Transformers –Understanding Delta/Delta Connections, (26min:36sec)

let's talk about Delta connected transformers Delta connected transfers have three transformer windings connected n to n with each other line conductors are connected to each point where the two windings connect let's see if we can take a look at the graphic here now Delta is called Delta simply because the way it's going to be displayed here shown it follows the Greek symbol which is a delta symbol and I'm sure Eric you know what Delta means anybody know what Delta means the actual word er well it's used as difference but I don't okay so it's out there right so take a look at this one winding this is the primary winding and let's just say that it's connected 480 volts so right here if you take a line one from utility and if you go line two for the utility that one physical transformer will make a graphic showing three different physical transformers and the actual wiring configuration that one transformer has line one connected to it and line two connected but there's three physical Transformers sitting on a pole what they did first was take this one transformer see there's two wires on the transformer one wire connects to the other wire of a transformer connects to the other wire transformer and then the other end so they're all connected and on end to each other then you bring line one to this one spot here line two to this point here and line three so we would call this h1 okay we'd mark that h1 h2 h3 you follow me now watch the voltage from line one the line two is 480 and take a look at the phase voltage right here that voltage is 480 from line to the line three that's 480 this votes right here is what is 480 from line one to line three it's 480 so each winding has 480 volts now for this example we've chosen to take the secondary winding and connect phase A to C connect C to B and B to a so we've chose so you have three different transformers with four buyers choose the primary and to is the secondary and all we do is you take the three transfer you just put them like what think about it's kind of perfect three tubs right if you put three tubs together what does it look like it looks like a delta just the physical tubs because the way to and one you know like you were going to do a bowling pins right there yep two three so now you do what you go from one to one one to one one to one that is connected in Delta then you have the primary and you do the same thing to the primary primary secondary connected in this case here Delta Delta let's follow what that means if I'm saying I want to have 240 volts secondary well if I that means that this winding right here is 240 volts this winding here is 240 volts and this winding right here is also 240 volts if you look at the phase root ratio the primary winding is 480 and the secondary winding is what 240 so if you're looking for voltage ratio this is a two-to-one both this ratio transformer ratios are identified through the phase themselves not the line now so phase to phase is 480 from line 1 to line 2 480 volts line 109 to 480 line 1 to line 3 well this transfer here is is 240 but they take in one center spot and they went ahead and a ran a wire off the center spot if this transformer is 240 volts and you make a connection in the center well obviously half of 240 volts is 120 and the other half of 240 volts is 120 so making a connection at this point right here this is going to be your x au terminal now I'm sure some you guys have heard this you create a neutral what's that word people say you generate a new neutral you you derive a neutral take a look at this that drives me nuts you're not deriving anything take a look at this you're simply having a whiniest 240 volts and they made a spot in the middle to make a connection and it just happens to be 120 between the two points and from the other phase up from the line conductor it's 120 now let's let's say it's line 1 the line to it 240 line 1 2 2 and that would be X 1 and we get X 2 X 3 in here and XO line 1 2 2 that's 240 and line 2 2 3 it's 240 this is a Delta Delta transformer now let's talk yes deep it's going to seem like you mentioned that the voltages are a 2 to 1 but that also is consistent with the windings now there's twice as many windings on the primaries are on the second or in each of those windings and by taking that center point you're taking half the windings of that one face-to-face connection to get half the voltage great point we're having twice as many windings here is we have over here and so that magnetic coupling creates to half the voltage now let's talk about why would you have a by the way um I'm not going to say why we do this yet but I don't want to leave it I'm going to go actually let me do right now why would you have a delta Delta transformer configuration with this center phase split and ground it anybody know why they go Delta Delta the reason being is this what is the voltage between the line conductors 240 240 now if we don't go Delta Delta we go Delta Y the voltage between the line conductors is going to be 208 we're getting a little ahead of ourselves here so the advantage is that I'm not going to go too far yet the advantage of a Delta Delta system is the secondary voltage is higher that means that what happens to the current flow of the conductors themselves the current flow is going to be what higher voltage current is what lower so you can have smaller conductors now also not an advantage but a Delta Delta will be able to give you line to neutral load so you can get some 120 volt loads out of a Delta Delta system like this however this transformer is designed primarily for industrial applications in warehouses where most of your loads are going to be single-phase 240 volts or they're going to be three-phase 240 volts and you have very very very little 120 volt loads by going to a Delta Delta system like this you're able to raise of the voltage and drop down the size of your service that's one of the advantages to a Delta Delta configuration let's go a little further now this is another way to look at what we just discussed here and you'll see this sometimes marked on the equipment itself