US Machine to Work on British 3 Phase

Sigh.

I was going to ask you a variety of questions about your mystery machine but I've come to realize that this will be another futile exercise. Instead of contacting the original designer/manufacturer of this mystery machine to see what if any modifications to this widget will allow it to function on a direct connection to the British power grid, you came to us with no information at all about this machine. You haven't even identified for us the type of machine you want to convert. It then dawned on me, you've already told us everything you understand about this machine. You know nothing.

If you feel like putting some effort into proving me wrong by telling us some technical information about this machine then many here will try to help you. Right now I believe this will just be "pearls before swine" because I suspect you will understand our answers just as much as I understand what your machine does.

The original manufacture is no more. The machine has a 3 phase motor rated at 460v. This is controlled by a frequency inverter. At worst I can replace this with a European one . The control system has a few contactors which are designed to work on 60hz. through a step down transformer.Will these be ok on 50hz at the slightly lower voltage?

I have three options, one is to run it on the lower voltage and frequency, another is to get a step up transformer, and the other is to rip out all the electrics and start again. Obviously I want to get the machine running at the most reasonable cost, hence the original question.

Thanks,

Paul

Contactors and transformers designed for 60 Hz should be safe from harm and work OK if they operate at 50/60 times 60Hz voltage i.e. 460 x 50/60 = 383 volts 50 Hz. So 415V would be 8% high, on that reckoning. So a step-up transformer to get 460V 50Hz will over-run the control contactors/transformers dangerously. As J. Raef wrote, all the controls may run from a 120V 60Hz single phase supply (there might be a transfo to a lower voltage) - a swop to a 230/115V 50Hz transfo supply would easy - or you might be able to go the whole hog and drop the control supply to 24V for safety reasons.

I am assuming when you write 415V, you mean you have measured it as 415V , rather than it being labelled 415V (415V nominal could easily be 440V, unless fully loaded) - one good factor is that British supplies are being reduced from 415/240V nominal to 400/230V to fit a new european standard of 400/230V (you have probably already been reduced!). You can probably still depend on the old statutary +/-6% variation from nominal voltage.

Current ratings will still be the 60 Hz values. But contactors/transformers should not fail quickly at "8% high" [meaning they might last 1 year instead of 20 years] - you should have plenty of time to find if your equipment will function, to tell if it is worth further effort - like getting new contactors/transformer to reduce control voltages. But gadgets like delay timers might not work well at 80% voltage ["415V" goes low] even though they most likely work at 90%.

The inverters usually rectify incoming supply to DC before inverting back to AC - rectifiers care little about frequency - but you will get only 415/460 = 90% of design maximum voltage.

You have not indicated if the inverter serves primarily to reduce the motor speed below its "60 Hz motor input" value (say 1750 rev/min) or raise it to higher values. For lower speeds, the inverter reduces voltage in proportion to speed (so it has voltage to spare on the input side). At a lower speed, the motor current (hence its power input) has to be reduced a lot, because its cooling fan runs slower - essentially, the inverter has to handle less power. For higher speeds, the inverter has to increase voltage in proportion to speed (i.e. over 460V), if rated torque is to be maintained - and power input to inverter must increase to match the increased shaft power.

Running an induction motor at 90% of its rated voltage reduces its torque to 80% rated - so is the machine torque/speed over-rated for what you need, or would that be a problem? The probable effect is that you will not be able to get more than 80-90% of the design maximum speed without dropping below design torque. Running equipment below rated voltage basically reduces stress, so long as you do not exceed rated (60Hz) current.

But as J. Raef writes, one needs to know something about the equipment to minimise the risk of trying it at a different frequency/voltage - in order to identify the transformers and contactors which will be at risk (items like indicator lamp assemblies might have transformers in them).

Do you have any circuit or wiring diagrams or parts lists/motor make/type? Since you are the prospective buyer, pressure the supplier for that information before purchase, indicating that you need to assess the modification costs - if he does not have it, he is not a dependable seller (who would know that having the makers use and maintenance documents is a vital adjunct to a used machine).

Even if the original machine maker is kaput, the inverter maker may still be alive to get information e.g. about operation with 50Hz supply - he may have supplied a different model to suit 50Hz supplies. And if the contactor maker is still going, you can probably change coils, as J. Raef suggests.

It depends on the value of the machine itself to you, compared to possible cost of a new inverter or even motor etc. You have not mentioned any "CNC" controls, so I assume "control" is just a matter of getting the motor running at the right speed.

Thanks very much for all your comments.

It does not seem so bad after all.

The inverter is used to vary the speed of the machine from 0- max. The machine is normally used at about half speed, being ramped up to the set speed,run and then ramped down to a crawl and then stopped. I will change the control system for a 24v system (its only three contactors) and fit a monitored emergency stop system. There are no timers or cnc systems. I have just found out there is a 1.5hp motor driving a hydraulic pump. I know running at 50hz it will be slower,but will it be ok at the lower voltage. The pump is not used anywhere near its max. capacity.

Thanks again for your help,

Paul.

The numbers [in your original post] of 33 amps at 460V 3 phase gives a power of 33 x 460 x √3 = 26 kVA or something like 15 kW shaft power for a motor. A lot more than 1.5 h.p/1 kW shaft power you now indicate! Unless this 1.5 h.p. is another (auxiliary) motor.

In essentials, one can run a, say, 3600 rev/min 60 Hz motor run on 50 Hz at 3000 rev/min, so long as you reduce to 460 x 50/60 = 383 volts supply. That makes the flux in the iron the same as at 60 Hz, giving potentially the same torque as 60 Hz rating - but since you are now running at 3000 rev/min, shaft power is reduced in proportion 3000/3600. Also, full torque current stays the same as at 60 Hz - although the windings are sized for that, as I noted, the cooling fan is going slower - which might give an overheating problem. The voltage across insulation is reduced, so that's fine, and running at 3000 c.f. 3600 rev/min reduces mechanical stress.

Continuous rated motors are robust, typically they can be run from cold for 1 hour at 150% rating before insulation reaches maximum temperature. If you are running a continuous cycle and are worried, you could measure the winding resistance cold and hot to check the motor temperature.

Regarding the inverter, my concern would be that there is a 60 Hz mains-fed transformer feeding the control board. This would give less output voltage than design, but be running over nominal flux at 415V 50 Hz reducing life. It will not be big or expensive to replace with a 50 Hz one giving the right output voltage.

Hi,

yes the 1.5hp motor is a seperate motor driving a hydraulic pump.

Thanks for all your help,

Paul.