I'm pleased to have helped your understanding - once again.
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kwired
Electron manager
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- NE Nebraska
Then what is the purpose of using that starting method?
I can see the current being higher after transition, I wouldn't necessarily call this motor stalling quite yet as the starting process is not finished. I would call it failure to start. If same motor will not complete starting process with this method, it definately will not start with across the line starting.
T
T.M.Haja Sahib
Guest
In the case of open transition manual wye delta starting,the transition is to be effected quickly,If the operator's action is slow, it may cause delta current higher than starting current on transition due to change in magnetic conditions in the motor.
Not a fair objection. :happyno:
Operator?
A manually operated star-delta starter?
I thought these went out of fashion before the Dead Sea reported sick.......
T
T.M.Haja Sahib
Guest
Yes. They still exist, for example, Siemens' Handle operated star/delta starter (3LW42).
And with an office in Chennai.
jumper
Senior Member
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ROTFL. I gotta remember that one!:lol:
GeorgeB
ElectroHydraulics engineer (retired)
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- Greenville SC
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A related INDIRECT advantage to a VFD and "fully" loaded" open delta
A related INDIRECT advantage to a VFD and "fully" loaded" open delta
A reported issue in the thread from which this was forked was phase imbalance with a full loaded open delta. In the case discussed, and to an extent in a VFD controlled (with controlled acceleration) motor, the imbalance will occur on the input to the rectifier of the VFD. This would (to a level unknown to me) result in a slightly lower capacitor voltage, but as Besoeker points out, with V/f characteristics, output voltage (to the motor) will be substantially lower than nominal during acceleration.
If at nominal speed after starting, with "line" voltage from the VFD, loading to well-over-specification slip will result in high currents; the curve by Besoeker suggests (yeah, I know different motors differ, but not LOTS) that if loaded all the way to 75% PU speed, I still have "rated" torque available, but if across the line, at 6 times FLA. The thread was discussing centrifugal pumps (probably multi-stage?) which might not follow the cubic power relationship, but almost certainly not a linear relationship ... so starting POWER requirements would be lower than running, and power required during the acceleration period would increase as speed increased.
Thus the use of a VFD would logically not only reduce starting (and maximum) transformer load, but also "eliminate" phase voltage imbalance, motor phase voltage being generated by the IGBT devices in the VFD.
Also as Besoeker points out, the torque required to stall a motor is, with most traditional 3 phase induction motors, significantly above FLA. I would expect that rather than stall (300+% FLA?), it would be "protected" by the VFD.
Manual wye-delta ... not the question ... it was stalling in operation, not in (beware my perhaps rudeness) improper starting of a different motor than is even being discussed.
A related INDIRECT advantage to a VFD and "fully" loaded" open delta
A reported issue in the thread from which this was forked was phase imbalance with a full loaded open delta. In the case discussed, and to an extent in a VFD controlled (with controlled acceleration) motor, the imbalance will occur on the input to the rectifier of the VFD. This would (to a level unknown to me) result in a slightly lower capacitor voltage, but as Besoeker points out, with V/f characteristics, output voltage (to the motor) will be substantially lower than nominal during acceleration.
If at nominal speed after starting, with "line" voltage from the VFD, loading to well-over-specification slip will result in high currents; the curve by Besoeker suggests (yeah, I know different motors differ, but not LOTS) that if loaded all the way to 75% PU speed, I still have "rated" torque available, but if across the line, at 6 times FLA. The thread was discussing centrifugal pumps (probably multi-stage?) which might not follow the cubic power relationship, but almost certainly not a linear relationship ... so starting POWER requirements would be lower than running, and power required during the acceleration period would increase as speed increased.
Thus the use of a VFD would logically not only reduce starting (and maximum) transformer load, but also "eliminate" phase voltage imbalance, motor phase voltage being generated by the IGBT devices in the VFD.
Also as Besoeker points out, the torque required to stall a motor is, with most traditional 3 phase induction motors, significantly above FLA. I would expect that rather than stall (300+% FLA?), it would be "protected" by the VFD.
Manual wye-delta ... not the question ... it was stalling in operation, not in (beware my perhaps rudeness) improper starting of a different motor than is even being discussed.
Got it from one of my lecturers.........don't exactly remember the context but his subject was economics.
Good point. Moving the goalposts comes to mind.
T
T.M.Haja Sahib
Guest
The question posed in the OP is general. It does not have any condition for motor stalling to occur after motor starting to be completed, independence of operator's action in causing motor stalling etc.,
If more specific information is provided as to how operator's action during starting could cause motor stalling, it is most welcome. Thanks.
If more specific information is provided as to how operator's action during starting could cause motor stalling, it is most welcome. Thanks.
The original question was general and most of us responded to it that way. And, I think many would see your subsequent inclusions of caveats as moving the goalposts.
This last may well be seen the same way. Most of us, I suspect, don't come across manual star-delta starters routinely. In forty years I have never included one in what we have supplied. None of our distributors offer them.
The last time I saw one in operation was in the early 1960s. From memory it was an Elliston oil immersed open transition unit.
To answer your question, it would involve an operator and if the operator took a week in between star and delta positions, I have a slight inkling that the motor might stop.
P.S. Congratulations on the improving punctuation.
T
T.M.Haja Sahib
Guest
What actually happens for motor stalling, the motor being fed by an under capacity transformer, while there is a delay in transition from star to delta would be highly interesting to know. Any takers, please?
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Well sometimes the gas goes stale, or you could have a dirty fuel filter, if not that maybe a timing issue.
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