Electrical & Electronics Engineering

Part 1 – Basic Electrical Engineering

Electrical engineering begins with understanding the fundamental electrical quantities.

1. Electrical Quantities

• Electric Charge (Q): The basic property of matter responsible for electrical effects. Symbol: Q. Unit: Coulomb (C). Electron charge = 1.6 × 10⁻¹⁹ C.
• Electric Current (I): The rate of flow of electric charge. Formula: I = Q / t. Unit: Ampere (A).
  Example: If 20 Coulombs pass through a conductor in 4 seconds, Current = 20/4 = 5 A.
• Voltage (V): The electrical pressure that causes current to flow. Unit: Volt (V). Formula: V = W/Q. A battery provides voltage to a circuit.
• Resistance (R): Opposes current flow. Unit: Ohm (Ω). Formula: R = ρL/A. Factors affecting resistance: Length increases → Resistance increases; Area increases → Resistance decreases; Temperature increases (metals) → Resistance increases; Material type.
• Conductance: The reciprocal of resistance. Formula: G = 1/R. Unit: Siemens (S). Good conductors have high conductance.

2. Ohm's Law

At constant temperature, current flowing through a conductor is directly proportional to the applied voltage.

Example: Voltage = 230 V, Resistance = 46 Ω, Current = 230/46 = 5 A.

Limitations: Not applicable for Diodes, Transistors, Electrolytes, Arc lamps, and Vacuum tubes.

3. Electrical Power

Power is the rate of electrical energy consumption.

Unit: Watt (W). 1 kW = 1000 W.

Energy: Energy = Power × Time. Units: Joule, Watt-hour, Kilowatt-hour (kWh). 1 Unit of electricity = 1 kWh. Example: 1000 W heater operates for 3 hours → Energy = 1 × 3 = 3 units.

4. Types of Electric Current

• Direct Current (DC): Current flows only in one direction. Examples: Battery, Solar cell, DC Generator. Applications: UPS, Electric vehicles, Electronics. Advantages: Constant voltage, easy battery storage.
• Alternating Current (AC): Current changes magnitude and direction periodically. Frequency in India = 50 Hz. Generated in power stations. Advantages: Easy voltage transformation, suitable for long-distance transmission, lower transmission losses.

5. AC Waveform

An AC waveform is generally sinusoidal. Important terms:

• Cycle: One complete positive and negative alternation.
• Frequency: Number of cycles per second. Unit: Hertz (Hz). Formula: f = 1/T.
• Time Period: Time taken for one cycle. Unit: Second.
• Peak Value: Maximum value of voltage/current.
• RMS Value: Effective value of AC. V_rms = V_max/√2, I_rms = I_max/√2. RMS values are used in practical calculations.
• Average Value: Average value over one half-cycle.

6. Kirchhoff's Laws

• Kirchhoff's Current Law (KCL): Sum of incoming currents equals sum of outgoing currents. Formula: ΣI = 0. Used in node analysis.
• Kirchhoff's Voltage Law (KVL): The algebraic sum of voltages around any closed loop is zero. Formula: ΣV = 0. Used in loop analysis.

7. Series Circuit

Characteristics: Current remains same, voltage divides, resistance adds.

Example: 10 Ω, 20 Ω and 30 Ω → Total = 60 Ω. Applications: Decorative lamps, Fuse circuits.

8. Parallel Circuit

Characteristics: Voltage remains same, current divides.

Advantages: Independent operation, common in domestic wiring.

9. Electrical Network

• Active Network: Contains voltage or current source.
• Passive Network: Contains only passive components.
• Bilateral Network: Characteristics remain same in either direction. Example: Resistor.
• Unilateral Network: Characteristics depend on current direction. Example: Diode.

10. Electrical Components

11. Electromagnetism

A current carrying conductor produces a magnetic field.

• Fleming's Left-Hand Rule (Motor direction): Thumb → Force, Forefinger → Magnetic field, Middle finger → Current.
• Fleming's Right-Hand Rule (Generator direction): Thumb → Motion, Forefinger → Magnetic field, Middle finger → Induced current.

