GENERATION OF ALTERNATING VOLTAGES AND CURRENTS:-
An alternating emf can be generated either by rotating a coil within a stationary magnetic field or by rotating a magnetic field within a stationary coil. The magnitude of emf generated in the coil depends upon the number of turns on coil, strength of magnetic field and speed at which the coil or magnetic field rotates.
SINUSOIDAL QUANTITIES (EMF , Voltage or Current)
It is not an accident that the bulk of electric power generated in electric power generated in electric power stations throughout the world and distributed to the consumers appears in the form of sinusoidal variations of voltage and current. There are many technical and economical advantages associated with the use of sinusoidal voltages and currents.
TERMINOLOGY
An alternating quantity (voltage or current) is one which changes continuously in magnitude and alternates in direction at regular intervals of time. It rises from zero to maximum positive value , falls to zero , increases to maximum in the reverse direction and falls back to zero again. The emf (or voltage) and current repeat the procedure.
The important ac terms are defined below:
> WAVEFORM:
The shape of the curve of the voltage or current when plotted against time as abcissa (base) is called the waveform. The waveform of an alternating voltage varying sinusoidally .The waveform of the induced emf in an alternator differs slightly from that of sine wave but for calculation purposes it is treated as such.
> INSTANTANEOUS VALUE:
The value of alternating quality at any particular instant is called instantaneous value. The instantaneous values of an alternating quantity can be determined either from the curve or from an equation of the alternating quantity.
> ALTERNATION AND CYCLE :
When a periodic wave, such as sinusoidal wave, goes through one complete set of positive or negative values , it is said to have completed one cycle. Alternation and cycle can also be defined in terms of angular measure.
> TIME PERIOD AND FREQUENCY:
The time taken in seconds by an alternating quantity to complete one cycle is known as time period or periodic time and is denoted by T.
> ANGULAR VELOCITY AND FREQUENCY :
If this quantity is divided by the time period, angular velocity of the sine function is obtained.
frequency is the product of pairs of poles to the number of revolutions made per second.
> AMPLITUDE :
The maximum value, positive or negative which an alternating quantity attains during one cycle is called an amplitude of the alternating quantity.
FORM FACTOR:-
Form factor is defined as the ratio of effective value to the average or mean value of a periodic wave.
PEAK FACTOR
peak or crest or amplitude factor of a periodic wave is defined as the ratio of maximum or peak to the effective or rms value of the wave.
PHASE
Phase of an alternating current is meant the fraction of the time period of that alternating current that has elapsed since the current last passed through the zero position of reference.
PHASE ANGLE
Phase angel of any quantity means the angel the phasor representing the quantity makes with the reference line.
PHASE DIFFERENCE
When two alternating quantities are considered simultaneously, the frequency being the same, they may not pass through a particular point at the same instant. One may pass through its maximum value at the instant when the other passes through the value other than its maximum one. These two quantities are said to have a phase difference.
The shape of the curve of the voltage or current when plotted against time as abcissa (base) is called the waveform. The waveform of an alternating voltage varying sinusoidally .The waveform of the induced emf in an alternator differs slightly from that of sine wave but for calculation purposes it is treated as such.
> INSTANTANEOUS VALUE:
The value of alternating quality at any particular instant is called instantaneous value. The instantaneous values of an alternating quantity can be determined either from the curve or from an equation of the alternating quantity.
> ALTERNATION AND CYCLE :
When a periodic wave, such as sinusoidal wave, goes through one complete set of positive or negative values , it is said to have completed one cycle. Alternation and cycle can also be defined in terms of angular measure.
> TIME PERIOD AND FREQUENCY:
The time taken in seconds by an alternating quantity to complete one cycle is known as time period or periodic time and is denoted by T.
> ANGULAR VELOCITY AND FREQUENCY :
If this quantity is divided by the time period, angular velocity of the sine function is obtained.
frequency is the product of pairs of poles to the number of revolutions made per second.
> AMPLITUDE :
The maximum value, positive or negative which an alternating quantity attains during one cycle is called an amplitude of the alternating quantity.
FORM FACTOR:-
Form factor is defined as the ratio of effective value to the average or mean value of a periodic wave.
PEAK FACTOR
peak or crest or amplitude factor of a periodic wave is defined as the ratio of maximum or peak to the effective or rms value of the wave.
PHASE
Phase of an alternating current is meant the fraction of the time period of that alternating current that has elapsed since the current last passed through the zero position of reference.
PHASE ANGLE
Phase angel of any quantity means the angel the phasor representing the quantity makes with the reference line.
PHASE DIFFERENCE
When two alternating quantities are considered simultaneously, the frequency being the same, they may not pass through a particular point at the same instant. One may pass through its maximum value at the instant when the other passes through the value other than its maximum one. These two quantities are said to have a phase difference.