so let's take a look at this here is phase a 480 volts phase B and then here is phase C on the primary and the secondary is 240 Steve you said the turns ratio is 2 to 1 which is the number of windings to get that voltage ratio here and H 1 so watch this see this goes here 2 goes to here it goes to here they're all connected in series aren't they but I'll connect it together there that's going to be a delta configuration and then where they join together it's going to be to transfer windings connected here line one this one and this one is line two this one this one is line three that's Delta and then on the secondary side we have these two connected they're all connected in series right here is half of one transformer winding because it's 240 volts is going to be the 120 volt loads that's another way looking at it here's another third way of looking at it here is h1 they're all connected together to line one and then line 2 connects these two transformers line three connects these here's the primary here's the secondary H X is it tied together here and x1 x3 is it tied together here and then X 2 s and line 2 so you take line 1 2 X 1 line 2 2 X 2 line 3 2 X 3 now a question that might come up is like okay well ABC or line 1 line 2 line 3 on the primary in line 1 line 2 and line 3 in the secondary or H 1 H 2 H 3 on the primary X 1 X 2 on the secondary does that mean that there's a phase rotation ABC phase rotation has nothing to do with this at all this has to do with what's the rotation supplied by the utility and that rotation if you maintain it properly we'll give you the whatever the rotation you're looking to follow now Eric do you guys get involved in your large industrial facilities is do you guys start with a phase rotation is it identified is it clear that we know that a B and C is a phase rotation or is this just whatever happens it happens and when you hook up a piece of three phase load you do a phase rotation of that then you make sure you connect the lead so that rotates in direction that you want how does that work it depends on who that's our intention our intention is that we'd like to have constant rotation throughout but it depends on the electrical inspector and the construction manager as to how meticulous they are because you hook it up and it's just connected now if you don't catch it you don't put a phase rotation meter on it too late you're not going to change it around and so and and the other thing about that that's real important to understand is that even if you have a standard today that says that everything's clockwise throughout you still have an installed base of stuff that is rotation varies all over the place so you're saying if you had phase rotation ABC coming in from the utility and then you bring in three phase conductors in a neutral and equipment rounding conductor you're connected there you're connected there we don't know how you connect it there and how you connect it there and what the rotation is going to be there unless you unless you have what black red blue wire brown orange yellow wire right physical wire that way it's a lot easier to maintain what the color coding throughout maintain whatever that rotation is going to be throughout if you're just pulling a bunch of black wire using some phase tape at the end well then obviously we're going to lose rotation well and you don't know about it anyway and what a lot of people do is they're at the very end at the motor okay they have an uncoupled motor they bump at the rotation they see it's going in the wrong direction so they switch to leads and so the rotation is always correct at the motor but what about upstream at the MCC you know is it clockwise or anti-clockwise at that MCC and then when you go upstream from that through another level of transformer to switch gear is that clockwise that anti-clockwise there so all right well we want to just to be aware of when it comes to rotation it has nothing to do with transformers okay that there's no connection there at all that's just simply to do with how you maintain your rotation coming up to that point right let's talk about primary and secondary line voltage this is pretty straightforward stuff the voltage measuring the primary conductor is called the primary line voltage the both is measured in the secondary is referred to as a secondary line voltage so if this is a 480 volt system on the primary and it's 40 volts line the line and on the secondary is going to be 240 volts line the line and if I went from line 1 to neutral so line the neutrals 120 if we're going to show volt meter if we had room we could put a voltmeter now that's fine so and also we'll talk about the high leg here in a second but let's take a look here line 1 2 neutrals 120 line 3 2 neutrals 120 line 1 2 line 3 is 240 and then line 2 2 line 3 is 240 because watch that should be shown here it's 480 480 480 120 120 120 and so 240 120 120 and 240 that was a little easier than to see how those values work out now interestingly here's a high leg is called a hi Alexia Delta Delta configured transformer is called a delta high leg and the reason they call high leg is because one of these conductors right here if you take a look at this both this measurement you go line two and you go to the neutral we'll talk more about this in a second that is actually going to be measured as a 208 both high leg voltage let's talk about this high leg conductor the term high leg wild leg stinger red leg and there are other terms that are being used in the industry are used to identify the conductor that has a secondary line voltage of 208 volts to ground now in reality it even though it's voltage to ground it really is the voltage to the neutral terminal of the secondary side of that system it's not really earth it's the actual neutral terminal I remember when I was working when I first was in a trade I'm ever hearing about these Delta high lakes systems in the and the the wild leg or the stinger they used to word singer a lot about that stinger and they told me one at my time they told me the voltage was a hundred and ninety-two volts like oh okay and then as I started going along and I started learning