3.4 Voltage-dependent over-current
The voltage-dependent over-current is a protection for generators without permanent magnets. This protection 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:
40 50 60 70 80 90 100 110
Voltage [%]
Current [%]
140
130
120
110
100
90
80
70
60
50
40
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.
DESIGNER'S HANDBOOK 4189341275A EN Page 70 of 196
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