Body
More on plugging.
http://www.industrial-electronics.com/Motor_Control_10-48.html http://www.industrial-electronics.com/Motor_Control_10-48.html
This site seems be a wealth of electrical engineering info. Here is the index page: http://www.industrial-electronics.com/index.html http://www.industrial-electronics.com/index.html
Regards
Ole
---In [email protected], <onielsen@...> wrote :
I just found an article about stopping a motor by reversing it while running. It's called plugging. Below are two figures from the article where one is showing the speed and braking torque and the other one is shoving the current. Here is the article: https://www.practicalmachinist.com/vb/general/reversing-3-phase-motor-stop-149599/ https://www.practicalmachinist.com/vb/general/reversing-3-phase-motor-stop-149599/. Look at the currents. The switch contact points have to carry perhaps 20 times the running current. If they don't have low resistance they're welded or vaporized as the dissipated power is proportional to the current squared. Thus if the current is 20 times greater than normal the power dissipation is 400 times greater than normal. If the contacts bounce the formed plasma may dissipate even more power as the resistance becomes greater while the current stays the same.
Regards
Ole
---In [email protected], <canowindracd@...> wrote :
Norm,
Very good info about the EMP. I've had quite a few experiences with it over the years. The last one was with a refrigeration unit being installed by other contractors in a supermarket food store and it blew up the lightning protection unit in the main Switchboard. We got the blame and we could not convince the owner otherwise and he didn't want to pay for our work of installing the lightning protection unit. Most times it has happened in my experiences has been associated with refrigeration and air conditioning systems. I did see something unusual with large motors in an off mode turning backwards in a brick-works when the metal detector stopped the motors of the feeding conveyors into the pan mixer. You do see some weird things sometimes and you go away scratching your head.
George
On Wednesday, 21 November 2018, 3:21:33 am AEDT, Norman Wootan nwootan@... [EVGRAY] <[email protected]> wrote:
Mick! I am getting just like Hector here by having to explain something over and over! I guess short memory is the cause for lack of understanding the whole project. First you have to go back to the 1981 ceiling fan, 1/6th HP capacitor run shaded pole motor problem. A wiring error by a Chinese assembly worker incorrectly wired the capacitor reversing switch into the neutral side of the circuit which provided a total isolation of charge while the switch was in transition from forward operation to reverse operation. Reversing switch would explode. This was my first encounter with the phenomenon which I researched and determined that it was a Magneto-Electric effect or better put, Magnetic flux annihilation-reconnect as we now know it. In Physics we have always been taught that energy cannot be destroyed but can change forms as we clearly see by simple experiment. With this knowledge tucked back in the memory bank, I had the occasion to encounter this phenomenon again in around 1984. A wealthy widow had remodeled her expansive Highland Park home (Dallas) and I had installed a projection TV system into her den. MS. Sharp called and said she had a Poltergeist in her den. When I arrived she served tea and told me to sit there and wait a few minutes. The TV screen and projector both started descending from the ceiling then reversed and went back up. Both these motors were shaded pole, capacitor run design so that switching via wall switch could reverse operation, either up or down against limit switches. Here is the Somfy motor example so you understand how they operate: https://www.youtube.com/watch?v=EMHEJ2iIu14&feature=youtu.be https://www.youtube.com/watch?v=EMHEJ2iIu14&feature=youtu.be When I went into attic to examine the motorized units the phenomenon occurred again. Sure enough the screen and projector descended half way down then reversed and retracted. Over my head was a powered turbo ventilator attic fan of shaded pole design which took off ZIIIIINNNNG , super fast acceleration up to a speed about 10X design speed but one big problem was that it took off backwards! The turbine took several minutes to coast down to a stop. A visit downstairs found that a small appliance like a counter top blender in the kitchen (shaded pole motor) would take off spinning backwards then stop. The only connection that all these motor had when sitting in a turned off state was a connection to the neutral buss. Interesting fact was that with the very small size motor windings and sudden fantastic acceleration up to very high speed (backwards) did no damage to the motors. I did an inspection to the mains breakers and house wiring including the service cabelling and earth ground at the mains panel. All was up to Dallas Code. While walking in side yard, I found a brand new installation of a 5 ton A/C Condensing unit. in addition to the older 5 ton unit. Both units were earth bonded via the Required (Highland Park Code) 10 ft. ground rod at the units. Both units were 5 Ton, 230VAC single phase. While I was looking at the A/C units , the new one tried to start against a locked rotor condition. From contactor closure to WHUUUUUMP, EMP shot which you could feel the brissance in the ground took about 1/2 second. This was the source of the EMP event which caused the neutral buss to carry this very unusual form of energy. The A/C guys came out and replaced the compressor and rectified the situation but I came away with a better understanding a very common phenomenon that most do not take time to fully understand nor appreciate the implications. By studing the ongoing research of the natural occurrence of this EMP phenomenon from Solar magnetic storms Magnetic Annihilation -Reconnect which have been duplicated in Labs gathering better understanding of phenomenon. I elected to bench top duplicate the situation which I had observed back in 1984 at the Sharp residence. Since I was doing HVAC, Electrical and Electronics Contracting, I had many compressors at my disposal just like the one in the Carrier A/C unit. By hydraulic locking the compressor via filling with oil and pinching off the suction and discharge lines you have a fully locked up sealed unit See:
This unit utilizes a 40mfd start cap and a 5mfd run cap controlled by current relay. When energized via 2 pole,230VAC, starter contactor, both the start and run windings are energized. When the Over current relay senses the locked rotor current of 84 amps ( motor in magnetic saturation) the circuit is opened leaving the stored energy in total isolation with no ground reference. A NECESSARY CONDITION TO GET THE MAGNETIC FLUX ANNIHILATION-Re-CONNECT PHENOMENON or EMP. This experiment is something anyone can duplicate and observe the phenomenon for yourself. The reversible ceiling fan is the simplest and easiest and less expensive to replicate. Most current available reversible fans utilize the electrical capacitor relocation via toggle switch to reverse rotation. All you have to do is open up circuit and re-wire the cap so that you have a momentary loss of ground reference (neutral) while the reversing switch is in transit. Reverse it several times and you will explode switch! Now Mick, what do you not understand?? I was just too curious to let this go by without finding an answer. Just remember the Axiom, Energy cannot be destroyed but it can change forms.
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