We have a medium voltage induction motor of following specifications installed at our Plantsite.
MV Induction Motor Protection
1400 kW, 6300 V, 3-Phase, 50 Hz, rated current 150.8 amperes, Insulation Class: F
Noraml Running current of the motor ranges form 145 to 154A.
and winding Temperature ranges from 100 to 120 degree Celsius.
01. The motor is being protected by a Muti-Function Motor protecrtion relay IMM7990 Make: CEE.
Settings of Protection Relay are:
49: 157.5A, 04 min
50: 1433.25A,0.1 sec
51LR: 1023.5A, 60 sec
51N: 6A, 0.1 sec
02. We have an additional secuirty on DCS which is:
Over Current Secuirty: 158A for 05 sec.
Under Current Secuirty: 92A for 03 sec
We are facing nuisance tripping of the motor on this DCS Over Current secuirty during power system transient conditions i.e. due to cuttin of some other MV motor or voltage dips in the system.
Please share your opinion that while having a Muti-Function Motor protecrtion relay IMM7990 installed on this motor(including thermal overload 49), Is this additional Overcurrent Secuirty on DCS is required or not?
Note: No other MV motor at our plant have this secuirty.