ABB Relion REG670, Руководство по применению

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Normally this scheme is set to achieve a sensitivity of around 20 percent of the used
CT primary rating so that a low ohmic value can be used for the series resistor.
It is strongly recommended to use the highest tap of the CT whenever
high impedance protection is used. This helps in utilizing maximum
CT capability, minimize the secondary fault current, thereby reducing
the stability voltage limit. Another factor is that during internal faults,
the voltage developed across the selected tap is limited by the non-
linear resistor but in the unused taps, owing to auto-transformer
action, voltages induced may be much higher than design limits.
Setting example
Basic data:
Current transformer ratio: 2000/1 A
CT Class: 20 VA 5P20
Secondary resistance: 6.2 ohms
Cable loop resistance:
<100 m 2.5 mm
2
(one way) gives 2 ˣ 0.8 ohm at 75° C
Max fault current: Equal to switchgear rated fault current 40 kA
Calculation:
EQUATION1207 V2 EN
(Equation 23)
Select a setting of
U>Trip=200 V.
The current transformer saturation voltage must be at least twice the set operating voltage
U>Trip.
( )
5 20 6.2 20 524 E P V
> + × =
EQUATION1208 V1 EN
(Equation 24)
that is, bigger than 2 ˣ U>Trip
Check from the table of selected resistances the required series stabilizing resistor
value to use. As this application requires to be so sensitive select
SeriesResistor = 2000
ohm, which gives an IED operating current of 100 mA.
Calculate the primary sensitivity at operating voltage using the following equation.
1MRK 502 071-UEN -
Section 7
Differential protection
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062 161
Application manual