2. APPLICATION
GEK-106243E
DTP Digital Transformer Protection
2-9
2.3.2 2
ND
ITERATION. NEW CT RATIOS FOR WINDINGS B AND C
2.3.2.1 Matching Error
Transformer winding
A
B
C
1.
100%
Ip
17.5
35
70
2.
New
CT
ratio 20
40
60
3.
100%
Isec
0.87
0.87
1.17
4. Relay currents for 100% Isec
0.87
0.87
1.17
5. Ideal relay taps: (select C=4.0)
2.97
2.97
4.0
6.
Actual
taps:
3.0
3.0
4.0
7. Check that the mismatch errors are: 0% (AB), 1.01% (BC), and 1.01% (CA).
2.3.2.2 CT Ratio Error
A
B
C
1.
Impedance
(ohms)
0.75
0.75
0.77
2. Current at 8 times the tap value
24
24
32
3.
Required
Es
for
CT
18
18
24.64
4.
Required
Ie
1
0.2
0.1
5.
Ratio
error
in
%
4.16%
0.83%
0.31%
All errors are less than 20%, therefore the CT ratios are OK.
2.3.3 PERCENTAGE RESTRAINT
SETTING K
1
(FIGURE 9)
Maximum tap changer range . .................... 10.00%
Maximum mismatch error: ...................... 1.01%
TOTAL ........................................................ 11.01%
Set the percentage restraint K
1
so that:
11.01% < K
1
≤
25%
Summary of Contents for DTP-B
Page 23: ...3 OPERATING PRINCIPLES 3 6 DTP B Digital Transformer Protection GEK 106243E ...
Page 53: ...10 INSTALLATION AND MAINTENANCE 10 2 DTP B Digital Transformer Protection GEK 106243E ...
Page 68: ...12 FIGURES GEK 106243E DTP Digital Transformer Protection 12 3 Figure 3 RS 232 Connection ...
Page 69: ...12 FIGURES 12 4 DTP B Digital Transformer Protection GEK 106243E Figure 4 Dimensions Diagram ...
Page 70: ...12 FIGURES GEK 106243E DTP Digital Transformer Protection 12 5 Figure 5 Front View ...
