Three Phase Electricity

[WardenJ]

Is there anyone here that can explain to me how three phase power works? I'm trying to understand the 440 3-phase system on the boat and I am at a total loss when it comes to anything beyond simple DC or household 110 systems (I dont even know household stuff that well). Any explanation of how three phase works and how the neutral and grounding come into play (especially on a steel boat), would be MUCH appreciated, thanks!

 

[heycods]

Re: Three Phase Electricity

I used to think it was simple, till I tied 4 110 v lightbulbs in series and touched one leg to a hot leg of a 440v power supply and the other to a grounded surface. the light bulbs exploded and turned to sand, I was lucky to escape with my eyes. I can wire motor relays and such in 3 phase systems and reduce to 110 through transformers for tools ect but I still dont understand it.

 

[SS MAYFLOAT]

Re: Three Phase Electricity

WJ, be very careful with 440. It can ruin your day in a heart beat. I have a bit of experience with it from working on irriagation for a golf course. When measuring that high of voltage, DO NOT USE BOTH HANDS with a test lead in each hand! The current can jump and go through you body. Always and only use one hand with both test leads of your meter.<br /><br />As for the 3 phase, each leg has its own sign wave. When all three are put together, the three sign waves become about 120 degrees apart. This gives more steady and constant current at the peaks of the sign waves. For example you have a 10hp electric motor. At 110v, it could draw 30 amps. On 240v single phase, it could draw 15, on 240v-3 phase, it could draw 10 amps. Then when you boost the voltage, that same 10 hp motor now could have a lot lower amperage draw of maybe 5. These figures are not accurate, but to give a basic idea of more power equals less current draw for your loads.<br /><br />3 phase helps keep amperage draw lower than a single phase circuit.<br /><br />I maybe confusing and not completely accurate on this. But I do know from a friends accident from it that it is nothing to play with. Maybe do a search and see some pics describing 3 phase may help. It is a great way to deal with large loads on an electric supply.

 

[JB]

Re: Three Phase Electricity

SS gives most of the basics. <br /><br />There are three wires, A, B and C. The three sine waves are A-B, A-C and B-C. They are each 120* out of phase with both of the others (+120* to one, -120* to the other).<br /><br />Three phase power is needed to run many high power, high torque electric motors. All three field windings are "run" windings and there are no "start" windings or "start" capacitors.<br /><br />Almost all three phase power is supplied to industrial applications.<br /><br />In home applications we get 220VAC, two phase, and use the two 110/115VAC voltages for routine home electric power.<br /><br />220VAC is two phase. Two 110V sine waves are 180* from each other and are added to get the 220V. The three wires give: A-B 110V, A-C 220V, B-C 110v 180* out of phase with A-B. Wire B is ground.<br /><br />Hope that doesn't confuse you.

 

[Ron G]

Re: Three Phase Electricity

Very good JB and SS.h#ll i got it in my shop and it still confuses the crap out of me.my grandfather and me wired it in was i was younger,we got a coverter and an eletrical motor to make our third leg.I wish i knew a 1/16th of what that man knew.

 

[jch7450]

Re: Three Phase Electricity

Ron we still have one of those coverters and it still works

 

[rwise]

Re: Three Phase Electricity

I have seen those converters as well. <br /><br />A couple of things here is only use your right hand when working with high voltage. The worst shock you can get is from your left hand to the right leg. if the motor runs backward, swap any 2 HOT wires, never mind which leg is the high leg. believe me it ain't fun getting shocked be 440! if in the palm of your hand the muscles contract and you grab hold, if on the back of your hand the muscles contract and pull away!

 

[WardenJ]

