Trip-Circuit Supervision - ABB REX 521 Technical Reference Manual, General

REX 521
4.1.10.
26
Protection Relay
Technical Reference Manual, General
When testing the general output relays, the user should notice, that normal operation
of the relay cannot be disconnected. If an output relay is permanently activated by
the configuration, it cannot be deactivated for testing.
For further information, see
page 7).
Table 4.1.9-1 Testing of inputs and outputs
Test object Using
Digital inputs HMI
Serial communication
Output relays HMI
Serial communication
IRF relay HMI
Serial communication

Trip-circuit supervision

The trip-circuit supervision consists of two functional units:
• A current limiter including the necessary hardware elements
• A software-based function block, named TCS1
The supervision of the trip circuit is based on the constant current injection principle.
By applying an external voltage over the relay's trip contacts, a constant current is
forced to flow through the external trip circuit. If the resistance of the trip circuit
exceeds a certain limit, for instance due to a bad contact or oxidation, the supervision
function will be activated and cause a trip-circuit supervision alarm signal after an
adjustable delay time.
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, the fault is detected.
Mathematically the operation condition can be expressed as:
(
U – R + R + R
c ext int
where:
• U = operating voltage over the supervised trip circuit
c
• I = measuring current through the trip circuit, appr. 1.5 mA (0.99...1.72 mA)
c
• R = external shunt resistance
ext
• R
= internal shunt resistance, 1k
int
• R = trip coil resistance
s
The external shunt resistance is used if the trip-circuit supervision, independent of
the circuit-breaker position, is desired. If the trip-circuit supervision is required only
in closed position, the external shunt resistance may be omitted.
Operator's manual
Test mode
required
Yes
Yes
Yes
No
Yes
Yes
) × ≥ ⁄
I 20 V ac dc
s c
Ω
1MRS 751108-MUM
(see "Related documents" on
Remarks
Physical inputs disconnected
Normal operation still active