destroyed since the contact is obliged to disconnect high level of electromagnetic energy
accumulated in the trip coil.
An auxiliary relay can be used between the protection relay trip contact and the circuit
breaker coil. This way the breaking capacity question is solved, but the TCM circuit in the
protection relay monitors the healthy auxiliary relay coil, not the circuit breaker coil. The
separate trip circuit supervision relay is applicable for this to supervise the trip coil of the
circuit breaker.
Dimensioning of the external resistor
Under normal operating conditions, the applied external voltage is divided between the
relay’s internal circuit and the external trip circuit so that at the minimum 20 V (15...20 V)
remains over the relay’s internal circuit. Should the external circuit’s resistance be too
high or the internal circuit’s too low, for example due to welded relay contacts, a fault is
detected.
Mathematically, the operation condition can be expressed as:
V
R
R
I
V
AC
DC
C
ext
int
s
c
−
+
+
×
≥
(R
)
/
20
A070986-ANSI V1 EN
(Equation 157)
V
c
Operating voltage over the supervised trip circuit
I
c
Measuring current through the trip circuit, appr. 1.5 mA (0.99...1.72 mA)
R
ext
external shunt resistance
R
int
internal shunt resistance, 1 kΩ
R
s
trip coil resistance
If the external shunt resistance is used, it has to be calculated not to interfere with the
functionality of the supervision or the trip coil. Too high a resistance causes too high a
voltage drop, jeopardizing the requirement of at least 20 V over the internal circuit, while
a resistance too low can enable false operations of the trip coil.
Table 733:
Values recommended for the external resistor R
ext
Operating voltage U
c
Shunt resistor R
ext
48 V AC/DC
1.2 kΩ, 5 W
60 V AC/DC
5.6 kΩ, 5 W
110 V AC/DC
22 kΩ, 5 W
220 V AC/DC
33 kΩ, 5 W
Due to the requirement that the voltage over the TCM contact must be 20 V or higher, the
correct operation is not guaranteed with auxiliary operating voltages lower than 48 V DC
1MAC059074-MB A
Section 6
Supervision functions
615 series ANSI
841
Technical Manual
Summary of Contents for Relion 615 series
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