3phase 3wire & 3phase 4wire how to connect the phase CTs and Neutral CTs to a Ref relay. give me the detailed diagram.

in the Current transformer secondary and primary side connections i have serious doubt. please clear it immediately.

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Roy... an immediate answer is not possible! Response time depends on your answer to, "Are you only interested in Xfmrs having a LV Secondary?"

Regards, Phl Corso, [email protected]

 

Phl Corso,

ya this is LV only. the S1,S2 or X1,X2(means secondary) P1,P2 (means primary). how will be the direction that is my doubt.

regards,
Roy
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Roy… first addressing the 3-wire case:

You probably are aware that the REF-protection method is rarely used on typical LV industrial-type xfmrs, whose capacity is about 3 MVA or less (of course, depending on the LV value!) If, however, you are considering a 3-wire system, without a neutral conductor, it can certainly be treated as any HV to MV xfmr, with or without a current-reducing impedance in the neutral-to-earth connection. As to CT connection, all four (4) CTs are paralleled!

Secondly, addressing the 4-wire case:

Presuming a neutral-conductor is used, and the neutral-to-earth link is located in the switchgear, then qty (5) CTs are necessary, three (3) for the phase-conductors; one (1) for the neutral-conductor; and one (1) for the neutral-to-earth link. All five (5) are paralleled!

Following are several similar threads found in Control.Com archives. They might provide insight to other concerns, for example, economy or comparisons to other more "conventional" protection methods:

o http://control.com/thread/1026243854
o http://control.com/thread/1026246060
o http://control.com/thread/1026247257

Regards, Phil Corso (cepsicon[at]AOL[dot}com)