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alternating current & alternating voltage

alternating current & alternating voltage

alternating current & alternating voltage

(OP)
I was wondering if anyone can explain alternating current and alternating voltage polarity as it relates to time.  If frequency is 60 Hz then I have 60 cycles a second.  If a cycle is half positive and half negative then every 120th of a second I have current reverse and polarity reverse.  Can anyone explain this  and maybe include a diagram that illustrates it?  I am a meterman and I am wondering why the meter wouldn't reverse direction as the polarity and current reverse.  Help

peetey

RE: alternating current & alternating voltage

"I am a meterman and I am wondering why the meter wouldn't reverse direction as the polarity and current reverse."

This is because the multimeter measures the effective value of the magnitude and not the instantaneous value.  

RE: alternating current & alternating voltage

The same reason an ac induction motor doesn't reverse direction 120 times a second.  An alternating magnetic field is created by the stator.  This induces a current in the rotor.  The magnetic field exerts a force on the rotor and "drags" it around as the field alternates.  In a single-phase motor, the only trick is getting the rotor started.  In a three-phase motor, there is a rotating magnetic field that pulls the rotor around.

I'd check out the Meterman's Handbook.   

RE: alternating current & alternating voltage

peetey, remember a simple bit of algerbra that a negative multiplied by a negative gives a positive result.

When both the current and voltage are both in the positive part of the cycle then V x I = positive.

When both the current and voltage are in the negativee part of the cycle then -V x -I = positive.

So the power flow is positive in both sections of the cycle.

It does get way more complex than this, but it gives a general idea.

 

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