# To calculate Phase angle or phase difference between voltage & current.

Discussion in 'Homework Help' started by rvb53, May 23, 2008.

1. ### rvb53 Thread Starter Member

Apr 21, 2008
28
0
hi everyone,

I need to calculate phase angle between voltage & current.....
TimeOffset /InputCurrent/ InputVoltage /OutputCurrent /OutputVoltage
0 /-2.99/ -9.58 /0.18 /-48.98
0.000333/ -0.05 /-4.42/ -0.05/ -69.89

I need to calculate the phase difference between inputvoltage & input current, outputvoltage & outputcurrent and phase difference between input stage & output stage.....
I need methods to calculate and formulae if possible .....
Pls help me...........................

Last edited: May 23, 2008
2. ### Papabravo Expert

Feb 24, 2006
10,021
1,758
Can we assume that the current and voltage waveforms are sinusoidal? If so it may be possible to crunch an answer. If not, then I think you are at sea.

3. ### rvb53 Thread Starter Member

Apr 21, 2008
28
0
hi papbravo,
thanx for quick reply...
my input voltage has swing from -160v to 150v
my input current has swing from -9amp to 15amp

bt I am unable to calculate the phase difference between them..........
pls give me any sort of ideas......I appreciate that....

4. ### Caveman Active Member

Apr 15, 2008
471
0
Are. they. sinusoidal?

5. ### Papabravo Expert

Feb 24, 2006
10,021
1,758
They might still be sinusoidal, but if they are, they have a DC component. I think you can eliminate the DC component when considering phase, but I'm really not sure about that.

6. ### Ratch New Member

Mar 20, 2007
1,068
3
rvb53,

OK, what are the units? Seconds, milliseconds, microseconds, amps, milliamps, microamps, volts, millivolts, microvolts? What is the frequency or period of the waveform. What is the offset of the waveform with respect to time zero.

Papabravo,

It would have to be. Have you ever heard of the phase of a sawtooth or square wave?

rvb53,
That tells me that the voltage has a -5 volt dc offset and a 310 volt P-P. and the current has a 3 amp offset and a 24 amp P-P.

Papabravo,

If the sinusoidal waveform has a dc component, then it is a composite wave form consisting of a zero frequency waveform and the nonzero frequency waveform. Pick which one to evaluate. Ratch

7. ### Papabravo Expert

Feb 24, 2006
10,021
1,758
Absolutely. Have you ever seen a phase locked loop with an exclusive-OR phase detector? Phase can be defined and measured for any periodic waveform, just as frequency can be defined and measured for any periodic waveform. The connection with angular measure in degrees, radianns, or grads is less clear than with sinusoids. Phase can also be measured in time units, or fractions of a period and doesnt necessarily require a factor of 2pi.

I know that complex waveforms are superpositions of simpler waveforms. What I don't know is where the reference point for phase measurements is in such a waveform. Does it occur at the zero crossings of the complex waveform, or does it occur at the zero crossings of the waveform without the DC component. I could deal with either choice, but on an exam or homework question you need to know what the conventional assumption is.

I know you know these things, but I was hoping to hear from the OP on the clarifications of what his data represented. We can make assumptions until the cows come home, but we'll never know for sure.

8. ### Ratch New Member

Mar 20, 2007
1,068
3
Papabravo,

Well, I am not so sure about that, and I will tell you why. Two reasons.

1) Let's take a symetrical square wave. Sure, you can define 180 degrees to be where it goes from positive to negative. But what if it isn't symetrical and the positive part is longer than the negative part? Same with any other wave except a sinusoid. You have to have the shape defined before you can superimpose some kind of angular grid on it. Now a sinusoid shape is well defined, so there is no question which point you mean by a angular value once you know its starting offset.

2) Fourier proved that any waveshape can be decomposed into one or more sinusoids of different frequencies and amplitudes. So if you say 30 degrees for such and so sawtooth wave, to what frequency are you refering? The fundamental maybe? How about a train of pulses? Do you
define the fundamental to be the lowest composite frequency of the square, triangular, or sawtooth pulse? Or do you define the frequency according to the period of the pulse plus the wait time to the next pulse? As you can see, I am trying to point out that the phase of a arbitrary nonsinusoidal waveform is rather ambiguous. Ratch

9. ### Papabravo Expert

Feb 24, 2006
10,021
1,758
Sounds good to me.

10. ### rvb53 Thread Starter Member

Apr 21, 2008
28
0
hi everyone,
input to system are sinusoidal inputvoltage swing of -150v to 150v and inputcurrent swing of -9amp to 14amp.
output of the system has rectifier voltage of only +ve half sine wave and current is also having +ve half sine wave......

11. ### roddefig Active Member

Apr 29, 2008
149
0
Hello rvb. Do you have information on the frequency? I think that may be an important piece of information. I also have am confused as to what your data represents. Are those the inputs and outputs of a system at different times? Would you mind formatting it a little nicer to make it clearer?

12. ### rvb53 Thread Starter Member

Apr 21, 2008
28
0
hi roddefig,
I found the anwser for phase, for any sine wave the phase difference between signals is just the difference between their respective peaks. For example, we have Voltage and current, then phase = (Vmax-Imax)*frequency*360.
hi roddefig, my frequency was 60Hz and the current and voltage values where for rapper control coil used in Electro-Static Precipitator(ESP) for air-pollution control(control of emissions of dangerous gases into atmosphere).