NCEES #532

[cruzy]

This is an easy points question that might trip me up on the test if I think about it too much. I got it right, but when I start thinking about it, I get confused. So they are asking for the relay tap setting, which in an 800:5 CT, that 5A is the tap setting, isn't it? Or is the questions pretty much asking "on which tap setting will the relay activate?", in which case I understand that yes, you would set it at 2. But in conventional CT's used just for metering purposes, the 5A would always be your tap setting, correct? So this question is pretty much just trying to make you show you know the difference between the different uses for the CT...

 

[Flyer_PE]

So they are asking for the relay tap setting, which in an 800:5 CT, that 5A is the tap setting, isn't it?

No. Electro-mechanical relays have physical tap connections that are used for setting the relay. The 800:5 CT ration could just as easily be expressed as 160:1. In order to get a relay actuation at 320 amps, the tap setting for the relay will still be 2.

 

[GabeM]

I don't have the problem in front of me right this minute, but I recall the problem stating "the tap setting is 5 A", then it goes on to ask you what it is.

I think what it means the first time by "tap setting" is where you connect the ammeter wires to the secondary winding. So by saying that "the tap setting is 5 A", it means that the turns ratio is 800:5. If the tap setting were 10, then the turns ratio would be 800:10.

Then the second time when it asks you what the "tap setting" is, it means the amps the relay would have to see for it to activate.

Does anyone agree that the the term "tap setting" has two meanings?

 

[cableguy]

Actually on a multi ratio CT, your tap settings are on the high side.

We use 3000:5 MRCT's at work. Frequently, we tap them at 1200:5. There won't be taps on the low side, as the equipment that brings the CT in (Schweitzer relays, in our case), are dead set on a 5A input.

 

[Flyer_PE]

^I thought most of the SEL relays could be ordered for either 5A or 1A input. I don't get to play with them very often, most of the relays I work with are electro-mechanical.

I double-checked the wording of the problem and the term "tap setting" is only used in reference to the relay. It lists the CT ration simply as 800:5.

 

[GabeM]

^I thought most of the SEL relays could be ordered for either 5A or 1A input. I don't get to play with them very often, most of the relays I work with are electro-mechanical.
I double-checked the wording of the problem and the term "tap setting" is only used in reference to the relay. It lists the CT ration simply as 800:5.

Did they use that term correctly? Now that I think about it, it makes more sense if it means what "tap" you connected the cables to, like cableguy's example of multiple taps on the high side of a current transformer.

I think the problem should ask for the "activation point setting" since we don't mess with taps on windings to adjust the activation point, right?

 

[cableguy]

{Replying to Flyer}

You're right, we work with 351R's and 351S's, and they do use different input ratios.

I've already packed my Sample Exam in the back of the car. Starting my drive to exam location hotel in about an hour.

{Replying to GabeM}

Tap setting is old school mechanical relay terminology. There's a plug that you stick in a hole in the front of the relay, that's called its Tap.

 

[GabeM]

I read this article a little bit and I think I get it now. There is a tap setting for the current transformer itself and there is also a tap setting for the relay coil. NCEES is asking for the tap setting on the relay coil.

 

[kris7o2]

Hi all,

Does anyone know how to draw this?