operation of motor under fluctuations

I'm not 100% sure of what you are describing, but in general the biggest risk is if you disconnect and reconnect too quickly. Is that what you mean?

I mean that if I change the setting of the protection by increasing the time from 1sec to 2sec in order to avoid the shut down of the motor, because in our plant if the moto compressor is shut down the process of production take a long time to restart.It's why i'm asking if there is no risk for the motor during fuctuation to run under single phase mini voltage during 2 Seconds.I hope you understand my question thank you.

A motor operating from a three phase unbalanced voltage source will experience an increase in its operating temperature. Even a small voltage unbalances may be enough to cause the motor to overheat and fail prematurely. A 1% voltage unbalance may result in a 6-10% current unbalance and these unbalanced currents will produce additional heating in both the stator and rotor windings and shorten the life of the motor insulation. It would be best to hire an Engineer to determine if your motor can be derated if the motor must operate at rated load with unbalanced voltages.

I hope this helps

BigMike

Dear,

What do you mean by word fluctuation ? Normally, Mini Voltage relays are meant for steady fall in voltages due to load variations. Normally, it is assumed that the voltages in the system are steady & when they are reduced below the set values, then relay operations will be justified.

In this case, All Motors are having Over load capacity. 10% over load for 30 min.

50% over load for 10 sec. With steady fall in voltages, & increasing the relay trip value to 2 sec. will not affect the motor. Prior to damaging the motor winding, Current relays will trip.

But, If, the fluctuations you are referring to is the Voltage dips, & Sudden rise ; then, in this case, since the motor shaft is rotating, there will not be much current surges due to inertia of the rotating rotor shaft. Only the torque surges should not damage the mechanical equipment, care to take.

Infact, We set the mini Voltage levels @85% of Vn @ 10 - 20 sec. trip delay

According to me, increasing the 2 sec. trip setting may be experimented with above criterias keeping in mind.

I mean fluctuationin in incoming line from the 60 kv network (power supply from energy distribution company) not from load variations.

Thanks

Pl inform following

1.What is Voltage setting of U/V relay?

2. What are other settings in relay?