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6F2S0757
2.2 Phase Undervoltage Protection
GRD130 provides three independent phase undervoltage elements. UV1 and UV2 programmable
for inverse time (IDMT) or definite time (DT) operation. UV3 has definite time characteristic
only.
2.2.1 Inverse Time Undervoltage Protection
The inverse time undervoltage protection element UV1 and UV2 have the IDMT characteristic
defined by equation (2):
()
+
−
×= c
Vs
V
k
TMSt a
1
(2)
where:
t = operating time for constant voltage V (seconds),
V = energising voltage (V),
Vs = undervoltage setting (V),
TMS = time multiplier setting,
k, α, c = constants defining curve.
The standard IDMT characteristic of GRD130 is illustrated in Figure 2.2.1.
In addition to the standard IDMT curve, the UV1 and UV2 can provide user configurable IDMT
curve. If required, set the scheme switch [UV∗EN] to “C” and set the curve defining constants k,
α, and c. The following table shows the setting ranges of the curve defining constants.
Table 2.2.1 Specification of IDMT Curves
Curve Description Curve Defining Constants
k
αc
Standard “IDMT” 1 1 0
User configurable curve 0.00 – 300.00 0.00 – 5.00 0.000 – 5.000
Definite time reset
The definite time resetting char-acteristic is applied to the UV1 and UV2 elements when the
inverse time delay is used.
If definite time resetting is selected, and the delay period is set to instantaneous, then no
intentional delay is added. As soon as the energising voltage rises above the reset threshold, the
element returns to its reset condition.
If the delay period is set to some value in seconds, then an intentional delay is added to the reset
period. If the energising voltage is below the undercurrent setting for a transient period without
causing tripping, then resetting is delayed for a user-definable period. When the energising
voltage rises above the reset threshold, the integral state (the point towards operation that it has
travelled) of the timing function (IDMT) is held for that period.
This does not apply following a trip operation, in which case resetting is always instantaneous.