3 phase motor connection type???

[Knobhead]

I’ve worked on 660V & 550V systems. Where you are just dealing with motors and not bothered about Fred needing 230V for his kettle, higher voltages mean smaller cables. OK if you needed 230V you had to put in a small transformer.

Every plant I worked on as an apprentice was 550V. I was involved with installing a new plant, it had got this weird voltage 433V! Some of the old guys didn’t know what to make of it, 230V without a transformer??? Just to add to the fun, after a few years the systems expanded so some areas had both 433 & 550 side by side.

Think about it, a 200A feed at:
433V = 150KVA
550V = 190KVA
660V = 230KVA
They all use the same grade of cable

 

[micknew]

This thread has been puzzling me.
Just realised that the live rail on railway is said to be 690V, so most of us will never come across a motor with that spec.
Also 230V 3 phase is a continental system.
A dual voltage 3 phase motor rated at 230V 3 phase would have to be connected in delta and at 400V would have to be connected in star.

 

[pmac10]

Tony, were those voltages (550.660V), at the secondary of an 11kv transformer supplying your site/plant? did it have to be further transformed to 400v? now i'm confused (easily achievable)

 

[Knobhead]

This thread has been puzzling me.
Just realised that the live rail on railway is said to be 690V, so most of us will never come across a motor with that spec.
Also 230V 3 phase is a continental system.
A dual voltage 3 phase motor rated at 230V 3 phase would have to be connected in delta and at 400V would have to be connected in star.

The 3rd rail is DC.
230V is as you say a continental / American system so dual voltage motors quite neatly get around the problem.

 

[Knobhead]

Tony, were those voltages (550.660V), at the secondary of an 11kv transformer supplying your site/plant? did it have to be further transformed to 400v? now i'm confused (easily achievable)

Yes the supplies were from 11KV transformers. Nearly 50 of them, ranging from 250KVA to 1800KVA fed from 14 of our own substations.

Just to confuse you even more if say we needed 230V for an office block we would install a 550/230 3Ph transformer. 230 between phases, 133 to the star point.

When we started to install 433V transformers I thought it was great. A neutral that you could use, no faffing about with 230V transformers. The old boys didn’t like it, they just couldn’t get their heads around it. One of the old duffers installed a new 230V board, it had got a neutral bar instead of two banks of fuses! What does he do? Connects phase to the bar and neutral to the fuses! Then have a guess which fool went to connect a new load to the board, I was flat on my back after touching the neutral!

 

[LEO]

Ha ha, sorry Silva...

Thanks for the info guys.

So where would I get the 690v from to connect it in star? If it's a 3 phase 400v supply, or I take it this would be the incorrect type of motor or the Delta config would suit at 400v??

In a application where the motor had to be connected in star at say 690v as stated on the id plate, where/how would you achieve this?

Sorry to go on but would like to know as much as poss.

Any info guys? Thanks again.

Cheers, LEO.

 

[Knobhead]

660V is used in some US/Canada industrial sites along with 433V. The standard 110/220V domestic supplies would be useless in Industry. As I said in an earlier post the higher the voltage the more power you can ram down a cable.

It’s a pain in the a*se working on a site with 2 different voltages. The works I referred to earlier had another wobbly to throw at you, on the 433V system the phase rotation was RYB, 550V was RBY.

It won’t be the first time I’ve gone to a shift hand over job to find a motor fitted just needing connecting. Check the name plate, right frame size, right RPM, WRONG bloody votage!

 

[LEO]

Cheers guys for your info + help to clear this up.

Excellent forum,

LEO.

 

[vaughant]

We still use some 500 volt stuff where I work,but they are trying to phase it out(no pun intended).If your involved with DC drives at all CEO you can get some mad voltages across them,try 700v DC at the output cables.I remember as someone who should have really known better clipping a cover back onto a siemens drive unit where there were small busbars linking them all together.I was explaining to the machinist how he shouldnt really run it at those voltages without these covers on and the dangers involved so I clipped the cover back while the drive was at it's heaviest load and the metal(poor idea) bit of cable to stop the thing falling off touched the busbar!!Lucky for me I was touching the plastic bit,a big bang and flash of blue/white light and the m/c cut out.I went to explain to the guy that this is a good example of why the covers are required and he had run 30metres away hiding behind a metal bin shaking!!!!Oh well,at least he experienced 1st hand the power of DC drives.I always switched machines off to put covers on after that.They hold voltage for a while as well,it said up to 4 minutes on the name plate which was maybe a touch extreme but we still had 90v DC there after 3 mins once.That would certainly hurt you.