Re: Three Phase Electricity

Believe me I have no intention of actually touching any of this, that's what the electrician is for. He is doing some research, talking with electrician buddies, and studying wiring diagrams before he even touches it.<br /><br />OK forgive my crude, probably wrong analogy, but this is what I am envisioning. The electric motor is a swivel chair and the electricity is someone standing next to the chair and is going to spin it as fast as he can. If he is three phase, he will push the chair three times (at 120* intervals) per revolution, whereas if he is single phase he'll push it once per revolution, so he only touches it in the same spot each time it comes around. If he wants it to go the same speed as if he were three phase, he would have to push it much harder (with more amps).<br /><br />What of neutral and grounding in three phase? <br /><br />There are a few reasons for my asking which may help put my question in context. First, I am simply curious since I don't get it <br /><br />Second, we're installing a household range in the galley, in place of a 440 cast iron unit that didn't work. The electrcian says we're probably going to have to use a transformer to make 220 for the range, but what of a neutral for lower voltage things like the indicator lights and whatnot on the range, and a ground? Where do those come into play in the three phase system and thus the boat as a whole?<br /><br />Third, can three phase be used for 110? We have 110 electrical panels on the boat, each with three leads coming in. Those leads, however, go right back to a breaker on the main distribution panel. On the bottom (output side) of the breaker are these three leads to the panel, on the feed side, it looks like it just comes off the three phase system. There are three grid bars in the 110 side of the main panel one for each of these leads that go into the panel (still with me?). The electrician said the whole main panel was hot, which led us to believe this was some kind of three phase 110 set up. If so, how does it work and where is the neutral and the ground? The thre leads in the smaller panel are labeled H, N, and G, but they just go back to the breaker on the main panel, I dont know if the labeling can be trusted.

 

[tommays]

Re: Three Phase Electricity

If your not useing a marine electrian i think your heading for trouble as much as its the same there are different rules on boats<br /><br /><br />Ac motors have poles and the electric has sine a wave at 60 hertz , the number of poles X herts = the final speed<br /><br />If your gen set is makeing power at 440 than there has to be a transformer somewere or the gen set may have 220 outputs also ?<br /><br />You need to see about this if you have 110 pannels you should already have 220 on the boat ? <br /><br />A 440 phase and a netural on a lighting circut will give 277 volt and a lot of plant lighting is done this way<br /><br /><br />tommays

 

[JB]

Re: Three Phase Electricity

On your swivel chair analogy, Warden: with single phase he pushes in the same spot every revolution. With three phase he pushes in three seperate spots, 120* apart, for three pushes per "cycle". For a given voltage, three phase draws less current and the motor is far more efficient.

 

[waterinthefuel]

Re: Three Phase Electricity

I took a major applicance repair course once. My instructor told me that the safest voltage was 440. It will hit you and blow an arm off, it won't lock you up like 120 or 240 will.<br /><br />I decided not to test his theory.

 

[bandit86]

Re: Three Phase Electricity

grounding is like every other system, but watch out for 3 and 4 wire 3 phase system. big difference. I dont know the voltages for 440, but at household voltages, 1 phase is 120V, 2 phases are 208. the 3 phase system will also be 208, but the 3 phase 4 wire system will give you 240V. big difference in motor and generator design, not interchangeable.

 

[WardenJ]

Re: Three Phase Electricity

Tommays: We're going to do this properly or not at all. Our electrician will be discussing the situation with others with marine experience and will refer one of them to us as necessary. This thread is about my curiousity and trying to understand the system. I don't know anywhere near enough to even think about touching it myself. The generators make power at 440 and there are transformers to 110 in the main distribution panel. There isn't anything currently on the boat that is operated by 220. The ventilation blowers are 440, as are the air compressors. Everything else is 110 such as lights, the fridge, etc.<br /><br />What confused me is that I couldnt figure out how the 110 panels were wired, and couldnt find a neutral point anywhere. It appears that the three leads feeding the panel are all hot with 110, and according to the wiring diagram they are staggered amongst the breakers in the panel (for example one breaker would be A-B, the next A-C, then C-B, C-A, and so on....I just made up those pairings since I don't have the diagram with me, but it goes something like that) Can these leads act as a hot lead one moment and neutral the next?<br /><br />Just thinking about it confuses me.

 

[SS MAYFLOAT]

Re: Three Phase Electricity

It does get confusing. There is also 240 3 phase open delta which is two leads each 240 to ground. Then the 3rd wire which has no voltage to ground becomes hot only when a load is put on it. <br /><br />Having the step down txfmrs will give you a cleaner and consistant power. There is many different txfmrs that can give you what you need for any application. I would think in your case, you have a floating neutral for your 110, a hot, and an isolated ground. Using a direct ground on the steel ship/boat could cause galvanic corrosion of the hull. Good Luck and hang in there!

