Transformers

[DerekC]

Im currently enrolled in a community college line school in the northeast. We have been studying transformers and im a little mind boggled on how the neutral conductor works on the secondary side of a single phase pole transformer. By my understanding the neutral carries the unbalanced load of the two phase conductors and is tapped off the middle of the secondary winding. I checked this by opening my home panel and amp probing my neutral and two phases and it worked out. What happens to the current that flows back to the transformer ?

[topgroove]

it completes the circuit. Lets say you could unplug everything in your house except one 60 watt lightbulb. When you turn on the light 60 watts of power flows from the X1 bushing through the bulb and then back out to the transformer to the X2 bushing using your neutral. Its a circle or complete circuit. This happens with every 120 volt circuit in your house. Lets say you have a 240 volt hot water heater in your house in this case your using the X1 and X3 bushings with a resistive load in between, in this case current flows through only the hotlegs.
Now things get real strange when you start to loose a neutral connection. If current has difficulty using the neutral to get back to X2 in a 120 volt circuit its gonna look for other ways to get back to the transformer. That means its gonna start using the other hotleg through a resistive load to get back to the transformer.
When you get to your first bad neutral call its always the same complaint. The customer will tell you half the house is real dim and the other half is real bright. when you get the fluke out and test the hotlegs under load you might find 80 volts on one leg and 160 volts on the other. (240 volts phase to phase).

loosing a neutral gets real expensive for a customer. In a blink of an eye you can lose your TV's , microwaves, fridge, stove any any thing else plugged in and in use at the time. a straight 240 applience like a heating element doesent know the difference except suddenly its got way more current flowing through it which may burn out the element.

hope this simple explanation help you out.

[Edge]

you need to go back to your books bub...

a single phase tx is just that single phase.... the secondary coil is one phase split in half....

x1 x2 x3

x2 is what splits it

if you move the neutral/case ground connection from x2 to either the x1 or x3 connection... you change the whole complexion of the coil...

now instead of having 240 phase to phase you might have 360 or one "leg" thats 120 to dirt and another thats 240 or maybe some thing even more fugged up depending on where you are...

hopefully some guys that are good with posting pictures and **** will chime in to help you out more than this... sorry I don't know if it's me or my computer but I can't seem to do it...

you got to remember a single phase pot is just that...

treat it as such


for what it's worth....

Edge

[Edge]

opps after reading grooves post I think your talkin more about the load issue... and his answer is much better... I prolly just need some sleep....

Edge

[DerekC]

Topgrove So when you loose a neutral basically u turn whatever the load is into a series circuit is that why the voltage adds like that ?

[DerekC]

Edge are you getting at depending off where you tap off the secondary winding either increases or decreases the amount of windings which works proportionally with the voltage .

This is so interesting hopefully things work out and i can really get my hands on some of this stuff.

[topgroove]

Topgrove So when you loose a neutral basically u turn whatever the load is into a series circuit is that why the voltage adds like that ?

Exactly... What edge is trying to tell you is that a secondary coil is simple a winding between X1 and X3. its tapped right in the middle and thats where X2 is.

[MI-Lineman]

Im currently enrolled in a community college line school in the northeast. We have been studying transformers and im a little mind boggled on how the neutral conductor works on the secondary side of a single phase pole transformer. By my understanding the neutral carries the unbalanced load of the two phase conductors and is tapped off the middle of the secondary winding. I checked this by opening my home panel and amp probing my neutral and two phases and it worked out. What happens to the current that flows back to the transformer ?

I think your real question is where does the current go after leavin the house? The source!! You'll here that over and over if ya continue in the electrical trade!!

All neutrals are interconnected or "bonded" and are part of the "system neutral". This system neutral provides a path back to the source for the "return" current! Kind of like the "complete circuit" T.G. was talkin about!

SO SOME DAY WHEN YOU'RE OUT IN THE FIELD WITH A CUSTOMER PISSIN AND MOANIN AT YA CAUSE HIS BILL'S SO HIGH EXPLAIN TO HIM YOU'RE ACTUALLY "RENTIN" THE ELECTRICITY! TO BUY IT WOULD COST A HELL OF A LOT MORE!!

Just kiddin! Don't do that!!

[topgroove]

Why NOT? That's friggin Funny!!

Now, on a Delta system...Where does the current go...after it leaves the house. And How.

To understand a delta or straight 240 volt circuit, you have to visualize each leg of 120. each sine wave is actualy reversing itself 60 times each second and the two sine waves are exactly 180 degrees apart. a typical 120 volt AC sine wave starts at zero goes up to positive 120 then back to zero and then to negative 120 volts and finally back to zero. because the two hotlegs are exactly 180 degrees out of sync with eachother you'll always have 240 volts potential between them.
Think of AC voltage of not really the electrons moving down a conducter but really electrons sloshing back and forth. The higher a voltage in a AC circuit the higher and lower its sine wave peaks and valleys are.

[pre_apprentice_ID]

Electricity is an amazing thing. It seems so complicated and very interesting, I've got a lot to learn........ I know powerlineman.com will be helpful throughout my schooling.