what is the CT of protection and CT of metering ? what is
class 5P10 & 5P20 and class PS ?
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Answer Posted / pin baloo
Standard accuracy classes:
At rated frequency and with rated burden connected, the amplitude error and phase error and composite error of a CT shall not exceed the values given in the following:
Accuracy class//Amplitude error at rated primary current(%)//Phase displacement at rated primary current(°)//
Composite error eC at rated accuracy limit primary current(%):
5P // ±1% // ±1° // 5%
10P // ±%3 // - // 10%
Marking: The accuracy class of a CT is written after the rated power. E.g. 10 VA 5P10, 15 VA 10P10, 30 VA 5P20
Accuracy limit current IAL:
Current transformers for protection must retain a reasonable accuracy up to the largest relevant fault current. Rated accuracy limit current is the value of primary current up to which the CT will comply with the requirements for composite error eC.
Accuracy limit factor kALF:
The ratio of the accuracy limit current to the rated primary current.
kALF = IAL/IN. (eq. 2)
The standard accuracy limit factors are 5, 10, 15, 20 and 30.
Marking: Accuracy limit factor is written after the accuracy class. E.g. 10 VA 5P10, 15 VA 10P10, 30 VA 5P20.
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