Differential Current Alarm - ABB Relion Technical Manual

1MRK 502 048-UUS A
6.1.3.3
Technical manual
where:
ID_A is the fundamental frequency differential current in phase A (in W1 side primary amperes)
ID_B is the fundamental frequency differential current in phase B (in W1 side primary amperes)
ID_C is the fundamental frequency differential current in phase C (in W1 side primary amperes)
I_A_W1 is the fundamental frequency phase current in phase A on the W1 side
I_B_W1 is the fundamental frequency phase current in phase B on the W1 side
I_C_W1 is the fundamental frequency phase current in phaseC on the W1 side
I_A_W2 is the fundamental frequency phase current in phase A on the W2 side
I_B_W2 is the fundamental frequency phase current in phase B on the W2 side
I_C_W2 is the fundamental frequency phase current in phaseC on the W2 side
Vn_W1 is transformer rated phase-to-phase voltage on the W1 side (setting parameter)
Vn_W2 is transformer rated phase-to-phase voltage on the W2 side (setting parameter)
As marked in equation 1
equation, represents the total contribution from the individual phase currents from the W1
side to the fundamental frequency differential currents, compensated for eventual power
transformer phase shift. The second term on the right hand side of the equation, represents
the total contribution from the individual phase currents from the W2 side to the
fundamental frequency differential currents, compensated for eventual power transformer
phase shift and transferred to the power transformer reference side. The third term on the
right hand side of the equation, represents the total contribution from the individual phase
currents from the W3 side to the fundamental frequency differential currents,
compensated for eventual power transformer phase shift and transferred to the power
transformer reference side. .
The fundamental frequency differential currents are the magnitudes which are applied in
a phase segregated manner to the operate - restrain characteristic of the differential
protection. The magnitudes of the differential currents can be read as service values from
the function and they are available as outputs IDMAG_A, IDMAG_B, IDMAG_C from
the differential protection function block. Thus they can be connected to the disturbance
recorder and automatically recorded during any external or internal fault condition.

Differential current alarm

The fundamental frequency differential current level is monitored at all times within the
differential function. As soon as all three fundamental frequency differential currents are
set above the set alarm level (IDiffAlarm), the pickup timer is started. When the pre-set
time, defined by setting parameter tAlarmDelay, has expired a differential current alarm
is generated and the output signal IDALARM is set to logical value one.
and equation 2, the first term on the right hand side of the
Section 6
Differential protection
97