mattmag
Premium,ExMod 2000-03
join:2000-04-09
NW Illinois
clubs:
 ·Mediacom
|  3-Phase Electric Service--Discussion
Here's one for you "high-line" kind of people out there. 
Tonight at our local 9-1-1 Center in the courthouse, the standby generator unit for the building fired up, for no obvious reason, or at least it seemed that way for awhile. I got a call telling me about this since I'm the Chairman of the 9-1-1 Board for the county, and also the de-facto expert on all things related to 9-1-1, whether I really know anything or not...
Anyhow, I arrived in the parking lot and yep, the generator unit is running, but we weren't aware of any failures at all. I went downstairs in the building, and checked the transfer switch equipment which was indicating no utility power on the control board. Hmmm... That's odd, since the dispatch folks didn't have an outage at all...
Went back outside, and gazed up at the overhead transformers, and saw that one of the primary leg fuses was opened, and hanging down. OK, that would do it!! Called the utility, and waited for them to arrive. When they did, they gave it all a lookover, and decided that perhaps the fuse was damaged from the storm earlier in the week, and it finally let go now. Seems logical. So, they dropped the fuse down, replaced the fuse core, and hung it back in. When they snapped in back up into place, BANG!!! along with a nice fireball from the general area. So, looks like a toasted transformer after all.
On looking closer after this brief re-power episode, you could see where one was starting to leak fluid. Bad sign. I ask the guy a little bit about the whole thing, and he mentioned that the service is setup in "Delta" configuration, which he said is no longer used for new installations, and now it is all a "Y" configuration, which he said gives better ground ability, and is more even at 208V, where the setup we have now is 208, with a 240V "wild" leg. Interesting. Of course, they can't re-config it at this point, so for now they are replacing the one transformer, which is a rather large unit that he said weighs in at about 2000 Lbs.
So, for you utility-minded guys and gals---can you explain the "Delta" vs. "Y" configurations a little? Seemed like something we could learn more about here!
-Matt |
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dgilbert
Good Bye My Friend
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join:2002-06-15
none
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| well, this is WAY OT for a DIY forum!
i have no clue why he said Wye setups are not used anymore, you use whichever one fits your needs best. BOTH are very common. also, if you change it you may have to change other things. i know the POCO at one of our tower sites was replacing old poles and wanted to convert us from Wye to Delta or just plain single phase if possible. we only use the 120v now, but the site used to be an old ATT Longline site and was setup for Wye. the Generator, transfer switch, adn most internal wiring would require changes to make it work.
before you evne consider it, GET A PROFESSIONAL ELECTRICIAN TO VERIFY WHAT YOU NEED.
BTW, what type E-911 system you running? i maintain a couple of Plant systems and used to maintain 8 CentraLinks.
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Lack of Preparation on YOUR Part does NOT Constitute an Emergency on Mine! |
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Jtmo
Premium
join:2001-05-20
Novato, CA
·Comcast
| reply to mattmag
If you lose a Y like you did, you can halve the voltage I believe. The Y can deliver more power with less current.
With a Delta you have reduced voltage but it is less catastrophic It's more fault tolerant.
But, that was a long, long time ago and it was a bit confusing then. |
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mattmag
Premium,ExMod 2000-03
join:2000-04-09
NW Illinois
clubs:
·Mediacom
| reply to dgilbert
said by dgilbert  :i have no clue why he said Wye setups are not used anymore, you use whichever one fits your needs best. BOTH are very common. He said the Delta config is the one they don't use anymore, and that's what we have. Maybe it's just the preference they have now? Who knows. I was just interested in the way they are wired to the primaries and such. I could see that one leg of the primary fed two different transformer inputs, and one of the transformers I believe had 3 outputs while the other two had two outputs in use.
