Ia Repeat-Ct Turns And Relay Tap Setting; Iia Repeat Percent Ratio Error; Ratings; Iii Percent Slope Setting - GE STD15C Instructions Manual

2.
3. a
ES CT
required,
Ratio Error
Exciting current on line
IA REPEAT CT TURNS AND RELAY TAP SETTING
1.
Try CT turns (necessary to change C
also for proper matching)
3. I s e c o n d a r y
Relay Current.
Ideal Relay
6. Use Taps
Mismatch error is less than
7.
Total Burden for 60 Cycle Relays

IIA REPEAT PERCENT RATIO ERROR

1. Burden on CT's
Line A. Z 0.192
Line 0.156 +
Line Cm Z 0.096 + 0.226
2. Impedance.
8 Times Tap, Amperes
3.
CT voltage required
5. required, from excitation curve
of Ratio Error
6.
Percent Error is less than 20%. so CT taps and Relay taps are satisfactory.

III PERCENT SLOPE SETTING

1. Assume load ratio. control maximum range
2. Relay Tap mismatch,
- - -
Continuous rating
twice value for any
carry zero current
the current transformer.
Courtesy of NationalSwitchgear.com
required
excitation curve
high; should try higher tap on CT to improve CT
is
(SET C 8.7)
0.205 0.965
0.568 0 . 9 1 2
0.890
IA above (Lines
Use 25% tdp.
The through current transformer
of taps or they will stand twice tdp value if all but one of
the full restraint current. equal to twice tap
1.085
36.8
27.8
29.b
1.00
50
3.4% 136%
15.7 39.6
40
0.99
0.79
0.99
1.37
4.40
4.6
TABLE I
36.8 25.6
35.6 23.4
1.1 0.25
3.1% 1 .
R A T I N G S
differential
0.8
0.833
69.6
58.0
125
80
1.56
2.70
69.6
61.9
0.17
0.3%
1 0 . 0 :
4 . 6 :
14.6%
transformer Will stand