Homework #1
Connect the CTs to the differential relays to
properly account for the transformer phase
shift
a
A
C
b
c
B
A
a
B
b
C
c
R
OP
R
R
OP
R
R
OP
R
1
Homework #2
a
A
B
c
b
C
I230
230kV 75MVA
IH
TH
87
I46
46kV
IL
TL
Given the bank information above and the information below, choose CT ratios and
differential relay taps so that the relay slope is not exceeded by mismatch
230kV CT available ratios: 1200/5, 800/5, 600/5, 400/5, 300/5, 200/5, 100/5
26kV CT available ratios : 2000/5, 1200/5, 800/5, 600/5, 400/5, 300/5, 200/5, 100/5
Differential relay taps: 3.2, 3.5, 3.8, 4.2, 4.6, 5.0, 8.7
Differential relay slope: 25%
2