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Topic Title: HV Voltage instrument transformer - 3P class burden issue
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Created On: 04 March 2014 09:05 PM
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 04 March 2014 09:05 PM
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Joined: 04 March 2014


I have voltage instrument transformer (VT) rated as followed: (110/sqrt(3))/(0.1/sqrt(3)) kV

secondary winding of my interest (4 secondary windings in total):

rated burden: 25 VA class 3P (protection type class).

VT is connected to distance protection relay (Alstom P433). Relay gives 0.5 VA burden per phase.

According to IEC 60044-2 and some other standards, the accuracy class shall be fullfilled from 25% to 100% of the rated burden.

It is seen that 25% of 25VA is 6.25 VA which is far above 0.5 VA.
Hence VT works under 25% of rated burden which results in increased measurement error.

Should the load resistors be used to obtain winding load between 25-100 % to get rated accuracy class?

Load resistors are commonly used for metering windings ( ie. 0.5 class) connected to energy meters for revenue metering.

However I've never seen (so far) resistors connected to protection class windings and I am not convinced if it is correct to let protection class winding be loaded belov minimum 25% of rated load.

Please give me any suggestions.


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