# C/T and Relay related Problems /Solutions



## EE-me (Sep 3, 2010)

Greetings fellow Electrical PE (POWER) Takers,

I took the exam in Oct 2009 and unfortunately did not pass it. I was close but there were some (about 4 or 5) problems on there that I was unprepared for. There were some problems related to (current transformer) CT and relay configurations at electrical service entrances. It was not just a function of knowing transformer relationships (ie. N2/N1 = V2/V1, etc )..I dont remember the exact problem (obviously) but no reference material that I have found covers this subject efficiently. Im a "facilities" related electrical engineer and have done design for for new and renovated facilities, construction, project management, etc and yet I dont know this stuff because it appears to be a topic that would only involve power companies (utilities) or contractors who install electrical services.

Did anyone have the same experience and can someone refer me to sample CT/relay problems &amp; solutions?

THANKS!!


----------



## Dark Knight (Sep 3, 2010)

EE-me said:


> Greetings fellow Electrical PE (POWER) Takers,I took the exam in Oct 2009 and unfortunately did not pass it. I was close but there were some (about 4 or 5) problems on there that I was unprepared for. There were some problems related to (current transformer) CT and relay configurations at electrical service entrances. It was not just a function of knowing transformer relationships (ie. N2/N1 = V2/V1, etc )..I dont remember the exact problem (obviously) but no reference material that I have found covers this subject efficiently. Im a "facilities" related electrical engineer and have done design for for new and renovated facilities, construction, project management, etc and yet I dont know this stuff because it appears to be a topic that would only involve power companies (utilities) or contractors who install electrical services.
> 
> Did anyone have the same experience and can someone refer me to sample CT/relay problems &amp; solutions?
> 
> THANKS!!


Protective Relaying Quick Reference...www.powereng.com. Also the Ugly booklets can help.


----------



## EE-me (Sep 3, 2010)

Thanks DK


----------



## pelaw (Sep 4, 2010)

From what I remember, the relay problems are about two things: 1) current in the sensing leg or voltage, and 2) time response.

Calculating the current is easy based on your post. It really is straightforward based on transformer formulas.

To acquaint yourself with time response, I suggest finding GE, SquareD, relay response tables and explanation on how to use them from manufacturer websites. This is really not that difficult.

Here is an example: http://www.geindustrial.com/publibrary/che...ET-6450|generic


----------

