53
Figure 56 Change set limit for switching cycle counter
8.5.3.2.1 Overcurrent
Overcurrent is the theoretically determined ratio of the root-mean-square current to the funda-
mental current in the capacitor (I
rms
/I
50Hz/60Hz
). It therefore indicates how large the proportion of
harmonic currents is in comparison with the fundamental current.
The choke factor (detuning) p of the power factor correction system is also taken into account in
this theoretical computation.
The overcurrent in the capacitor can only be computed accurately if the system's choke
·
factor (detuning) is entered correctly. If the system is not detuned, the value p = 0% should be
entered.
8.5.3.2.2 Detection of voltage blackout (sag)
The detection of voltage sag is a function designed to protect the capacitors and their contactors
against power cuts that are short enough to make the capacitor contactors open and immedia-
tely close again.
This function has the following setting options:
Detecting phase:
The phase to which the operating coil of the capacitor contactor is
·
connected
Number of ¼ cycles:
Time before an undervoltage alarm is given
·
Adjustable from a ½ wave to a full wave of the sinusoidal voltage
signal in increments of ¼ waves
Example:
In a 50 Hz supply, ½ wave = 10 ms, ¾ wave = 15 ms, full wave (
4
/
4
) = 20 ms
Voltage sag in % (100% being the nominal supply voltage):
This is the root-mean-square voltage setting at which the voltage blackout (sag) detection
function is to react.
Presettings: Half-wave detection, alarm given if voltage at L1 drops below 85% of the nominal
voltage.
Settings:
Voltage blackout (sag):
85%
Number of ¼ cycles:
2 (½ wave)
Detecting phase:
L1
For this very important function to operate effectively, it is vitally important that the phase selected
for the instrument power supply to the switching outputs is the same one selected for the voltage
measurement.