On the equipment part, we used to run all Motorola stuff, with the Centralink phone switch and Centracom II consoles. Just about a year ago we replaced it all with Zetron equipment, complete with all touch-screen controls for phones and radio. Very nice stuff. |
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mattmag
Premium,ExMod 2000-03
join:2000-04-09
NW Illinois
clubs:
·Mediacom
| reply to Jtmo
said by Jtmo :With a Delta you have reduced voltage but it is less catastrophic It's more fault tolerant. That seems to be the case tonight. Most stuff kept running fine, and gave no indication of the failure. |
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keithps
Premium
join:2002-06-26
Soddy Daisy, TN
·Limestone Cable
| reply to mattmag
Delta configuration only works well when you have fairly balanced loads on all 3 phases, say a large 3 phase motor. Delta is usually limited on the voltage output it can support, as without a ground, you can only get the voltage from phase to phase. So if you set up a delta for 240V, you can only get 240V because you can only tap phase-to-phase (A to B, A to C, B to C). A wye setup allows an additional lower voltage by tapping phase to ground. So a 240V wye setup will also support a 120V single phase setup. This works well in businesses with very unbalanced loads on each phase. Delta is phased out because you can accomplish the same thing with a wye, but have more flexibility. |
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Greg_Z
Premium
join:2001-08-08
Springfield, IL | reply to dgilbert
I do believe that a City would have professional Electricians, due to like ours, which has a City owned Utility company, all of the Electricians are Professionals. |
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sdgthy
@optonline.net | reply to mattmag
Here's a little bit about the differences between delta and wye: »www.elec-toolbox.com/usefulinfo/xfmr-3ph.htm |
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Kringle
Dr.D
Premium
join:2004-02-27
Pierrefonds, QC | said by sdgthy :
Here's a little bit about the differences between delta and wye
Pretty comprehensive link. I'll stop writing my descriptions now... |
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dgilbert
Good Bye My Friend
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join:2002-06-15
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| reply to mattmag
yep, that is what re[laced the Centralinks on most of my customers, Bellsouth(AT&T) beat motorola's price by close to 75% so most of the counties around here went that route. NOW they found out that the ATT tech know absolutely nothing about the systems and for a long time they had major issues keeping them running. My local E911 guy swears he won't ever do it again!
Back to teh OP, i meant Delta and said Wye. but the jist of it was both configs are still very common.
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Lack of Preparation on YOUR Part does NOT Constitute an Emergency on Mine! |
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whizkid3
Premium,MVM
join:2002-02-21
Queens, NY
·Earthlink Cable Mo..
1 edit | reply to mattmag
The utility guy you spoke to at the truck, either knows little about distribution system design, or you misunderstood at some points, mattmag. It is a 'high' leg, not a 'wild' leg (although this could be their slang, or he has colorful vernacular). Maybe the utility is providing 'high leg' delta secondary service? I see this fairly often - mostly in other countries. Its a pain in the ass to design the building distribution system (to the NEC), and 3 phase panelboards are very costly. I just assume, convert it to 208/120 volt service with a transformer. The high-leg delta is usually a four wire service; it provides one 240/120 volt single phase (like houses) service which is more beneficial than straight 240 volt delta, albeit at a severely reduced ampacity as the 240v phase-to-phase connections.
If the primary side cut off switch opened, you certainly lost power on your end, and the generator was doing its job. Do you have a UPS? This would explain why it seemed no one lost power. It would be nuts to build a 911 call center, of any size, without a UPS covering all critical communications and IT functions.
quote:
If you lose a Y like you did, you can halve the voltage I believe. The Y can deliver more power with less current.
If we're talking wyes and deltas with the same voltage, thats not correct. Less current per wire (one is 3w the other is 4w), but only if you had an inbalance on the neutral., which is not the way you want to go. quote:
With a Delta you have reduced voltage but it is less catastrophic It's more fault tolerant
If the delta is non-grounded, then that's true. Its less susceptible to ground faults. The vase majority of utility primary systems are delta. To begin with, its less wire and less cost. I don't know what you're talking about, Jtmo, with regard to 'reduced voltage'.
quote:
So a 240V wye setup will also support a 120V single phase setup. This works well in businesses with very unbalanced loads on each phase. Delta is phased out because you can accomplish the same thing with a wye, but have more flexibility.
Its a simple matter to have a transformer with a delta primary and a wye secondary within the business, and every business on this utility secondary will. Otherwise there 120 volts would not be available in the building. Delta - is certainly not phased out. What would be phased out is the wimpy 240/208 volt (high leg) distribution.
