Using 50 hz rated engines in 60 hz countries 2

[pmatos]

Hello everyone,

First of all, if this is not the correct way to ask this question, my apologies to all.

I´m not an electrical engineer, however i´m tasked with a feasability study, for the instalation of a production line, wich is currently installed in Europe, to a South American country.

One question that has poped is about the electrical current supply in the destination country, and wether the line, in it´s current condition, will be able to operate, without major alterations, on the destination country, with the different AC current specifications.

Not being an expert, my first thought was, no, it won´t, but after reading a bit, i became more confused, therefore my question.

1 - Current line location: Europe, power supply 3 phase 400 v, 50 hz
AC. About 85% of all of the line´s motors are controlled via
VFD´s, wich of course, are wired to receive imput 400v. Most of
the motors are wired (saw the plates) dual-rated, 50 hz and 60 hz,
but some are 50hz rated only. Motors range from 0,5 HP to 20 HP.

2 - Destination country: information about AC power supply sketchy,
but AFAIK is 3 phase 240 v, 60 hz.

Question: suposing the VFD´s can take 240V, 60hz, or if they are replaced with suitable VFD, can the line, and it´s motors run safely??
Or will we have to scrap entire range of motors and VFD?

Once again, sorry if the question is too generic.
Will apreciate any imput.

Best regards to all

 

[waross]

The motors will run on the VFDs. The VFDs may work on either 50 Hz or 60 Hz.
As a general rule, 50 Hz motors will work well on 60 Hz with the following caveats:
The voltage should be increased in the ratio of 60/50.
The motors will run faster in the ratio of 60/50 but the torque will stay about the same.
This applies to the motors only. The characteristics of some loads are such that they demand greater torque at increased speeds. A 50 Hz motor may often be used at 60 Hz for these loads, but it must be larger than the motor required at 50 Hz.
Centrifugal pumps are not suitable candidates for conversion to 60Hz unless the motor size is increased.
But, with a VFD, the maximum frequency may be set to 50 Hz and all will be well.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[cranky108]

As far as the VFD's and 240 V, a transformer can be used to boost the voltage to 400 V. If that is what you want.
Depending on the size, and assuming small, these are widely available, with different taps for a fine adjustment.

As said above (in a different way) at 60 Hz, the base speed is some divisable of two from 3600 rpm. Where at 50 Hz the base speed is 3000 rpm.

And to confuse things, many motors are rated at a slightly lower voltage than the expected source. Example: a 440 V motor is intended to operate at 480 V source. The assumption is there is some voltage loss in the cables. At least in the US it is that way.

 

[waross]

Sorry, I missed the 240 Volt issue. I agree with cranky108's transformer suggestion. One suitable transformer may service several VFDs.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[pmatos]

Thanks for all the answers, you guys cleared most of my doubts.

So, i can either go with the VFD´s suitable for the current available ( more expensive i think, more units to replace), or in alternative, install a power transformer from 3-phase 240 v 60 hz to 3-phase 400V 50 hz, and power the existing VFD, thus no more changes necessary, correct?

As for the issue of rpm and torque, resulting from change from 50 hz to 60 hz, since most of the motors are VFD controled, that will not matter much, or am i assuming this wrongly?

Btw power installed at the moment is about 50 kVA @100 amps.Any recomendations about power transformers for this capacity?

 

[SceneryDriver]

pmatos,
You got it almost correct in your last post; you can and should install a power transformer of appropriate kVA to supply 400v to your VFD controlled motors. Understand though, that the transformer will give you 400vac at 60Hz. There is NO frequency conversion within the transformer.

Your VFD's will not care if fed 50Hz or 60Hz power, as long as the voltage is within their tolerance range. The VFD's convert the incoming power to DC and then synthesize the AC waveform sent to the motors; incoming line frequency has no relationship to VFD output frequency.

Your non-VFD controlled motors will run at 6/5 of the speed they ran at on 50Hz. As written about by others above, this may or may not be an issue for you. If it is an issue, you may need to place VFD's on those motors or change gearing to compensate for the increased speed. See Waross's post above for a great description.


-SceneryDriver

 

[cranky108]

If your other motors are small, it may be easy to change them with a 60 Hz motor. Some of this may depend on the equipment they are driving. Or just reduce the voltage, if the speed is not criticle.

 

[GuntherA]

may another solution be to use a motor-generator set to do both the voltage and frequency conversion and drive the whole line at it's european supply frequency and voltage?

 

[cranky108]

An MG set may not work that well at 60 Hz to 50 Hz conversion. There are not many speeds that are common between the two. A sudo conversion is possible with an induction motor at 60 Hz and generator at 50 Hz but the frequency won't be very exact.

The VFD's are a better option.

 

[pmatos]

Thanks again to all for the help! special thanks to cranky108,scenerydriver and waross.

Gunther, the generator alternative was and still is being considered due to the location, and local current availability restraints, but it´s a stop gap measure, not a long term viable solution, due to costs.

In short, and if i understood all correctly, the best solution would be:

1 - current available: 3 phase 220v 60 hz
2 - instalation of a power trasnformer to beef up voltage up to +- 3 phase 400v 60 hz
3 - feed VFD with this current, since it´s in their voltage range, altough the frequency is 60 hz. the VFD output will then drive the
motors at 50 hz, wich is theirr output frequency. Problem solved!!!
4 - motors not run trough VFD, can be fed the current from the PT, but will run at higher speed. This will not be a problem, because these
motors are only a small quantity from the total, and their use is not constant, only ocasional to rectify other elements of line, i.e.,
they function a few seconds each use. velocity increase in their use, and with the gearing used, isn´t critical.

Only thing left is to find a suitable supplier of power transformer in the voltage range and capacity required. Perhaps a local one, or from a somewhat nearby country, such as the US.

Best regards everyone

 

[waross]

As a final reality check:
Compare the cost of a suitable transformer and 480 volt VFDs with the cost of suitable 240 Volt VFDs.
My gut feel is that the transformer and 480 Volt VFDs will come in cheaper, but in smaller sizes I may be mistaken.

Bill
--------------------
"Why not the best?"
Jimmy Carter