GE SR745 Protective Relay

[ElectricalTestTech]

I was wondering if anyone had any type of spreadsheet or formula on how to calculate the currents needed to operate different parts of a differential slope. I am looking to be able to type in a primary winding current, and have it calculate the amount of secondary current needed to trip on differential. I have contacted GE and they do not have anything and basically state that we should just trust the relay. I have had so many relays fail in the past year that I do not trust their relays.

.2*CT diff p/u
25% slope1
1*CT break
98% slope 2

16MVA, 1200:5 primary, 3000:5 secondary, 13.8kV-4.16kV, Dyn1

I have a spreadsheet that allows me to input Winding 1 test amps and Winding 2 test amps. Based off of those it will tell me if I will see a trip or no trip. But I want to know the specific calculated pick up instead of having to continuously change my current values in the spreadsheet to get an approximate pick up.

Thanks

[Relay1]

I was wondering if anyone had any type of spreadsheet or formula on how to calculate the currents needed to operate different parts of a differential slope. I am looking to be able to type in a primary winding current, and have it calculate the amount of secondary current needed to trip on differential. I have contacted GE and they do not have anything and basically state that we should just trust the relay. I have had so many relays fail in the past year that I do not trust their relays.

.2*CT diff p/u
25% slope1
1*CT break
98% slope 2

16MVA, 1200:5 primary, 3000:5 secondary, 13.8kV-4.16kV, Dyn1

I have a spreadsheet that allows me to input Winding 1 test amps and Winding 2 test amps. Based off of those it will tell me if I will see a trip or no trip. But I want to know the specific calculated pick up instead of having to continuously change my current values in the spreadsheet to get an approximate pick up.

Thanks

I sent a couple of spreadsheets to your e-mail address. Hope they help!

[ElectricalTestTech]

I sent a couple of spreadsheets to your e-mail address. Hope they help!

Thank you. I will check them out tomorrow. I am trying to figure out this algorithm. It makes me mad that GE can’t provide a tool that other manufacturers do. I’ll be back at it tomorrow morning

Thanks again

[Reef Donkey]

I sent a couple of spreadsheets to your e-mail address. Hope they help!

Would you mind sharing them with me as well. I've ran into this same issue.

[Relay1]

Would you mind sharing them with me as well. I've ran into this same issue.

Hello Reef Donkey,

Hopefully there is a SEL-387 spread sheet attached here that may help you.

Relay1