Most utility delta secondary distribution I see is 480 volts, and serves buildings with higher loads - (which most have). It also provides 480 volt delta directly to large motors (think air conditioning systems). These buildings will have 480-480/277v and 480-208/120v transformers. 277 volt lighting, which most large office buildings have today. Both are more effficient and cost less to wire. Even more popular is 4 wire, 480/277 volt wye secondaries (or 460/265v in NYC). The only transformers that are needed are to provide 208/120 volt service. Buildings of the size that I picture mattmag talking about tend to have 3 phase, 4 wire wye, 208/120 volt service. |
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mattmag
Premium,ExMod 2000-03
join:2000-04-09
NW Illinois
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·Mediacom
| said by whizkid3 :The utility guy you spoke to at the truck, either knows little about distribution system design, or you misunderstood at some points, mattmag. It is a 'high' leg, not a 'wild' leg (although this could be their slang, or he has colorful vernacular). He definitely said "wild" leg, and actually that's a term I have heard around here for many years. Guessing it is one of those terms that varies by region. It is a four-wire service, and the voltages are as you noted- 208-240-120.
said by whizkid3 :Do you have a UPS? This would explain why it seemed no one lost power. It would be nuts to build a 911 call center, of any size, without a UPS covering all critical communications and IT functions without them off of UPS. Yes, we have a UPS, but it is only utilized on critical loads, so nearly all of the lighting circuits are not on it. That's why it is usually quite apparent anytime we lose power, as the lights will go out! In this case, at least in the call center, no lighting was affected by the loss of the single leg. Also, since it was after business hours for the rest of the courthouse, the remainder of the building was already unoccupied.
said by whizkid3 :Even more popular is 4 wire, 480/277 volt wye secondaries (or 460/265v in NYC). The only transformers that are needed are to provide 208/120 volt service. That's the configuration he said is the way they like to go now. Since we already have a fairly new generator and transfer switch that is set up for the current Delta service, it isn't likely we will ever see it change. The only part I would like to change is to move the service underground, but even that carries a pretty high price tag with it.
The way it is now, the pole with the three transformers on it is just outside the door into the call center area, next to the building in the parking lot. If it ever fell over for some reason, it would land on our generator!! Talk about losing your primary AND your backup in one motion... |
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leibold
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join:2002-07-09
Sunnyvale, CA
clubs:
| 
A good explanation of the high-leg delta from Siemens |
Wye is way more convenient than Delta in supplying mixed loads in a building.
However the special situation of the high-leg Delta may indeed be such that it will be discontinued since it promotes unbalanced loading of distribution systems.
One thing that I didn't see mentioned yet is that it is perfectly fine to attach a Delta load to a Wye distribution system (In such a case the neutral wire from the Wye distribution remains disconnected from the input of the Delta load). However you are not allowed to connect a Wye load to a Delta distribution system (unbalanced loads would cause voltage fluctuations, never mind the safety issues surrounding the grounding of the neutral wire).
How easy or difficult a change by the utility company would be for Mattmag depends on how he currently utilizes the high-leg delta power he receives.
Scenario 1: the backup generator too is providing a high-leg delta output and his building does not perform any transformation. 120V loads are connected between phase 1 or phase 3 and neutral. 208V loads are connected between phase 2 and neutral and 240V loads (if any) are connected between any two phases. In this case any change by the utility to plain Delta or Wye distribution would require significant changes.
Scenario 2: the backup generator provides a plain Delta or Wye 3 phase power. The output of the automatic transfer switch goes to a Delta-Wye transformer providing 208Y/120V as is typical for light commercial applications. 120V loads are connected between any phase and neutral while 208V loads are connected between any two phases. As long as the voltage itself doesn't change, it doesn't matter in this scenario whether the utility is providing a Delta or Wye 3 phase power.
Scenario 3: the backup generator is single (split) phase 240/120V. Despite the fact that the utility currently provides a high-leg delta all loads are either 120V (between phase 1 or phase 3 and neutral) or 240V between phase 1 and phase 3. This would mean that 3 phase power (while available) isn't actually being used as such and a switch to residential style single phase service would not require any changes.
