Running of a 500V Compressor Motor On 400V

its going to cook the motor, stop being an idiot and install the proper t-former

How about the frequency? What do you have? What is the motor designed for?

500V is used in mines and quarries

I'm trying to get my head around a star-delta DC motor, to say nothing of the OP's motor.

Puzzeled too. A DC motor on the compressor! All the ones I have checked out ar 400V AC motors. Is this some special application or a home work question or a misread spec plate?

Dear Mr.JRaef,

It is true that 500 Volts is not standard, but one company formed about 200 years back in London, still ha s branch and working in India, it is using still 500 Volts.

DHAYANANDHAN.S

When you start upon a star, makes no difference where you are, if your voltage is too low, the smoke comes out.

Jiminy Cricket.

• I'm trying to get my head around a star-delta DC motor, to say nothing of the OP's motor.

D'oh! <slaps forehead>

Missed the "star-delta" thing. Damn these eyes...

This sounds like the rating in star mode, the delta mode probably 380v....we need complete info off starter and motor....

Indeed while 400 V 50 Hz and, for some larger more recent drives, 690 V 50 Hz, are the most common 3-phase low voltages in continental Europe, 500 V 50 Hz 3-phase is still used in some large industrial plants (e.g. cement and chemical plants). As they can't replace thousands of motors easily, there's now typically a mix of 500 V 50 Hz and more recent 400 V 50 Hz as well as in some cases 690 V 50 Hz in the same plant. In some countries the same plugs can be either 400 V or 500 V (mostly legacy connector systems). 500 V 50 Hz is phased out where possible but will likely coexist with 400 V 50 Hz for quite some time.

We had an old paper making machine got from Germany. The voltage of this machine was 500V 50HZ and so the compressor is also of 500V 50HZ and has a star delta starter. The machine has become right-off and the compressor is spare. Designing a step up transformer from 400 to 500V is a secondary concern.

Every time comments by Tornado are very nice.

When I started quarries 40+ years ago all our plants were on 525V. Later as new kit came in the plants ran with a mixture of 525V and 433V.

We did toy with the idea of converting them to all 433V, we gave that idea up as an expensive pipe dream. The shear cost of 1500 new motors never mind the new larger cabling consigned the idea to the bin.

I was involved in the first dual voltage system so it became 2^nd nature knowing what was on each voltage.

The OP mentioned that this motor was from a printing plant. The last printing plant I worked on again had two systems. This time 433V and 380V. The plant services being to UK specifications, the presses to Belgian and German.

The foundry I worked at used 660V and 433V.

It's not all that unusual in old industries for dual voltages to exist side by side. It's just a bit mind blowing when you first come across it.

500V motor working at 400V (80% of 500V) will be able to give ~64% torque.

If this is good enough for the compressor, I don't think the motor will have any problem.

The 'load' is caused by the compressor screw element. This relates directly to the speed and pressure. The motor is matched to deliver the power at full load.

Running at 400 volts will reduce the power to 64% of 75kw = 48kw (it's to do with V²). The motor will therefore become overloaded when trying to deliver little more than half the rated airflow.

The screw element needs to run at half speed to avoid overload, or at half rated pressure.

The latter easy to achieve by setting the max pressure controls, but not very useful because you probably need the full air pressure for your pneumatic machines to work properly.

Halving the speed of the screw by changing pulley wheels would be somewhat easier if belt driving, but your compressor is probable direct coupled through a gearbox, making it impossible.

If you do not reduce the screw speed or pressure, then the motor will try to match the air consumption, and anything much over half load will cause the motor to 'slow down' pulling more current than designed, and soon to overheat.

For testing purposes, ie, running up to speed and pressure, should present no problems, but as soon as air is consumed, over which you have little control (I guess) then things will start to go wrong if unattended.

If you Google the "Atlas Copco GA808" you will find several descriptions rating it at 400v.

Dear Mr.signode,

The motor will draw more current and windings will get over heated. The power at 400 V will be (400/500)^2, to that of power at 500 V, and hence (400/500)^2 = (0.8)^2 = 0.64 and hence the current drawn will be 1/(0.64) = 1.5 Times more and there fore winding will get over heated/burnt.

DHAYANANDHAN.S

Obviously ignored by many so I shall point this out. How on earth can he test this compressor on load, and obtain meaningful results of any use if the the required voltage is 500V? Torque reduction or not, his test is totally without foundation and any result, has no value.

It is an old compressor. See:

http://www.machinerypark.com/stationary-compressor-atlas-copco-ga-808-used-be-8790

It seems to me the rated voltage is 400 V [it is not 500V!] 50 Hz.

It could be your network rated is 480 V 60 Hz. Then it may work fine.

Dear Signode, Can we request for the nameplate photograph...