Toshiba GR-200 Series Instruction Manual page 230

Rapid change detector
2.19.3
The FRQ operation is stopped substantially by an under-voltage block feature, but the FRQ
operation cannot be stopped in the case of some 'Out of step' or 'Loss of synchronism'. When
'out of steps' are raised in the particular system, there are possibilities that excess FRQ
tripping is carried out after 'Out of step trip'. To avoid an extreme FRQ tripping during sudden
frequency change, the function has rapid change detector (RCD) to stop issuing a FRQ trip
signal.
Figure 2.19-5 illustrates that 'Over loading due for Power shedding' is not steeper than
the decline of 'Out of step' or 'Loss of synchronism' (see also Figure 2.19-6). Therefore, with the
RCD and PLC programing, the user can program such that the FRQ function only issues a trip
signal for 'Over loading or Power shedding'. For your information, the RDC function is designed
not to operate when the FRQ has experiencing changing phase angle rapidly.
Expecting time in
Power shedding
at 40%
Figure 2.19-5 Lapse time (Δt) and Power shedding (%) for Δf change
Lapse time (sec)
1.0
Margin (40~100%) for
expecting Power shedding
0.5
0.1
0 20 40 60
Expecting of Power shedding
- 211 -
Δf/Δt=0.5Hz/0.2sec
=2.5Hz/s
80 100
Amount of Power
shedding (%)
6F2T0200 (0.15)
GRE200 (1,2)