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Differential relay

    • 19 posts
    August 4, 2019 1:12 AM PDT

    I had a trip on circuit breaker ACB for a generator and after investigation found that the trip was due to differential. The generator's current transformer is 1250/5A and switchboard's is 1250/1A. This relay is from Alstom P343 but this relay is not able to calculate current from two different current transformers. Any other solution to protect against differential trip?

    • 89 posts
    August 4, 2019 4:28 AM PDT

    David,  the relay instruction book seems to indicate it can calculate current from two different sets of CTs (OP5-15). I still have not seen if the two sets can be different ratios.  Assuming they can be two different ratios the 1250:1 may have saturated on a through fault. 

    http://systemcontrols.co.in/datasheet/MicompP343,P346,P342,P344.pdf


    This post was edited by Steve Ward at August 5, 2019 7:12 AM PDT
    • 89 posts
    August 5, 2019 7:11 AM PDT

    The issue could be as simple as a relay setting. 

    Do you have any fault data ?