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drjim
Premium,MVM
join:2000-06-13
Torrance, CA
clubs: | reply to mattmag
Splitpair (Wayne) is pretty good with this stuff. You might want to PM him....
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One man's Magic is another man's Engineering. |
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whizkid3
Premium,MVM
join:2002-02-21
Queens, NY
·Earthlink Cable Mo..
4 edits | reply to leibold
said by leibold :One thing that I didn't see mentioned yet is that it is perfectly fine to attach a Delta load to a Wye distribution system (In such a case the neutral wire from the Wye distribution remains disconnected from the input of the Delta load). That's done usually where power quality is a concern (most places). The delta primary is run through a delta-wye transformer, with the wye secondary. This provides great isolation between the two, and greatly mitigates harmonics and imbalances on the secondary from passing to the primary feeders. The secondary is wired in a three-wire delta configuration, although a wye service and corresponding neutral is available at the transformer secondary. From here you are typically connecting machinery or another step-down transformer (with the 208/120v 4 wire wye). The proper planning must be done to ensure that the voltages on the wye secondary are correct to provide 3-wire delta distribution.
Thanks for posting that diagram, liebold. Siemens is the one company I know of that makes panelboards for high-leg systems. They are very costly with regards to standard 3-phase panelboards. I often see standard three-phase panels used incorrectly. The Siemens panelboards prevent the connection of 120V single-pole breakers from being connected to the high-leg (which would end up giving you 208v to the neutral). The big problem with this system, is that the utility side is often inbalanced. Likewise, the transformers are often overloaded on the side with the 120V available. (The 120v windings can often only put out about 10% of the power available phase-to-phase).
As far as 'wild' leg goes, I have never heard such a thing. 'High' leg is the proper term. |
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whizkid3
Premium,MVM
join:2002-02-21
Queens, NY
·Earthlink Cable Mo..
| reply to mattmag
said by mattmag :said by whizkid3 :Do you have a UPS? This would explain why it seemed no one lost power. It would be nuts to build a 911 call center, of any size, without a UPS covering all critical communications and IT functions without them off of UPS. Yes, we have a UPS, but it is only utilized on critical loads, so nearly all of the lighting circuits are not on it. It was probably the 'b' phase lost on the utility transformer primary. End result is you still had 120V lighting power available and didn't notice it. |
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disconnected
@snet.net
| reply to leibold
Both Harris and Nautel, in their broadcast transmitter installation manuals, note that Delta configuration is prefered over wye, because of better voltage balance between legs (has to be within 5% on each leg, or the power transformer in the transmitter will overheat).
Most of the transmitter sites I work with have delta power. |
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UHF
All static, all day, Forever
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clubs:
 ·Qwest.net
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| reply to whizkid3
said by whizkid3 :As far as 'wild' leg goes, I have never heard such a thing and it amazes me that you've heard it for many years, I've heard it called "wild leg" too. Maybe it's a Midwest thing. |
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nunya
SEE ROCK CITY 475 MILES
Premium,MVM
join:2000-12-23
O Fallon, MO
clubs:
·AT&T CallVantage
| reply to mattmag
We call it "wild leg" & "high leg" here. Unfortunately, Delta systems were very popular with the local utility in in St. Louis many years ago.
We have an extra special monster called a "corner grounded" or "grounded b phase" delta system implemented in many older installations. This is not installed anymore, but many are still functional. I hate these.
Most likely you folks have your own transformer(s) on site to get a Y service, or there is a separate service for the 120V.
Delta and Wye systems are pretty much the same in efficiency. Delta systems are more common where the utility only provides "primary in". Usually heavy commercial & industrial.
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mattmag
Premium,ExMod 2000-03
join:2000-04-09
NW Illinois
clubs:
·Mediacom
| said by nunya :We call it "wild leg" & "high leg" here. Well there's two more of us now, I'm glad to hear! I know I haven't been dreaming that... 
said by nunya :Most likely you folks have your own transformer(s) on site to get a Y service, or there is a separate service for the 120V. No separate service or transformer on site that I know of. There is only the three primary wires from the utility that feed three transformers on the pole, and that runs straight into the main disconnect in the basement where we also installed the generator transfer switch. Maybe I will get some pics posted to help show how it is set up. |
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