MNSPTOC Negative Phase Sequence Overcurrent Protection

Thanks for your Reply. I explain the core issue as below

Fan motors were tripped due to NPS protection triggered by an unbalanced grid voltage.

Negative phase sequence protection i.e. MNSPTOC is provided in numerical relays for all HT / LT motors rated 75KW and above. It was determined that the NPS protection settings were excessively sensitive.

This has resulted in unnecessary motor trips. To address this issue, NPS settings of HT and LT motor above 75 KW were reviewed and more precise setting w.r.t. motor NPS curves provided by OEM have been derived. These setting remain within the permissible limits specified by the OEM for different motor ratings. And are proposed to be implemented as new settings.

1200KW 11KV PICK UP SETTING 0.06 TIME 7200 Sec.

1800KW 11KV PICK UP SETTING 0.06 TIME 4000 Sec.

75KW 0.415KV PICK UP SETTING 0.15 TIME 1650 Sec.

But in my opinion 7200S (2Hrs) and 4000S (1.11hrs) should not be implemented in the REM 630/616 Relay. The relay detects heating effect and ultimately translating it to neg seq current equivalent. Please correct me if I am away. Thanks

Can Pdf file is added on this forum if yes how can?

With the settings proposed, what happens if Negative phase sequence current happens to be 40%? Shouldn't you have a faster protection element to take care of large Negative phase sequence current.

Large Negative phase sequence current can appear when there is single phasing and it can be worse if the motor Start command is given when one of phases is open.