INSTANTANEOUS DIFFERENTIAL CURRENT IN PHASE L1 (AMPERES)
DIFFERENTIAL CURRENT AND VALUE REQUIRED FOR START (AMPERES)
BIAS CURRENT IN PHASE L1 (AMPERES)
ANGLE BETWEEN INCREMENTAL CURRENTS IN PHASE L1 (RADIANS) AND INTERNAL FAULT SIGNAL
Tim e in seconds
TRIP COMMAND IN PHASE L1
IEC15000477-2-en.vsd
Pre-fault instantaneous current
is equal to the charging current
Internal fault
Fundamental frequency differential current
Value required for trip
Internal fault declared in 5 ms
Angle under internal fault = approx. 0°
Angle between incremental currents = 90°
Trip command in 6 ms
Internal fault
IEC15000477 V2 EN-US
Figure 41: Sequence of events after an internal fault at t = 400 ms
Before the internal fault occurs, instantaneous differential current is composed only
of the power line capacitive charging current (approximately 92 A). This current is
not visible in the fundamental frequency differential current because it is removed
by the exact method of charging current compensation.
The fundamental frequency differential current becomes greater than the value
required to trip. This happens 4 ms after fault occurrence (a start signal is issued
but the respective Boolean output is not shown here). The value required to trip
(dependent variable) is a function of the chosen operate-restrain characteristic and
magnitude, and of the bias current (independent variable).
The relative angle between incremental currents at both ends of the protected line
falls from the initial 90 degrees to close to 0 degrees (1.145 degrees) 4 ms after the
fault occurrence. This angle is not available as an output signal.
Internal fault is declared in 5 ms, and the harmonic block that could delay the trip
is deactivated. L4CPDIF initiates an internal trip decision in 6 ms by which time
1MRK 505 382-UEN B Section 4
Analog and binary signal transfer for line differential protection
Communication set-up 670/650 series 2.2 51
Application Guide
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