Plugging Switch Question

[macmckim]

Have request from client at power plant (US) to supply a plugging switch for a large induction motor used on a ID fan.
Client want it for motor protection in stop operation staff from restarting the motor if motor overheats or stalls.
Do no have any experience with this device and would appreciate some advice on what is device and possible supplier. TIA

 

[jraef]

LOL, what you want is an ANTI-plugging relay, essentially a timer that locks out the control circuit for a period of time. Other names for it are Backspin Timer, Coast Down Lockout Timer, Short-Cycle Timer etc. You can search for those names, or it really isn't that difficult to build it from an Off-Delay timer if you know what you are doing.

The ANSI / IEEE Device code number for that is as follows:

86) Locking-Out Relay is an electrically operated hand, or electrically reset relay or device that functions to shut down or hold an equipment out of service, or both, upon the occurrence of abnormal conditions.

Many solid state Motor Protection Relays already have that function built-in, as do most high-end soft starters. Not a bad idea to have a good MPR on an ID fan for lots of other reasons as well, and if you need a new soft starter for it anyway, look for one with that function built-in.

"Our virtues and our failings are inseparable, like force and matter. When they separate, man is no more."
Nikola Tesla

 

[MikeHalloran]

Plugging is the act of reversing a motor while it is running at full speed. It is not generally a good idea.

An idiot (no names please) might, for instance, install a reversing switch and briefly plug, say, a 115VAC 1/15HP PSC 1.0 rpm gearmotor with a small inertial load, to keep it from coasting.

In the extant case, said motor did stop almost instantly, but exact measurements were not made because of the smoke, noise, and general drama of an associated 15 amp circuit breaker launching itself completely out of a panelboard. It is not clear if the breaker exploded on impact with the floor, or if it was already disassembled to the atomic level when it took flight.

Further development of the subject apparatus resumed with a small stepping motor, 72:1 worm gear, 2.5:1 timing belt drive, and ramping controller.





Mike Halloran
Pembroke Pines, FL, USA

 

[itsmoked]

Man what an idiot! Stay away from him!!

 

[ScottyUK]

Hi Mike,

Please post the brand of the circuit breaker - I want to make sure we never let on onto our site!

I witnessed the mess made of a large two-speed fan - about 90kW - which ran one way in low speed and the other in high because of incorrect phase rotation on the low speed winding. Switching between speeds essentially plugged the motor from about 700 rpm reverse to 1450 rpm forward. There were no blades on the hub, and the gearbox casing fractured under the strain. Thankfully no one was near the fan at the time of the event.



----------------------------------

One day my ship will come in.
But with my luck, I'll be at the airport!

 

[MikeHalloran]

The breaker was whatever commercial generic the company was using at the time. It did its job; it broke.

The gearmotor, a Bodine, survived.



Mike Halloran
Pembroke Pines, FL, USA

 

[fsmyth]

Some guys have ALL the fun.
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