Standard for High-Accuracy Instrument Transformers
|Publication Date:||22 September 2005|
This standard defines one new 0.15 accuracy class for voltage transformers, two new 0.15 accuracy classes for current transformers, two new current transformer burdens, and two new current transformer routine accuracy test methods. These supplement IEEE Std C57.13™1. The new burdens shall be considered for use when current transformers are to be used with electronic meters, and the total in-circuit burden will be less than B-0.1 (2.5 VA at 5 A, 0.9 power factor) defined in IEEE Std C57.13. The new accuracy classes, 0.15 and 0.15S, are available to complement the capabilities of solid state electricity metering of equipment associated with the generation, transmission, and distribution of alternating current.
There are two important differences about these new accuracy class definitions as they apply to routine current transformer test requirements:
a) A low current test is required at 5% of rated current (0.25 A secondary), in lieu of the 10% of rated current test specified in IEEE Std C57.13. This test point corresponds with the light load test point of transformer rated electromechanical and solid state electricity meters as specified in ANSI C12.20.
b) Routine testing for current transformers certified to meet 0.15 or 0.15S accuracy must include accuracy reading(s) using new burden definition E-0.04. The intent of burden E-0.04 (1.0 VA at 5 A, unity power factor) is to approximate the lowest secondary circuit burden that can occur in practical applications. Testing a current transformer at this burden is analogous to the routine no-load voltage transformer test required by IEEE Std C57.13.
1 Information on references can be found in Clause 2.