51N and SKM

[Zogzog]

OK, am I missing something here? How do you put a 51N relay into SKM? Do you add a seperate relay? When I try to add a function to the 50/51 relays I cant get the right taps for the 51N.

 

[davidbeach]

Put the relay into the library with the taps and settings it has and it can be used. The built in library is not necessarily complete and all encompassing but you can add anything you want.

 

[Zogzog]

So yopu are saying to add a seperate relay for the 51N? I cant assign a CT ration because it does not have its own CT, it uses the common nuetral from the 3 phase relays.

 

[DanDel]

The only way to do this in SKM, unfortunately, is to put in a separate relay for each relay function, with it's own CT.

Other software, like ETAP, will allow you to enter a multifunction relay with all of its functions and levels, connected to multiple CTs (and PTs). You can then assign whatever CT to each function, by designating a CT as residually connected.

 

[davidbeach]

SKM allows multiple functions per "relay". It's been a while since I used the program, but you can have the phase characteristics using one library model and the ground characteristics using a different library model. As I remember you can't then plot both on the same TCC (that may have changed since then), but you can plot them on separate TCCs.

 

[Zogzog]

Thanks all for your responses. At least I dont feel as stupid as I did earlier today.

David, I tried that and am still having the same problems you mentioned. I think an email to SKM is in order.

 

[rbulsara]

Enter as separate relay..essentially in SKM each relay represents a TCC curve and for each curve its a separate device. Seems logical to me.

Same for a ground fault function in a trip unit, its entered as a separate device.

 

[rbulsara]

CT ratio will be same as that of the phase CTs.

 

[Zogzog]

I was able to create a seperate function for the phase relays for the 51N. I was able to select the relay from the library and save it as a seperate function for graphing it with the upstrean 51N. Thanks again for everyones assistance.

 

[DanDel]

rbulsara, it may seem logical until you use other types of software.

ETAP allows all functions of a relay (50/51, 50/51N, 50/51G, 51V, 67, Neg. Sequence, etc.), with multiple levels (some relays have four 50/51, two 50/51N, etc.), with one or more CT or PT inputs, and one or more trip outputs, all in one relay, just like it is in real life. It provides automatic phase and GF graphs for each circuit, with the proper curves in each, all of which are selectable anyway.

This sure makes the one-line look better than SKM or others, and it makes the input, manipulation of settings, and output setting sheets much easier also.

Another example is that I could never understand why some software requires you to pick the phase and GF trip functions separately for a LV C/B! If a LV C/B has a GE MicroVersaTrip trip unit, for instance, what are the chances of it having a GF function that's not a MicroVersaTrip? ETAP has one place to put in all the setting info, just like the real C/B.

That sounds more logical to me.

 

[rbulsara]

dandel:

I would agree with you too. Are ETAP and SKM comparable costwise?

 

[DanDel]

I believe they are. I use both, but my company pays for them.

 

[rbulsara]

Thanks, dan.