A six lead motor is possible to connect as wye or delta. So it should be possible - under circumstances - to do the same with a twelve lead motor. Is it a two-speed motor?
You need to post more details. 12 leads doesn't define it specifically as Skogs said.
It could be 2 speed or dual voltage or dual voltage part winding etc. etc. If dual voltage (i.e. 230/460v) then 12 leads usually means it is Star-start Delta Run, but is not necessarilly rated to run in Star permanently.
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Sorry, the electrical field is wide and I am just getting familiar with motor terminology. What I meant to ask is if a 12 lead 3600 rpm three phase induction motor can be turned into an 1800 rpm motor by moving the motor tap connections to the line.
Not likely, unless specifically designed as a 2-speed motor (consequent pole)....not a very common beast. If there is only one speed on the nameplate, that's the rough speed the motor should be used at.
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The only way is a complete rewind. The horsepower of a standard frame motor generally drops to 50% when it is wound for 1800 instead of 3600.
Hope that it is a belt drive and change the pulleys.
yours
Much thanks for the responses. The reason for the post are the star delta motors we use at the plant. They are 12 lead 3600 rpm squirrel cage induction motors. I have searched this site on this type of motor and everything I can find about the switch from star to delta is that when the motor is configured in star, it must be turning close to data plate rpm at switch to delta. As far as I can tell our motors form one star winding when in star (start) and at switch to delta (run) it forms two windings in parallel. At switch to delta our motors are turning 1800 rpm. I have verified that when in star the uncoupled motor turns at 3600 rpm. When connected to the load the motor turns at app. 1800 rpm at transition (6 seconds) and if you increase transition time the motor can not achieve over 2200 rpm. Motor is pulling 200% FLA while in star and still pulls 200% FLA when switched to delta when current starts falling fast to 50% FLA with the inertial load. The motor load is only an inertial load during this test. With the motor connected to the inertial load it then increases to 3600 rpm after the switch to delta. I have checked other motors and they are also switching at 1800 rpm at transition with out any problems. I was trying to understand the conflict with the information found on this site and the way our motors work.
" ..far as I can tell our motors form one star winding when in star (start) and at switch to delta (run) it forms two windings in parallel." I think you are referring power cable forms in parallel not windings. This is true if your viewing it at the control cubicle.
Can you post the nameplate of your machine?
What is the load or the Functional operation of the machine?
wrsharper,
What you are experiencing is the main drawback of star-delta starting: its limitations. When connected in star, the effective voltage is reduced through the windings by the square root of 3, so the winding voltage is 57% of line voltage. Torque in an AC motor is directly proportional to the square of the voltage at the windings, so in this case it is .572 or .33, which means you get only 33% torque out of the motor. At that much of a torque reduction, your motor is having trouble accelerating the load to the necessary speed for a good transition to delta. So what is happening is that when you transition, it is almost as if you did not have a reduced voltage start at all. The transition spike is going to be just as high of magnitude as if you started across-the-line, only slightly shorter in duration because the motor was already moving. Increasing the time to transition will help a little as you may have observed, but all in all you are toying with the thermal limits of the motor by doing that.
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We haved pretty much shelved this project for the moment and decided to buy a new motor instead of another rewind. I think that the motor is damaged internally because when the uncoupled motor is configured in delta, I am measuring three currents on the output of M1 and M2 contactors. Two measure app.100A and one measures app.75A. When configured in star the uncoupled motor has balanced currents of app. 30A. The electrical upstream of the motor has been checked throughly. The 25% uncoupled delta imbalance tells me that something is wrong in the motor. Since the uncoupled motor current is good in star then I think that one of the windings has trouble from M2. This motor received quite a shock when two leads caught fire and shorted two phases in the peckerhead. This tripped the local 1000A breaker and blew a fuse in the pad mounted utility transformer.
I have another problem with a little 1.5HP conveyor motor driven by a AB PowerFlex VFD that I hope you can point me in the right direction. The problem has been existant since installation several years ago. The motor has dedicated conduit from the VFD. The problem is a intermittent VFD ground fault. The motor and wiring are in good shape. There is also an adjacent VFD that also faults for the same reason but much rarer. Do you think that line reactors or load reactors or EMC or combination thereof would help? Also we have problems with SLC's once in a while losing their memory where VFD's are in the same cabinet. We presently do not use any power conditioning where VFD's and SLC's share a power sourse. Our power factor has been checked and I am told that we have a very good power factor for the plant.
You should really post that second paragraph as a separate thread rather than tacking it onto this thread. When you do that, please come back here and red flag your post and ask that the second paragraph be deleted (and this response as well). That will keep things cleaner.
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