Alarm Level Operation - ABB RELION 670 SERIES Applications Manual

1MRK 506 369-UUS -
7.1.4.5
Line distance protection REL670 2.2 ANSI
Application manual
Where 200mA is the current drawn by the IED circuit and 50mA is the current drawn by
each CT just at pickup. The magnetizing current is taken from the magnetizing curve of
the current transformer cores, which should be available. The current value at TripPickup
is taken.

Alarm level operation

The 1Ph High impedance differential protection HZPDIF (87) 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 TripPickup.
As seen in the setting examples above the sensitivity of HZPDIF (87) 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 (87) function, or be a check about the fault condition, which is performed by a
ground 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.
Section 7
Differential protection
151