UK 230Vac to 415Vac @ 10Hp

Folks I have a real need to provide a 3 phase ring for my workshop since the utility company want the guts of $30,000 (yes I have typed that right!) to supply 3 phase.

In the UK we get 230Vac @ 50Hz 1 phase only and all 3 phase stuff in UK runs on 415-440Vac.

I will have a total of 10Hp around the shop but will only run a single machine at any one time so the max single motor is 8Hp. These are all woodworking and metalworking machines with motors (no CNC stuff).

I am looking at both a Rotary and an Auto-transformer as viable options.

I have a number of transformers available and a few 3 phase motors around 5-10hp. I can step-up from 230Vac to 415Vac 1ph.

What do I need to provide a auto-start converter to provide the workshop ring at 3phase 415V 50Hz?

Can I scale up a US design?

George Shaw

Start with finding a single phase transformer that will boost your 230 volts to 415 to 440 Vac. I would get at least a 10 kva transformer and possibly a 15 kva transformer as you may want to oversize the RPC depending on how hard that 8 HP load is to start. What is the 8 HP load?

If you can not find an appropriate transformer, 2:1 transformers are commonly available and it can be combined with a buck/boost transfomer to drop the voltage from 460 volts into your range.

Then build a minimum 10HP RPC. The capacitors for start and run caps will be a little tricky as you may have to series some up to get the voltage rating required. But the good news is that you will only need about 1/3 the amount of capacitance as required for 230 volt/60 hz operation.

I do not believe the autotransformer convertor is a viable solution for multi load configuration as I believe that method must be tuned for the load it supplies.

Obviously the details are left out but this is the how I see the big picture.

Also check recent postings. More details for a step up three phase system were discussed within the last week.

"Can I scale up a US design?"

RPCs generally scale well, but the scale factor is not always a linear function of line voltage.

In fact, for capacitance it is a second order function of line voltage.

So, for a 415 volt RPC, the normal rules-of-thumb for capacitance are multiplied by (240/415)^2 = 0.33, while the minimum working voltage is multiplied by (415/240) = 1.73.

For a 10 HP 240 volt RPC, the caps, according to the ROT which was developed for 240 volts, would be 40, 80 and 120 µF (370 volts AC, oil-filled); and 1200 µF (250 volts AC, electrolytic).

However, for a 415 volt RPC, this would be 13.2, 26.4 and 42.9 µF (645 volts AC, oil-filled); and 429 µF (432 volts AC, electrolytic).

For caps with these unusual voltage ratings, you should consider using two identical caps in series, in order to double their working voltage. Two identical caps in series gives you double the maximum working voltage, while it also halves the effective capacitance.

So, applying that to the ROT which is adapted to 415 volts, you would require 2 x 26.4, 2 x 52.8 and 85.5 µF (370 volts AC, oil-filled); and 2 x 858 µF (250 volts AC, electrolytic).

As those capacitances are not integral values, select the next standard capacitance. But, always use identical capacitors in series, as otherwise the voltage will not divide equally across the two series-connected capacitors.

And to ensure good voltage sharing, and also to provide a "bleeder" for safety, place a 1,500 ohm, 5 watt wire-wound resistor across each capacitor.

George,

I think Bill Simmons response is right on target. The autotransformer converter is best suited to a single motor. It is tuned to that motor for full load but works fine below full load. In your application, voltages to the run cap would be in the 600-700v range for a 1500rpm (50 hz) motor. It would be quite a chore to build one, let alone one for each motor.

I have been building autotransformer converters for 20 years using standard dry transformers wired as autotransformers since I could get close to required voltages without a specially wound tapped autotransformer. All 240v 1ph to 240v 3ph. (0.5 hp to 5hp) I easily built one for each machine as I acquired them (one person hobby shop). I have not built one since reasonably priced VFD’s came along.

Autotransformer converters still would have a use for large hp machines that start under load. RPC’s are not very good at starting air compressors. For example if your shop had a 10hp RPC and you wanted to add a 10hp compressor, you would probably have to go with a 30hp idler or consider using an autotransformer for the compressor only.


Joe

Hello,
There is some information at the following web address...

http://www.integerspin.co.uk/convertor.html

I'm sure the person behind the site is also a member here.


J Grainger

if I had this problem I´m sure I would purchase somthing like this:
http://cgi.ebay.de/TOP-Stoeber-Frequenzumrichter-FDS-1040-B-TOP_W0QQitemZ200075711369QQihZ010QQcategoryZ65451QQrdZ1QQcmdZViewItem
Many smaller 3phase motors in europe are wound for 230V delta, or 400V wye. If you find a 230/400 V rating on the type plate you will need no step-up transformer, just a VFD, and set the bridges in the motor´s connection box correctly.(adjust safety breakers too)
How many km of power cable would they rig up for 30.000??? I used to think the power co.s in europe would all prefer 3phase supplys to keep their load balanced. Most any place here has 3phase, no matter the people use any motor at all, just for ovens, boilers and the like.
best regards, Dietrich

Thanks to all who have offered advice. I have "found" a 3ph 10hp motor to use as an idler and will probably experiment with driving it with a 110Vac 1phase 2hp motor (it's what I have lying around). My workshop has a 110Vac 1ph feed so powering the "pony" is no problem. I intend cutting the pony out of circuit when the speeds match @ 2980 (both motors are rated at 2980rpm) but leaving it physically connected to the idler. the idler will be fed with 415Vac to two legs from a transformer stepping up from 230Vac 1ph mains.