FIELD OF THE INVENTION
The present invention relates to an improved configuration of the Controlled
Shunt Reactor (CSR) with a triggered Spark Gap on the secondary side of the
CSR instead of the Thyristor Valve. More particularly, the present invention
relates to a controlled shunt reactor for reducing losses in switch-over voltages in
long transmission lines.
BACKGROUND OF THE INVENTION
Long transmission lines have a fixed shunt reactor connected to it to reduce
switching over-voltages. This reactor is always in circuit and contributes to the
losses vis-a-vis reduction in voltage even when it is not required to be operated
for the desired purpose in the circuit. It is known that a Controlled Shunt Reactor
(CSR) is used in the circuit to eliminate the avoidable loss on reduction in
voltage.
The CSR consists of a 100% impedance transformer with a switch on the
secondary side. The switch on the secondary when closed, the transformer acts
like a fixed reactor and when the switch is opened it acts like an open circuit.
The switch on the secondary side comprises a circuit breaker disclosed in parallel
with a thyristor valve for quick insertion of the CSR. Figure 1 shows a simplified
block diagram of the prior art On/Off CSR.
According to prior art, the thyristor valve of ON/OFF type controlled shunt
reactor, remain in the circuit in a blocked or OFF mode resulting in snubber
losses, and producing heat when the CSR is not required to be in the circuit. This
results in higher losses in the system. As the thyristor valves are continuously in
the circuit, there is a requirement of continuous monitoring of the health of the
thyristor valves. This also makes the system more complex and affects its
ensured availability when in need.
In the prior art, during each operation of switching ON of the controlled shunt
reactor, the thyristor valves get heated up and about 10 to 15 minutes gap is to
be provided for cooling the thyristor valve. During this period, the thyristor
valves are not available for any further operation thus reducing the availability of
the CSR for switching.
Indian Patent 241303 entitled "An Improved Controlled Shunt Reactor",
describes a controlled shunt reactor comprising thyristor valves connected
across the secondary side of a 100% impedance transformer. A controller is
provided for issuing switching commands to the thyristor valves through a base
electronics and thyristor monitoring unit. A bypass circuit breaker is provided in
parallel to the thyristor valves, and a bypass choke is provided in series with the
circuit breaker. The controller triggers the thyristor valves into a conducting
mode for a short duration only during which the current is transferred from said
thyristor valves to the circuit breaker. This scheme is similar to the prior art
scheme shown in Figure 1.
Indian Patent 211256 entitled "An Apparatus For Providing Reactive Power
Support Required By Power Systems", discloses a controlled shunt reactor
comprising water cooled thyristor valves connected across the secondary side of
a 100% impedance transformer.
Indian Patent 213469, entitled "Controlled Shunt Reactor Of Transformer Type"
teaches a controlled shunt reactor comprising water cooled thyristor valves
connected across the secondary side of a 100% impedance transformer with
firing angle variation.
The prior art circuit of the CSR proposes a circuit breaker in parallel with thyristor
valve for quick insertion of the CSR. But the limitation of the method is that it
requires an elaborate arrangement with series connected thyristors with its
controller, the valve base electronics, triggering, monitoring and protection
systems. The losses in the prior art are much higher as the snubber circuits get
heated up when the CSR is in the OFF mode.
Therefore, a need therefore exists, for reducing the losses in the controlled shunt
reactor when it is OFF. There also exists a requirement to increase the
availability of the CSR as in the prior art after one operation of turning ON the
CSR, it cannot be switched for the next 10 to 15 minutes, which is the cooling
time required for the thyristor valves.
A prior art CSR comprises a thyristor valve absent forced cooling, and connected
to a secondary side of the rector transformer in parallel to a bypass breaker. The
line voltage of the primary side of the controlled shunt reactor is monitored and
the controller decides whether to turn ON or OFF the CSR. When the CSR has to
be turned ON the thyristor valve is triggered and within 10ms the CSR is turned
ON. Simultaneusly a 'CLOSE" command is also given to the Bypass Circuit
Breaker (BPCB) and it "CLOSES" in about 100 to 120ms. When the Bypass Circuit
Breaker is "CLOSED" the entire current is diverted from the thyristor valve to the
BPCB. This now relieves the thyristor valve, but during the turn ON time the heat
generated in the thyristor valve would raise the junction temperature of the
thyristors. Hence about 10 to 15 minutes cooling time is required before the
BPCB can be opened or the CSR can be turned OFF.
In the prior art when the CSR has to be turned OFF, the bypass circuit breaker is
opened and the thyristor valves are blocked. The secondary of the CSR
transformer is in open circuit mode. As the open circuit voltage has to be blocked
by the thyristor valve there as losses in the thyristor valve due to heating of the
snubber circuits and other associated circuits.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to propose a controlled shunt
reactor for reducing losses in switch-over voltages in long transmission lines,
which eliminates the disadvantages of the prior art.
Another object of the invention is to propose a controlled shunt reactor for
reducing losses in switch-over voltages in long transmission lines, which
eliminates provisions of expensive thyristor values including a thyristor
monitoring unit
A still another object of the invention is to propose a controlled shunt reactor for
reducing losses in switch-over voltages in long transmission lines, which
increases availability of the controlled shunt circuit for specific operation.
A further object of the invention is to propose a controlled shunt reactor for
reducing losses in switch-over voltages in long transmission lines, which is simple
in construction and economic for manufacturing and use.
