Basics of Electrical and Electronics

Unit 1 & Unit 2 Presentation

Unit 1: Elementary Concepts

1. Concept of Potential Difference, Current, and Resistance

• Potential Difference (Voltage, V): Difference in electric potential between two points. Measured in Volts (V).
• Current (I): Flow of electric charge. Measured in Amperes (A).
• Resistance (R): Opposition to current flow. Measured in Ohms (Ω).
• Power factor is given by $ \cos\theta $.

2. Ohm’s Law

• Formula:
  [ V = I \times R ]
• Voltage is directly proportional to current when resistance is constant.

3. Series and Parallel Circuits

Series Circuit

• Single path for current.
• Total Resistance:
  [ R_t = R_1 + R_2 + R_3 + … + R_n ]
• Current remains same in all components.
• Voltage divides across components.

Parallel Circuit

• Multiple paths for current.
• Total Resistance:
  [ \frac{1}{R_t} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3} + … + \frac{1}{R_n} ]
• Voltage remains same across components.
• Current divides among branches.

4. Voltage and Current Dividers

• Voltage Divider Rule:
  [ V_x = V_{total} \times \frac{R_x}{R_{total}} ]
• Current Divider Rule:
  [ I_x = I_{total} \times \frac{R_{total}}{R_x} ]

5. Power and Energy Calculations

• Power (P): Rate of energy transfer. Measured in Watts (W).
  [ P = V \times I ]
• Energy (E): Total power used over time. Measured in Joules (J).
  [ E = P \times t ]
• Electricity Bill Calculation:
  • Energy is measured in Kilowatt-hours (kWh).
  • Cost = Units Consumed × Rate per kWh.

6. Kirchhoff’s Laws

Kirchhoff’s Current Law (KCL)

• Sum of currents entering a junction = Sum of currents leaving the junction.
  [ \sum I_{in} = \sum I_{out} ]

Kirchhoff’s Voltage Law (KVL)

• Sum of all voltages in a closed loop = 0.
  [ \sum V = 0 ]

7. SI Units of Work, Power, and Energy

Unit 2: Single Phase and Polyphase A.C. Circuits

1. Generation of Single Phase Sinusoidal A.C. Voltages

• Alternating Current (AC): Current that varies sinusoidally over time.
• Generated using rotating coils in a magnetic field.
• AC Voltage Equation:
  [ v(t) = V_m \sin(\omega t) ] where:
  • ( V_m ) = Peak Voltage
  • ( \omega ) = Angular Frequency
  • ( t ) = Time

2. AC Quantities and Phasor Representation

• Phasor: Represents AC quantities as rotating vectors in a complex plane.
• Amplitude (Magnitude): Peak value of voltage or current.
• Phase Angle: Difference in phase between voltage and current.

3. Pure R, Pure L, and Pure C Circuits

Pure Resistive Circuit

• Voltage and Current are in phase.
• Power = ( P = V \times I ).

Pure Inductive Circuit

• Current lags voltage by 90°.
• Power = ( P = 0 ) (purely reactive).

Pure Capacitive Circuit

• Current leads voltage by 90°.
• Power = ( P = 0 ) (purely reactive).

4. Impedance and Admittance

• Impedance (Z): Total opposition in an AC circuit. Measured in Ohms (Ω).
  [ Z = R + jX ] where ( X ) is reactance.

• Admittance (Y): Reciprocal of impedance. Measured in Siemens (S).
  [ Y = \frac{1}{Z} ]

5. Active, Reactive, Apparent Power and Power Factor

• Active Power (P):
  [ P = V \times I \times \cos \phi ]
• Reactive Power (Q):
  [ Q = V \times I \times \sin \phi ]
• Apparent Power (S):
  [ S = V \times I ]
• Power Factor (PF):
  [ PF = \cos \phi ]
  • PF close to 1 → Efficient system.
  • PF close to 0 → High reactive power, inefficient system.

6. Polyphase A.C. Circuits

Introduction to Three-Phase Supply

• Three-phase systems are used for efficient power transmission.
• More power with less conductor material compared to single-phase.

Balanced Three-Phase System

• Equal phase voltages and 120° phase difference.

Relation between Line and Phase Quantities

• For Star Connection:
  [ V_{L} = \sqrt{3} V_{ph}, \quad I_L = I_{ph} ]

• For Delta Connection:
  [ V_L = V_{ph}, \quad I_L = \sqrt{3} I_{ph} ]

7. Power in Three-Phase Circuits

Star Connection

[ P = \sqrt{3} V_L I_L \cos \phi ]

Delta Connection

[ P = \sqrt{3} V_L I_L \cos \phi ]

• Power is same for both Star and Delta connections.

Simulations & Verifications

• Verify Power Factor for RL and RC Circuit using Multisim.
• Verify Line and Phase Values for Star & Delta Connection using Simulation.

End of Presentation