and eventually I started learning transformers I started finding out the voltage is 208 but remember this 192 or 198 both Detroit let's see how that voltage gets calculated and we're going to talk more about that in just a little bit but let's just go on right now let's take a look at this graphic the voltage what I'd want to show here would be see see this is 208 volts and the Eric I might be totally wrong about this and maybe you can do some math and prove me right or wrong and I don't care which I just wanna make sure I'm right here if this winding is shown as 240 volts right and if this winding is shown as 120 volts and if we know the angle what is this thing called it's a 30-60-90 right triangle but this is called something this is called a cosine tangent not that way not sure where you're going with that but okay so the 30-60-90 right triangle okay whatever this is if I know what this angle is here well I took a piece of ground meters if I took a graph paper and I draw this and I go this direction of let's say 24 inches and I go 24 inches this way and I go 24 inches this way right and I go 12 inches this way and then I take a ruler just a scale ruler and I go this way will I measure 20.8 inch absolutely positively okay that's what I thought and so so I wanted you to understand how this voltage if you're measuring from this neutral point to this point over here you're measuring between this winding coupled together with this winding but because this winding is 240 and this winding is 120 and so it's not what do you call that I guess it's hype the hype is this hypotenuse the the 240 is actually the hypotenuse and so the 120 is a short leg the 208 is the long leg and so if you can simply apply that Green's theorem here as well that's what I was thinking yeah oh not that I have any clue what he's talking about what theorem is that Pythagorean theorem you know a squared plus B squared is equal to C squared okay that one I know yeah okay that's oh I thought one I know so then this would be what is this a squared C squared and so the 120 squared plus 208 squared would be equal to 240 squared what about if I knew this and this how would I get this 240 squared minus the 120 squared is your a square root after that yeah well just write it down on paper and do whatever okay all right let's do it this way just trust me if you have 120 here and you have 240 here then you're going to get joy all right Eric a challenge for you I need to do this calculation for me is what about if this was not 240 volts and this was not 120 volts but this was 230 volts and this was 115 so in the 70s we didn't have a 120 240 volt system we had a 115 / 230 volt system then in that particular case my highlight would not have been 208 volt it would have been what 1 1 199 and 110 if back a long time ago maybe in the 50s we used to actually have a hundred and 10 volt system we buy the 110 221 I'm in the middle 110 times square root of 3 is 192 and that's where that comes from so the 192 came from the 50s right the old-time electricians working on a 110 220 volt system and then we start getting to 60s and then we're starting to get into a 115 to 30 and then of course not very long after that we start getting into 120 240 now this also kind of works its way back a little bit that we're running on voltages today of what on the primary 14 for you guys remember what the voltage is were before that before 14 for utility primary voltage 12,000 force oh no before that was 13 8u but he's keeping my second one second one was before 13 8 13 6 now 32 13 - well and what was before 13 to 12 12 for 780 and let me give you if you want to do the math on that 12 470 going to 30 it would be 4 to be 12 point for 13 - that is 5% more 13 to 5% more is 13 8 13 8 5% more is 14 for the history of utilities is that they started with a voltage and then they started having such a great load and utility transformers and transfers have a tap to it they'll allow you to tap up - and they would then start tapping up to 5% to peak that then became the standard then they came up with new transformers and they kept raising the standard 5% so you had a 151 10 to 20 then you had a 115 to 30 and then you had a 120 120 240 so that's why the high leg or the stinger value went from 192 to 198 now we're up to 208 so that's the history of what those numbers mean but this is what's important is if you go from let's take a look at this graphic here the voltage from line 2 to that neutral is 208 volts now this application usually is used in industrial applications where you have the line the line 240 volt loads and a little bit of 120 volt loads but guess what you have to do with the panel you have to make sure that every B phase is not connected to a 120 volt load right because the beam is connected to a 120 volt load would be operating at 208 volts and I remember one time going to a public work set up at a city and I was doing something in the warehouse and the Public Works building and I noticed you know when you go to panel you never have enough breakers openings right and on us look at this look at the all the extra spaces in the panel that is so cool and not only that but that's kind of strange why would they have those spaces I mean I thought they were all in the bottom but okay no big deal I drop a breaker in there hook it all up i hook up something at a hundred twenty volts toasted it immediately that my first experience with a high leg Delta system is I didn't know what I should have done was number one it needs to be identified right we need to have some kind of identification though it's highlight and then you got to realize you cannot connect line to neutral load see a single pole breaker if you look at the breaker it's rated 120 or 120 / 240 which means the maximum both this line to neutral is 120 so you couldn't even put a single pole breaker on that phase in the first place and of course it's Choi bolts the ground in today's application and then we'd have a problem so let's take a look at this graphic here so it's this B phase here and maybe we'll get a graphic one day showing some empty spaces in there okay Mike's making it out you can do that it's this B