DATAKOM DKG-705 User’s Manual
705_USER.doc
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10. PROTECTION FUNCTIONS FOR PARALLEL WITH MAINS
The dkg-705 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
P_A23 (
Parallel Check
Timeout) in order not to detect a mains failure during transients caused by the closing of the contactors.
WARNING:
Do not forget that the protections are disabled during Parallel
Check Timeout. 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 deenergized,
-a Parallel Mains Fail warning is generated,
-a specific warning to the related protection function is generated.
Separating the generator from the mains in case of a mains failure is requested as condition in
most countries for connection of synchronous generators to the mains.
10.1 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, the ROCOF 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:
P_A25 ROCOF df/dt Limit:
10.2 VECTOR SHIFT FUNCTION
The Vector Shift measures and stores the periods 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
th
and 5
th
cycles. If the difference
exceeds the predefined limit 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:
P_A26 Vector Shift Limit
10.3 OVER/UNDER FREQUENCY FUNCTION
The mains frequency measures the frequency of the mains for each period. If the frequency is
outside limits for 4 successive periods, it detects a mains failure. The response time of the mains
frequency is approximately 4 cycles.
Related parameters:
P_522 Mains Frequency Low Limit
P_523 Mains Frequency High Limit
