scheider electric MiCOM P746, Technical Manual

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P746/EN AP/G31 Application Notes
(AP) 6-
18
MiCOM P746
4.3 Trip relays and Trip Circuit Supervision
Any relays contact can be used for tripping signals from busbar protection, overcurrent
protection and breaker failure.
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
P746. Although there are no dedicated settings for TCS, in 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.
4.3.1 TCS scheme 1
4.3.1.1 Scheme description
P2228ENa
Optional
AP
FIGURE 2: 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 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.
Resistor R1 is an optional resistor that can be fitted to prevent maloperation of the circuit
breaker if the opto input is inadvertently shorted, by limiting the current to <60mA. 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.