RVSS motor starter and branch circuit

[Isaiah]

We have an existing 460V 3phase 60hp TEFC induction motor that needs to be upgraded to 75hp. (This application is for a torque motor that controls a large gate). The motor starter is a RVSS-reduced voltage soft starter- which will probably have to be increased in size. But does the motor branch circuit need to be upsized to the locked rotor current (I.e. 6 x motor FLA)
since it’s a high torque scenario? Or does the RVSS mitigate that requirement?


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[herding_cats]

Adding 15 hp load? The entire branch circuit, OCPD and any disconnects upsized absolutely. 75 hp = 96A (430.250)

RVSS does nothing to this required service.

 

[Isaiah]

Adding 15 hp load? The entire branch circuit, OCPD and any disconnects upsized absolutely. 75 hp = 96A (430.250)

RVSS does nothing to this required service.

Agreed, but what about from the RVSS to motor itself?


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[herding_cats]

Yes replace it.

https://www.automationdirect.com/adc/shopping/catalog/drives_-a-_soft_starters/ac_motor_soft_starters?_gl=1*1ou7axz*_up*MQ..*_gs*MQ..&gclid=Cj0KCQiAuvTJBhCwARIsAL6DemikfmbBN0svnzC1V3dLlxB3dBmiUKWXwW61Gc4dTEewcKYaDS02zLoaAkHgEALw_wcB&gbraid=0AAAAAD_dnO3RpW0Z71cRlwNkCEVqAX-r7#Nominal_Input_Voltage_i_ms=%22440-480%20VAC%22&start=0&Amperage_Rating_i_ms=%2296A%22

 

[Isaiah]

Yes replace it.

https://www.automationdirect.com/adc/shopping/catalog/drives_-a-_soft_starters/ac_motor_soft_starters?_gl=1*1ou7axz*_up*MQ..*_gs*MQ..&gclid=Cj0KCQiAuvTJBhCwARIsAL6DemikfmbBN0svnzC1V3dLlxB3dBmiUKWXwW61Gc4dTEewcKYaDS02zLoaAkHgEALw_wcB&gbraid=0AAAAAD_dnO3RpW0Z71cRlwNkCEVqAX-r7#Nominal_Input_Voltage_i_ms=%22440-480%20VAC%22&start=0&Amperage_Rating_i_ms=%2296A%22

Thanks Cats. But does the RVSS mitigate the need for locked rotor current sizing to the motor?


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[herding_cats]

I was wondering about that. Most all soft starters are sized by LRA. I'll research. Good question thanks!

 

[herding_cats]

What is the conditions severity and starts per hour? Is the initial load heavy? Is it using a gearbox reduction?

 

[Isaiah]

What is the conditions severity and starts per hour? Is the initial load heavy? Is it using a gearbox reduction?

Those are all great questions - I won’t have the answers until Monday.


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[herding_cats]

ok sounds good. I'll meet you back on this thread.

 

[Joethemechanic]

I've done a lot of gate/valve operators and all of the electric ones have been gear motors. 75 HP sounds big. We did some butterfly valves for Philly Southwest wastewater treatment plant and they were big valves (combined wastewater/stormwater flow for that whole drainage area), and those were only like 20hp if that

 

[herding_cats]

That's what I'm trying to figure out. A gear reduction motor drive is not a "high torque" load. The biggest high torque loads are on massive air compressors, giant blowers, conveyor drives in mining, gravel etc. Extreme situations. I just want him to get the correct soft start for the upgraded 75 hp motor upgrade.