4
Supervision
functions
The trip circuit supervision function and the
energizing current monitoring function can be
locally disabled by turning switch switch SG1/2
on the front panel in position 1. The locally
performed selection in the control module over-
rides the selection made over the SPA bus, us-
ing parameters S200 and S202.
Trip circuit
supervision
(modified 96-02)
The trip circuit supervision unit in the control
module consists of three functional units; a con-
stant current generator, a measuring and time
delay circuit and an output circuit for signal-
ling. The input/output circuits are galvanically
isolated from each other. The constant current
generator forces a 1.5 mA measuring current to
flow through the circuit breaker trip circuit. The
constant current generator is connected over the
OPEN contact of the feeder terminal circuit.
Under no-fault conditions the voltage over the
OPEN contact or the constant current genera-
tor must exceed 30 V dc, when the voltage drop
caused by the 1.5 mA measuring current in other
parts of the supervised circuit are observed.
Mathematically the operation condition can be
expressed as:
Uc - (R
h
(ext.) + R
h
(int.) + Rs) x Ic
≥
30 V dc
(Formula 1)
where
Uc
= operating voltage over the supervised
trip circuit
Ic
= measuring current through the trip
circuit, approximately 1.5 mA
R
h
(ext.) = external shunt resistor value
R
h
(int.) = internal shunt resistor value, 1 k
Ω
Rs
= trip coil resistance value
The resistor R
h
(ext.) must be so calculated that
the trip circuit supervision current through the
resistor is low enough to leave the trip coil of
the circuit breaker unaffected. On the other
hand the voltage drop over the resistor R
h
(ext.)
must not be too high to jeopardize the operat-
ing condition presented in Formula 1 above.
The following values are recommended for re-
sistor R
h
(ext.) in figure 1:
Operating voltage Uc
Shunt resistor
R
h
(ext.)
48 V dc
1.2 k
Ω
, 5 W
60 V dc
5.6 k
Ω
, 5 W
110 V dc
22 k
Ω
, 5 W
220 V dc
33 k
Ω
, 5 W
