Medium Voltage Transformers.

Your motors need 3470 V at 50Hz. And note that they will lose some 15% in speed and power (power = speed * torque, how it was put by someone on this forum).

There is urgentcy in your question.If the power source available is at 50Hz,you have to use it as it is.To change it is not practical and difficult.

The rotation per minute of the motor,RPM = ( 120XFrequency ) / P. Where P is the number of poles of the motor to be used.Frequency is the frequency of the supply in Hz.For e.g.a 4-pole ,50Hz motor will rotate at 1500 RPM.For 60Hz motor taking 50Hz supply,it will rotate at lower RPM.For pump application,this will reduce the suction head and pumping capacity.Please check the performance charactoristic curve of the existing pump.

The power transformer can operate at 50 or 60 Hz, however I think the losses will likely to increase.You should use 50Hz transformer.You are in 11kv area.The voltage is the same as many commonwealth countries with British influence,you should source from countries that can give you ex-stock 50Hz 11kv step down to 6.6kv or 3.3kv or o.433kv motors with corresponding voltages.What is the Kv and KVA or Kw of the existing motor ?

Regards,

Khor

Hi The motor is rated for 650 KW.Thanks