GE T60

8-10 T60 Transformer Protection System GE Multilin
8.2 DIFFERENTIAL CHARACTERISTIC TEST EXAMPLES 8 COMMISSIONING
8
8.2.4 TEST EXAMPLE 3
Yg/D30° TRANSFORMER WITH PHASE B TO C FAULT ON THE DELTA SIDE.
Transformer: Y/D30°, 20 MVA, 115/12.47 kv, CT1 (200:1), CT2 (1000:1)
Figure 8–4: CURRENT DISTRIBUTION ON A YG/D30° TRANSFORMER WITH AN a TO b FAULT ON THE LV SIDE
Three adjustable currents are required in this case. The Phase A and C Wye-side line currents, identical in magnitude but
displaced by 180°, can be simulated with one current source passed through these relay terminals in series. The second
current source simulates the Phase B primary current. The third source simulates the delta “b” and “c” phase currents, also
equal in magnitude but displaced by 180°.
TEST PHASE INJECTED CURRENT DISPLAYED CURRENT STATUS
W1 CURRENT W2 CURRENT DIFFERENTIAL RESTRAINT
Balanced
Condition
A 0.25 0° 0 0° 0 0° 0 0° Not Applicable
B0.5 –180° 0.8 0° 0 0° 0.8 0°
C 0.25 0° 0.8 –180° 0 0° 0.8 –180°
Min Pickup
change the
Min PKP to
0.2 pu
A 0.25 0° 0 0° 0 0° 0 0° Block
I
d
= 0.051 < Min PKP
B0.5 –180° 0.95 0° 0.154 0° 0.948 0°
C 0.25 0° 0.95 –180° 0.155 0° 0.950 –180°
Minimum
Pickup
A 0.25 0° 0 0° 0 0° 0 0° Operate
I
d
= 0.102 > Min PKP
B0.5 –180° 1.05 0° 0.253 0° 1.049 0°
C 0.25 0° 1.05 –180° 0.255 0° 1.050 –180°
Slope 1
return the
Min PKP to
0.1 pu
A 0.25 0° 0 0° 0 0° 0 0° Block
I
d
/I
r
= 13.2%
B0.5 –180° 0.92 0° 0.123 0° 0.919 0°
C 0.25 0° 0.92 –180° 0.123 0° 0.919 –180°
Slope 1 A 0.25 0° 0 0° 0 0° 0 0° Operate
I
d
/I
r
= 15.9%
B0.5 –180° 0.95 0° 0.153 0° 0.948 0°
C 0.25 0° 0.95 –180° 0.153 0° 0.948 –180°
Intermediate
Slope 1 & 2
A2 0° 0 0° 0 0° 0 0° Block
I
d
/I
r
= 84.3%
< 86.6%
computed
B4 –180° 1 0° 5.37 –180° 6.37 0°
C2 0° 1 –180° 5.37 0° 6.37 –180°
Intermediate
Slope 1 & 2
A2 0° 0 0° 0 0° 0 0° Operate
I
d
/I
r
= 87.5%
> 86.6%
computed
B4 –180° 0.8 0° 5.57 –180° 6.37 0°
C2 0° 0.8 –180° 5.57 0° 6.37 –180°
Slope 2 A 4 0° 0 0° 0 0° 0 0° Block
I
d
/I
r
= 93.7%
< Slope 2 = 95%
B8 –180° 0.8 0° 11.93 –180° 12.73 0°
C4 0° 0.8 –180° 11.93 0° 12.73 –180°
828738A1.CDR
Y/d30° Transformer
F
I (f) = 0.5 pu –270°
A
∠
I (f) = 0.866 pu –90°
b
∠
I(f)=0
a
I (f) = 0.866 pu –270°
c
∠
I (f) = 1 pu –90°
B
∠
I (f) = 0.5 pu –270°
C
∠
A
B
C
A
B
C