☑ Transformer Impedance Motor Starting

There is no other load which is fed by the transformer. Here it is around 300 to 400 kva.

An Example Of Calculating Transformer Size And Voltage Drop

Induction Motor Auto Transformer Starter Power And Torque

6 Auto Transformer Starter Transformer Electrical Impedance

Certain type of drives requires a minimum source impedance for functioning properly.

Transformer impedance motor starting. Transformer starter is suitable for both star and delta connected motors and the starting current and torque can be adjusted to a desired value by taking the correct tapping from the auto. The power system has two voltage levels 11kv and 415v and is fed via a single 4mva generator g1. So atleast you have to consider 30 to 40 load in the transfomer and add that to the motor starting kva.

Normally transformers will be loaded 50 of its rating. The power factor calculated above is the motor locked rotor power factor or the motor starting power factor. In this situation an isolation transformer with required z is inserted in front of the drive.

Typical motor starting power factor is 10 30. When selecting a transformer to feed a motor it is important to note that the starting current of a motor can 6 to 7 times the full load running current or even higher if it is a high efficiency motor. The 11kv bus has a standing load of 950kva s1 and we want to model the effects of starting a 250kw motor m1.

You have not considered the existing load in the transformer during motor starting as if we are starting the motor alone without any other load. A motor starting study should be made if the motor horsepower exceeds approxi mately 30 of the supply transformers base kva rating if no generators are present. In a transformer the ratio of currents is inversely proportional to the voltage ratio provided that the no load current is neglected.

With auto transformer starting if a tapping of the transformer ratio x is used then the voltage per phase across the motor is xv 1. For estimating the motor starting power factor the resistive component of the locked rotor impedance should be included. Isolation transformers with appropriate z can be inserted in front of large non linear loads to control harmonics reduce voltage notching.

Following points to be considered even assuming that prior to starting of this motor. Therefore at the starting the motor current is given by the equation. There is a standing load of 600kva at 415v s2 supplied by a 16mva transformer tx1.

1 300kw is the output rating of motortherefore efficiency of motor should be considered to find fl current 2 10 tolerance on percentage impedance of transformer should be considered. Motor starting power factor calculation.