351-7 formula

[VisokiNapon]

I am looking for a formula how to calculate the relay settings reverse power on SEL 377-1. I found some other formulas but I am not sure if they are applicable to this relay. I couldn't find anything in SEL manuals.
I have 25kW system, CT ratio 200:5, PT ration 36:1. I know I need some Generator info also to get the calculations but I would like to know what the formula for calculating out the settings is.

 

[DTR2011]

perhaps check SEL 300G manual (Generator Relay)

 

[davidbeach]

Not familiar with a 377-1. The 351-7 does exist, and does have reverse power elements, and the manual does a pretty decent job, and their application engineers are very helpful.

 

[VisokiNapon]

Sorry, typo... I got it right in the heading, 351-7 is correct.

 

[davidbeach]

The manual will explain the process of setting the relay. The determination of the actual setting is up to you as the engineer. What do you want the reverse power to accomplish?

 

[JG2828]

If used to prevent motoring try this formula:
Im = secondary current to the relay
Im = (Primary kw at motoring x 1000) / (generator terminal volts x ct ratio x Sqrt(3))
You will need to set a time delay to prevent tripping during synchronizing and stable system swings.

 

[JG2828]

Actually that is the formula to set a directional overcurrent relay for use with reverse power. I'm not sure if it applies to the 351-7.

 

[ASimmons23]

SEL 351S Manual, Page 3.59, talks about the power elements in the relay. I would start there and see if that helps you setup your logic and wordbits.