Mains pro 1.6.1 Global Guide
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Proper setting of Vector shift limit has to be examined at the field tests, especially at very low setting of the
protection limit (under 3°). Vector shift is very fast method and may be sensitive to disturbances, naturally
present in the electricity grid.
Note:
Due to high sensitivity, Vector shift protection is not evaluated in the transient states, e.g. when Alt
settings functionality is turned on or off,
is performed or Vector shift limit is being set.
Functionality is blocked in the sine wave period, when such an event occurs.
8.6 81R Rate Of Change Of Frequency (ROCOF)
ROCOF is another fast "Loss of Mains" protection stages provided in MainsPro. It is based on the similar
principle as Vector shift, i.e. dependence of the generator speed and voltage on the load size. The variations of
frequency delivered by the gen-set depend on the load fluctuations and speed of the compensated fuel inlet. In
case of operation in parallel with large network, these changes are absorbed in the network and frequency is
stable. When the connected area disconnects from the mains into island operation, the frequency becomes
instable. MainsPro ROCOF stage provides fast evaluation of the frequency instability and TRIPS immediately
in case of fast frequency changes. The threshold is set by the setpoint
ROCOF, A.ROCOF [Hz/s] (page 58)
As the ROCOF stage provides very sensitive protection, software filter may be set using the LOM: ROCOF filt
setpoint. By appropriate setting of those two setpoints, perfect ratio between sensitivity and speed of reaction of
ROCOF protection may be established at the field tests.
Note:
ROCOF is sensitive to voltage jumps, therefore it is recommended to be disabled during tests of
overvoltage and enabled after tests are finished.
8.7 Phase rotation, incorrect phase polarity
MainsPro provides check of the phase sequence and polarity. The correct connection is indicated in the wiring
instructions e.g. on MainsPro box or in chapter
, where clockwise rotation system is expected
on the mains side. It may happen, that e.g. by redesign in the mains or generator site installation, the phase
rotation changes. MainsPro ensures in such case, that this state is indicated and it prevents incorrect closing of
the circuit breaker by its standard protective functionality. To allow phase sequence or incorrect phase polarity
check, the phase angle between the 3 voltage vectors is expected in range 120° +/- 30°. If wrong phase
arrangement is detected,
is issued and the appropriate LED signalization is given. The
reconnection of measurement terminals is necessary to ensure further proper functionality of the unit.
