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Stopping An Ac Motor Connected With High Inertia Load


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#1 AB2005

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Posted 25 August 2010 - 06:55 AM

Hi dears;

I have been working on an electric trolley project which would be used for material handling. The trolley has a 7.5Kw AC motor which speed would be controlled by an inverter. There is an issue that how to quick stops the trolley during (consider its own weight, having load on it and its high speed) normal working or during an emergency case. As I donít have experience of such job, so I want to share this case with my friends.
There are several possibilities in my mind to stop the trolley;

1) Applying DC injection brake.
2) Installing a mechanical brake then stop the trolley via mech brake + DC Injection brake.
3) Minimum Deceleration time
4) Regenerative brake (with a resistor connected with drive)

Can any expert share his experience with me? I fear that a wrong way to fast stop the trolley can damage the inverter.

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

#2 marke

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Posted 29 August 2010 - 06:06 AM

Hello AB2005

There are a number of options as you have listed.There is also the active front end option.
When you are stopping such a load, you either stop at the natural slow down rate of the load, or you have to extract energy from the load.
You can dissipate the energy mechanically, using a mechanical brake, or electrically.
Electrically, you can dump the energy into a brake resistor which will convert the energy into heat. You must be sure that the resistor is able to dissipate the full speed kinetic energy of the load.
Another option is to use DC injection in which case, the load energy will be dissipated in the rotor.
The third option is to use an active front end VFD in which case the excess energy is returned to the supply.

If you have a number of VFDs together, you can connect the DC bus in parallel and in this situation, the excess energy may be used by other drives provided that they are "motoring".

Best regards,
Mark

#3 AB2005

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Posted 01 September 2010 - 08:22 AM

Thanks Mark,

I think brake resister option is good as there would be many number of start/stop per hour expected. With dynamic brake, it is possible that motor would be heat up very soon.

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

#4 marke

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Posted 01 September 2010 - 09:43 AM

Hello AB2005

Yes, it is better to take the energy away from the motor rather than dissipate it in the motor.
Using a brake chopper and resistor is one way, but you will waste a lot of energy each time you stop.
If you are doing frequent stops, there is a case to use an active front end as the energy is returned to the supply rather than wasted as heat.
The additional cost of the active front end can be covered by the reduced energy consumed.

Best regards,
Mark.

#5 AB2005

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Posted 02 September 2010 - 07:05 AM

But this time I have purchased the inverter (Mitsubishi FR-A740-11K), a simple vector drive. Now I am working on wire up the inverter with a 47.0 OHM brake resistance and then will a test run.

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




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