7.2 Voltage-dependent over-current
The voltage-dependent over-current is a protection for generators without permanent magnets. This protec-
tion occurs when a short circuit is present and the voltage drops. When a short circuit occurs, the voltage will
make a drop and the current will rise for a very short period and then drop to a lower level afterwards. The
short circuit current level can drop below the rated current of the generator, and thus the short circuit will not
be tripped, which may result in personal injury or damaged equipment. When the short circuit is present, the
voltage will be low. This can be used for tripping at a lower current, when the voltage is low.
The parameters for this are 1101 to 1115. The set points for the different levels are set in parameters 1101 to
1106. The set point refers to six different current levels and voltage levels. All values are in percentage to the
rated values that are set in parameters 6000 to 6030. The six voltage levels are already determined, so only
the current levels must be set. The six set points will create a curve, which will be explained by an example:
The six different set points have been set to the values shown in the table below.
Parameter 1101 1102 1103 1104 1105 1106
Voltage level
(Fixed/not adjustable)
50 60 70 80 90 100
Current level
(Set point/adjustable)
50 55 65 80 100 130
The six values can then be transferred to a curve, which is more readable:
When the actual values represent a point above the curve, the breaker should be tripped. The curve shows
that the generator breaker will trip when two requirements are met: The generator voltage is below 50 % of
rated, and the current is above 50 % of rated.
Timer, outputs, enable and fail class are set in parameters 1111 to 1115. The timer in 1111 decides how long
the fault will exceed the limits, before an action will take place. The action/fail class is decided in parameter
1115 and can be set from a warning to a shutdown. As a default, this will be set to trip the generator breaker.
The outputs can be used to activate a relay. This will make it possible to send a signal to external equipment
regarding this specific alarm. It is possible to configure two relay outputs for the alarm. The protection function
is activated as a default, but can be disabled in parameter 1114.
AGC 100 Designer's Reference Handbook
4189340766 UK
Protections
DEIF A/S Page 108 of 152
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