THE CAUSES OF THE DROP-
OUT FUSE FAULTS
After analyzing the main causes of the drop-out fuse
faults, we can find that most of such troubles are caused
by worst contact of the contactor which induced high
temperature on the electrical contact (shown in Fig. 2),
increasing the contact resistance and then the rate of
temperature rise and finally causes burning, welding,
arcing of the contact and progressing to drop out.
Therefore, the main causes of drop-out fuse faults are
from the high temperature of worst contact of the
electrical contact.
Fig. 2: Burned-out of the upper stationary contact on
PRW type drop-out fuse
PRINCIPLE AND STRUCTURE OF THE
AUXILIARY CONTACT
When the upper stationary contact of the drop-out fuse is
burned out, a special designed auxiliary contact is
installed on the arc-extinguishing tube to form an
auxiliary circuit. Such auxiliary contact can not only
maintain the power supply until a new fuse set is
substituted but also can reduce the temperature of the
fault upper stationary contact.
When the auxiliary contact is installed on the drop-out
fuse, there established two electric circuits, the
fundamental circuit and the auxiliary circuit, on the fuse
installation (refer to Fig. 3). The fundamental circuit is
made up of the upper movable contact of arc-
Burned-out of the
upper contact
C I R E D 21st International Conference on Electricity Distribution Frankfurt, 6-9 June 2011
Paper 0574
Paper No 0574 2/3
extinguishing tube and the upper stationary contact of
fuse, and the auxiliary circuit consists of the auxiliary
contact and the upper stationary contact. Thus the
auxiliary circuit and the fundamental circuit forming a
shunt circuit, so the current on the fundamental circuit
will be reduced and the temperature rise will be lowered.
Auxiliary contact is made up of three parts: the base, the
left contact plate and the right plate. We can assemble the
base of auxiliary contact and the upper contact of arc-
extinguishing tube by using a bolt and the auxiliary
contact will be located in the same central axis of the fuse
tube. Two contact plates are tilted a certain angle in the
opposite direction, so we can easily put the arc-
extinguishing tube on the drop-out fuse using the hard
pole. Because bulges of the contact plates of the auxiliary
contact are separated from the burning part of the upper
support of the drop-out fuse, the auxiliary contact can
keep a good contact resistance and prevent the situation
from deterioration in the event of maintaining the original
effectiveness. In the meantime, the two sides contact
plates can clamp the upper support of the fuse to instead
the original contact that had been burned to keep the firm
contact of the fuse tube with the upper support. So the
auxiliary contact plays a role not only in shunting the
current flow but also in firming circuit.
Fig. 3: Structure of the auxiliary contact for the PRW type
drop-out fuse
ANALYTICAL TESTS
When the upper stationary contact of drop-out fuse cannot
be used due to burn out, we install the auxiliary contact in
the fuse to form an auxiliary circuit. Then the auxiliary
circuit will be obtained as the only electric circuit, Table
1 shown the experimental value after installing the
auxiliary contact (take the fuse that rated current is 100A
for example).
Table 1: Test data when the upper contact of fuse cannot
be used during burning out
Circuit
Condition
Theoretical
Contact
Area (mm2)
Loop
Resistance
(μΩ)
Temperature
Rise (K)
Original
Circuit
(Fundamental
Circuit)
62 1204 24
Current
Circuit
(Auxiliary
Circuit)
540 1986 32
The Table 1 illustrates the auxiliary circuit which is
composed of the auxiliary contact and the upper
stationary contact becomes the current circuit. The
original circuit is made of copper and the current circuit is
made of copper and stainless steel, so the resistance of
current circuit increases. However, since the rate of heat
dissipation increases because of decreasing of unit current
density due to the contact area of current circuit is larger
than the original circuit, the measured value of
temperature rise meet the requirements of the national
standard (GB/T 15166.4-94) [1]. So it means that the
auxiliary circuit can well play a role in emergency
response when the fundamental circuit cannot be used
because of burning out.
If the auxiliary contact is installed just during the
beginning of the red-hot phenomenon appears on the
upper stationary contact then the fundamental circuit and
the auxiliary circuit will form a shunt circuit. Table 2
shows the experimental value after installing the auxiliary
