VSD Overspeed

[Rheinhardt]

Dear Friends,

I have the following situation which I find very strange with an ABB VSD that we are using on a hoist. The situation is as follows the hoist basically stacks plates into different bays..

Now the VSD that control the hoist motor was actually working fine till the following happened.. When the hoist move upwards everything is fine and it controls at the required RPM .. The problem is when I move downwards the unit just accelerates over the Maximum RPM and then Trips on Overspeed Even when adjusting my Maximum Speed Down to 600RPM the motor accelerates over 1500 RPM.

When I manually release the brake the unit starts moving downwards slowly which means my Gearbox is obviously not maintaining the weight of the hoist

Question

1. What could cause this to happen.. No Parameters were changed on the VSD. Could it be a Hardware issue, or a faulty VSD

2. Would changing the GearBox ratio help with the effect that Gravity has on the hoist and limit the acceleration.

Any advise would be well appreciated.

Kind Regards


--Off all the things i've lost , i miss my mind the most--

 

[CJCPE]

If the VFD has dynamic braking, the braking may have stopped working.

The gearbox may have become easier to overhaul than it was when it was first installed. Has the ambient temperature changed?

A gearbox with a greater speed reduction would require more torque to overhaul, but adding dynamic braking to the VFD would probably be easier.

 

[jraef]

I agree. From the outset I immediately thought the braking was lost in the VFD. Possibly the resistor bank has opened (or a wire going to it).

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http://www.jraef.com

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[Rheinhardt]

CJCPE,jraef

Thank you for your replies, i hav found the problem to be on the external dynamic breaking kit, the external chopper circuit is the problem, the supplier never remove it..

Thanks again


--Off all the things i've lost , i miss my mind the most--