Three-Phase Motor Needs Jogging to Start

Please start by describing the type of motor.

What exactly does "manual jogging" mean? Do you mean an electrically operated jog or does someone grab the shaft of the motor and gives it a spin?

If it is electrically jogged, the motor does not care whether it is jogged or started. Does the contactor try to pull in when you try to start it as it does when you try to jog it? Are there separate contactors for "run" and "jog" conditions?

More data is required.

North of 60,

I agree, more data is required.

I have heard the term "manual jogging" used to describe manually actuating the contactor (not arc flash safe).

As to "Revolving Magnetic Field Mechanism" Is it the stator, which has a revolving magnetic field, or the rotor which has a magnetic field that revolves?

?????????

Actually... both fields rotate and the rotor is always slipping relative to the stators field. No slip... no torque.

Its the stator fields being "activated" one after the other that produces a circulating field. the rotor is just a lump of different metals......with a few ballraces.....

Nothing more, nothing less.....

Nick Tesla would rotate in his grave!

As a 3 phase induction motor rotor? Why not?

Do you really think that in a synchronous motor the rotor is just a lump of metal? Interesting, then what do the slip rings do. Maybe you're thinking this is an induction or squirrel cage motor. Then I wonder how NEMA now classifies lumps of metal (induction rotors) into four different design classes; A, B, C, and D. (There use to be two more soft start classes E and F but with soft start circuitry being now available they dropped them.)

Most people are not interested in "how" the lump of metal is built up.......but if you are really "hot" to know and understand how one is built up, here is a picture and also a good link describing exactly how it is done:-

Squirrel Cage Rotor

The fine detail is in the link....by the way, you can easily see one of the Ball races I mentioned at the RH side, the other is hidden in the end plate.......but looks much the same to the untrained eye.....

Note that the "Cage Bars" are angled slightly to the direction of rotation (eg not exactly at 90° to the rotation), to reduce noise and increase smoothness, especially during run up......this is an important and badly misunderstood area in the design....

I am not sure when this started to be made, but some time in the last 40 years I would guess as the ones I used to work on and repair in the RN in the 60's and early 70's did not have the bars angled....I was unable to come up with a date, but maybe someone else can help us.....

I hope you can forgive my my previous simplification of the design, (I did not understand that we were writing for Electrical Theory 101 here on CR4!) but most people would either already know or could lookup a website themselves or simply not be bothered either way I feel......

Nobody with the slightest intelligence would try and build a motor with just "a lump of metal" as the rotor, so I did not realise that I was treading in such hallowed and dangerous ground when I wrote!

But for most people a Squirrel Cage Rotor will always remain "a lump of metal"

, especially if it fell on their foot at some point!!!

Have a great day in spite of me.....

The next time that it comes up in converation/CR4, I will call it a "Thingy", will that be OK with you?????

Sounds like you are missing one phase either from the supply or one winding is open.

Thats my take as well......

Hi Andy. Yeah, once it starts rotating it induces the other fields. Not sure about some of the comments. In what country do they have 3 phase DC? ;)

There is no such thing....

There are some brushless DC motors that have electronic control to control speed and direction.......they have 3 field windings.......there is a faint possibility that the OP means one of these, but I doubt it somehow.....

Nope. Shorted across all three poles.

j.

First thing to do is get a clamp meter and measure the current draw on each leg. Compare this to the motor rating plate. Compare each reading to the other phases. Then you have some information from which you can begin troubleshooting...

Nice answer. You get a GA. Measure what is actually happening first before proceeding. This will show if there's an open or short somewhere.

Simple suggestion would be to clean the commutators and motor brushes, since it's probably coming from the DC operation. The coils that supply the power might be in need of servicing or replacement as well.

Ah... we are talking about a three phase motor.

yeah.. I was referring to slight chance this is an older 3 phase brush motor with commutators. Something I read about over 60 in the post or the engineers life span thus far...

There is really only one type of motor that could match what you are describing, and that is a synchronous motor. However, that type of motor uses slip rings, not a commutator, to connect a DC source to the coils of its rotor. Perhaps that is what you are thinking of.

??????

We are talking about a 3 phase AC motor!!!!! No commutator, no DC.....

What reading.

Have you check the motor coil winding, the voltage at the motor terminal?.

Okay... as far as the 3 phase direct current motor that I have and was thinking that potentially by long shot, this answer searching individual might also have...

