Schweitzer Relay- 51a & 51b

[Humble2000]

Under relay settings for 50 , I see two settings 50a,50b
50Na and 50Nb, what are these parameters represent?

 

[davidbeach]

Which relay? Lots and lots of Schweitzer relays out there and they have many different combinations of elements.

 

[Humble2000]

351 A-FDR

 

[davidbeach]

The SEL-351A (no FDR in the relay name) has 51AP, 51BP, 51CP (and xxxC, xxxTD, xxxRS) to allow setting time overcurrent differently for each phase. Nothing of the sort starting with a 50 or a 50N. Where are you seeing these? My source is SEL's AcSELerator settings software.

 

[Humble2000]

Well, I guess there are two settings for instantanious over crrent settings for phase and ground. 50a and 50b.
These are settings that customer set their relay at,so it maybe their own designation type. the values are
50a:3840
50b:640
51:640
50Na:3840
50Nb:900
50N:400

 

[slavag]

Sorry.
I don't know this relay, but here my 0.02$.
50a and 50b are two steps of DT overcurrent protection
51 is IDMT OC
51Na and 50Nb are two steps of DT ground overcurrent protection. 51N is IDMT GP.
For my pinion are standard IEEE codes.
50a and 50Na are inst steps.
Best Regards.
Slava

 

[Humble2000]

What is DT?

 

[jghrist]

Well, I guess there are two settings for instantanious over crrent settings for phase and ground. 50a and 50b.
These are settings that customer set their relay at,so it maybe their own designation type. the values are
50a:3840
50b:640
51:640
50Na:3840
50Nb:900
50N:400

It must be the customer's designation for separate overcurrent elements. There are six 50 phase (pickup settings 50P1P, 50P2P...) and also six 50 neutral ground elements (pickup settings 50N1P, 50N2P...). There is only one 3Ø 51 phase element. All six phase elements operate from the same current input. You have to look at the logic settings to determine what is being done with the different elements.

 

[dpc]

DT = Definite Time

 

[davidbeach]

My guess is that jghrist has it. 50a and 50b are customer designations for (probably) 50P1P and 50P2P while 50Na and 50Nb are (probably) 50N1P and 50N2P. But don't get the 50Nx elements confused with the 50Gx elements.

 

[dpc]

But don't get the 50Nx elements confused with the 50Gx elements

Like all the rest of us do.

 

[slavag]

David and Dave.
Please for me and others. Once and forever.
Are 50N means residual connection ( or internal calculation) of 3 phases.?
Are 50G is connection to the zero-CT?
it's terible mix of termenolgy
Best Regards.
Slava

 

[Humble2000]

Yes they are , the values for
50P1P=50b=640
50P2P=50a=3840
there is a 50P3P which is not used anywhere( at least i cant find it).
So what are these two values ( 51B and 51a) represent. I know that they have defined 50a as Hi set instantanious, what about 50b ?

 

[davidbeach]

On the 351 (all flavors) N is measured through the IN terminals while G is calculated IA+IB+IC. Likewise with 551 I believe. Then there are the 321 and 311; both use a calculated IA+IB+IC for the protection elements - the fourth current input is for current polarizing - but the 321 has N elements while the 311 family has G elements. Gotta know which relay you are working with.

Then there are other manufacturers of relays that have N (or G, could be) elements that you have to select whether they are residual or measured.

 

[davidbeach]

Humble2000, that's how the elements are set; what they are used for is defined in the logic of the relay program, set by the user. It is impossible for us to know what they are used for without the relay logic, and that might only tell what outputs they activate. To know what the outputs do would require schematics and control diagrams. All that would be rather more than what this site is intended for.

 

[dpc]

Slava,

Prior to digital relays, there was a "general" consensus in the US regarding this terminology:

G = relay connected to a single CT in grounded neutral
N = relay connected to the neutral of three CT secondary circuits ("residual") connection.

But this was never a standard, AFAIK. SEL decided to (mostly) do it the opposite of this. I guess whoever sells the most relays gets to make the standards.

I have to double-check this every time I set a relay.

 

[jghrist]

Yes they are , the values for
50P1P=50b=640
50P2P=50a=3840
there is a 50P3P which is not used anywhere( at least i cant find it).
So what are these two values ( 51B and 51a) represent. I know that they have defined 50a as Hi set instantanious, what about 50b ?

Just a guess: There is a 67P1D set that makes 50b a definite time element. The definite time setting allows coordination with downstream devices, maybe on the secondary side of some large transformers, with shorter time than an inverse characteristic would allow. 50a Hi set trips instantaneously for close-in faults.

Are the 51B and 51a typos or are you throwing in some settings you didn't discuss before?

 

[suhagpatel]

On the 50N vs. 50G issue SEL is backwards from the IEEE standard. 50N in an SEL relay is the measured value, whereas 50G is the calculated value Ia+Ib+Ic=Ig. The IEEE standard states 50G is measured and 50N is calculated.

 

[dpc]

Which IEEE standard?

 

[jghrist]

I don't have a copy of C37.2, Device Numbers, handy, but I have a document that references it and it says:

Suffix "N" is generally used in preference to "G" for devices connected in the secondary neutral of current transformers, or in the secondary of a current transformer whose primary winding is located in the neutral of a machine or power transformer, except in the case of transmission line relaying, where the suffix "G" is more commonly used for those relays which operate on ground faults.

This seems to match the Schweitzer convention except for the SEL-321.