Hi, Can some one explain the relationship between Voltage, Frequency. Is frequency is affecting the electrical consumption.
According to the formula P= Root (3) V . I. Cos (Pi).
Frequency is not causing any affect on Power until unless it is having a relationship between V or I..
Can some one clarify this.
Regards, Sridhar
What do you mean Cos(Pi)?
Frequency just describes the cycles per second, or Hertz, that the Voltage is. Here in the US its 60 Hertz. It is constant. The Pi in the formula is also a constant.
"Hi, Can some one explain the relationship between Voltage, Frequency. Is frequency is affecting the electrical consumption.
According to the formula P= Root (3) V . I. Cos (Pi).
Frequency is not causing any affect on Power until unless it is having a relationship between V or I..
Can some one clarify this. "
The power formula you have is for a three phase AC load. For a pure resistance load, eg a simple load like a heater, the voltage and current are always in line with each other. If you drew graphs of the two, and placed one over the other, they would line up perfectly.
That is not true for a load that has inductance or capacitance, eg a motor. In that case, the inductance of the motor will cause a phase shift between the voltage and the current. If you place the graphs together, you will see that while the frequency is exactly the same, one curve is shifted slightly relative to the other.
Since power is the product of voltage and current, the instantaneous power is still V*I, but the average power is affected by the amount of shift between the voltage and current curves. That's where the Cos() function comes in. The angle used in the cosine function is the angle between the voltage and current in the load. For a pure resistive load, the voltage and current would be in perfect alignment and the angle would be zero, giving cos(0)=1. As you add inductance or capacitance, the angle will become non-zero, resulting in a reduction in power. Another way of looking at this intuitively is that as the the voltage and current go out of alignment, when multiplying instantaneous voltage and power along the two curves, since they no longe line up, the power will obviously be reduced.
Just to further clarify, regarding frequency, the OP is correct. Frequency of an AC load does not affect power
"Frequency just describes the cycles per second, or Hertz, that the Voltage is. Here in the US its 60 Hertz. It is constant. The Pi in the formula is also a constant. "
The argument of the cosine function is the angle between voltage and current in an AC load. It varies depending on the inductance and/or capacitance of a particular load. The symbol used for the angle is normally theta, not Pi as the OP stated.
"Are you sure about that? Frequency affects induction, and if induction affects affects power, then frequency affects power"
Well, you've got me there. That was an incorrect statement. I had the equation for 3 Phase power that the OP gave in mind and the fact that freq is not part of it. But of course you are right, the frequency has a big effect on any load with inductance or capacitance. And that effect gets into the OP's power equation by virture of the fact that the phase angle between voltage and current contained in the equation is itself a function of the frequency.
Thanks for correcting that!
Exactly! Why not just say -1 then? LOL
"Exactly! Why not just say -1 then? LOL "
It's an obvious mistake in an equation which is otherwise correct. Instead of Pi, the correct variable usually used is theta.
-1?
Nick
All of this reminds me of the guy who was taking Electricity 101. He was trying to remember the equation for power for a test. His buddy said "Just remember 'twinkle, twinkle little star. Power is equal to I(squared) R.'" When the test results came back our student had not done very well. "I got mixed up" he said. "All I could remember was ' Shining in the sky so high, Power is equal to R(squared) I' "
Sorry about straying a little off topic. The devil made me do it. Charlie
Are you sure about that? Frequency affects induction, and if induction affects affects power, then frequency affects power.
Some good answers here...Might I just add that in a resistive circuit, as posted, voltage and current are in phase so there is 0 phase angle between voltage and current and thus no losses other than the resistance. In a capacitive or inductive circuit there is reactance. The formula for capacative reactance is 1 divided by 2pi*f*c and for inductive reactance it is 2pi *f*l. As you can see, as the frequency goes up so does the reactance of the circuit and thus the overall power is reduced. With typical AC power the 60 cycles are constant so the only variable is the capacitance or inductance of the circuit which will cause the current to lead or lag the voltage and leave you with less power. Hope that helps........Ross
"The formula works just as well for single phase power. Your description is quite correct for any number of phases. "
P= Root (3) V . I. Cos (Pi).
It does? The cube root arises because it's a three phase circuit.
"Frequency does not effect power, as a purely inductive or capacitive load does not draw any power (not counting any losses due to the tiny resistance of the conductors themselves, which means that you can never
really have a purely inductive or capacitive load!). "
That's true for a purely inductive or capacitve load, but isn't true in the general case. Consider a load consisting of a resistor in series with an inductor. Connect a voltage source with a frequency of zero (DC) and the inductor offers no impedance and the load is purely resistive. It looks just like a resistor and the power dissipated is V**2/R.
Now change the frequency to the other extreme, making it virtually infinite. Now the inductor effectively blocks current and the power dissipated (in the resistor) is close to zero.
The formula works just as well for single phase power. Your description is quite correct for any number of phases.
Bill Gill
The formula works just as well for single phase power. Your description is quite correct for any number of phases.
Bill Gill
The formula works just as well for single phase power. Your description is quite correct for any number of phases.
Bill Gill
The formula works just as well for single phase power. Your description is quite correct for any number of phases.
Bill Gill
"Are you sure about that? Frequency affects induction, and if
"Induction is NOT 'affected' by frequency! "
"Induction" most certainly is affected by frequency. The basic definition of induction is the inducing of a voltage in a conductor by a changing magnetic field. With zero frequncy, you have zero induced current. Start increasing the frequency of the magnetic field, eg by moving a magnet back and forth, or allowing a nearby coil's magnetic field to vary, and there will be an increasing induced current in the conductor.
I think what your referring to is that the "inductance" of say a particular coil is fixed and determined strictly from the physical properties of the coil and it's measured in henrys and not dependent on frequency. I think what Toller meant was fairly clear from the context of the discussion concerning power. And that is that in the general case, the amount of power consumed by a given piece of equipment depends on the frequency of the source it is being driven with. That's because induction is frequency dependent and the impedance of a load containing inductance and/or capacitance will change as a function of frequency.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.