Hi there,
Can anyone help!
I Would like to run a 7.5kw motor D.O.L.
On the name plate it shows two lots of information 50Hz 400v/690v Delta/Star 14.2/8.3A And below it showing
380-420/660-725v Delta/Star 15.0-14.5/8.7-8.4A

the motor drives a screw feed MOVING CEMENT to a height of 15ft. I was thinking of starting the motor using a reversing starter so I could reverse the screw feed if it became jammed.

Any Idears please!

Cheers Terry.

What is your power supply?

This is fairly straight forward however as a starting point and to facilitate equipment selection your 3-phase supply and control voltages must be known.

Schematics for reversing DOL starters are readilly available from many of the web sites owned by switchgear suppliers such as Sprecher + Schuh, Allen Bradley, ABB, Siemens, Moeller etc etc.

Post your supply information here together with a list of your preferred switchgear suppliers and we'll do our best to assist further.

Regards,
GGOSS

[quote name='jraef' date='May 15 2007, 10:42 PM' post='6068']
What is your power supply?[quote]
HI Jraf.
supply voltage is 3 phase 415v
cheers.

[quote name='GGOSS' date='May 16 2007, 07:37 AM' post='6070']
This is fairly straight forward however as a starting point and to facilitate equipment selection your 3-phase supply and control voltages must be known.

Schematics for reversing DOL starters are readilly available from many of the web sites owned by switchgear suppliers such as Sprecher + Schuh, Allen Bradley, ABB, Siemens, Moeller etc etc.

Post your supply information here together with a list of your preferred switchgear suppliers and we'll do our best to assist further.

Regards,
GGOSS

HI GGOSS

Im fine with the control side of things,
my concern is connecting of the motor. Do I connect it in delta( 380-420v ) Supply voltage is 415v 50 Hz.
Also would I be right in wanting to start the motor D.O.L. bearing inmind the motor is 7.5Kw and I have always thought motors above 4Kw cannot be started D.O.L.

Regards
Clarin

Hello Clarin

Motors much larger than 7.5KW are started DOL all the time, but there can be local regulations that limit the maximum size that you can start DOL. The problem is related to the start current and what you are allowed to draw.
You must connect the motor as it is designed to be connected. If it is designed to be delta connected at 415 volts (most common) then that is how you connect it. The actual reversal is achieved by reversing two phases that go to the motor.

Be careful with the control. Use mechanically interlocked contactors for best security, but make sure that both can not close at the same time, and that there is a delay between opening one, and closing the other.

If there is a problem with DOL start in your locality, add a simple soft starter between the reversing DOL starter and the motor.

Best regards,

HI Marke,
Thank you for your comments and information.
I have been running the motor connected in Delta D.O.L. For a couple of days now all seems well. I was a bit concerned I was using a d.o.l. starter and not a star/delta starter given the size of motor.

Thanks again!
Clarin.

I am not a fan of star delta starters. In many cases, they are used to get past the regulations, but do more damage than DOL.
The requirement for star delta starters is really to reduce the start current and this only works provided that the motor gets to full speed before the change over, and then only if there is a open period of up to half a second between the star and delta phase. In reality, this rarely happens, so the star delta starter changes over at part speed, draws almost LRC and has a massive current and torque transient at the transition.
- I refer to the star delta starter as the political starter. The reduced voltage starter that complies with the regulations, but does more damage than without it!!

Best regards,

HI THERE

I need to start a 37kw motor 380v DOL
The RPM is 1400 and has negligable load
Would this be an acceptable method and if so what size overload should be used?

Please advise

Hello Clive

There should not be a problem starting a 37KW motor DOL as far as the motor is concerned, but there could be a problem with the supply or your local regulations.
The motor will draw a very high overload current for the duration of the start. This overload can be in the order of 600% to 900% of the rated current of the motor and on a weak supply can cause excessive voltage drop.
Some local supply authorities do not allow DOL starting on their networks because the voltage drop during start can affect other equipment. You will need to ensure that you supply is strong enough to allow for a DOL start, and that there are no regulations preventing you from using it.

Standard motor overloads are designed for DOL starting so you can use any standard motor overload. If the load was a high inertia, than the start current would stay high for longer as the motor would take longer to start. In that case, you may need to use a slower overload relay.

Best regards,

Hi Marke

Thanks kindly for that info - Great help!

Clive

If local regulations have no restriction and your supply is enough, DOL starter is much better than Star Delta Starter. Instead of bimetal termal overload, try to use CT type overload protector which can adjust both starting delay time and amp adjustment.

Regards

Dr Win

Hi Dr Win

Thanks kindly for that info

Clive

Hi Clive,

A softstater is the best bet for a 37kw motor.

It ramps the speed and hence there is no electrical strain as well as much lesser mechanical strain.

Softstarters used to be costly, but nowadays the prices are reasonable.

PS: I am not working in any softstarter manufacturing company.

Good luck.