Application Notes P54x/EN AP/La4
MiCOM P543, P544, P545 & P546
(AP) 6-63
AP
3.5.1 TCS scheme 1
3.5.1.1 Scheme description
Figure 21 TCS scheme 1
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 400 ms. 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 in the opposite state.
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 400 ms delay.
Resistor R1 is an optional resistor that can be fitted to prevent mal-operation of the circuit
breaker if the opto input is inadvertently shorted, by limiting the current to <60 mA. The
resistor should not be fitted for auxiliary voltage ranges of 30/34 volts or less, as satisfactory
operation can no longer be guaranteed. The table below shows the appropriate resistor
value and voltage setting (OPTO CONFIG menu) for this scheme.
This TCS scheme will function correctly even without resistor R1, since the opto input
automatically limits the supervision current to less that 10 mA. However, if the opto is
accidentally shorted the circuit breaker may trip.
Auxiliary voltage (Vx) Resistor R1 (ohms) Opto voltage setting with R1 fitted
48/54 1.2 k 24/27
110/250 2.5 k 48/54
220/250 5.0 k 110/125
Note: When R1 is not fitted the opto voltage setting must be set equal to
supply voltage of the supervision circuit.
3.5.1.2 Scheme 1 PSL
Figure 21 shows the scheme logic diagram for the T
CS scheme 1. Any of the available opto
inputs can be used to indicate whether or not the trip circuit is healthy. The delay on drop off
timer operates as soon as the opto is energized, but will take 400 ms to drop off / reset in the
event of a trip circuit failure. The 400 ms delay prevents a false alarm due to voltage dips
caused by faults in other circuits or during normal tripping operation when the opto input is
shorted by a self-reset trip contact. When the timer is operated the NC (normally closed)
output relay opens and the LED and user alarms are reset.
The 50 ms delay on pick-up timer prevents false LED and user alarm indications during the
relay power up time, following an auxiliary supply interruption.
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