Figure
shows the sequence of events after an internal fault. In this example, the fault
occurred at t = 400 ms in the middle of the power line. The operate time in the example below
is obtained from the software algorithm only without considering the delays due to the
hardware and communication.
INSTANTANEOUS DIFFERENTIAL CURRENT IN PHASE L1 (AMPERES)
DIFFERENTIAL CURRENT AND VALUE REQUIRED FO R START (AMPERES)
BI AS CURRENT IN PHASE L1 (AMPERES)
ANGLE BETWEEN INCREMENTAL CURRENTS IN PHASE L1 (RADIANS) AND INTERNAL FAULT SIGNAL
Time 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 dif ferential current
Value required for trip
Internal fault declared in 5 ms
Angle under internal fault = approx. 0°
Angle between incremental current s = 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 the start signal
has been confirmed 3 times in succession as a special security measure. The trip command will
Section 4
1MRK 505 382-UEN E
Analog and binary signal transfer for line differential protection
42
Communication set-up, 670/650 series
Application Guide
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Summary of Contents for Relion 670 series
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