Phase converter problems

[dlt27]

Hi, thanks in advance to anyone who can help.
I have been asked to install a 22kw transwave phase converter. I have been told it needs a 120a single phase supply and it can run a 3 phase board supplying various 3 phase machines.
I phoned and asked what the size of cable would be needed for the outgoing 3 phase supply from the converter to the 3 phase board. All I was told was that the outgoing cable from the converter to the 3 phase board depended on the maximum load it would be supplying as there is no overloed protection in the converter.
However the converter comes with a 32a 5 pin commando socket attached.
As I haven't fitted one before I just wondered if anybody could give any advice?
I was told the machine would probably be ok on an 80a type c breaker for the supply and 25mm tails. I also asked if disconnection times would be met because I wasn't sure how converter would affect zs values. Again all I was told was that I was only responsible for single phase supply not the outgoing!
Can anyone explain in layman's terms how these converters generate 3 phase from single phase.
Thanks again.

 

[dlt27]

Am I right in thinking for supply 22000/230 =95.65 A =25mm2 cable and outgoing 3 phase 22000/ 400 x 1.732= 31.69A = 6mm. Thanks

 

[Pete999]

Hi, thanks in advance to anyone who can help.
I have been asked to install a 22kw transwave phase converter. I have been told it needs a 120a single phase supply and it can run a 3 phase board supplying various 3 phase machines.
I phoned and asked what the size of cable would be needed for the outgoing 3 phase supply from the converter to the 3 phase board. All I was told was that the outgoing cable from the converter to the 3 phase board depended on the maximum load it would be supplying as there is no overloed protection in the converter.
However the converter comes with a 32a 5 pin commando socket attached.
As I haven't fitted one before I just wondered if anybody could give any advice?
I was told the machine would probably be ok on an 80a type c breaker for the supply and 25mm tails. I also asked if disconnection times would be met because I wasn't sure how converter would affect zs values. Again all I was told was that I was only responsible for single phase supply not the outgoing!
Can anyone explain in layman's terms how these converters generate 3 phase from single phase.
Thanks again.

Are you an Electrician only your profile doesn't give much information.

 

[westward10]

Is this a static inverter, I would not have thought this suitable for supplying a dist board.

 

[Deleted member 105166]

@dlt27 - there's some simple "how it works" explanation here: http://www.powercapacitors.co.uk/wp...onverters_inverters_single_phase_supplies.pdf

 

[dlt27]

Thanks. Still not sure, are my calculations for cable sizes right. I have allowed unity for PF correction, should probably allow 0.85 being a motor....

 

[sparkdog]

Don't stick your test gear on the output. I had my loop tester fried by one.I don't think its a proper sine wave it produces.

 

[dlt27]

It's a rotary phase converter. The spec is it's a 22kw and on transwave website.
I just wanted to know if I was sizing the cables correctly as haven't done one before. Thanks

 

[dlt27]

Yes I have been an electrician for 15years, but still learning!!

 

[Lucien Nunes]

If it's a rotary, it will produce a passable sine wave and all calculations are as per normal supplies, although the tolerances on the output side perhaps wider than typical mains supplies and the loop impedance rather higher. It is a specially wound 3-phase machine that motors on one of its phases and generates the other two. Unlike a static converter, the rotational symmetry of the machine maintains a reasonably accurate phase relationship irrespective of load, so it doesn't require matching to particular loads.

Transwave reckon on 4A input per hp of load driven. A 22kW machine will run 30hp making the max input current 120A when the full capacity of the converter is used. Often, converters are deliberately overspecced to ensure reliable starting of large motors, in which case you might find that the total load is much less than 30hp and the maximum input much less than 120A, hence the comment about 80A. The converter does look like a motor as far as the single-phase supply is concerned.

When you have it running, I would be interested to know what the Zs is on the output side and whether it is significantly different between phases. It might also be non-linear, as short-circuit might demagnetise the machine and collapse the output voltage. In which case it might not be possible to trigger the magnetic tripping of MCBs on the load side over a moderate fraction of the converter rating.

 

[sparkdog]

Probably OK on test equipment then.
The one that fried my loop tester was a static transwave.

 

[dmxtothemax]

if you look at the pictures in the link ?
there are indeed rotary convertors !
basically its an single phase electric motor,
driving a three phase generator.

 

[dlt27]

Thank you Lucien nunes much appreciated.
Could I overload an mcb to check it trips ok on the 3 phase board otherwise there will be no protection to the individual machines/ cables.
I will carry out all tests when installed and report back. Coould you explain what you mean by non linear (sorry I'm just an install electrician and only know he basics about motors). Thanks gain

 

[dlt27]

Just found out about non linear loads, however is there any way to test to see if it's non linear. Thank you

 

[Lucien Nunes]

I think you might have misunderstood my comment about non-linearity, which was rather a side issue about the loop impedance possibly not being a true impedance where I=V/Z for likely values of fault current. It doesn't relate to the load, so don't worry about that.

there are indeed rotary convertors !
basically its an single phase electric motor,
driving a three phase generator.

Not quite. A motor driving a generator is called... a motor-generator! A rotary converter is different; it's a single machine that is neither motor nor generator, with all the necessary windings operating within one magnetic circuit. Historically they were often used for converting AC to DC and vice versa, in which case they had sliprings and a commutator on the same armature. For this application, in fact an ordinary 3-phase motor can be used as a converter, but it has to be oversized and does not do as good a job as the custom-designed Transwave. Motor-generators are more versatile than rotary converters, but they are larger and less efficient, because all the power has to be converted to mechanical and back to electrical.

 

[dlt27]

Thanks again lucien.