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2.10.7 Frequency Element FRQ
GRT100 has two elements for trip or alarm. Each element operates either in overfrequency or
underfrequency.
2.10.8 Overexcitation Element V/F
The characteristic is based on the ratio of voltage to frequency. The alarm is definite time
delayed, while the tripping characteristic is either definite time or inverse time, as shown in
Figure 2.10.7.
sec
V/Hz
0
L
H
HT
TVFH
LT
(log T)
A
TVFA
H: High level (definite time tripping)
L: Low level
(
pick up level
)
HT: Operating time at high level
LT: Operating time at low level
A
: Alarm level
TVFH: Operating time at high level setting
TVFA: Alarm time
Figure 2.10.7 Characteristic of Overexcitation Element
The inverse time characteristic of V/F is expressed by the following equation.
t =
K
2
(V/F) − K
1
where,
t : operating time
V : voltage (any phase-to-phase voltage)
F : frequency
V/F=(Vm/Fm) / (Vs/Fs)
(Vm: Input voltage, Fm: Input frequency, Vs: Setting of rated voltage, Fs: Rated frequency)
K
1
=
(LT) × L − (HT) × H
(LT) − (HT)
K
2
=
(LT) × (HT) × (H − L)
(LT) − (HT)
The V/F element has a reset feature with definite time reset (RT). When the V/F falls below the
reset threshold, the integral state of the inverse time function is reset to the initial value after the
RT time.
Example: V/F=(Vin/Fin)/(V/Fs)=(130/50)/(100/50)=1.3, in case of Vin: Input voltage (130V),
Fin: Input frequency (50Hz), V: Rated voltage (100V), Fs: Rated frequency (50Hz)