Phasors According to Rattus:
In view of the conflicting ideas about phasors from a recent thread, I will attempt to clarify the issue.
Definitions:
For our purposes, a phasor is a complex number providing the magnitude and phase of a sinusoidal voltage or current. For example,
Vb = 120Vrms @ -120 degrees
Might describe Vb in a 3-ph wye.
Some include impedances in this definition. For example,
Z = 100 Ohms @ 45
Describes an inductive impedance,
Z = (70.7 +jwL) Ohms
These phasors are sometimes called fixed phasors or static phasors because their values do not vary.
Rotating phasors provide complex values as functions of time. For example,
vb(t) = 170[cos(wt ? 2pi/3) + jsin(wt ? 2pi/3)]
Discussion:
Phasors describe any sinusoidal voltage or current?single phase or polyphase makes no difference. The idea that single phase values cannot be described with phasors is dead wrong!
Rotating magnetic fields in 3-ph motors should not be confused with the rotating phasors describing the 3-ph voltages and currents! A motor designer might describe the magnetic field at a fixed point with a phasor, but the rest of us would use them only for voltages and current.
In view of the conflicting ideas about phasors from a recent thread, I will attempt to clarify the issue.
Definitions:
For our purposes, a phasor is a complex number providing the magnitude and phase of a sinusoidal voltage or current. For example,
Vb = 120Vrms @ -120 degrees
Might describe Vb in a 3-ph wye.
Some include impedances in this definition. For example,
Z = 100 Ohms @ 45
Describes an inductive impedance,
Z = (70.7 +jwL) Ohms
These phasors are sometimes called fixed phasors or static phasors because their values do not vary.
Rotating phasors provide complex values as functions of time. For example,
vb(t) = 170[cos(wt ? 2pi/3) + jsin(wt ? 2pi/3)]
Discussion:
Phasors describe any sinusoidal voltage or current?single phase or polyphase makes no difference. The idea that single phase values cannot be described with phasors is dead wrong!
Rotating magnetic fields in 3-ph motors should not be confused with the rotating phasors describing the 3-ph voltages and currents! A motor designer might describe the magnetic field at a fixed point with a phasor, but the rest of us would use them only for voltages and current.
