Circuit Breaker Function; Circuit Breaker State Monitoring; Trip Relays And Trip Circuit Supervision; Tcs Scheme - GE P741 Technical Manual

Application Notes
MiCOM P741, P742, P743
4.

CIRCUIT BREAKER FUNCTION

4.1

Circuit breaker state monitoring

An operator at a remote location requires a reliable indication of the state of the switchgear.
Without an indication that each circuit breaker is either open or closed, the operator has
insufficient information to decide on switching operations. The relay incorporates circuit
breaker state monitoring, giving an indication of the position of the circuit breaker, or, if the
state is unknown, an alarm is raised.
4.2

Trip relays and Trip Circuit Supervision

Relays contacts 1, 2, and 3 of every PU are used for tripping signals from busbar protection,
overcurrent protection and back-trip breaker failure. Even if these relay contacts 1, 2, and 3
are not used in the PSL, they are closed if there is a trip command from these functions
listed above. However, these relays can be affected in PSL for additional functions (breaker-
failure retrip for example).
The dwell time of these three contacts is controlled by the [CB CONTROL, Prot Trip Pulse]
setting and ensures that a minimum tripping duration is always applied.
The trip circuit, in most protective schemes, extends beyond the relay enclosure and passes
through components such as fuses, links, relay contacts, auxiliary switches and other
terminal boards. This complex arrangement, coupled with the importance of the trip circuit,
has led to dedicated schemes for its supervision.
Several trip circuit supervision schemes with various features can be produced with the P74x
range. Although there are no dedicated settings for TCS, in the P74x, the following schemes
can be produced using the programmable scheme logic (PSL). A user alarm is used in the
PSL to issue an alarm message on the relay front display. If necessary, the user alarm can
be re-named using the menu text editor to indicate that there is a fault with the trip circuit.
4.2.1

TCS scheme 1

4.2.1.1 Scheme description
This scheme provides supervision of the trip coil with the breaker open or closed, however,
pre-closing supervision is not provided. This scheme is also incompatible with latched trip
contacts, as a latched contact will short out the opto for greater than the recommended DDO
timer setting of 400ms. If breaker status monitoring is required a further 1 or 2 opto inputs
must be used. Note: a 52a CB auxiliary contact follows the CB position and a 52b contact is
the opposite.
When the breaker is closed, supervision current passes through the opto input, blocking
diode and trip coil. When the breaker is open current still flows through the opto input and
into the trip coil via the 52b auxiliary contact. Hence, no supervision of the trip path is
provided whilst the breaker is open. Any fault in the trip path will only be detected on CB
closing, after a 400ms delay.
Optional
FIGURE 2: TCS SCHEME 1
P74x/EN AP/Na7
(AP) 6-21
AP
P2228ENa