 

[tommays]

Re: Three Phase Electricity

There has to be a netural bar in the 110 volt pannel <br /><br />I cant say hows in done in your boat, but in our building we get in 440 3 phase and a netural from the street which feeds the transformers which are 440 3P to 208 3P <br /><br />The 208 3P and netural is hooked up to the A-B-C and netural bar, you can run 110,208 or 208 3P from a pannel<br /><br />If you put a meter to any two feeds in the 110 box i would be very suppprised if it does not read 208 or 220 <br /><br /><br /> <br /><br />tommays

 

[WardenJ]

Re: Three Phase Electricity

SS: What is a floating neutral? <br /><br />Regarding a direct ground to the hull, I could have sworn I read that you want a single grounding point on the hull where everything grounds to maintain a single potential. Otherwise how would the ground current (if present) find it's way to earth? In this case it would be a ground in the sense that it is only energized when there is a problem (like the toaster is shorted out), not a neutral that has current running in it under normal circumstances, which I still have no idea where it goes. Doesn't a DC system ground to an engine which is bolted to frames which are part of the hull? <br /><br />Tommays: I thought there should be a neutral bar in the panel too, but there isn't. An example is our shaft tachometers, which get their 110 feed from this panel. One of the 110 wires to the tachs comes from one breaker in the panel, then the other goes to the breaker below it. I would have thought one of the leads is hot and the other is neutral, but then the neutral would have gone to a neutral bar, not to another breaker. <br /><br />I will test it again, but if I remember correctly, I put a meter on two leads in the box (the one labeled H and the one labeled N...but I dont trust the labels because the box isnt stock) and it read 110. I also put the leads on H and G and got 110. I dont think I did N and G.

 

[SS MAYFLOAT]

Re: Three Phase Electricity

I can be wrong on that WJ. If something on the AC side failed/grounded, you don't want any chance of it back feeding into the DC system. With two different electrical systems, (especially with 440) exta precautions could be taken to prevent any possibility. Could be why the double breakers are used. Similar to a GFCI in a typical household.<br /><br />A short in one of the circuits should trip both breakers. If a short happened and tripped one breaker and caused an open to the neutral in the load, the neutral would still be hot. Therefore needing a seperate breaker for the neutral.<br /><br />Does the light switches have double poles? One would be for the hot and the other for the neutral.<br /><br />Vessels to my knowledge cannot have an earthen ground for obivious reasons of being in the water. If I see our electrician (ex Navy electrician) he may give me some more insight to pass on to you.

 

[rwise]

Re: Three Phase Electricity

Originally posted by waterinthefuel:<br /> I took a major applicance repair course once. My instructor told me that the safest voltage was 440. It will hit you and blow an arm off, it won't lock you up like 120 or 240 will.<br /><br />I decided not to test his theory.

I can personally say that is not true! 440 will grab and hold you there! trust me on this one, if it were not for a young black gent I would not be here today!

 

[mattttt25]

Re: Three Phase Electricity

jb- isn't 220V 3-phase power 4 wires and 220V single phase 3 wires?

 

[WardenJ]

Re: Three Phase Electricity

Ok i think I might be on to something....maybe. <br /><br />If our system is three phase delta, there will be no neutral wire present because of the three phases being staggered. This allows for current to travel both directions using only the three hot legs, so in a sense, they are all "hot" and they are all "neutral". When one leg is max positive, another (or the combination of the other two) is max negative and acts as the neutral for the max positive one. As another becomes max positive, the first one becomes part of the negative, and so on....is this correct in any way? <br /><br />I could run a single phase device by connecting between two properly paired phases or by using one leg to neutral (ground), and get something like 277 volts out of a 480 volt three phase system.<br /><br />It looks like my 110 panels are 3 phase as well (if that is possible), and they are wiring phase-to-phase in order to get 110 for the devices like the aforementioned shaft tachometers. This is why measuring across two phases gave me 110 and measuring phase to hull gave me like 50 volts or so. <br /><br />For the household range that I want to install, the way to get 240 would be taking a leg of the 480 to ground for 277, however I cant do this on a boat if I cant use the hull as a ground. <br /><br />So now here is my question: <br /><br />Can I use a 480 three phase to 240 three phase transformer then wire the range phase-to-phase just like the 110 stuff is done? It seems to me that this would make the oven and stove burners work, but not necessarily the lower voltage indicator lights and control panel for the oven since those would still require some kind of neutral.<br /><br />Am I on the right track or did I just make it more confusing?? Thanks