Probably not, but hey, I have what was considered a 3 phase/speed/split motor that hooked up to AC as long as the common was common 100% of the way (thus, making it DC operated).

If the common works it's way to a ground when the ground is also a ground, it shorts out a system.. maybe not completely, but nonetheless, it creates a short.

So here's the deal... maybe the answer to the question is that IF this motor is a newer motor was at one time set up in a wiring situation as spelled out above, the older motor (or whatever potential crossed common to ground) dragged the newer AC motor down and shorted the field. Just a thought... But since I've never been union, I look at reworking the old hack jobs without complaint and the extra break in between.

Kind of like that old wall switch that gives you the shock when you flip in Aunt Emma's Chicago basement apartment... Or the grounded to common water pipes in Iraq done up with mixed wiring schematics from across the globe where common and ground sometimes interchange.

Just a thought or two.

Sorry, but, little of this makes sense, at least to me anyways.

Most properly its a 3 phase AC motor running on two phase.

First check the winding of the motor for continuity

Second check the wire from conductor to motor terminals for continuit

Third check the voltage output of the ""RUN"" conductor. The voltage value must be more or less the same

Fourth check the voltage input of the ""RUN"" conductor. The voltage value must be more or less the same

Definitely your problem is somewhere between the above steps

Good luck

If you have an missing input phase or an open winding on your motor, your motor will not start by itself and/or burn if connected to a mechanical load.

If this is a new motor, check the rotor's skew also, the squirrel cage bars should look "twisted" from one end to the other, if they're straight the motor is defective and won't start by itself.

I've been working in the electric motor manufacturing for 20 years and have seen no reasons other than these, assuming you're suppliying the right voltage.

I once had a 3-phase 208volt motor that didn't want to start, after smoking the motor and pulling my hair out, I found a damn spider had set up residence in one leg the of contactor. JUST A THOUGHT

Hence the word "debugging".

Wasn't the original computer fault also such a "Bug"......

Indeed.

You did not mention that you have voltage and current problems after the motor has started.

I assumed that your problem maybe due to excessive voltage drop during motor starting.

You may not need provisions for jogging the motor if you increase the rating of the transformer or generator feeding the motor.

The motor should be able to accelerate if there's an adequate voltage at its 3 terminals during motor starting period, which is about 10 to 12 seconds.

Cheers,

Rudy C. Fernando

Hello Guest,

It sounds like you may have a 'bearing' problem either on the 'drive' end or the back of the motor?

Just a thought on the small amount of info' you wrote.

bb

Good point and a GA. This may have nothing to do with the electrical side of an electromechanical system.

Hello redfred,

Hope you are fine?

I thank you Sir for the GA!

I wrote only where I would start looking!

bb

There is no such mechanism, in the manner you write, its an integral feature of a 3 phase AC motor, not something that you can put in or take out.......

Nor can you "repair" it.....

Its a thinking problem......

From the mechanical side, what about the breakaway torque of the load?

Or is it a variable speed drive that isn't ramping up enough to create the torque?

But more likely than not a dropped phase.....

Fit an impulse variator.

Guest

Have a look at this site for information (http://www.bodine-electric.com). You can download the famous Bodine handbook to get a better understanding of how motors operate or perform a search to find useful information pertaining to motors, gearmotors or controls (3 phase winding for example). The knowledge you gain may be able to help you troubleshoot the problem, since there could potentially be several reasons for your dilemma, whether they be mechanical or electrical. Many things could've gone south, and these would be dependent on whether it is a brushed, brushless, AC, etc. motor unit.

Future CR4 member

if you can turn a shaft by hand, please try to check a thermal resistance or any inter lock systems (protection system to start the motor).

This probably has gone on long enough that the OP has solved the problem. So we will probably never get our questions answered about what type of 3 phase motor the OP has or what was the specific problem found. For anyone searching 3 phase motor problems and finding this thread there's a likely problem not mentioned in the gaggle of postings. Single phase motors sometimes solve their problem of starting to rotate the rotor by having a capacitor delayed starter circuit. While 3 phase motors do not have the same problem of generating a rotating stator field that single phase motors do, they still sometimes have a different kind of starter circuit. Sometimes in an induction motor the locked rotor (start) current exceeds the supply's peak current limitations. In these cases a soft start circuit maybe used that senses shaft rotation to delay applying full voltage to the motor.