Star Delta Starter

..."when you connect the delta connection motor into a star connection mode, the effective per phase voltage is reduced to (1/1.732) times hence to maintain the torque/speed it will draw 1.732 times higher current.

hence the motor will continue to run for some days/weeks or months depending upon your ambient and other cooling factors. but after a certain period, its winding will definitely burnt out"...

http://control.com/thread/1447398263

Is this part of an energy saving scheme?

There are companies peddling units that switch from delta to star to save energy. They don’t work, the motor will take the power it needs to meet the required mechanical load.

Nice reply .it covers all required points

I don't think that's right. I agree with SolarEagle's #1, if it's at rated load current is √3 x higher in star.

As you say, he'll only get away with it if it's lightly loaded, any advantages not worth the trouble IMO. But why 33%? I'd have thought it's OK at load 1/√3 = 58%, which needs current = nominal FLC (in delta).

incidentally, in spite of the thread title, he doesn't seem to be asking about star-delta starting, just running in star or delta.

"what will happen if the motor meant for delta connection is made to run in star for longer periods. whether motor will fail or continue to run."

From the thread what I understand is that the motor is designed to run in Delta for the perticular load and the motor is starting with full load. The starting current will be high and is to be limited , hence the motor is designed to start in Star and run in Delta. So the motor will faill if it is continue to run in Star for prolonged time.

OK but if it's to run in delta it either uses DOL delta or star/delta. If it's to run in star it uses DOL star. But it doesn't alter the answer to OP's question.

He didn't say it runs at rated load. Concensus is it will (maybe) operate in star at reduced load.

This concept is not promoted. Yes you are right we had some pre indepenedence (Pre 1947) motors of British make in some of the old Factories (especially Ordnance Factories which produced Military equipment for British Army) which were highly over rated. This is a story of 1960 and early 70. But after 1970 India started producing Machinery and Electrical Motors and Electrical equipment in a big way and after 1990 due to Industrial development we had shortage of Electricity required more than production capacity and gone on a big way for energy conservation and management. India is now producing energy saving 5 star rated electrical equipment which are now used in almost all modern equipment and machinery. Now in India the basic consideration of new installation is minimum wastage of energy .Now we in India cannot even think of installing over rated motors for any utility as the value engineering deparment will not agree to it .We are facing shortage of Electricity compared to production Capacity. To overcome the shortage The government of India has an ambitious target of generating 100GW of solar power by 2021-2022 under National Solar Mission.

The only reason I even know this is because I have seen countless posts from people in India asking this exact same question over and over throughout the past 10 years or so. I have challenged the statement of people who pursue this issue, thinking that it was folly, only to have them point out to me that it was official government policy in their district and very commonly done for the reasons I just repeated. I am not there so I can't say it's true from first hand knowledge, but this thread posting was not an isolated instance. I know very well that India is working hard to upgrade infrastructure and equipment, but as I'm sure you know, it's a big place with a lot of diversity, so I have a feeling that, policy or not, this thought experiment is persisting.

You are right India is a very large country and there are many under developed areas. There can be many Engineers and technicians who may not be aware of the policies. But still the Government policy is what exactly I said and all officials are bound to follow it (Government policy is http://www.powermin.nic.in/en/content/energy-efficiency )

All Government offices and Private organizations, Government Factories and Private Factories (Small and large), Electricity Boards are properly educated to comply with Government policy. I can say it with authority because I was a part of the team for the implementation of Energy conservation and Management.

The motor will continue to run .As an Engineer you must know why a star delta starter is provided . The motor is supposed to start in star and must run in delta.So why the starter will not go from star to delta must be notised by the operator as the motor will not be able to carry the full load and will be overloaded. To avoid burning of the motor corrective repair should be carried out. You must know the reason why the starter has not gone from star to delta after the set time. .

Star and Delta connections are not only for starting purposes but primarily these connections are determined by the supply voltage.

Most of our motors which are under 4kw motors can be connected in star or delta depending on the supply voltage, 400V =star and 230V= delta. The phase voltage on both examples are the same ,230V.

Essentially you are decreasing the magnetizing current of the motor by changing the V/Hz ratio, thus less torque. The motor will not fail if you set the protection correctly.

Why will you do this?

Just use the correct connections, set the overload as per nameplate, and you will have nothing to worry about.

Thank you all for such wonderful discussion. I got my answer.