Help with a 3 phase star delta motor

[silva.foxx]

I'm not convinced of the two-speed motor in this topic but just to bolster the input...

http://www.quillpp.co.uk/Lafert/Lafert2Speedmotors.htm

A case study utilising them for ventilation;
http://www.retscreen.net/fichier.php/877/GPCS219 (Two Speed Pool Fan).pdf

... or just a little light reading for those with insomnia!

 

[sheriff78]

The old starter packed up about a year ago so they called an electrician to sort it, he installed a DOL starter which just turns the motor over at a slow speed. The motor is attached to a extraction fan which sucks the fumes out of 10 metal dipping tanks. the customer has tried to get the original electrician back to sort it but he has dissapered. The customer has said that the fan use to start slow for around 20 seconds and then it would speed up to full speed. I presumed that this was a star delta set-up so i have installed a new star delta starter. I need to replace the wiring because there are only 3 wires at the motor at the moment
I just need to check that the motor will increase speed when it changes from star to delta otherwise i will be back to square one
I cant remeber which way the motor is wired at the moment. It has 3 little links which can be swapped to change it from one to the other.
Which will increase the speed of the motor is it star or delta

thank for all your help and time on this

 

[Steve1412]

From what I remember if the links in the motor terminal box are in a straight line across three terminals its star...if the links are arcoss two terminals each link its delta.
Running in delta will get the max out of the motor.

 

[Marvo]

I would also just wire the motor delta and run it on a 3-wire DOL system. At 5.5Kw Y-D isn't really necessary unless it's a large diameter plastic construction blade set. I would set the thermal overload in the DOL starter at the max run current on the motor plate minus 10%. If there's an overload tripping problem then look for the reason ie blade angle to high, fan running in reverse, blades trailing in grease build-up on the fan housing, motor bearings failing, poor winding insulation etc etc.

Soft starters, VFD's and Y-D starters are unnecessary complications and expense unless you see a good reason for them.

 

[sheriff78]

Thanks for everyones help on this.

Just one last question. if one of the windings had failed could this cause the motor to run slower ( if it was running on 2 phases instead of 3) or would it not run.

Also i have noticed that the last electrician has swapped the yellow and red phase over in the bottom of the contactor. would this cause the fan to run slower.

I am back out there on monday trying to sort things.

i will try and swap the windings from star to delta first

then if nessarcery i will wire it as star/delta.

The fan has taken out the overload after around 20mins of running a couple of times. the overload is set at 5A at the moment so i have incresed this slightly. what could cause this.

alos the fan that it is running is around 2.5foot wide

 

[Knobhead]

From what I remember if the links in the motor terminal box are in a straight line across three terminals its star...if the links are arcoss two terminals each link its delta.
Running in delta will get the max out of the motor.

That is Star
Delta there will 3 links

 

[malcolmsanford]

Thanks for everyones help on this.

Just one last question. if one of the windings had failed could this cause the motor to run slower ( if it was running on 2 phases instead of 3) or would it not run.

Also i have noticed that the last electrician has swapped the yellow and red phase over in the bottom of the contactor. would this cause the fan to run slower.

I am back out there on monday trying to sort things.

i will try and swap the windings from star to delta first

then if nessarcery i will wire it as star/delta.

The fan has taken out the overload after around 20mins of running a couple of times. the overload is set at 5A at the moment so i have incresed this slightly. what could cause this.

alos the fan that it is running is around 2.5foot wide

If you lost a winding and as long as it was not shorting to earth then that could make the fan run slower. Easy to check just test all 3 windings and see what values you get.

Swaping over the phase will just change the direction of the motor it will not affect the speed it runs at.

If the motor is not runing at full speed ie "labouring" then it will increase the amps, like a water pump if you over design it's capacity ie you need to deliver 50 litres per minute but fit a pump that will deliver 500 litres a minute it will trip out on over load.

 

[jpmiff]

Hi

no need to run the motor in star delta, check the current the motor pulls on each phase, the o/load unit for the motor would trip with an out of balance load and the motor would get hot if the motor was two phasing.
if the fan needs to go faster have a look at an invertor

 

[Knobhead]

To be brutally honest I really don’t think you’re competent to carry out this work! I don’t think you have the basic concept of a 3 phase motor.
Sorry

 

[sheriff78]

No motors arent what i specialise in. I specialise in stage lighting and testing. the last time i dealt with motors was 14 years ago at college. That is why i have asked for the help and support of people who do. If everyone did the same then maybe we wouldnt have so many bodge jobs out there.

 

[Marvo]

Capable of doing the job or not is your decision at the end of the day. To me it sounds like you know enough to work safely so if the job is outside your skill set it could just work out expensive if you damage the motor.

Whatever you decide to do with the installation as long as the motor is running within it's specified run current on the info plate and as long as the current draw on all 3 phases is within 5% of each other then you shouldn't cause any damage further to what might have already been done.

 

[silva.foxx]

Firstly, a 5.5kw motor on 3ph 400v will draw approx 11 amps FLC so the overload, at 5 amps is undersized. Ensure your overload can be set to 11 amps.

The motor, according to the nameplate, should only be connected in either star Y

or delta

If it's a dual voltage motor then it'll be 400v Y, if a bog-standard 3ph motor more likely delta but confirm that with motor plate. If you connect it incorrectly you'll soon smoke the motor.
I'm sure you do understand that the connection has no real-life function as a speed control. If that motor is a 1500rpm motor then changing from star to delta will not change the speed for use.

Of course, you can use star-delta as a starting method only, not a speed control. The 'slow' speed in star-delta is the reduced torque building up to overcome the inertia of the load.

To reiterate the two-speed motor possibility (albeit unlikely) this utilises the star and delta connections to alter the usage and connections of the windings... but lets forget this option now.

Finally as one of the posters mentioned... bell the motor windings out then ensure you are getting full voltage through the DOL to the motor. Good luck. Please let us know what you find.

.

 

[Steve1412]

That is Star
Delta there will 3 links

I know thats why I said 'the links will be across two terminals each!!!'

 

[sheriff78]

I have belled the windings out and they all came out equal at 4.6 ohms. The motor is currently wired in delta. I think the customer has given me so duff information which has confused things.

I was told that it used to run faster until the last electrician came in

They forgot to mention that.

The motor has been removed and rewound since then

also the fan unit is supposed to be cleaned regulary but this has not been carried out.

Could the problems with speed be that the load is to much for the motor.

The belts are to tight

maybe it was rewound differently to the original.

These are all things that would of been nice to know a little earlier

If the motor is daul voltage how would this be marked on the plate?

thanks

 

[silva.foxx]

If a dual voltage motor the plate would be similar to;

220-240/380-415v Y/D... so 220-240v ie. off a 1ph inverter would be connected in delta else 380-415v in star. 4.5 amps in delta. 2.6 amps in star.

.