Essential Electrical Engineering Concepts Summary

Posted on Mar 6, 2026 in Electrical Engineering

Unit 1: Basic Electrical Principles

1. Ohm’s Law

At constant temperature, current is directly proportional to voltage; V = IR.

2. Kirchhoff’s Laws

  • KCL: Algebraic sum of currents at a node is zero.
  • KVL: Sum of voltages in a loop is zero.

3. Resistance, Inductance, Capacitance

  • Resistance (Ohm): Opposes current flow.
  • Inductance (Henry): Opposes current change.
  • Capacitance (Farad): Stores electric charge.

4. Active and Passive Elements

  • Active: Voltage sources, current sources.
  • Passive: Resistor, inductor, capacitor.

5. Current Calculation Example

Current through 100 Ω resistor: I = V/R = 220/100 = 2.2 A.

6. Thevenin and Norton’s Theorem

Any linear network can be replaced by an equivalent voltage source (Thevenin) or current source (Norton) with an equivalent resistance.

7. Resistor Calculation Example

Current in 5 Ω resistor: 2 A; Power: 20 W.

8. Time Constant (τ)

  • RL circuit: τ = L/R
  • RC circuit: τ = RC

9. Types of Electrical Sources

Independent voltage source, independent current source, and dependent sources.

10. Superposition Theorem

Total response equals the algebraic sum of responses due to individual sources acting alone.

Unit 2: AC Circuit Analysis

1. Define Impedance of an AC Circuit

Impedance is the total opposition offered by an AC circuit to current flow.

2. State Admittance and Unit

Admittance is the reciprocal of impedance; its unit is the siemens.

3. Inductive Reactance (XL)

Inductive reactance: XL = 2πfL ohms.

4. Capacitive Reactance (XC)

Capacitive reactance: XC = 1/(2πfC) ohms.

5. Average and RMS Voltage Values

Average value is the mean over a half cycle; RMS equals the effective DC value.

6. Define Form Factor and Peak Factor

  • Form factor: RMS / Average
  • Peak factor: Maximum / RMS value

7. Define Instantaneous Value, Frequency, and Time Period

Instantaneous value is the value at any instant; frequency is cycles per second; time period is the reciprocal of frequency.

8. Define Phase and Phase Difference

Phase represents waveform position; phase difference is the angular displacement between two waveforms.

9. Condition for Series and Parallel Resonance

  • Series resonance: Occurs when XL equals XC.
  • Parallel resonance: Occurs when inductive and capacitive susceptances are equal.

10. Define Resonant Frequency and Q-factor

Resonant frequency is the frequency at resonance; Q-factor indicates the sharpness of resonance.

Unit 3: Transformers

1. Conditions of an Ideal Transformer

No copper loss, no core loss, infinite permeability, zero leakage flux, and 100% efficiency.

2. What is Turns Ratio?

Turns ratio is the ratio of the number of secondary turns to primary turns.

3. List Various Losses in a Transformer

Transformer losses include copper losses, hysteresis loss, and eddy current loss.

4. What is a Step-Up Transformer?

A transformer that increases voltage from the primary to the secondary winding.

5. Applications and Advantages of Autotransformer

Used in voltage control and motor starting. Advantages include copper saving, high efficiency, and smaller size.

Unit 4: Rotating Machines

1. Material Used for D.C. Machine Brushes

Carbon or graphite brushes are used due to good conductivity and self-lubricating properties.

2. Applications of DC Motor

DC motors are used in electric trains, cranes, elevators, rolling mills, and electric vehicles.

3. Applications of Induction Motor

Induction motors are used in fans, pumps, compressors, conveyors, and household appliances.

4. Calculate Speed of 4-Pole Machine (50 Hz)

Synchronous speed = 120f/P = 120×50/4 = 1500 rpm.

5. Applications of Synchronous Generator

Synchronous generators are used in power stations to generate large-scale AC electrical power.

Unit 5: Electrical Installations and Safety

1. Different Types of Cables

Types of cables include VIR, PVC, TRS, lead-sheathed, and XLPE cables.

2. Energy Consumed by Heater

Energy consumed by a 1000-watt heater in 3 hours equals 1000 × 3 = 3000 Wh or 3 kWh.

3. Use of MCB

MCB protects electrical circuits from overload and short-circuit faults.

4. Define Earthing and Its Importance

Earthing connects metal parts to the ground, preventing electric shock and equipment damage.

5. Full Form of M.C.C.B.

MCCB stands for Moulded Case Circuit Breaker.