Alarms
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5.6 ZERO SEQUENCE VOLTAGE
Zero Sequence Voltage alarm is sometimes known as Neutral Voltage Displacement alarm and
indicate a difference in potential between the Earth and the calculated Neutral position of a 3 wire
delta, which ordinarily should be zero.
Zero sequence voltages can occur for a number of reasons, including:
•
An earth fault in a High Voltage (H.V.) line. For example an overhead cable falling to the
ground, or a large tree falling against it.
•
An upstream fault causing a breaker to trip, leaving the H.V. line with no earth reference. This
causes the H.V. line to ‘float’ relative to earth.
5.7 POSITIVE SEQUENCE VOLTAGE
Positive Sequence Voltage is present in all utility mains and generator supplies.
The Positive Sequence Voltage Alarm activates if the Positive Sequence Voltage falls below the
configured trip level for the configured amount of time.
5.8 NEGATIVE SEQUENCE VOLTAGE
Negative Sequence Voltage occurs due to imbalance in the terminal voltages of the phases.
A small imbalance in phase voltages can lead to a larger imbalance in phase currents (negative
sequence currents) and cause problems with equipment in the load such as induction motors and
variable speed drives so must not be left unchecked.
5.9 ASYMMETRY
This alarm occurs If the voltage between any two phases exceeds the amount configured in the
Asymmetry Alarm.
For example :
L1=230, L2=235, L3=226
Asymmetry is largest value – smallest value = 235 – 226 = 9V
5.10 PHASE ROTATION
This alarm occurs If the phase rotation is detected as being incorrect. The DSEP100 expects the
rotation to be in the order L1, L2, L3 as connected to terminal blocks Ua, Ub, Uc.
