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Vfd & Gear Motor - Over Voltage Tripping


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#1 farooqmali

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Posted 12 February 2012 - 11:50 AM

Hi,

Am using a 2.2KW 5.5Amps 150% torque VFD with a 2.2KW gear motor for a roller conveyor application. The VFD is suppose to run at 87Hz, but its getting tripped on OV (over voltage) after 65Hz. Total capacity of conveyor is 20Ton, when light loads are placed, VFD is not tripping, when we test with a 7 Ton load VFD was only able to run till 65Hz.

We change the VFD to a higher capacity and higher torque (200%) version, but its the same. What could be the reason for this OV ? Is this happening because of some regenerative energy from motor to VFD ? Can it be resolved by using a DBR ?

Any expert suggestions are highly appreciated, thanking in advance.

Rgds,
FMA

#2 jOmega

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Posted 15 February 2012 - 10:46 PM

The key parameter to observe is the DC Bus Voltage.

the OV trip is caused by the DC Bus Voltage exceeding the preset limit.

Cause:

either the AC line voltage is going too high .... could be caused by spike transients on the AC line....


OR


the mechanical load is causing the motor to overspeed and regenerate energy back onto the DC Bus.



Question for you: ------ What is happening just before and at the time the OV trip occurs ?

Another question for you: ------- Tell us about the orientation of the conveyor .... is it horizontal ? is it inclined downward ?

And what is the load that is being placed on the conveyor .... please describe .

#3 farooqmali

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Posted 16 February 2012 - 04:41 AM

Hi Jomega,

Thx for ur reply.

Yes, the VFD is tripping at 820DCV, also noticed the torque is between -5 and -20 while tripping.

This is a horizontal conveyor for material transportation, there are three conveyors one after other (3VFD's as well), load is heavy steel structure (steel bar).

With lighter loads, load moves from 1st to 3rd conveyor w/out any problem, as the load increases the VFD get trip after certain frequency, VFD may ramp to preset speed and run for few secs and then trip on OV.

Can this be caused because of noise, we have the same VFD (but with built in emcf) and same application and has no problems.

Thx for your valued suggestions.

Rgds,
Fma

#4 jOmega

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Posted 17 February 2012 - 03:55 AM

For our discussion, the following conditions.

The first conveyor to receive the head end of the bar we shall call Conveyor #1

The next conveyor in line shall be called Conveyor #2

and the last conveyor to recieve the head end of the bar we shall call Conveyor #3


As you said, each conveyor has its own VFD ....

So which VFD trips first ...... #1 ? #2 ? or #3 ?


Does only ONE of the VFDs trip or more than one ?

If more than one ..... which trips first ...... second ...... third ?




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