scheider electric MiCOM P746, Technical Manual

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Commissioning and Maintenance P746/EN CM/F21
MiCOM P746 (CM) 10-19
6.2.1.1.2 If 2 currents are available:
This method will be preferred whenever possible.
Note: The 2 CTs can have different ratios. This must be taken into account
when injecting at the CT secondary side.
A
A
P746
Busbar
protection
Test
Box
I1
I2
P3748ENb
FIGURE 4: CONNECTION FOR BIAS CHARACTERISTIC TESTING
CM
I = I + I
bias 2 1
= constant
i
bias
i (t)
diff
Slope
kCZ
P3759ENc
45°
Acz
0
I = =
diff
D
I
I - I
A1 A2
Bcz
Slope
k2
Injections
Bz
Az
I = =
diff
D
I
I - I
A1 A2
Note: The easiest way to test the thresholds is to inject an increasing slope
for I
1
and a decreasing slope for I
2
.The I
bias
= I
1
+ I
2
is thus constant
and
Δ
I = I
diff
= I
2
- I
1
is increasing.
IMPORTANT: FOR THE CHECK ZONE, THE I
BIAS
INCLUDES ALL THE SUBSTATION
FEEDER CURRENTS.
To test the thresholds:
I
bias
is fixed to a lowest value of ID>2/k2 and IDCZ>2/kCZ, the Az and Acz points will thus be
ID>2 and IDCZ>2. So I
bias
= I
1
+ I
2
= fixed value (Points A)
To test the Differential slopes and Blocking algorithm:
I
bias
is fixed to a value greater than ID>2/k2 and IDCZ>2/kCZ the Bz and Bcz points will thus
be I
bias
x k2 and I
bias
x kCZ. So I
bias
= I
1
+ I
2
= fixed value (Points B)
When we reach the point Xcz the P746 LED 8 will operate and when we reach the point Xz
the differential element will operate.