Instruction manual
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AQ G3x7 Generator protection IED
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voltage during operation then the voltage can be applied to distinguish between faulty state
and normal operating state. This is the application area of the voltage dependent overcurrent
protection function.
The function has two modes of operation, depending on the parameter setting:
•
Voltage restrained
•
Voltage controlled
The overcurrent protection function realizes definite time characteristic based on three phase
currents. The operation is restrained or controlled by three phase voltages. The function
operates in three phases individually, but the generated general start signal and the general
trip command is the OR relationship of the three decisions.
The function can be blocked by a user-defined signal or by the voltage transformer supervision
function block, if the measured voltage is not available.
This function can be applied as main protection for medium-voltage applications or generator
overcurrent protection.
The function is basically a definite time overcurrent protection function, but the current
threshold is influenced by the measured voltage. The function has two modes of operation,
depending on the parameter setting:
•
Voltage restrained (parameters “Restr. Mode” is set to “Restrained”)
•
Voltage controlled (parameter “Restr. Mode” is set to “Controlled”).
Voltage restraint characteristics
In this case the algorithm dynamically changes the threshold value of the current, based on
the measured phase voltages:
•
Above the “U_Highlimit” value then the function operates if the current is above the
“StartCurrent” value.
•
If the voltage is below the “U_lowlimit” value then the character
istic is lowered automatically
to the “StartCurrent*Ik_limit/100.
•
Between the two setting values the threshold value is increasing along a straight line.