pplication Notes
P74x/EN AP/N
1, P742, P743 (AP) 6-
4.2.3 TCS scheme 2
4.2.3.1 Scheme description
Optional
Optional
P2230ENa
FIGURE 4: TCS SCHEME 2
Much like scheme 1, this scheme provides supervision of the trip coil with the breaker open
or closed and also does not provide pre-closing supervision. However, using two opto inputs
allows the relay to correctly monitor the circuit breaker status since they are connected in
series with the CB auxiliary contacts. This is achieved by assigning Opto A to the 52a
contact and Opto B to the 52b contact. Provided the “CB Fail / Control by” is set to “52a
and <” (CB Fail column) the relay will correctly monitor the status of the breaker. This
scheme is also fully compatible with latched contacts as the supervision current will be
maintained through the 52b contact when the trip contact is closed.
When the breaker is closed, supervision current passes through opto input A and the trip
coil. When the breaker is open current flows through opto input B and the trip coil. As with
scheme 1, 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.
As with scheme 1, optional resistors R1 and R2 can be added to prevent tripping of the CB if
either opto is shorted. The resistor values of R1 and R2 are equal and can be set the same
as R1 in scheme 1.
4.2.4 Scheme 2 PSL
The PSL for this scheme (figure 5) is practically the same as that of scheme 1. The main
difference being that both opto inputs must be off before a trip circuit fail alarm is given.
FIGURE 5: PSL FOR TCS SCHEME 2
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