American electricity in Australia

[tek9]

We got a call from an old customer with a machine shop who had been a customer of my father,now his son runs the place.Motor burned out on a lathe,he had it rewound and a local electrician said the voltages were all wrong,motor would burn out.My daughter had a look, agreed,said the voltages to ground should be,120,or 208 phase to phase,she found 120 2 legs,208 1 leg,was puzzled,i told her,that's a center tapped delta,must be an m/g set somewhere,sure was,told her it's a high leg delta,just wire it up and it'll be ok,she did that,it worked,but slowed drastically under load,cause,one HRC fuse open,causing single phasing,this must be almost extinct in the US now,any thoughts on how this system developed?

 

[GoldDigger]

We got a call from an old customer with a machine shop who had been a customer of my father,now his son runs the place.Motor burned out on a lathe,he had it rewound and a local electrician said the voltages were all wrong,motor would burn out.My daughter had a look, agreed,said the voltages to ground should be,120,or 208 phase to phase,she found 120 2 legs,208 1 leg,was puzzled,i told her,that's a center tapped delta,must be an m/g set somewhere,sure was,told her it's a high leg delta,just wire it up and it'll be ok,she did that,it worked,but slowed drastically under load,cause,one HRC fuse open,causing single phasing,this must be almost extinct in the US now,any thoughts on how this system developed?

What I have heard is that it may have started, at least in residential use, from a need to add a three phase motor for air conditioning to an environment where all of the other loads were 120 or 240.
For non-residential, I would say that the motivation was that incandescent light bulbs were available cheaply in 120 volt while motor loads needed 240 three phase. Providing three phase with a large center tapped pot on one phase and either one or two smaller straight 240V pots to complete the three phase supply seems to be a natural progression too.

Basically, both of them derive from the presence of 120/240 single phase 3-wire in the US from the early days forward.

On the other question of why the motor bogged down, perhaps the motor load was too much for the capacity of the smaller single pot (if an open delta) leading to poor voltage regulation and excess current on the high leg conductor. The typical high leg delta is provisioned by POCO based on the assumption that the three phase load will be relatively small compared to the 120/240 load.

 

[tek9]

Saw this in America when I worked there,often saw a large single phase 3 wire transformer,and a small,stinger or parasite transformer,as POCO guys called them.

 

[Besoeker]

On the other question of why the motor bogged down, perhaps the motor load was too much for the capacity of the smaller single pot (if an open delta) leading to poor voltage regulation and excess current on the high leg conductor. The typical high leg delta is provisioned by POCO based on the assumption that the three phase load will be relatively small compared to the 120/240 load.

Or that Ozland is 50Hz?

 

[GoldDigger]

Or that Ozland is 50Hz?

:thumbsup:
Although that by itself does not explain why the fuse in the high leg went first. (If that actually is a pattern rather than a random occurrence.)

 

[Besoeker]

:thumbsup:
Although that by itself does not explain why the fuse in the high leg went first. (If that actually is a pattern rather than a random occurrence.)

If it emulates UK practice there would be no high leg.

 

[GoldDigger]

If it emulates UK practice there would be no high leg.

True, but apparently it does not. Maybe an American engineer or electrician cobbled something together.
As the OP stated: "...she found 120 2 legs,208 1 leg,...."

 

[tek9]

Or that Ozland is 50Hz?

The service was 11kV 4 x2MVa Padmounts,1 spare,load was relatively light,but the factory was wired by the yanks during the war with 50Hz and 60Hz stuff,120 volts required for lights,outlets,british round 2 and 3 pin,Aussie Crowsfoot and yank 2 pins,roungd ground pin,all in thick walled ceramic lined RMC.They had this stamping press that had Ward Leonard Control,after about half hr,synchronous drive motor started hunting,caused by leaky 200v paper caps in the tube control system,we replaced them all with 1500v types used in tv sweep circuits,and 1 6A8gt tube.Love that old tube stuff,factory with it's frankenstien room,my daughter was not happy with the sign,qualified MEN only,and,don't work here drunk with all this stuff,as not only will it kill you,but as you can see it will hurt the whole time youre dying,pointing to a picture of a shapely young witch,landing on the top caps of 2 RF transmitting tubes,black cat jumping out of his skin.

