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1MRS 750942-MUM
Combined Overvoltage and Undervoltage Relay
Technical Reference Manual
REU 523
Characteristic of the undervoltage stages
The IDMT characteristic curve group C is designed for undervoltage stages U< and
U<<. Stages U< and U<< can be configured to use different characteristics. The
relationship between time and voltage at IDMT characteristic can be expressed as
follows:
where
t = operate time
k = time multiplier k< or k<<
U = measured voltage
U< = set start value for U< or U<<
a = constant 480
b = constant 32
c = constant 0.055
p = constant (see table 4.1.4.5-1)
The C-type characteristic is illustrated in Fig. 4.1.4.5.-3.
Table 4.1.4.5-1 Values of constant p
Time/voltage
characteristic
ABC
p
232
ts[]
ka×
b
U<U–
U<
------------------ 0.5–×
p
-------------------------------------------------- c+=
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