Example 1: Two-Winding Transformer - No Tap Changer; Figure 51: Triple Slope Characteristic; Figure 52: P642 Used To Protect A Two Winding Transformer - GE P642 Technical Manual

Chapter 6 - Transformer Differential Protection
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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:
Power 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%
●
A
B
C
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Figure 52: P642 used to protect a two winding transformer

122
Idiff/Inom
Is-HS2
Is-HS1
Operate region
Is1
90 MVA
132 kV/33 kV
YNd9
400:1
Protected zone
B
Phase & amplitude
Correction
+
Zero sequence filtering
D
Restraint region
K2
K1
TC and CT errors
Is2
Earthing
transformer
B
Phase & amplitude
Correction
B B
Zero sequence filtering
B B
D D
Ibias /Inom
2000:1
a
b
c
+
P642
P64x-TM-EN-1.3
P64x