 

[GoldDigger]

Love that old tube stuff,factory with it's frankenstien room,my daughter was not happy with the sign,qualified MEN only,and,don't work here drunk with all this stuff,as not only will it kill you,but as you can see it will hurt the whole time youre dying,pointing to a picture of a shapely young witch,landing on the top caps of 2 RF transmitting tubes,black cat jumping out of his skin.

The "good old days"????

 

[cadpoint]

Maybe the motor is like some run on sentences, it could take it till it went poof!

 

[Besoeker]

The service was 11kV 4 x2MVa Padmounts,1 spare,load was relatively light,but the factory was wired by the yanks during the war with 50Hz and 60Hz stuff

How is the 60Hz obtained?

 

[kwired]

We got a call from an old customer with a machine shop who had been a customer of my father,now his son runs the place.Motor burned out on a lathe,he had it rewound and a local electrician said the voltages were all wrong,motor would burn out.My daughter had a look, agreed,said the voltages to ground should be,120,or 208 phase to phase,she found 120 2 legs,208 1 leg,was puzzled,i told her,that's a center tapped delta,must be an m/g set somewhere,sure was,told her it's a high leg delta,just wire it up and it'll be ok,she did that,it worked,but slowed drastically under load,cause,one HRC fuse open,causing single phasing,this must be almost extinct in the US now,any thoughts on how this system developed?

Unless the motor has a neutral connection, all it cares about is line to line voltage, which If it is 240 and they only rewound for 208 there could be some problem.

One advantage of a Delta three phase system is the ability to supply with "open delta" configuration and save costs on conductors and transformers. May seem pointless in cities but in rural areas needing a fourth conductor in the distribution does become a cost issue, especially if the load doesn't justify it.

 

[rt66electric]

6- wire system

6- wire system

I have demo'ed a six-wire system

same building OLD machine shop.

It had 3-wire 240 delta w/ meter, and, a seperate, 120/240 3-wire w/meter.

 

[kwired]

I have demo'ed a six-wire system

same building OLD machine shop.

It had 3-wire 240 delta w/ meter, and, a seperate, 120/240 3-wire w/meter.

Most likely was either 2 separate systems or two different feeds from the same system.

 

[mbrooke]

If it emulates UK practice there would be no high leg.

Has the UK ever used high leg deltas or ungrounded deltas? Seems like something only done in the states.

 

[Besoeker]

Has the UK ever used high leg deltas or ungrounded deltas? Seems like something only done in the states.

As far as I'm aware, not for LV distribution.

I have used ungrounded delta transformers as part of a 12 or 24-pulse system for variable speed drives or rectifiers. But these were dedicated units.

 

[AdrianWint]

The LV distribution is exclusively 400/230 Wye. That is the ONLY LV service available anywhere in the UK.

Delta is used on the HV & EHV transmission system and all the way down to 11kV to avoid the cost of the fourth wire but these circuits tend to be configured a WYE source (centre tap grounded - to allow ground fault detection) & delta sink.

Adrian

 

[mbrooke]

The LV distribution is exclusively 400/230 Wye. That is the ONLY LV service available anywhere in the UK.

Delta is used on the HV & EHV transmission system and all the way down to 11kV to avoid the cost of the fourth wire but these circuits tend to be configured a WYE source (centre tap grounded - to allow ground fault detection) & delta sink.

Adrian

Don't industrial customers get 415/720 or 577/1000Y? I would imagine that's to low for major customers.

 

[Besoeker]

Don't industrial customers get 415/720 or 577/1000Y? I would imagine that's to low for major customers.

None that I know of.
Commercial and light industrial is served by 400/230V as a rule.
Larger industrial concerns get 11kV which, for large machines, is sometimes used directly. We have supplied a number of larger variable speed drives operating directly from 11kV.
But the great majority are fed from 400V/3ph/50.

 

[kwired]

None that I know of.
Commercial and light industrial is served by 400/230V as a rule.
Larger industrial concerns get 11kV which, for large machines, is sometimes used directly. We have supplied a number of larger variable speed drives operating directly from 11kV.
But the great majority are fed from 400V/3ph/50.

And from what I understand dwellings or other "light commercial" applications only needing single phase supply will generally be supplied by one phase and neutral conductor from a 400/230 wye system.

Now maybe if you only need single phase in an isolated area they maybe supply you from a simple two wire single phase transformer?