Alarm Level Operation - ABB REC670 Applications Manual

Section 7
Differential protection
7.1.4.5
IEC05000749 V1 EN-US
Figure 54: Current voltage characteristics for the non-linear resistors, in the range 10-200 V, the average
range of current is: 0.01–10 mA
140

Alarm level operation

The 1Ph High impedance differential protection HZPDIF function has a separate
alarm level, which can be used to give alarm for problems with an involved current
transformer circuit. The setting level is normally selected to be around 10% of the
operating voltage U>Trip.
As seen in the setting examples above the sensitivity of HZPDIF function is
normally high, which means that the function will in many cases operate also for
short circuits or open current transformer secondary circuits. However the
stabilizing resistor can be selected to achieve sensitivity higher than normal load
current and/or separate criteria can be added to the operation, like a check zone.
This can be either another IED, with the same HZPDIF function, or be a check
about the fault condition, which is performed by an earth overcurrent function or
neutral point voltage function.
For such cases where operation is not expected during normal service the alarm
output should be used to activate an external shorting of the differential circuit
avoiding continuous high voltage in the circuit. A time delay of a few seconds is
used before the shorting and alarm are activated. Auxiliary relays with contacts that
can withstand high voltage shall be used, like RXMVB types.
The metrosil operating characteristic is given in the following figure.
1MRK 511 401-UEN A
M16850-196 v6
Bay control REC670 2.2 IEC
Application manual