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889 GENERATOR PROTECTION SYSTEM – INSTRUCTION MANUAL
PROTECTION
CHAPTER 4: SETPOINTS
Recommendations for configuring the Differential/Restraint characteristic
The following setpoints define the differential/restraint characteristic:
Minimum Pickup:
This setpoint is expressed in xCT of Winding 1. The minimum pickup
defines the minimum differential current required for operation. The pickup setting must
be higher than the amount of differential current that is seen under normal transformer
loading conditions, and must be higher than the maximum differential current that is seen
during transformer tap changer operation.
For example, for a 20MVA, 25MVA, or 28MVA power transformer with a 138kV/4.16kV ratio,
and class C current transformers CT(w1) 200:5, and CT(w2) 3000:5, the CT errors and the
minimum pickup setting is calculated as follows:
Winding 1 (138kV) CT – reference. Magnitude factor: M(w1) = 1
Winding 2(4.16kV) CT – non reference. Magnitude factor: M(w2) = 4.16 *3000/138*200 =
0.4521
Based on emergency MVA rating:
Winding 1 rated current = 28MVA/(138kV*sqrt(3)) = 117 Amps
Winding 2 rated current =28MVA/(4.16*sqrt(3)) = 3890 Amps
The accuracy of the Class C current transformer is defined in the IEEE standard C37.110 as
not exceeding 10% for symmetrical current magnitudes of up to 20 times the rating for a
standard burden resistance:
117Amps *10% = 11.7 Amps = > 11.7/200 = 0.0585 xCT(w1)
Содержание Multilin 889
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Страница 126: ...3 48 889 GENERATOR PROTECTION SYSTEM INSTRUCTION MANUAL SOFTWARE INTERFACE CHAPTER 3 INTERFACES ...
Страница 530: ...4 400 889 GENERATOR PROTECTION SYSTEM INSTRUCTION MANUAL TESTING CHAPTER 4 SETPOINTS ...
Страница 575: ...CHAPTER 8 MAINTENANCE ENVIRONMENTAL HEALTH REPORT 889 GENERATOR PROTECTION SYSTEM INSTRUCTION MANUAL 8 3 ...
Страница 580: ...A 4 889 GENERATOR PROTECTION SYSTEM INSTRUCTION MANUAL REVISION HISTORY CHAPTER A APPENDIX A ...