Motor tails

[arcserv]

How do i identify the correct conections of an unlabelled 6 wire motor. Is there a test to establish which is U1V1W1 or U2V2W2

[Darren]

In order to identify the start and end of each winding you are going to need to first identify each coil. Mark 1 end of each coil with U V W. Then use a 12VDC power supply across 1 coil put a 100ohms reostat in series to keep the current down. Put a mulitmeter across another coil. Turn on the dc and look at the polarity of the voltage across the other coil. If Positive then your red lead is connected to the same end as on the power supply, lets ay the start. Do the same across all 3 windings and you will have all the starts and all the ends. S you find the end of each coil make it accordingly.

[Darren]

Sorry, fingers in gear brain not. That is a Galvanometer not multimeter. Watch for direction of needle deflection.

[marke]

hello arcserv

 

How are the tails terminated? are they connected to an unlabeld stud patter, and if so, are there links in place to set for star or delta configuration??

 

Best regards,

[arcserv]

Hi Mark. Motor is 90kW that has been rewound some years ago and has never been put back inservice. Tails are unmarked. Motor is labeled as Delta configuration. . The easy part is finding the pairs.. I was hoping for a simple test like the Galvanometer one. Unfortuanately i do not own such an instrument.. Taking the motor to one of our sites for trial and error connections and connecting to a suitable supply is time consuming. I did one trial reversing one of the windings,but blew 200/250M rated fuse and did not wasnt to thrash the new soft start i had fitted.

Point of interest -- motor is for Jaw type crusher fed from from Softstart. It replaced an ancient slipring 585 RPM 70 BHPmotor with liquid secondary resistance starter.

I have located and fitted an old 90kW ASEA TEFC motor which now is running. But would like to sort tail conections on this other motor..

Thanks Derek

[marke]

Hello arcserv

 

From your message, I take it that there are just six flying leads that are not erminated onto a stud board or similar. This tends to make things more difficult, however provided that you can work out the three pairs, then one option is to select one end of each pair and assume that it is the start, and temporarily label as such. Connect the other three ends together so that the motor is now connected in star. Assuming that you have sufficient supply available to start the motor in delta, then you can definitely start the motor in star. With the motor open shaft, try a DOL start on the motor while connected in star. The current will be limited by the star connection. The motor should spin up to full speed easily and the currents should be balanced. If you have one winding that is drawing a significantly different current, try reversing that winding. - remember that only one winding can be reversed, two must be the same. I would not expect an easy star with a winding reversed.

If you are concerned about the start current, you could further reduce the voltage across the windings, either by the use of an autotransformer (perhaps you have an old AT starter somewhere, or by putting equal resistance or inductance in series with each winding. If you use a series impedance, it must be able to provide a reasonable level of current for lone enough to make some measurements. With equal impedances in series with each winding, you should be able to measure the voltage across each winding. If a winding is reversed, I would expect to see a significant difference in voltage across it relative to the other two.

I am not sure how much current you will need through the windings to show up the difference, but you can soon find this out by trial and error.

 

In replacing a slip ring motor with a cage motor and soft starter, you will find that the start time will be longer and the start current will be higher. If the cage motor has a very poor speed torque curve and a high Locked Rotor Current, you may not be able to start the crusher. I see that you have oversized the motor which is good, but perhaps more important is the speed torque curve of the rotor and the LRC.

 

Best regards,

[arcserv]

Thanks Mark

Yes indeed Starting Jaw Crushers is a nightmare for Softstarters. I work in a number of quarries and have replaced older AT and Liquid starters with Soft Starts. I normally try to start the motors with no Kick start.. This last motor must have low start torque as i had to employ 2 sec of kick start at 70% LRT to get it away. Start time is 10 secs. Next project is a 90 kW Gyrotary and 40kW Jaw and smaller plant to be fed from a genset.

Would love to sit down and talk soft start issues for my applications school of hard knocks and suck it and see only goes so far when buying and installing this sort of gear.

[arcserv]

Oh to have the luxury of information, both of these motors we are discussing are old and have little to no information with them.

[marke]

Hello arcserv

 

Good luck, sorting it won't be too bad. In the mena time feel free to post any questions about soft starters and motor control on this forum, there are a number of experts who frequent the site and I am sure that you will get the answers you need, if not ask again!!

I for one, am quite happy to answer questions as long as it does not involve too much time or doing homework by remote control!!

 

If you have not already done so, have a look at my web site at http://www.LMPhotonics.com which has a lot of the basic application information that is needed to correctly select and apply motor starting systems.

I also run training seminars around New Zealand at times, and further afield when so requested. Perhaps you may find them of interest.

 

Best regards,