Dynamic Braking under Power Failure
Dynamic Braking under Power Failure
(OP)
We have to make some electrical engineering changes in a portal crane. The best solution in terms of efficiency, manteinance, etc, involves using AC motors. The question is, is there any commercial AC system capable to provide dynamic braking (to dissipating resistors) in the event of a complete (emergency) power failure?
Hoist drive motors are around 35 Kw.
Hoist drive motors are around 35 Kw.





RE: Dynamic Braking under Power Failure
Never heard of it. Most hoist ( all of them I have worked on that is ) motors have a mechanical brake that must be held open for the motor to run. Loose power the brake goes on and the load stays where it is.
I think any kind of dynamic braking would just let the load down slowly, which could be dangerous.
RE: Dynamic Braking under Power Failure
That said, it is very dangerous to rely upon any electronic brake method for use on a hoist application unless there is a mechanical brake available to hold the load when braking power is gone. I have seen several manufacturers use a DC injection brake to stop a hoist, then set the mechanical brake to hold it. The DC Injection brake just serves to lengthen the lifespan of the mechanical brake. The problem with this is that when the motor starter is opened, triggerring the DC injection brake to energize, there needs to be a time delay of at least 25-50ms to allow the motor field to colapse before energizing the DC, otherwise the SCRs will short. If the hoist has a high gear ratio, the hoist load can drop during that delay. I have only seen it work on a hoist with a 300:1 gear ratio.
That which does not kill me, makes me stronger... and pissed off!
RE: Dynamic Braking under Power Failure
We have to make some electrical engineering changes in a portal crane. The best solution in terms of efficiency, manteinance, etc, involves using AC motors. The question is, is there any commercial AC system capable to provide dynamic braking (to dissipating resistors) in the event of a complete (emergency) power failure?
///As the above posting indicates, there is a system capable to provide dynamic braking. However, the crane application will require an increased safety. The safety can be increased by redundancies. Therefore, the braking system redundancy is appropriate.\\\
Hoist drive motors are around 35 Kw.
RE: Dynamic Braking under Power Failure
RE: Dynamic Braking under Power Failure
Wouldn't a battery UPS system be a more useful solution.
RE: Dynamic Braking under Power Failure