Current/Voltage in an AC Generator

In summary, AC generators produce current and voltage in opposite directions, depending on the cycle. Phase shift occurs when current and voltage lead or lag the other by 90 degrees.
  • #1
infamous_Q
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0
I'm slightly confused about something. In an AC generator at one point in the revolution it produces a positive voltage or current, and then in the other half of the revolution it produces a negative voltage or current...what I'm confused about is which is it producing negatively - the voltage or current?

also extra question: if a negative voltage is applied to a load..the load (whatever it is..) won't work. Correct?
 
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  • #2
Positive or negative are simply assigned for the purposes of reference. In fact, at one point about a century ago there was a guess made and its wrong! So physics/math is largely based on an incorrect assumption and tech schools teach electron flow. About the only difference is a negative sign.

A light bulb for example doesn't care which way the electricity flows. For AC its irrelevant (except for grounding and safety) which lead is typically hooked up because its going to switch 60 times a second.

So its positive voltage AND current for the first part of the cycle and then negative voltage AND current for the second part of the cycle. They work hand-in-hand and are in-sync like in a DC circuit when applied across a resistive load but can shift with reactive loads that have capacitance and inductance.
 
  • #3
so what is it if its positive voltage and negative current? or positive current and negative voltage?
 
  • #4
That is called a phase shift. Current can lag or lead voltage by 90 in either direction. There is an old mnemonic: "ELI the ICE man" that is used to remind people how inductive loads and capacitive loads affect the voltage/current phases. Voltage(E) Leads in an inductor(L) current(I) and Current(I) leads in a capacitor(C) voltage(E). There's also one about bad girls and victory garden walls, but that's for another thread...

Anywho, a purly inductive load will only have a 90 degree shift as will be a purely capacitive load(neither of which actually exists).

Here, I'll get you started: http://home.planet.nl/~heuve345/electronics/course/course.html

Enjoy, and good luck.

I would recommend looking into phasors(and the Diff Eq leading up to said mathematical constructs) to understand and determine how these shifts occur and what the results are.
 
  • #5
Hmm, I've heard the bad boys mnemonic about resistor color codes but not the one about lead/lag. PM? :smile:

infamous - with a load like a light bulb there is no way to have a positive for one and a negative for the other. If you have your hand on a chair and push it moves one way, and if you pull then it moves the other way. Assign one direction as "positive" and the other as "negative" and you have a very similar setup, you push or pull and the chair follows your direction.

The voltage either pushes or pulls and the current follows the same direction as the voltage at the same time (outside of the phase shift mentioned above) so just think of the voltage as the boss and the current does what it tells it to do without ever listening to hear "simon says"
 
  • #6
ok. thanks for your help guys!
 

1. What is an AC generator?

An AC (alternating current) generator is a device that converts mechanical energy into electrical energy by using electromagnetic induction. It is commonly used to generate electricity in power plants.

2. How does an AC generator work?

An AC generator works by rotating a coil of wire between the poles of a magnet. As the coil rotates, it cuts through the magnetic field, creating an induced current in the wire. This current alternates direction as the coil rotates, producing an AC current.

3. What is the difference between current and voltage in an AC generator?

Current refers to the flow of electrons through a circuit, while voltage is the force that drives the current. In an AC generator, the voltage is constantly changing as the current alternates direction.

4. What is the frequency of an AC generator?

The frequency of an AC generator refers to the number of complete cycles of AC current produced in one second. In most countries, the standard frequency is 60 Hz, meaning the current alternates direction 60 times per second.

5. How is the voltage controlled in an AC generator?

The voltage in an AC generator can be controlled by adjusting the speed of rotation of the coil or by changing the strength of the magnetic field. This allows for the production of different levels of voltage to meet specific power needs.

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