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GE SR745 Protective Relay

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    GE SR745 Protective Relay

    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

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  3. Relay1's Avatar
    Relay1 is offline
    I use to be disgusted, now I'm just amused!
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    Diff Spreadsheets

    Quote Originally Posted by ElectricalTestTech View Post
    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!

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    Quote Originally Posted by Relay1 View Post
    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 canít provide a tool that other manufacturers do. Iíll be back at it tomorrow morning

    Thanks again

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