Ibias /Inom
I
diff/Inom
Is1
Is-HS1
I
s-HS2
Is2
K
1
K2
Restraint region
O
perate region
V03110
TC and CT errors
Figure 51: Triple slope characteristic
5.2 EXAMPLE 1: TWO-WINDING TRANSFORMER - NO TAP CHANGER
Consider a two-winding power transformer with the following specifications:
● P
ower rating: 90 MVA Transformer
● Connection type: YNd9
● Voltage specification 132:33 kV.
● HV CT ratio: 400:1
● LV CT ratio: 2000:1
● Percentage reactance: 10%
B
90 MVA
132 kV/33 kV
YNd9
400:1
Phase & amplitude
Correction
+
Zero sequence filtering
BB
D
BB
D
BB
D
Phase & amplitude
Correction
+
Zero sequence filtering
A
C
Protected zone
a
b
c
2000:1
P642
V03115
Earthing
transformer
Figure 52: P642 used to protect a two winding transformer
Chapter 6 - Transformer Differential Protection P64x
122 P64x-TM-EN-1.3
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