The differential current protection detects current faults in the protected
zone between the current transformers. The differential current
protection consists of two parts, the stabilised differential current
protection and the high set differential current protection.
The alarm response of the stabilised differential current protection is
dependent on the operating characteristic and the measured restraint
and differential currents (evaluation is made per phase). The operating
characteristic separates the operation area (grey) and the restraint area
(white) in the figure. The restraint current is the highest value of neutral
and consumer side RMS currents. The differential current is the RMS
value of the fundamental frequency part of the sum (or difference) of the
neutral side and consumer side currents.
The alarm response of the high set differential current protection only
depends on the differential current. That is, the RMS value of the
fundamental frequency part of the sum (or difference) of the neutral side
and consumer side currents.
Differential
current
[%]
Restraint current [%]0
Region 2 Region 3Region 1
diff min
I
More information
See AC configuration and nominal settings > AC configuration > [Source] AC configuration for more information
about changing the reference direction of the current transformer.
Configure the parameters for the Stabilised differential current protection under Configure > Parameters > Generator > Current
protections > Stabilised differential current.
Table 3.52
Stabilised differential current default parameters
Parameter Range Default
I diff. min. 5 to 100 % of I
nom
15 %
Region 1: End 10 to 150 % of I
nom
75 %
Region 2: Slope 10 to 50 % of I
nom
20 %
Region 2: End 100 to 1000 % of I
nom
200 %
Region 3: Slope 30 to 100 % of I
nom
75 %
Delay 0 to 60 s 0.00 s
Enable Not enabled, Enabled Enabled
Latch Not enabled, Enabled Enabled
Alarm action Trip generator breaker + AVR + stop engine*
Configure the parameters for the High set differential current protection under Configure > Parameters > Generator > Current
protections > High set differential current.
Table 3.53
High set differential current default parameters
Parameter Range Default
Set point 50 to 1200 % of I
nom
800 %
Delay 0 to 60 s 0.00 s
Enable Not enabled, Enabled Enabled
Latch Not enabled, Enabled Enabled
Alarm action Trip generator breaker + AVR + stop engine*
DESIGNER'S HANDBOOK 4189340911K UK Page 78 of 521
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