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Guru
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90° Supplies? Information Only.

01/01/2014 10:12 PM

As you all know I'm from the UK, now retired. I have an interest in power distribution.

90° supplies? Are these still used in the US? In remote areas do they still persist?

This is purely out of historical interest in supply systems.

Also of interest are corner grounded ∆ systems.

I've never worked on them so any information is gladly received.

I have worked on some weird and wonderful earth free systems (up to 2.6MW). They were a nightmare for fault finding!

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Guru
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#1

Re: 90° supplies? Information only.

01/01/2014 10:29 PM

Hi Tony,

For the 2 phase supplies, I never saw it in reality. Wiki however points to some places in Canada and some remote US base spots. I assume it is still used occasionally.

My answer is not helping out a lot, but I can wish you a happy New Year.

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#2

Re: 90° supplies? Information only.

01/01/2014 10:45 PM

"As you all know I'm from the UK"... i don't know that you are from UK ,

Okay , coming to your answer :

two phase power supply in USA

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Guru
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#4
In reply to #2

Re: 90° supplies? Information only.

01/01/2014 11:11 PM

"i don't know that you are from UK "

The Union Flag should give that away. I'm proud of my heritage and don't hide in anonymity.

It would be good to get anecdotal and helpful information from people "in the know".

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#6
In reply to #4

Re: 90° supplies? Information only.

01/02/2014 12:54 AM

oh sorry, i didnt noticed that.. i saw only your location "under the major oak". so i thought that u were sitting under the major oak with robin hood and his merry men...

Now as i know your location, i come under your "in the know" term, the answer would be :As long as the scoo-tee type transformer manufacturing exists there would be a yes to your question.

for more answers search google: for scott-tee manufacturers and contact them. or LMGFY....

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#7
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Re: 90° supplies? Information only.

01/02/2014 4:31 AM

I live in Nottinghamshire, hence the "Under the Major Oak"

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#8
In reply to #6

Re: 90° supplies? Information only.

01/02/2014 7:07 AM

What country did you think robin hood and his merry men lived in?

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#14
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Re: 90° supplies? Information only.

01/04/2014 12:44 PM

Hollywood...

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#3

Re: 90° supplies? Information only.

01/01/2014 10:59 PM

If, by 90 deg systems, you are talking about two-phase systems, where the voltages are out of phase by 90 degrees, in our service territory I think they have all been retired, but I cannot say that is the case across the US. The last system I was aware of was retired some 15-20 years ago, and served a large elevator. We had been serving the customer from a three-phase service, supplying the two-phase, 90 deg voltage, through a Scott-tee transformer connection.

The original power plant at Niagara Falls (~1895) was a two-phase plant, as were many of the small plants that were originally installed as part of early city power systems. I would doubt any such systems would exist in remote areas, as three-phase systems (and single-phase) were the dominant system by the time those remote systems were built; but, there may be two-phase systems still in use in some downtown systems (rumors area there may be some remaining systems in Philadelphia ...)

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#5
In reply to #3

Re: 90° supplies? Information only.

01/01/2014 11:16 PM

Thanks Oscar, gives me something to read tomorrow. It's 04:14 here and I'm done for

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#9

Re: 90° supplies? Information only.

01/02/2014 11:06 AM

Hi Tony,

That term, "90° supply" would throw me as well. But the reason I responded is because I have heard some strange sounding references to residential power feeds as 2 phase when it is actually single phase with a center tap on the secondary.

It almost comes across as "electrical slang" but it is inaccurate. The same reference would also say that the top half of the center tapped secondary as being 180° out of phase with the bottom half. The unspoken assumption is that the center tap is chosen for ground.

The implication is that a phase shift of 180° is simply a polarity reversal. With that being the case, would a 90° power supply take power from only one half of a center tapped secondary? It sounds reasonable to me......

As far as the corner grounded delta goes, I believe that practice has mostly stopped because it has some serious and potentially dangerous drawbacks. The most obvious problem is that you really need to have a balanced load so that you don't trash the bearings of the generator. If you do that, however, then one third of your circuits can not be connected to ground at all (else it changes the loading).

I like to limit my ungrounded circuits to DC systems, less than 50 Volts. For three phase AC systems, I would be hard pressed to work with anything other than a Wye with the neutral grounded. Magnetic isolation is a good thing. Providing a ground between the primary and secondary of a transformer takes away the benefits of magnetic isolation.

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#10

Re: 90° supplies? Information only.

01/02/2014 11:59 AM

These are the two transformers I know of that can produce an output at 90° phase angle.

I was curious as to whether they were still used.

Scott

LeBlanc

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#11
In reply to #10

Re: 90° supplies? Information only.

01/03/2014 12:29 PM

Tony,

They are still used occasionally, mainly in rural areas. They work well for loads which are mostly single phase, but occasionally require 3 phase. I have one supplying the headgate structure of a hydro canal. Nearly all of the load is single phase for lights, heat & controls. The motors for raising and lowering the canal inlet gates are 3 phase, but only run about once/day. I've also seen them supplying family farms, small dairy farms and the like.

Your nomenclature (90° power supply) is accurate. This is not a true 3-phase power source where each phase is 120° from the others. It works very well on the overdesigned motors of the past (mine are actually 1921 open-frame elevator motors designed for 25 Hz), today's motors are built much closer to design limits and may not operate as well on this source.

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#13
In reply to #10

Re: 90° supplies? Information only.

01/04/2014 1:10 AM

I see the Scott always in a T when drawn. How is the core in practice? Some pics? Tks

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#15
In reply to #13

Re: 90° supplies? Information only.

01/04/2014 1:19 PM

The only Scott-t connections I have seen n the field were as illustrated in TonyS's response #10, top two drawings. Two separate single-phase transformers

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#12

Re: 90° Supplies? Information Only.

01/03/2014 11:27 PM

TonyS,

Others have correctly identified the 90° phase angle as the virtually-abandoned 2-phase distribution system. In my 40 +/- years as an electrician I have been told it was in use at one customer's rural area, but found they actually had the 120° 3-phase there. 2-phase had three different connection methods--3-wire and 4-wire as mentioned in the wikipedia article, and 5-wire (picture a plus sign with wires at each end and the crossing point).

The NEC requires systems to be grounded if this can be done to limit voltage on the ungrounded conductors at 300VAC from ground. If you only have 3-phase loads then a corner-grounded 240-V delta is possible--this is widely used in our area, with the grounded phase being the "B" phase. Electricians who work on it can easily mistake it for a typical single-phase 3-wire system because the B-phase is often not fused, at least in the older installations.

If you have mostly 3-phase but a small number of 120-V single-phase loads, then a "high-leg" (or "red-leg" or "wild-leg") delta is used--the drawback to this is the 208V to ground on that leg, which by code must be the B-phase.

Most common are the 4-wire wye distributions, which give 208/120 V or 480/277 V.

I've never seen a corner-grounded 480V delta, but I have seen a couple ungrounded 480V delta's.

--JMM

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#16

Re: 90° Supplies? Information Only.

01/06/2014 10:25 AM

Many of the rural electric cooperatives in the USA still use and require a grounded Delta system for protective metering circuitry applications.

The voltage level depends on the application requirements and many are at 480, 240, & 120 VAC in commercial services.

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Anonymous Poster (3); Codemaster (1); dvmdsc (2); jmueller (1); NotUrOrdinaryJoe (1); OscarPhilips (2); pwr2thepeople (1); SHOCKHISCAN (1); TonyS (4)

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