11
Voltage/time
characteristic
(Modified 99-10)
At inverse time characteristic the operate time
of the overvoltage stage will be shorter the
greater the deviation from the setting value.
The operation of the U> stage is based on inverse
time characteristic, when the selector switch
SG1/3 on the front panel is in position 1. The
relationship between time and voltage at inverse
time characteristic can be expressed as follows:
t = + c
(b x - 0.5)
where t = operate time [s]
k> = time multiplier
U = measured voltage [V]
U> = set start voltage [V]
a = constant 480
b = constant 32
c = constant 0.035
p = constant
At an IDMT mode of operation the recording of
the tripping time of the overvoltage stage does
not start until the voltage exceeds the setting
value by 6%. The operating time accuracy stated
in the technical data applies when the voltage
exceeds the setting value by 10%. The overvoltage
stage includes two characteristics with different
inversities. The characteristic is selected with
the programming switch SG1/4. The degree of
inversity is determined by the factor p as follows:
Characteristic p (constant)
A2
B3
k> x a
1000
100
10
1
0,1
0,01
1,1 1,2 1,3 1,4 1,5
U/U>
0,05
0,2
0,4
0,7
1,0
k>
t/s
1,0
Fig. 5. Characteristic curve set A of overvoltage stage U>.
U - U>
U>
p
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