Circuit Breaker Fail Implementation; Circuit Breaker Fail Timers - GE P642 Technical Manual

P64x
3

CIRCUIT BREAKER FAIL IMPLEMENTATION

Depending on the P64x model (P642, P643, P645), up to five independent sets of circuit breaker failure settings are
available, supporting one phase current and one earth undercurrent function for each set. Each CB Failure set can
be enabled or disabled by the settings T1 CBF Status, T2 CBF Status, T3 CBF Status, T4 CBF Status and T5 CBF
Status respectively.
You can enable or disable each Earth undercurrent element with the IN< Status setting. If enabled, you can set
each earth undercurrent element as measured or derived using the IN< Input setting. When enabled, it can be set
as measured or derived. Depending on the model, you can use single phase CTs connected to the three nuetral CT
connections TN1, TN2 and TN3 for CB failure function (see wiring diagram). You define this with the IN< Terminal
setting.
3.1

CIRCUIT BREAKER FAIL TIMERS

The circuit breaker failure protection incorporates two timers, CB Fail 1 Timer and CB Fail 2 Timer, allowing
configuration for the following scenarios:
Simple CBF, where only CB Fail 1 Timer is enabled. For any protection trip, the CB Fail 1 Timer is started, and
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normally reset when the circuit breaker opens to isolate the fault. If breaker opening is not detected, the CB
Fail 1 Timer times out and closes an output contact assigned to breaker fail (using the programmable
scheme logic). This contact is used to back-trip upstream switchgear, generally tripping all infeeds
connected to the same busbar section.
A retripping scheme, plus delayed back-tripping. Here, CB Fail 1 Timer is used to issue a trip command to a
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second trip circuit of the same circuit breaker. This requires the circuit breaker to have duplicate circuit
breaker trip coils. This mechanism is known as retripping. If retripping fails to open the circuit breaker, a
back-trip may be issued following an additional time delay. The back-trip uses CB Fail 2 Timer, which was
also started at the instant of the initial protection element trip.
You can configure the CBF elements CB Fail 1 Timer and CBF Fail 2 Timer to operate for trips triggered by
protection elements within the device. Alternatively you can use an external protection trip by allocating one of the
opto-inputs to the External Trip DDB signal in the PSL.
You can reset the CBF from a breaker open indication (from the pole dead logic) or from a protection reset. In these
cases resetting is only allowed if the undercurrent elements have also been reset. The resetting mechanism is
determined by the settings Volt Prot Reset and Ext Prot Reset.
The resetting options are summarised in the following table:
Initiation (Menu Selectable)
Current based protection
Sensitive Earth Fault element
Non-current based protection (e.g. 27/59/81/32L)
External protection
P64x-TM-EN-1.3
CB Fail Timer Reset Mechanism
The resetting mechanism is fixed (e.g. 50/51/46/21/87)
IA< operates AND IB< operates AND IC< operates AND IN< operates
The resetting mechanism is fixed.
ISEF< Operates
Three options are available:
● All I< and IN< elements operate
● Protection element reset AND all I< and IN< elements operate
CB open (all 3 poles) AND all I< and IN< elements operate
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Three options are available.
All I< and IN< elements operate
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External trip reset AND all I< and IN< elements operate
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CB open (all 3 poles) AND all I< and IN< elements operate
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Chapter 10 - CB Fail Protection
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