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Reducing Starting Current 3 Phase Motor


Vladster

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Hello,

 

 

I'm new to the forum and soft starters. I have the following problem:

 

Motor 3 phase 400V 15 kVA (Asynchronous)

Starting current 85A

Max. rpm 3000

Application: use on a tower crane for hoisting.

 

Wish: starting current somewhere around 55A

 

 

I hope this is enough info to recomend a solution to my problem.

 

 

Thank you in advance.

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Why you want to reduce the starting current?

It can only be reduced by using Soft Starter or a VFD. If motor is designed for 400V Delta, then you can install a Star Delta starter too but soft starter is a good idea.

 

"Don't assume any thing, always check/ask and clear yourself".

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Hello,

 

 

I'm new to the forum and soft starters. I have the following problem:

 

Motor 3 phase 400V 15 kVA (Asynchronous)

Starting current 85A

Max. rpm 3000

Application: use on a tower crane for hoisting.

 

Wish: starting current somewhere around 55A

 

 

I hope this is enough info to recomend a solution to my problem.

 

 

Thank you in advance.

 

 

Welcome to the forum.

 

In looking over the data you provided, something doesn't seem quite right.

 

I've looked at several different manufacturer catalogs of IEC motors and here's what I found.

 

Rated current is between 27 & 29 amps.

 

Ratio of starting current Is to rated current In is between 6.0 & 6.6

 

Let's assume that In is 27 amps and Is/In is 6.0

 

That would make starting current Is 162 amps

 

You reported that the starting current is 85 amps which is about half of what would be expected.

 

Perhaps you can clarify this for us, and also, is your motor a "brake motor"; i.e. has an integral electro-mechanical brake ?

 

Thank you.

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Welcome to the forum.

 

In looking over the data you provided, something doesn't seem quite right.

 

I've looked at several different manufacturer catalogs of IEC motors and here's what I found.

 

Rated current is between 27 & 29 amps.

 

Ratio of starting current Is to rated current In is between 6.0 & 6.6

 

Let's assume that In is 27 amps and Is/In is 6.0

 

That would make starting current Is 162 amps

 

You reported that the starting current is 85 amps which is about half of what would be expected.

 

Perhaps you can clarify this for us, and also, is your motor a "brake motor"; i.e. has an integral electro-mechanical brake ?

 

Thank you.

Yes it has a electro magnetic brake. It is designed for use with three speeds.

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http://b.imagehost.org/0249/Motor2.jpg

 

Hi Vladster.

 

Thank you for that excellent information about the motor/application.

Please tell me if my assumption is correct.

 

The motor starts as a 12-pole then switches to a 4-pole and then is switched to a 2-pole ....

 

May I also assume that the motor switch points ... are determined by the operator who operates some type of switch that engages each of the three different pole configurations ?

 

Could you also be kind enough to advise the manufacturer of this crane/motor/control ....

 

Thank you.

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Hi Vladster.

 

Thank you for that excellent information about the motor/application.

Please tell me if my assumption is correct.

 

The motor starts as a 12-pole then switches to a 4-pole and then is switched to a 2-pole ....

 

May I also assume that the motor switch points ... are determined by the operator who operates some type of switch that engages each of the three different pole configurations ?

 

Could you also be kind enough to advise the manufacturer of this crane/motor/control ....

 

Thank you.

 

The motor is controled via radio remote control. The manufacturer od the crane is Potain. I will try to find the pole connections and drop them here.

 

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  • 4 weeks later...
The motor is controled via radio remote control. The manufacturer od the crane is Potain. I will try to find the pole connections and drop them here.

 

Vladster,

 

Potain's parent company is Manitowoc. They are located about 115 kilometers from where I live. I've sent them an inquiry about the crane you have, and requested data on the motor and control. I've also asked them about the possibility of using a soft-starter to reduce the starting current as you previously have stated.

 

To this date, they have not responded.

 

I will try again after the holidays.

 

That said, here is my analysis based upon the information you have provided.

 

Because the motor is a special design (12-4-2 pole) utilizing a pole switching controller, the use of a soft-starter is not practical without a major redesign of the control system.

 

An additional factor against the use of a soft-starter lies in is what you hope to achieve; i.e., reduction in the starting current

from 85 amperes to 55 amperes. (This would be in the hoisting direction.) The reduction in starting current would also reduce the starting torque developed by the motor. Thus, you would have to derate how much load the hoist could 'pick' when starting. The reduction would reduce the rating (specifications) of the crane's hoist.

 

If it were possible / practical to engineer a soft-starter into the control scheme, the soft-starter control scheme would have to be configured so that it is only active when the hoisting mode is engaged. You would not want the soft-starter in the circuit when starting in the 'lowering' direction.

 

Conclusion:
It is not practical to integrate a soft-starter into the existing control scheme.

 

 

 

 

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