Surely the 480Vac system has nothing to do with the standard 208Vac one ?

In South Africa we normally use a 400Vac 3-phase system for the 230Vac distribution to single phase equipment. Mining industry however often uses 525Vac. There seems to be no mathematical relationship between our 525Vac and 400Vac or the USA's 480Vac and 208Vac !

Granted that the square root of 3 times your 208Vac is equal to 120Vac and similarly our 400Vac equals 230Vac but where does the 480Vac (USA) and 525Vac (Mining) voltages come from ?

 

Hi,

Usually from a transformer.

Regards,

Jacek Dobrowolski, M. Sc. E.E.
Software Eng.

 

Graham,

480 VAC 3-phase "Y" systems are widespread in the USA. Motor currents are lower than on 208 VAC systems and the 277 VAC "phase-to-neutral" is an very efficient voltage for flourescent lighting ballasts.

Zvi

 

In the US, 480 volts is a standard nominal three wire system voltage as specified by ANSI C84.1.

Regarding 525 volts, it may be a utilization voltage rating of equipment, that is a remnant of older standard system voltage of 550 volts.

A good reference for this type of information is IEEE "Red Book" - Electric Power Distribution, ANSI/IEEE Std 141-1986 or later.

 

The answer could be as simple as compensation for the anticipated long cable runs prevalent in mining with economical cable sizes.

Regards

cww

 

550V is common in power plants, because you get slightly more efficient motors, can get more horsepower for the size, and its still considered low voltage as long as it is less than 600V.

Maybe that's the same reason mines use 525V.

 

I believe that various voltages and frequencies came into common use due to historical accident. The mining industry was one of the early large scale users of electricity, and many mines built their own power plants. Since such systems operated in isolation, the voltages and frequencies chosen were arbitrary. Once a voltage or frequency came into extensive use in a particular industry, there would be great incentive to continue using for the sake of compatability with existing machinery.

We use 600VAC as the standard industrial voltage around here. This is still considered to be low voltage. I think you will find that the rules for classifying voltages were written to codify existing practice, rather than the reverse.

If you want an example of odd power systems, some ships used to (and perhaps some still do) use 120VDC rather than AC. They still used standard receptacles. A co-worker used to work on the lake freighters, and told me of the rather amusing story of someone plugging a radio into one of these outlets. The result was some horrible noises and a puff of smoke.

Standards often don't arise because anyone "planned" it that way or because they were "better". Often it is just because the less commonly used methods gradually fall out of use.

 

Michael is right-on.

Much of the oil-patch industry uses/used 830V... and yes, that value is sqrt(3) x 480V (ca).

Some time ago I presented a study that demonstrated considerable savings if a refinery's LV distribution system was 830V instead of 480V. The savings, of course, was related to copper reduction.

Regards, Phil Corso, PE Boca Raton, FL [[email protected]] ([email protected]) {[email protected]}

 

Well said Michael. If I may, I will amply on what you said below.


Michael Griffin wrote:
> I believe that various voltages and frequencies came into common use due to historical accident. The mining industry was one of the early large scale users of electricity, and many mines built their own power plants. Since such systems operated in isolation, the voltages and frequencies chosen were arbitrary. Once a voltage or frequency came into extensive use in a particular industry, there would be great incentive to continue using for the sake of compatability with existing machinery.
>
> We use 600VAC as the standard industrial voltage around here. This is still considered to be low voltage. I think you will find that the rules for classifying voltages were written to codify existing practice, rather than the reverse.
>
> If you want an example of odd power systems, some ships used to (and perhaps some still do) use 120VDC rather than AC. They still used standard receptacles. A co-worker used to work on the lake freighters, and told me of the rather amusing story of someone plugging a radio into one of these outlets. The result was some horrible noises and a puff of smoke.

In the first half of the last century is was very common for oil rigs, mines, motor schooners, and small ships to use 120 VDC. This was because they lacked dedicated power plants. Instead they had a generator that shared an engine, sometimes steam, with a windlass or ships propulsion. As these engines performed their windlass or propulsion tasks their RPM varied from 0 to thousands. If they used an alternator the frequency would vary way beyond limits. The DC voltage still varied but
within controllable limits. Sometimes they would float a 120 V battery to help stabilize the voltage and provide lighting when the engine was shut down.

Sometime in the 1930s a four tube set (plus rectifier) was designed for small table model radios. The filaments were designed for a the same current so they could be connected in series. With the rectifier operating stright off the line and seriesed filaments, no transformer was needed. In turn this meant the radio would operate off AC or DC.

The radios were sometimes referred to as "American Fives". RCA advertised theirs with an ocean liner in the background stating they would work anywhere. The great irony was these radios were not very sensitive and didn't work worth a damn unless they were close to the transmitter. This meant your ship board American Five only worked as long as you were in port. Oh yes, they you had to have them plugged in properly on DC. The plugs were not polarized and wouldn't work on -120VDC.

> Standards often don't arise because anyone "planned" it that way or because they were "better". Often it is just because the less commonly used methods gradually fall out of use.
>
> > 550V is common in power plants, because you get slightly more efficient
> > motors, can get more horsepower for the size, and its still considered low
> > voltage as long as it is less than 600V.
> >
> > Maybe that's the same reason mines use 525V.
> >
> > On November 6, 2003, Curt Wuollet wrote:
> > > The answer could be as simple as compensation for the anticipated
> > > long cable runs prevalent in mining with economical cable
> > > sizes. <
> <clip>
>
> --
>
> ************************
> Michael Griffin
> London, Ont. Canada
> ************************

 

This was apparently true for "large" ships as well. Lake freighters are limited by the size of the locks only, and at that time were generally larger than comparable ocean going ships. However, no doubt it was more important for the electrical systems of large ships to be compatable with those of small ships than it would be for them to be compatable with shore based systems. The point you made about battery power was no doubt critical as well, and quite possibly the deciding factor. If they shut down the boilers, they would still need lighting. If they used AC they would either need auxiliary steam boilers or an MG set.

To add to the odd power tales, we used to use 25 Hz rather than 60 Hz until the late 1940s. The 25 Hz frequency arose because one of the first power plants at Niagara Falls generated that. The builders of this plant selected that frequency more or less by accident. They originally were building the plant to produce compressed air. (Compressed air used to be sold as a utility service. You can still see the old pipe lines from one such system near Cobalt in nothern Ontario).

After construction was begun on the plant, the owners decided to complete it as an electric generating plant instead. However, at that point the turbines were already ordered, which meant the operating speed was fixed at what the air compressors were intended to rotate at. Picking a suitable number of poles for the generator resulted in a generating frequency of 25 Hz.

Subsequent generating plants had to be compatable with this early one if they wished to sell electricity to the same customers. This frequency became the local "standard" until a major effort was made to convert to 60 Hz. It is unfortunate however that the opportunity was not taken for the 25 Hz and 60 Hz regions to select 50 Hz, which would have resulted in a single (barring a few exceptions) world standard.

--

************************
Michael Griffin
London, Ont. Canada
************************

 

You can find a little more information on the history of voltages and frequencies as well as some other interesting historical electrical facts at:

http://www.ieee.org/organizations/history_center/faqs.html

Bill Mostia
=====================================================
William(Bill) L. Mostia, Jr. P.E.
Partner
exida.com
Worldwide Excellence in Dependable Automation
[email protected] (b) [email protected] (h)
www.exida.com 281-334-3169
These opinions are my own and are offered on the basis of Caveat Emptor.

 

What will be the changes required for the motors to be used for 690V, 3ph, 50HZ. Is there any standard LT motors are available for this voltage?

I need some help on this.

Regards,
p.s.pandi