Electrical and Electronic Principles and Technology: AC Supplies

2. DC and AC Supplies

2.2. AC Supplies

Introduction to AC Supplies

Alternating Current (AC) is the most common form of electrical power used for residential, commercial, and industrial purposes. Unlike Direct Current (DC), which flows in one direction, AC reverses direction periodically, typically in the form of a sine wave. This reversing nature makes AC more efficient for transmitting electricity over long distances, which is why it is used in national power grids.

AC supplies are generated using alternators in power stations and can be easily stepped up or down in voltage using transformers. Understanding AC characteristics, waveform properties, and its behavior in circuits is essential for grasping how electrical systems operate on a large scale.

AC Supplies – Notes

1. Definition

AC Supply (Alternating Current Supply) is a type of electrical current that changes direction periodically and varies in magnitude with time.

2. Waveform

The most common AC waveform is the sine wave.
Other types: Square wave, Triangular wave (used in some electronic systems).
In a sine wave:
$V(t) = V_{max} \sin(\omega t)$
$V (t) = V ma x sin (ω t)$

3. Characteristics of AC Supply

Parameter	Symbol	Description
Frequency	f	Number of cycles per second (Hz)
Period	T	Time taken for one complete cycle (T = 1/f)
Amplitude	$V_{max}$ Vmax	Peak voltage
RMS Value	$V_{rms}$ Vrms	Effective value = $\frac{V_{max}}{\sqrt{2}}$ 2Vmax
Phase	θ	Describes the shift between waveforms

4. Comparison: AC vs DC

Feature	AC	DC
Flow Direction	Reverses periodically	Constant in one direction
Transmission	Efficient over long distances	Less efficient
Generation	Alternator	Battery, DC generator
Voltage Change	Easy with transformer	Difficult
Common Use	Power grids, appliances	Electronics, vehicles

5. Sources of AC Supply

Alternators (in power plants)
AC generators
Inverters (convert DC to AC)
Mains electricity (e.g., 230V, 50Hz in India)

6. Applications of AC Supply

Powering homes and industries
Running electric motors and appliances
Lighting systems
HVAC systems
Transmission and distribution systems

7. Important Formulas

Instantaneous Voltage:
$V(t) = V_{max} \sin(\omega t + \phi)$
$V (t) = V ma x sin (ω t + ϕ)$
RMS Value:
$V_{rms} = \frac{V_{max}}{\sqrt{2}}$
$V r m s = 2$

$V ma x$
Power in AC Circuits:
$P = V_{rms} I_{rms} \cos(\phi)$
$P = V r m s I r m s cos (ϕ)$
(Where
$\cos(\phi)$
cos(ϕ) is the power factor)

8. Types of AC Loads

Resistive: Heaters, incandescent bulbs
Inductive: Motors, transformers
Capacitive: Capacitor banks