starting a slipring motor

[Siggi]

I just found this forum and have the following question:

 

is it possible to control the speed of a slipring motor with a resistance starter ?

 

I have heared something about a system with GRR and SPRS whatever it is

[marke]

Hello Siggi

 

Welcome to the forum.

While you can not directly control the speed of a slip ring motor by changing the resistance values, you can chang the speed torque curve, and provided you have a load with a torque curve that increases with speed, the net result will be that the motor and load will slow down as you increase the rotor resistance.

Tis techniques used to be used a lot on some applications but is les common today.

One of the majore disadvantages of this type of system, is that the slip losses are high and are dissipated in the rotor resistors. This is very inefficient unless you can recover those losses somehow.

For example at half speed, the power dissipated in the resistors is equal to the power fed to th load!!

 

There are slip recovery systems available to reduce these losses.

 

Best regards,

[Siggi]

Hello Mark

 

thank you for your answere

 

does it mean, in cas e I want to reduce the speed from nearly 100% down to 90% of the rated speed by changing the resistor, the load (troque) must be extremely constant to make sure that the speed is constant.

In other words, I can use resistos for speed reduction only with constant load (torque)

[marke]

Hello Siggi

 

Yes, in effect, by altering the value of the rotor resistance, you are increasing the slip of the motor. If you increase the load for a given resistor value, the motor will slow down. If you reduce the load for a given rotor resistance, the motor will speed up.

 

If you have a load such as a pump or a fan or a loaded conveyor, you will have reaonably good speed regulation, but if you have a load where the torque is not constant, then you will get variations in speed.

 

Best regards,