SEL-451 relay CT Connections, Delta or Wye

Hey dennis,

Why wouldn't you consider the SEL engineers information to be correct? We have had 3 phase, AC power around for more than 100 years. There really isn't new about this subject matter.

Stick to the advice of your local engineering experts. Their knowledge comes from a long history of mistakes that brought about the electrical code.

Oh, by the way, the electrical code was mostly written by the fire department. Care to take a guess as to why?

In my original post, the relay engineer has less experience than I have, and I believe him to be mistaken.

You mention 100 years, I'm getting close, and then you divide by 1.732 and I'm there :-).

OK, I get it now. But before I spend the time thinking about this problem, I would like to ask for clarification. In your original post, you mentioned three CT's on two lines of a generator (if I remember correctly). It would be helpful if you could upload a sketch of this arrangement.

I believe this is a good question but I think the relay engineer may have jumped to his conclusion before he understood what you asked of him. Unfortunately, that is a common mistake. It should be easy enough, however, to test this and I know just the place where you will be likely to obtain a correct answer for free.

What I am thinking about is how the current in a delta configuration might be re-mixed with other currents when it is converted to a "Y" configuration. The signal would still be there but it's magnitude would be reduced causing the relay to miss the event. The laws of conservation say that the signal is merely split or shared by the other devices thereby making them less sensitive.

Please sketch and upload the existing and proposed configuration that you described. I think it will help to produce some better answers. I like to use MSPaint because it is so easy to use. Create the drawing, save it, and attach using the camera icon in the editor and then we should be on track to providing a meaningful answer or direction.

Does that mean you'll be 58 on March 6th?

I would contact SEL and follow all of their requirements for the relay you are using.

Any deviation from the SEL wiring requirements will render the relay(s) inaccurate or inoperative.