87T Connection

[ciy]

Dear all,

There is a transformer need to add the other differential relay (87T2) for redundant.

As I know, the practice connection is the separate as attached figure 1.

The 87T2 in series with 87T1 as figure 2 is not a good solution, however, no other CTs are available.

My issue is if I have to connect 87T1 and 87T2 in series illustrate as figure 2.

Please advise what correction that I can make for saving the performance of relay? how to make the setting?

Best regards,

Stanley

 

[davidbeach]

There should be two lines between the two relays. Done quite often, doesn't affect how the relays are set.

 

[ciy]

Dear davidbeach,

Thanks for your reply.

Upon your explanation, I cannot follow your idea of "two lines between two relays".

Please explain more detail of two (2) 87T in series, provide connection scheme or three-line diagram for reference shall be appreciated.

Best regards,

Stanley

 

[davidbeach]

The high-side CTs are connected to both relays. Likewise, the low-side CTs are connected to both relays. This is, of course, assuming the use of numeric relays; I don't know if you can have two relays share CTs using obsolete relay technologies.

 

[ciy]

Dear davidbeach,

Thanks for your explanation.

The numeric relay is the key point.

Best regards,

Stanley

 

[odlanor]

I guess we could be more clear. Your figure 2 can be detailed:

The high-side phase terminals CTs are connected to high coil side of first relay, the other side of same relay coil will be connected to high coil side of second relay. The other side of second relay coil will be interconnected to return to neutral side terminal of high side CTs.

The low-side phase terminals CTs are connected to low coil side of first relay, the other side of same relay coil will be connected to low coil side of second relay. The other side of second relay coil will be interconnected to return to neutral side terminal of low side CTs.
For numeric relay, Dyn connection is setting by relay.

 

[ciy]

Dear odlanor,

Your description is really more detail and clear.

I am appreciated for your kindly explanation.

Best regards,

Stanley