MV Motor Winding Temparature Increasing

The abnormal temp. rise could be due to a very high dv/dt. May be an inverter duty motor would suit, which would have a Class 'H' insulation on the winding wire.

But, wait! You have siad that you have a 6.6kV motor and you operate it with a 3.72kV VFD...? Are you sure?

6.6 KV Star connection , using 3.72 KV delta connection, it is o.k. No doubt about it.

<...Manufacturer.....said it is not meant for VFD application. What may be the reason?...>

Manufacturer.....said it is not meant for VFD application.

Shouldn't the motor be in delta? Would make more sense.

Am I being to simplistic here? The motor is connected in STAR

√3 of 6.6KV is 3.8KV. The VFD is rated at 3.7KV. The motor should be in DELTA

tempreture incresing for motor windings is due to many problems,,,

first is that you should cheak all the connection..... loose connection either on one terminal or three terminal also occur tempreture rise in motor winding....second is connection of motor i.e star delta making here is link more information you can see here

http://www.joliettech.com/3ph_motors_single_speed.htm

and another mechinal reason for temp rising is that your load is over load to your motor shaft i.e uncoupled your motor rotor and cheak the motor on no load

If the motor was not designed for VFD operation then it will get too hot.

You didn't mention what speed you were operating at. So figuring you have a VFD then we can assume it might be rotating slower than it would be without. (otherwise why bother with the VFD)

When the motor turns slowly then the cooling airflow is reduced and it gets hot. Fast.

Try an external forced air cooling supply to supplement the cooling airflow of the motor's fan.

Do you know the motor "Service Factor"? If it is 1.0 125 C. is Max. for full load and the insulation may already be damaged. If it is S.F. 1.15 max. allowable is 180 C. and you are OK, but heat is a motor killer. You probably should use a form wound O.D.P. motor and add a cooling fan if you are not running at rated RPM. A Star run configuration will reduce the Voltage on the windings if you don,t need the full torque from a Delta. At 70% load why run Delta? Good Luck.

Let me add one other thing; A 40 C. rise above 40 C. ambient is 80 C. If the Insulation is Class H you are good to 180 C. but for every 10 C. above that you cut the motor life in Half... 135 C. is hot for 70% load but the insulation is good for that Temp.

What is the running speed of the motor? As already ponted out in this forum,if the speed is less corespondingly cooling is also less from the integral cooling fan attached to the motor. If so you may try cooling with external fan

If the motor is not suitable for VFD application, as said by manufacturer, due to high dv/dt( PWM from drive), high heating effect, insulation system of the motor( specially at the begining of the slots, where magnetic wires enter the slots) will be damaged in due course of operation of the motor.Abnormal temperature rise of the motor may be due to various reasons as indicated below:

due to unbalance currents in three phases,

due to unbalance line voltages,

due to unbalance phase inductance and ressistance,

due to improper connections/ loose connections in terminals,

due to slow speed running by VFD affecting desinged cooling system(for normal operation with star connection at 6.6Kv) of the motor.

How much is the cable length of the motor from VFD panel? Please check it. Due excessive cable length(as recommended by the Drive manufacturer) you may have to add reactors in series to nullify effect of Standing Wave generated by Drive.

Manindra