SUMMARY OF THE INVENTION
Accordingly, there is provided A controlled shunt reactor (CSR) for reducing loss
in switch-over voltage in long transmission lines, comprising:
• a triggered spark gap connected across the secondary of the CSR;
• a bypass circuit breaker provided in parallel to the spark gap;
• a controller for issuing switching commands to said spark gap through
a trigger pulse unit;
• characterized in that said controller provides a trigger command to
the trigger pulse generator which in turn generates trigger pulses
to the spark gap to trigger the gap within 5ms and during the
transfer of current to said bypass circuit breaker.
The present invention replaces the thyristor valve when a forced triggered spark
gap or a trigatron. When the CSR has to be turned ON, the spark gap is
triggered and within Sms the CSR is turned ON. In parallel a "CLOSE" command
is also given to the bypass circuit breaker (BPCB) and it "CLOSES" in about 100
to 120ms. When the bypass circuit breaker is "CLOSED" the entire current is
diverted from the spark gap to the BPCB. This now relives the spark gap and
within 30 seconds the spark gap is available for subsequent operations.
When the CSR has to be turned OFF the Bypass circuit breaker will be opened.
Now the spark gap is in the open state and the secondary of the CSR
transformer is in open circuit mode. But as the spark gap in the open state does
not draw any current there are no losses in the spark gap, thus eliminating the
losses in the thyristor valve when in Blocked or OFF mode.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - shows a simplified diagram of the prior art On/Off CSR.
Figure 2 - shows an On/Off CSR with a triggered Spark Gap according to the
invention.
Figure 1 in schematic form shows a typical controlled shunt reactor in ON/OFF
mode. The thyristor valves "I" are connected across the secondary of a 100%
impedance transformer "T". Shorting or opening of the secondary terminals of
the transformer "T" results in full rated MVAR or nil MVAR reactive power being
drawn from the 400kV system. The switching commands are issued by the
controller "2" to the thyristor valve "I" through the base electronics and
thyristor monitoring unit "3".
The controller "2" describes the "ON" and "OFF" duration depending on the
transmission line voltage. In the prior art, when the transformer "T" had to be
switched "ON" (secondary to be shorted), the thyristor valve "I" would be given
a triggering command through the base electronics and thyristor monitoring unit
"3" this would result in switching "ON" of the transformer "T" within 10ms. In
parallel a close command would be issued to the Bypass breaker "4". The
Bypass breaker "4" would close in 100 to 120ms thereby transferring the current
from the thyristor valve "I" to the Bypass breaker "4". As considerable amount
of heat is generated in the thyristor during turn on period a cooling period of 10
to 15 minutes have to elapse before an open command can be given.
In the prior art, when the transformer "T" had to be switched "OFF" ( secondary
had to be opened). An open command would be issued to the Bypass breaker
"4". The Bypass breaker "4" would open within 100 to 120ms thereby
switching "OFF" the transformer "T". Now the thyristor valve "I" would support
the secondary voltage in the "Blocked" mode. But in this mode there would be
losses in the snubber and the associated circuits of the thyristor valve "I". Also
as the thyristor valves comprise of a number of thyristors in series the health of
these individual thyristor have to be continuously monitored.
As improved controlled shunt reactor of the present invention is shown in block
diagram form in Figure 2. Items like the 100% impedance reactor transformer,
the bypass circuit breaker and the controller are represented by similar
references as shown in Figure 1.
The improved controlled shunt reactor of Figure 2 comprises of a triggered spark
gap "5" and trigger pulse generator "6".
In the present invention when the controller "2" decides the "ON" and "OFF"
duration depending on the transmission line voltage, then the transformer "T"
has to be switched "ON" (secondary to be shorted). The spark gap "5" would be
given a triggering command through the triggered pulse generator "6" this
would result in switching "ON" of the transformer "T" within 5ms. In parallel a
close command would be issued to the bypass breaker "4" . The bypass breaker
w4" would close in 100 to 120ms thereby transferring the current from the spark
gap "5" to the bypass breaker "4". As no cooling period is required within 30
seconds the CSR is ready for subsequent operations.
When the transformer "T" had to be switched "OFF" (secondary had to be
opened). An open command would be issued to the bypass breaker "4". The
bypass breaker "4" would open within 100 to 120ms thereby switching "OFF"
the transformer "T". Now the spark gap "5" would support the secondary
voltage. As there are no losses in the spark gap in the "Open" state the losses in
the CSR are reduced. As the spark gap is a single device unlike the thyristor
valve which is a string of thyristors in series and monitoring system like the
thyristor monitoring is not required, thereby simplifying the scheme.
We claim:
1. A controlled shunt reactor (CSR) for reducing loss in switch-over voltage
in long transmission lines, comprising:
• a triggered spark gap connected across the secondary of the CSR;
• a bypass circuit breaker (4) provided in parallel to the spark gap;
• a controller for issuing switching commands to said spark gap through
a trigger pulse unit;
• characterized in that said controller (2) provides a trigger command to
the trigger pulse generator (6) which in turn generates trigger pulses
to the spark gap (5) to trigger the gap within 5ms and during the
transfer of current to said bypass circuit breaker (4).
2. A controlled shunt reactor for reducing loss in switch-over voltage in long
transmission lines substantially as herein described and illustrated with the
accompanying drawings.

A controlled shunt reactor (CSR) for reducing loss in switch-over voltage in long
transmission lines, comprising: a triggered spark gap connected across the
secondary of the CSR; a bypass circuit breaker (4) provided in parallel to the
spark gap; a controller for issuing switching commands to said spark gap
through a trigger pulse unit; characterized in that said controller (2) provides a
trigger command to the trigger pulse generator (6) which in turn generates
trigger pulses to the spark gap (5) to trigger the gap within 5ms and during
the transfer of current to said bypass circuit breaker (4).