Alstom MiCOM P546 - 1.28.1 IDG curve

P54x/EN OP/La4 Operation
(OP) 5-84 MiCOM P543, P544, P545 & P546
OP
A feature also exists whereby the protection can be enabled upon failure of the differential
protection communication channel (not applicable to sensitive earth fault). Earth fault
Overcurrent IN> can be set to:
 Permanently disabled
 Permanently enabled
 Enabled only in case of VT fuse/MCB failure
 Enabled only in case of protection communication channel failure
 Enabled if VT fuse/MCB or protection communication channel fail
 Enabled if VT fuse/MCB and protection communication channel fail
In addition, each stage (not for SEF) may be disabled by a DDB (467,468,469 and 470)
Inhibit IN > x (x = 1, 2, 3 or 4).
The VTS element of the relay can be selected to either block the directional element or
simply remove the directional control.
The N> and ISEF> Function Links settings have the following effect:
VTS Block - When the relevant is set to 1, operation of the Voltage Transformer Supervision
(VTS) will block the stage if it directionalized. When set to 0 the stage will revert to non-
directional upon operation of the VTS.
The inverse time characteristics available for the earth fault protection are the same as those
for the phase overcurrent elements, but with the addition of an IDG curve characteristic.
Details of the IDG curve are provided below:
1.28.1 IDG curve
The IDG cu
rve is commonly used for time delayed earth fault protection in the Swedish
market. This curve is available in stages 1 and 2 of Earth Fault and Sensitive Earth Fault
protections.
The IDG curve is represented by the following equation:
t = 5.8 - 1.35 log
e







N > Setting
in seconds
Where:
 = Measured current
N>Setting = An adjustable setting which defines the start point of the characteristic
Although the start point of the characteristic is defined by the N> setting, the actual relay
current threshold is a different setting called “IDG s”. The IDG s setting is set as a multiple
of N>.
An additional setting IDG Time is also used to set the minimum operating time at high levels
of fault current.
Figure 56 – illustrates how the IDG ch
aracteristic is implemented.