Liquid Starter For Slip Ring Motors

[paris]

Hi,

 

When we use a liquid starter for a slip ring motor, does the rotor voltage affects the starter selection?

I want to replace a 400kW_4poles_6000V slip ring motor. The original motor has rotor voltage 700V. New motor comes with 400V (rotor voltage)

Is it possible to use the same liquid starter?

 

Thanks,

[marke]

Hello paris

 

Welcome to the forum.

 

Yes, the resistance of the starter is determined by the rotor voltage and current.

If these are different, you will get very different starting characteristics and you may have major switching transients/surges when you switch out the final stage.

 

So, I would say NO you can not use the existing starter without major surgery.

At just over half the voltage, I would expect the rotor to draw almost twice the current, so new everything on the rotor side.

 

Best regards,

[paris]

Thanks Marke,

 

I know about what you say. And you are 100% right if the starter is a typical resistance.

What I am not experienced in, is what if we have a liquid starter.

 

I heard that it's possible in liquid starters to adjust the resistance (easily, by changing the distance between the electrodes, or by adjusting the liquid properties) enabling you to use them for almost any rotor voltage.

 

If you take a look to the web sites of liquid starter manufacturers, you can see that they produces only 3-4 types of starters, and size selection is possible only by the motor power.

 

best regards,

Paris.

 

[marke]

Hello Paris

 

Yes, that is correct, you can alter the characteristics of the resistance by altering the area of the electrodes, the spacing of the electrodes and the stength of the electrolyte.

 

The problem that you have however, is that the rotor current is alost double, so you will need to check all conductors switches etc to ensure that they can carry the current.

 

Best regards,