
TDR9000
™
Circuit Breaker Test System User’s Guide
72A-1898 Rev. A 11/01
A-17
Monday
, November 26, 2001 1:09 pm
Insertion Resistor
Figure A.17 shows how an insertion resistor is used to modify the TRV
(courtesy of ABB Power T&D Company, Inc.).
Figure A.17 Transient Recovery Voltage: Insertion Resistor Operation
Many circuit breakers, especially those used in transmission circuits,
employ resistors for operation. They were originally used during opening
operations and still, if present, provide a useful function at these times.
Such resistors serve one of two functions: In a multibreak circuit breaker
they are used to help to distribute the transient recovery voltage more
uniformly across the several breaks. They can also be used to reduce the
severity of the transient recovery voltage at the time of interruption by
introducing damping into the oscillation. When the fault current has
been switched by S
2
, a remaining current flows through R. This must be
interrupted subsequently by opening the auxiliary interrupter S
1
.
The primary use of the resistors in modern circuit breakers is to reduce
voltage transients on closing. If the source is stiff, a high percentage of the
source voltage is impressed across the line at the time the circuit breaker
closes to energize a transmission line. If the line is open at the far end, or
terminated in a load such as an unloaded transformer which has a high
surge impedance, the wave essentially doubles at the far end. Such high
switching surges put severe stress on components at that location, and
led to the introduction of transmission circuit breakers with closing
resistors that are pre-inserted at the time of line energization. Switch S
1
is
closed first; the voltage across it is shared by R. The voltage impressed on
the line is reduced by the factor Z
0
R+Z
0
and all the waves generated as a
consequence are correspondingly reduced. The switch, S
2
, is closed a
short time later, after the surges on the line have subsided.
S
2
S
1
R
Z
0
Main
Contact
Insertion
Resistor
Auxiliary
Contact
Содержание TDR9000
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