Relay settings

[charlie b]

I need a translator, or at least an instructor. I have gone through the exercise of comparing a set of fuse curves and an MV cable's damage curve. I now need to check the cable against an upstream relay. I have been given the settings, but I do not know how to interpret them. Can anyone tell me how to use the information shown on the attached settings sheets?

 

[Pharon]

I'm just gonna take a shot in the dark here, in the interest of maybe learning something myself:

"51 (0.5-20 x CTR), setting: 3.57" -- 51 is the AC inverse time relay (short/long time), CTR = CT Ratio, 600/5 or 120; so 3.57 x 120 = 428.4A

Very Inverse (see attached pic)

"50-1 (0.5-175 x CTR), setting: 121.1" -- 50 is the instantaneous time function, 121.1 x 120 = 14,532A @ 0.01 seconds

The 51N relay sounds like residual ground fault current settings, using the same logic above for the trip points.

 

[kingpb]

The relay in question is a Siemens, Model 7SJ802. The previous post is accurate.

However, the thumbnail provided appears to be missing a Time Dial setting for this relay.

This needs to be confirmed to determine the actual adjustment for the 51 and 51N, both.

Also, the 51N means that the relay is using the three single phase CT current inputs to calculate the residual current. The alternative is if it said 51G, then that would mean you are using a zero sequence CT; all three phases pass through the CT to measure current.

 

[mivey]

However, the thumbnail provided appears to be missing a Time Dial setting for this relay.

Next to the curve: 2.1 and 2.73

 

[kingpb]

Next to the curve: 2.1 and 2.73

ahh yes, my eyes deceive me, again. :blink:

 

[JoeStillman]

51 is the long-time pickup
ANSI Very Inverse refers to the slope of the long time segment (or else the short time, see below).
50-1 is the instantaneous pickup
50-1 is (I think) the short-time delay.

If you hit the "Toggle" button, you switch between the phase curve and the ground-fault curve.

If you assign the relay to a TCC file in SKM, you can adjust each setting and watch how the shape of the curve changes. I like to make a temporary TCC file for the one device, just so I can be sure I understand the settings.