contact (take the fuse that rated current is 100A for
example).
Table 2: Test data when the upper contact can be used
Circuit
Condition
Theoretical
Contact
Area (mm2)
Loop
Resistance
(μΩ)
Temperature
Rise (K)
Original
Circuit
(Fundamental
Circuit)
62 1204 24
Current
Circuit
(Fundamental
Circuit+
Auxiliary
Circuit)
540+62 750 21
Table 2 illustrates the auxiliary circuit and the
fundamental circuit will form a shunt circuit after the
auxiliary contact is installed in the event that original
circuit of the fuse can be used, so the current on the
fundamental circuit will be reduced, the temperature rise
of fundamental circuit will be lowered, the red-hot
phenomenon of the upper stationary contact will be
relieved and the total loop resistance will be decreased. In
summary, the auxiliary circuit can well play a role in pre-
emergency when the fundamental circuit can be used.
Figure 4 shows the case when the auxiliary contact is
installed and operating in shunt with the original
stationary contact thus the current on drop-out fuse is
200% of the rated current. At the moment the fuse-
element is burned out and the leaf spring drops out, so the
fuse can still protect the device and isolate faults (take the
fuse that rated current is 100A for example).
C I R E D 21st International Conference on Electricity Distribution Frankfurt, 6-9 June 2011
Paper 0574
Paper No 0574 3/3
Fig. 4: The case of the auxiliary contact has been installed
and operates in parallel with the normal contact the
current on drop-out fuse is then be 200% of the rated
current
PRACTICAL APPLICATION
Since the auxiliary emergency contact of drop-out fuse
was researched and developed successfully in 2009 in
Songjiang Power Supply Company, Shanghai Municipal
Electric Power, we have already applied the new rescue
measures to dispose drop-out fuse faults about one
hundred times in the 18 months. The average time for
resume the power supply for each such fault is only 4 to 5
minutes. After running through a period of time, the
auxiliary contact has no any heat generation or other
abnormal phenomena and operates in good condition.
When faults of the upper stationary contact on the PRW
type drop-out fuse happen, we can restore power supply
in the shortest time by using auxiliary contact, so the
reliability of power supply will be improved. In the mean
time, it can also dispose fuse faults temporarily and
maintain operation in period of time until the restoration
of the fault fuse to a new one is carried on in the planned
maintenance schedule. Especially, it can greatly decrease
hot line rescue works at night, so it can not only reduce
the labor intensity, but also greatly increase the safety of
live working. During this time, the fuse can still protect
the device and isolate faults by burning out the fuse-
element except that the arc-extinguishing tube can not
drop out.
CONCLUSIONS
The application of auxiliary contact is a new rescue
measures to dispose the PRW type drop-out fuse faults. It
can shorten the outage duration, improve the power
supply reliability, reduce the labor intensity and increase
the safety of live working. Moreover, the device is easy in
construction and manufacturing cost is very low. So the
new technique will have remarkable social benefit and
economic benefit by the comprehensive application of
drop-out fuse in distribution network.
REFERENCES
[1] Xiaoyong Han, Peng Li, Zhongji Hou, 1994,
Alternating-current high-voltage fuses General test
method（GB/T 15166.4-94） , Standards Press of
China, Beijing, China, 47-48.
[2] Zhongji Hou, Jimei Wang, Fuqing Chen, Kejian
Tang, 1994, Alternating-current high-voltage fuses
Terminology（GB/T 15166.1-94）, Standards Press
of China, Beijing, China, 1-7.
[3] Baoxin Zuo, 1996, "Failure and faults disposing of
high voltage fuse", Journal of Electrotechnics. vol. 4,
49-50.
[4] Hui Zhu, 2008, "A rescue measures to dispose faults
of contact of drop-out fuse", Distribution
&Utilization. vol. 1, 42-43.
Liang Li (1980- ), male, master, power engineer, the main
work is technology management of live working in
distribution lines.
The fuse-element
is burned out
The leaf spring
drops out


USING AUXILIARY CONTACT FOR THE DISPOSITION OF DROP-OUT FUSE FAULTS ---A NEW RESCUE MEASURES TO SHORTEN THE RESTORATION TIME AND INCREASE THE POWER SUPPLY RELIABILITY IN FAULT RESCUE

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USING AUXILIARY CONTACT FOR THE DISPOSITION OF DROP-OUT FUSE FAULTS ---A NEW RESCUE MEASURES TO SHORTEN THE RESTORATION TIME AND INCREASE THE POWER SUPPLY RELIABILITY IN FAULT RESCUE

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