Hitachi 670 Series Application Manual page 49

1MRK505382-UEN Rev. K
Setting
NoOfUsedCTs
TapTransformer
DiffMode
Figure 42
= 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.
ANGLE BETWEEN INCREMENTAL CURRENTS IN PHASE L1 (RADIANS) AND INTERNAL FAULT SIGNAL
IEC15000477 V2 EN-US
Figure 42:
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).
Communication set-up, 670/650 series
Application Guide
Value
2
0
Master
shows the sequence of events after an internal fault. In this example, the fault occurred at t
INSTANTANEOUS DIFFERENTIAL CURRENT IN PHASE L1 (AMPERES)
Pre-fault instantaneous current
is equal to the charging current
Internal fault
DIFFERENTIAL CURRENT AND VALUE REQUIRED FOR START (AMPERES)
Fundamental frequency differential current
BIAS CURRENT IN PHASE L1 (AMPERES)
Internal fault
Angle between incremental currents = 90°
TRIP COMMAND IN PHASE L1
Sequence of events after an internal fault at t = 400 ms
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Analog and binary signal transfer for line differential protection
Remark
Total number of CT groups in the protected zone.
Tap transformer not included in the protected zone (and its current
therefore not directly measured).
Differential function activated.
Value required for trip
Internal fault declared in 5 ms
Angle under internal fault = approx. 0°
Trip command in 6 ms
Time in seconds
IEC15000477-2-en.vsd
Section 4
43