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Proof of low-leakage reactance type

Views : 840
Update time : 2024-09-25 10:03:38
It shall be demonstrated that: 

– the current transformer has a substantially continuous ring core, with air gaps uniformly distributed, if any; 

– the current transformer has uniformly distributed secondary winding; 

– the current transformer has a primary conductor symmetrical with respect to rotation;  

– the influences of conductors of the adjacent phase outside of the current transformer housing and of the neighbouring phases are negligible. 

If compliance with the requirements of low-leakage reactance design cannot be established to the mutual satisfaction of manufacturer and purchaser by reference to drawings, then the results of a direct test and of an indirect test shall be compared as follows: 

For class TPX, TPY and TPZ current transformers, the factor of construction  Fc shall be determined according to 2B.3.3. If  Fc is less than 1,1, the current transformer shall be regarded as low-leakage reactance current transformer. 

For all other protection classes, the composite errors of the full winding obtained with a direct test method and with the indirect test method shall be compared. 

For the direct test, either of the methods given in 2A.5 and 2A.6 may be applied. The primary test current shall be: 

ALF x Ipr  for class P and class PR;  

Kx  x Ipr   for class PX and class PXR.  

For the indirect test, the method given in 7.2.6.203 b) shall be applied. The voltage applied to the secondary terminals shall be equal to:  

EALF  for class P and class PR;  

Ek  for class PX and class PXR.  

Proof of low-leakage reactance design shall be considered to have been established if the value of composite error from the direct method is less than 1,1 times that deduced from the indirect method. 

NOTE  According to its definition (3.4.235), the term “low-leakage reactance current transformer” is not universal, but related to its protection performance, e.g. protection class.  
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