Rate Of Change Of Frequency (Rocof) - ComAp MainsPro G99TT Global Manual

As shown in the timing diagram the voltage jumps to another value and the phase position changes. This
procedure is called phase or vector surge. MainsPro G99TT continuously measures the cycles, starting each
zero up ward slope. The time cycle is internally compared to the reference time. In case of vector surge the
zero up ward is delayed and the device trips instantaneously. The trip angle Δ
sensitivity of the vector surge detection is adjustable by the setpoint
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,
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 stage provided in MainsPro G99TT. It is based on a 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 gen-set speed regulation
capability. 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 unstable. MainsPro G99TT 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
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.
MainsPro G99TT 1.0.0 Global Guide
Image 8.7 At mains failure
Fault reset (page 32)
60). As the ROCOF stage provides very sensitive protection, software filter
and consequently the
VS lim, A.VS lim [°] (page
is performed or Vector shift limit is being set.
60).
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