Current Transformer - Imag Specifation

[YERUK123]

Why is that Magnetizing current ( Imag ) measured or Specified mostly at Vk /2 (Vk= Knee point Voltage ) in the Current Transformer discription ?

 

[YERUK123]

Guys Any response for the above question ?

 

[veritas]

Which Current Transformer description are you referring to? Some standard?

A bit more info is needed.

 

[scottf]

Normally if a Iexc (excitation current) limit is specified it is specified at Vkp (knee-point voltage).

I've seen Iexc limited at Vkp/2, but it's very rare. My assumption when that was specified was that someone was trying to spec a CT to match exactly to an existing unit and took it to another level above Iexc @ Vkp.

 

[YERUK123]

@ Vertias : Class of CT is PX or X , Standard is IEC
@ Scottf : Some manufcaturer specify it Imag ( magnetising Current ) at Vk (Knee Point Voltage ) and Few at Vk/2 . But These are for new substations and not matching any other existing CT

 

[veritas]

The IEC 60044.1 standard says Ie is the maximum exciting current at the rated knee point emf and/or at a stated % thereof.

I have never seen it yet specified at a fraction of Vk but the standard allows for it. The reason why Ie is specified in this way is to ensure matched characteristics at Vk for a group of CT's used for a differential application. Matched characteristics minimises the spill current due to CT mismatches. In other words, it is intended to ensure superior performance than say if a Class P CT was used for the same application.

Alternatively stated the B-H characteristic passes through the same point for the matched CT's.