MV Switchgear Motor Starter

[petersonra]

So just curiosity here. I don't work much with MV stuff. Maybe once or twice a year.

I currently have a project where the switchgear vender (Eaton) supplied motor starters for 4160 V motors in the switchgear. One is 1000 HP, the other 1250 HP.

I am not real sure what is in the switchgear because I cannot find any drawings, but it appears there is breaker that powers a motor starter of some time (I am told the motor starter consists of two vacuum contactors which seems odd). Control power for the motor starters comes from the 4160 V fed from the breaker. There is a 120 V plug in the switchgear so you can power up the motor starter from a local 120 V supply. This makes it really difficult to test the thing since to test it you have to go unplug the control power cable and plug it into an extension cord or the control power outlet.

I have never seen this arrangement before. Is this common?

Most motor control I have done with MV gear was just a breaker that had motors on it I could use to turn the breaker on and off and it fired up the motor directly, usually with some kind of motor control relay monitoring the motor that trips the breaker if necessary.

This thing also has a motor protection relay. it seems to be wired into the motor starter rather than the breaker though.

 

[xptpcrewx]

So just curiosity here. I don't work much with MV stuff. Maybe once or twice a year.

I currently have a project where the switchgear vender (Eaton) supplied motor starters for 4160 V motors in the switchgear. One is 1000 HP, the other 1250 HP.

I am not real sure what is in the switchgear because I cannot find any drawings, but it appears there is breaker that powers a motor starter of some time (I am told the motor starter consists of two vacuum contactors which seems odd). Control power for the motor starters comes from the 4160 V fed from the breaker. There is a 120 V plug in the switchgear so you can power up the motor starter from a local 120 V supply. This makes it really difficult to test the thing since to test it you have to go unplug the control power cable and plug it into an extension cord or the control power outlet.

I have never seen this arrangement before. Is this common?

Most motor control I have done with MV gear was just a breaker that had motors on it I could use to turn the breaker on and off and it fired up the motor directly, usually with some kind of motor control relay monitoring the motor that trips the breaker if necessary.

This thing also has a motor protection relay. it seems to be wired into the motor starter rather than the breaker though.

What you are describing is pretty typical for a MV soft starter.

 

[petersonra]

What you are describing is pretty typical for a MV soft starter.

I hope it is not a soft starter. That would be really bad for this application.

 

[xptpcrewx]

I hope it is not a soft starter. That would be really bad for this application.

Two contactors in a starter bucket usually means there is an auto transformer involved.

 

[petersonra]

Two contactors in a starter bucket usually means there is an auto transformer involved.

I was thinking a bypass contactor.

 

[xptpcrewx]

I was thinking a bypass contactor.

Below is an example of a MV soft-starter employing a reactor and bypass contactor. The control circuit (top rung) shows a local plug/receptacle powered by the CPT as well as an external customer receptacle dedicated for testing purposes.

 

[petersonra]

Thanks for the picture. I have asked our end user contact to have his electrician take some photos of what is inside the switchgear cabinet just so we can know for sure what we are dealing with.

If it was something of this arrangement, could we just disconnect the reactors and set the timer to 0 to effectively make it an across the line starter? Or is there some non-intuitive reason that cannot be done.

 

[xptpcrewx]

Thanks for the picture. I have asked our end user contact to have his electrician take some photos of what is inside the switchgear cabinet just so we can know for sure what we are dealing with.

If it was something of this arrangement, could we just disconnect the reactors and set the timer to 0 to effectively make it an across the line starter? Or is there some non-intuitive reason that cannot be done.

Yes, but implementing across-the-line starting would be as easy as adding a jumper between the coil controller inputs (terminals MA and RA). You could leave everything else as-is including the reactor and timer settings. Across-the-line starting was most likely specified in the design, and could be a bad thing given it will sag down the system voltage.

 

[petersonra]

Yes, but implementing across-the-line starting would be as easy as adding a jumper between the coil controller inputs (terminals MA and RA). You could leave everything else as-is including the reactor and timer settings. Across-the-line starting was most likely specified in the design, and could be a bad thing given it will sag down the system voltage.

This thing is for testing generators. It is supposed to put a strain on the generator.

 

[xptpcrewx]

This thing is for testing generators. It is supposed to put a strain on the generator.

In that case, I cant see why not.