Basic EE Chapter 3

 Basic Electrical Engineering Chapter 3 

What is AC waveform

A waveform is a representation of how alternating current (AC) varies with time.The most familiar AC waveform is the sine wave, which derives its name from the fact that the current or voltage varies with the sine of the elapsed time.

Amplitudes

The first characteristic of AC power is its "amplitude". Amplitude is the maximumv alue of current or voltage. It is represented by either of the two peaks of the since wave. This voltage level is also referred to as the peak voltage, and can be either positive or negative. 

In an electrical circuit operating on alternating current (ac), amplitude is measured as the Voltage (V) level and is expressed as +V and V, depending on the direction of the current. Amplitudes are always positive numbers, An amplitude cannot be negative since it is defined as a half the distance, which cannot be negative, between the maximum value and the minimum value.

Frequency

Alternating current (ac) frequency is the number of cycles per second in an ac sine wave. Frequency is the rate at which current changes direction per second. It is measured in hertz (Hz), an international unit of measure where 1 hertz is equal to 1 cycle per second. 

The relation between the frequency and the period, T, of a repeating event oscillation is given by F=1/T 50 Hz and 60 Hz power sources are most often used in international power systems.if frequency increases, the secondary voltage or emf increases. And secondary voltage decreases by the reduction of supply frequency.

But with high frequency there is increase in transformer losses like core loss and conductor skin effect.The equipment in your home, factory or office is designed to operate at 50hz with in tight tolerance so it’s very important to keep the frequency of our power supply stable.

Cycle

Cycle = One complete wave of alternating current or voltage. Alternation = One

half of a cycle.

Time Period

Time Period = the time required to produce one complete cycle of a waveform.

The formula for time is: T (period) = 1 / f (frequency). λ = c / f = wave speed c (m/s)

/ frequency f (Hz). The unit hertz (Hz) was once called cps = cycles per second.

Phase

When the two quantities have the same frequency, and their maximum and

minimum point achieve at the same point, then the quantities are said to have in

the same phase.

Phase Difference

The two alternating quantities have phase difference when they have the same

frequency, but they attain their zero value at the different instant. The angle

between zero points of two alternating quantities is called angle of phase

differences.

Consider the two alternating currents of magnitudes Im1 and Im2 are shown

vectorially. Both the vector is rotating at the same angular velocity of ω radians per

seconds. The two current obtains the zero value at different instants. Therefore, they

are said to have the phase difference of angle φ

The quantity which attains its +ve maximum value before the other is called a

leading quantity, whereas the quantity which reaches its maximum positive value

after the other, is known as a lagging quantity. 

The current Im1 is leading the

current on Im2 or in other words, current Im2 is the lagging current on Im1.