MainsPro, SW version 1.4, ©ComAp – January 2013
MainsPro Application Guide
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 LOM: ROCOF. 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.
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 Wiring 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, TRIP is issued and the
appropriate LED signalization is given. The reconnection of measurement terminals is necessary to
ensure further proper functionality of the unit.
Application tips
Automatic return to mains
Some utilities require that the protection unit provides an automatic return of the generating unit back
to parallel operation with mains. This automatic return usually does not happen immediately after the
mains parameters are within limits, but with pre-defined time delay. For such case, the unit allows
setting a time delay during which the Fault reset can be automatically performed after the set time
runs out.
Appropriate setting of automatic fault reset by setpoint Basic: Auto FR Del timer allows setting the
waiting time reserved for mains parameters to settle in their fault-free conditions after a TRIP. This
state is indicated by flashing red signal of the TRIP LED. If during this time any measured value
reaches out of the preset limits, MainsPro terminates the automatic fault reset count-down and goes
back into fault indication state. The automatic fault reset is reset and started again in the moment
when all measured values are back in limits again. After automatic fault reset is count down to zero,
the unit performs automatic fault reset and terminates the TRIP status.
Binary switches
MainsPro allows basic remote operation by means of binary signals wired from an external logic to
MainsPro binary switches. The signals may be also provided remotely, e.g. through radio or GSM
communicator devices. As an example for the many similar devices on the market, see the uGATE
communicator below. Ask for more information about this product at protections@comap.cz.
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