Schweitzer Engineering Laboratories SEL-352-1, Instruction Manual

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Date Code 20010731 Breaker Logic 3-33
SEL-352-1, -2 Instruction Manual
CRTC minutes 80
3
minutes 240
= =
For the example, 80-minute cooling time constants were selected for CRTC and TRTC.
If you select an inaccurate cooling time constant, the resistor energy models may not be realistic
for some time after breaker operations. For instance, if the cooling time constant is too short, a
breaker resistor may actually contain more energy than is modeled and cause pending failure and
failure energy levels to be less conservative than intended.
F
LASHOVER
C
ONDITIONS
Application Description
Breaker failure protection during flashover conditions is completely independent from the other
protection logic. Use this protection in addition to the other protection or by itself.
When an open breaker pole flashes over, the following conditions can be used to detect the
failure:
œ
One per unit system voltage can be measured across the breaker pole before the
flashover occurs.
œ
Once the flashover starts, voltage drops and current flows.
Because these two criteria may also describe breaker close operations, the flashover protection
scheme should be disabled during breaker operations and for several cycles after.
The relay provides two schemes for detection of circuit breaker flashover. Scheme 1 uses
potential measurements from both sides of the breaker to detect flashover. Scheme 2 uses a
potential measurement on only one side of the breaker to detect flashover.
Operating Characteristic
Scheme 1 (Flashover, Six Potential Transformers)
Scheme 1 uses the voltage across the circuit breaker, derived from PTs on both sides of the
breaker, and the current through the breaker to detect flashover. If PTs are only available on one
side of the circuit breaker, the second scheme may be used to detect breaker flashover.