phase then C it's okay if you're going to go line the line loads because of both this line the line is what 240 so line the line if we show up bolt made here that would be okay the problem is that the B phase to the neutral terminal is 208 um I do know of a case of a guy doing this now let me see if I have a picture here let's go to next slide here an important point so if you have a high leg system the high leg is required to go on to the B phase of a panel board switch board switch gear or motor control center okay so required to go on the B phase maybe not motor control centers just pandaboy switch boards the switch gear supposed to go on the B phase but years and years ago the requirement was that the base high leg went on the C phase watch what happen if for like maybe 80 years in the industry high Lake Delta systems replaced on the C phase then it was in the seventies they said now we want to move the highlight to the B phase so there are installations out there today that was installed let's say prior to the seventies where the high leg is on the C phase what's your point Mike okay my point is this you go and you do a service change you pull the high leg off a big deal you put that put the gear back on again it's a high leg system where would you put the high leg if you were going to put her in it you're going to put it where you're going to put it now a new codes where you Cory put what on the B phase the problem is what all the wiring in that building had which phase connected to the high leg C had a friend of mine give me a call one day like it 7 o'clock in the morning he was going knots he couldn't figure out what happened he did a service change to a building overnight when they got in the morning start turning on the power they kept wiping out equipment as people enter they kept wiping everything out he did not realize that the high leg was on the C face of that equipment when they took it down he didn't identify which the high leg so that when he reconnected he connected it so the high leg was on the B phase wiped everything out to make it even worse take a look at this graphic here the utilities require the high leg to be on the C phase now Mike do you know anybody remember what isn't heavy with metering which they strap the B phase straight through on the metering oh the B phases is strapped straight through what does it mean there's no there's no there's no metering on the B leg I feel this show this should show right here solid without without establish the B phase the middle ones strapped right through not the C phase that's why they put it on the C phase but the C phase is the high leg right but they strap that they strap the B phase through on the Delta metering so that's in the utility now okay so you're saying this might be solid right what a meter cuz they only use two phases no yeah they only meet her on two phases okay all right so the meters are design that we need to I wonder why they want the high leg on the outside then see and some of the new meters I'm hearing that's not an issue anymore that's right the new smart meters it doesn't care about the wild like it's still going to work it's going to go okay so it's just way the meters were designed and we got to realize when the highlight was on the sea phase the meters were on the sea phase that right so they design the meters that way when the code change the highlight to go from the sea phase to the B phase the agility guys are like we're right now we're not changing our standard because you guys change your standard so be aware of the utility requirements that the high leg probably is going to be on the sea pace even though we might have smart meters will matter the practice is that utilities want to maintain the practices that they've been practicing I'm sure that makes sense if you think about that long enough okay so high leg goes in the B base high leg is required to be identified 408 3 F 1 requires us to put some kind of marking at the switchboard switch gear and panel boards to identify that this has B phase 208 bolts the ground I'm trying to think is anything else on high legs yes steep well we talked about how this 240 volt Delos system may be used in industrial areas and so on but there's also you know commercial applications or small businesses where you may have a 120 240 volt single-phase system and all your equipment is 240 your air handlers your shop whatever it is and your grow and want to go to three-phase then going to 208 volt system would cause you problems with that voltage so that's another place where the Delta connected may come into play for an expansion of existing gotcha gotcha um another thing is that I don't think we're seeing many three-phase installations being installed but a high light Delta system was also used a lot when you had only one 3 phase load years and years ago you'd have single-phase 120 volt loads and then you had one three-phase motor which was the elevator then they would bring in to five hundred thousand a six gauge wire and you'd have fusible disconnects and you put four hundred amp fuses and you put like a 60 amp fuse on phase B and that we used to then have what is called a delta breaker that's where you had a single phase panel and you three face breaker and that's prevent prohibitive to be installed now we could actually bring in one phase which the high leg on the breaker and then it went to the three phase load but then the two single phases traveled on that so you might see some older installations with a delta high leg say well why are you covering something that's because you know what I'm sure there are thousands if not millions of installations hundreds of thousands elations and if you don't understand this and you get places only once or twice in your career you need to be able to take the volt meter and always measure you're both right line 1 line 2 line 3 so you understand what the system voltage is going to be so that you can do a better job to make sure you do it a safe installation

Channel: MikeHoltNEC

Views: 147,971

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Id: dlscWJRm38M

Length: 26min 35sec (1595 seconds)

Published: Mon Apr 14 2014