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I have Micom P127 which is Tripping by DEF for a forward fault SQH PSS, What is this fault ?

The 67N function in P127 is not working on a similar way to Px40 series
In P127 the polarizing magnitude is Vresidual (as it can be found in the manual) whilst in P14x it is -Vresidual.
This is the reason why Alstom Grid recommends an angle of -60º and Schneider is recommending an angle of 120º.
In fact, it is the same angle, but the first one taking into account that the polarizing voltage is -Vresidual whilst in P127 is Vresidual.

For the RCA configuration in P127
we should follow Schneider Electric recommendation and should have set -45º+180º = 135º.

With a -45º setting, his tripping area goes from +45º to -135º, taking the polarizing magnitud (Vresidual in P127) as the reference.

In the disturbance record, it can be checked that the current lags the polarizing voltage (Vresidual) with an angle of -90º.
Therefore, in forward area of 67N of P127.

Find the attachment

If we configured RCA = 135º (following what is written in the Technical Guide of P127), the forward zone would have been between +45º to 225º, in this case the relay would have seen the fault in the reverse zone and would have not issued the trip.

So in summary, the RCA setting is not correct. 

we hope this information helps.

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