ABB REU 610 Technical Reference Manual page 32

REU 610
32
Voltage Relay
Technical Reference Manual
Characteristic of the undervoltage stages
The IDMT characteristic curve group C is designed for undervoltage stages U< and
U<</U <. Stages U< and U<</U
1
characteristics. The relationship between time and voltage at IDMT characteristic
can be expressed as follows:
×
k 480
t[s]=
−
U< U

×
32

U<

t = operate time
k = time multiplier k< or k<<
U = measured voltage
U< = set start value U< or U<</U
p = constant (see Table 5.1.4.6.-2)
The C-type characteristic is illustrated in Fig. 5.1.4.6.-3.
If the ratio between the voltage and the set value is lower than 0.3, the
operate time is the same as when the ratio is 0.3.
Table 5.1.4.6.-2 Values of constant p
Time/voltage
characteristic
p
< can be configured to use different
1
p

−
0.5


<
1
A
2
1MRS755769
(4)
B C
3 2