Stopping motors

[electgut21]

HI, I like to know if anyone knows of a way to stop a motor quickly by using a switch in the control circuit. Its 3 phase motor and the heaters in the starter are not fast enough.

 

[hurk27]

HI, I like to know if anyone knows of a way to stop a motor quickly by using a switch in the control circuit. Its 3 phase motor and the heaters in the starter are not fast enough.

put an electric brake on the back of it?
install dynamic braking contactor?
use a soft start with reverse braking?

 

[augie47]

HI, I like to know if anyone knows of a way to stop a motor quickly by using a switch in the control circuit. Its 3 phase motor and the heaters in the starter are not fast enough.

The "heaters" are essentially nothing more than a switch in the control circuit. If opening the control circuit (via switch or heaters) is too slow the methods Wayne lists are options. What HP motor are you referencing ?

 

[electgut21]

I should explain . Lets say a motor under normal running conditions pulls 5 amps and when a problem comes up it pulls more than the 5 amps. I would like to stop it as soon Ias I can , lets say 6 or seven what ever keeps the motor from doing dammage. The heaters take to long , i need quick action. It is like a conveyor system.

 

[hurk27]

Rethinking this, if your wanting to remove power faster from an overloaded condition, then try electronic overload blocks, but be careful as with motors startup current can be a big problem when sizing the OCPD, this is why heaters are used for motors, as they act like a time delay to allow a motor to start up, but at the same time protect for overload, sizing them closer to the RLA of a motor can work if the motor is not always at 100% loaded but keeping them from tripping while starting can be tricky.

 

[hurk27]

I built a starter to do this once, because if the motor didn't shut down fast when the garnet started to jamb it would cause more damage, costing thousands to repair, used two motor starters, one set for startup current, the second set for the RLA which was about 65% of FLA.

When the garnet drive was first energized the startup controller would bring the motor up to speed, then the current monitors would drop out and switch it over to the running controller set at 70% of FLA. this can be done by current or time delay control

 

[rcwilson]

There are motor load relays that can be connected to monitor the actual motor kW (HP) and give a trip output. They are more accurate than just monitoring amps.

Google search for motor load monitor relays. Time Mark and other motor control companies sell good ones. Some have built in time delays and logic to allow the starting current then switch to instantaneous tripping on overload.

 

[ptonsparky]

You can program VFDs to do this. The output relays could be programed to shut down at a set amp within a set period of time. You can have the overloads disabled during start. All sorts of different ways, depending on the model of VFD or how much other stuff you want to add into the control circuits.

Are you trying to protect the motor or what it drives?

 

[Power Tech]

Marshining belts on machines have been stopped traditionally with a mechanical break.

Just a contactor, moves the product 20 feet and stops dead.

 

[hurk27]

I think what he is saying, is with the OL's set for FLA, and lets say a conveyor has parts that break off and jamb the conveyor causing more parts to be damaged, the OL's will not be fast enough to turn off the motor in a case like this, we had a large conveyor that used light weight tubing bolted to each side and when one broke off from normal wear, it would fall down and cause others to break off, having a sensor to stop the motor as soon as the first bar jambed against other bars would prevent a much larger amount of damage.

So having some kind of current monitor that would ignore the startup current, but watch the RLA closely is what he needs.

But as I see it, the varying loading of a conveyor system would be a nightmare to get that close.

 

[Jraef]

Your Overload "heaters" are only there to protect the motor from severe thermal damage. If you need mechanical protection as well, it's best to do that with a Load Monitor relay. They look at actual shaft power (calculated) and can be set to trip much earlier than an Overload Relay would, plus as mentioned, they can be programmed to ignore the starting current. The one I like best is from a company called Emotron. They aren't cheap, but they are very good.

http://www.usa-emotron.com/shaftpowermonitor.aspx

 

[hurk27]

Your Overload "heaters" are only there to protect the motor from severe thermal damage. If you need mechanical protection as well, it's best to do that with a Load Monitor relay. They look at actual shaft power (calculated) and can be set to trip much earlier than an Overload Relay would, plus as mentioned, they can be programmed to ignore the starting current. The one I like best is from a company called Emotron. They aren't cheap, but they are very good.

http://www.usa-emotron.com/shaftpowermonitor.aspx

With the conveyor system I mention above we installed a shear pin system, an engineer calculated the max drive torque, and set it up on the drive sprocket, later it was changed to a calibrated slip clutch Assembly (shear pins were too costly):roll:. both worked great as the conveyor would stop on the first jamb.

 

[Power Tech]

TD off and a mechanical break.

Cheap, and adjustable with a wrench, too simple.:roll:

 

[electgut21]

There are some good methords to do the job. We do have sear pins in the system but for some reason that has not been sucessfull. The motors are 2 and 5 hp 480 volts. The electonic relays sound like a good way to handle it. Thanks guys for your input.

 

[weressl]

I should explain . Lets say a motor under normal running conditions pulls 5 amps and when a problem comes up it pulls more than the 5 amps. I would like to stop it as soon Ias I can , lets say 6 or seven what ever keeps the motor from doing dammage. The heaters take to long , i need quick action. It is like a conveyor system.

It seems like you need an instantaneous overcurrent relay that is bypassed with a TD relay during startup and possibly an electromechanical break on the motor shaft if the inertia keeps rotating the motor after the emergency stop from the IOC relay.