Chapter 3
Behaviour of the Isolation Unit
Version: A.02
Product Description ENS26
Page 9 of 20
Issue: 20.09.2005
3.3
Deviation of the mains power frequency
The testing of the frequency is performed directly at the mains voltage.
The threshold values for the mains frequency are set as follows:
Fluctuation
Threshold value
Test interval
Overfrequency
50.2 Hz
Every 200 ms
Underfrequency
47.5 Hz
Every 200 ms
Channel 1 also measures the phase position between the outer conductors.
In the event of a
phase difference in excess of 30 degrees
, the feeding
point is disconnected from the power supply.
If the rate of change of the frequency (RoCoF) exceeds
1 Hz/s
, discon-
nection from the supply is also triggered.
3.4 Impedance
jumps
The mains impedance is monitored. The time-dependent change of volt-
age near the crossover (phase shift), caused by test signals, with various
voltage values forms the basis for calculating the mains impedance.
All the impedances measured in one second are used to establish an aver-
age value. The number of measuring pulses is dependent on the number of
ENS connected in the network.
Depending on the power characteristics, the triggering threshold for an
impedance jump is adapted between 1 ohm and 0.2 ohm.
Note
A threshold of 0.5 ohm is set ex works.
The automatic adaptation of the switching threshold is described in Sec-
tion 3.8.
