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D-500 MK2 User Manual
32. PROTECTION FUNCTIONS PARALLELING WITH MAINS
The D-500 includes a comprehensive set of protection functions to detect quickly a mains failure during
parallel with mains operation.
The protections are enabled after the timeout defined by the parameter Parallel Check Delay in order not
to detect a mains failure during transients caused by the closing of the contactors.
Do not forget that the protections are disabled during Parallel
Check Delay. Set this timeout as short as possible.
If any of the protection functions detects a mains failure during parallel with mains:
-the mains contactor is immediately de-energized,
-a Parallel Mains Fail warning is generated,
-a specific warning to the related protection function is generated.
Immediate disconnection of the generator from the mains in
case of a mains failure, is required in most countries for
paralleling of synchronous generators to the mains.
32.1. ROCOF FUNCTION (rate of change of frequency)
The ROCOF measures the frequency of the mains for each period. If the frequency change exceeds the
predefined limit for 4 successive periods, then the ROCOF function detects a mains failure. Thus the
response time of the ROCOF is approximately 4 cycles.
However the ROCOF will not detect relatively slow changes in mains frequency.
Related parameter: ROCOF df/dt
If the parameter is set to zero, then the protection function will be disabled.
32.2. VECTOR SHIFT FUNCTION
The Vector Shift measures and stores the period of last 5 cycles. At the end of each cycle it compares the
average period of last 2 cycles with the average period of 4
predefined limit, then the vector shift detects a mains failure. Thus the response time of the vector shift is
5 cycles.
However the vector shift will not detect relatively slow changes in mains frequency.
Related parameter: Vector Shift Limit
If the parameter is set to zero, then the protection function will be disabled.
th
th
and 5
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Firmware V-6.3
cycles. If the difference exceeds the
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