ABB Relion 670 Series Applications Manual page 134

Section 7
Differential protection
100
=
IP
5
EQUATION1769-ANSI V1 EN-US
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
7.1.4.5 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
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.
IEC05000749 V1 EN-US
Figure 55: Current voltage characteristics for the non-linear resistors, in the range 10-200 V, the average
range of current is: 0.01–10 mA
128
× + × £
(200 2 30) approx
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.5.2 A
1MRK 511 401-UUS F
(Equation 23)
TripPickup is taken.
TripPickup .
Bay control REC670
Application manual
M16850-196 v6