12. Electromagnetic Induction

Discovered by Michael Faraday. Whenever magnetic flux linking a conductor changes, EMF is induced.

• Faraday's First Law: Changing magnetic field induces EMF.
• Faraday's Second Law: Induced EMF is proportional to rate of change of magnetic flux.

Lenz's Law: Direction of induced EMF opposes the cause producing it. This obeys conservation of energy.

13. Magnetic Circuit

• Magnetic Flux (Φ): Unit: Weber (Wb).
• Flux Density: Formula: B = Φ/A. Unit: Tesla.
• Magnetomotive Force (MMF): Formula: MMF = NI. Unit: Ampere Turns.
• Reluctance: Opposition offered to magnetic flux. Equivalent to resistance in electrical circuits.

14. Self and Mutual Inductance

• Self Inductance: Voltage induced in the same coil due to change in its own current. Unit: Henry.
• Mutual Inductance: Voltage induced in one coil due to current change in another coil. Used in Transformers, Induction coils.

15. Heating Effect of Electric Current

According to Joule's Law, heat produced:

Applications: Electric heater, Iron box, Water heater, Electric kettle, Fuse.

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Part 2 – Electrical Machines, Power Systems & Measuring Instruments

This section covers the core Electrical Engineering topics that are frequently asked in TNPSC Combined Technical Services (CTS) examinations.

16. DC Generator

A DC Generator converts mechanical energy into direct current (DC) electrical energy based on Faraday's Law of Electromagnetic Induction.

Principle: When a conductor rotates in a magnetic field, an EMF is induced.

Main Parts: Yoke, Pole Core, Pole Shoe, Field Winding, Armature Core, Armature Winding, Commutator, Carbon Brushes, Shaft, Bearings.

Working: Prime mover rotates the armature → Conductors cut magnetic flux → EMF is induced → Commutator converts alternating EMF into DC output.

• Separately Excited Generator: Field winding supplied from an external source. Better voltage control.
• Self-Excited Generator: Shunt Generator, Series Generator, Compound Generator.

Applications: Battery charging, Electroplating, Welding, DC laboratories, Exciters.

17. DC Motor

A DC Motor converts electrical energy into mechanical energy. Principle: A current-carrying conductor placed inside a magnetic field experiences a force (Fleming's Left-Hand Rule).

Back EMF: When a motor rotates, it generates an EMF opposite to supply voltage. It controls armature current, prevents excessive current, and improves efficiency.

18. Transformer

A transformer transfers electrical energy from one circuit to another through electromagnetic induction. It works on Mutual Induction.

Construction: Laminated Iron Core, Primary Winding, Secondary Winding, Insulation, Oil Tank, Conservator, Breather, Bushings.

• Step-Up Transformer: Secondary voltage > Primary voltage. Used in transmission.
• Step-Down Transformer: Secondary voltage < Primary voltage. Used in distribution.
• Core Type: Windings surround the core.
• Shell Type: Core surrounds the winding.

Transformer Losses:

• Copper Loss: Due to winding resistance. Formula: I²R.
• Iron Loss: Includes Hysteresis Loss and Eddy Current Loss. Reduced by laminated core.

Efficiency: Efficiency = Output/Input × 100. Power transformers generally have efficiency above 95%.

Applications: Transmission, Distribution, Chargers, UPS, Electronic devices.

19. Three-Phase System

Almost all industrial power systems use three-phase supply.

Advantages: Less conductor material, higher efficiency, smooth power, suitable for heavy motors, economical transmission.

• Star (Y) Connection: Neutral available, lower phase voltage, domestic distribution. Relation: V_L = √3 V_P.
• Delta (Δ) Connection: No neutral, high power capability, industrial loads. Relation: V_L = V_P.

20. Three-Phase Induction Motor

The most widely used industrial motor. Works on rotating magnetic field.

Construction: Stator (produces rotating magnetic field); Rotor (Squirrel Cage or Slip Ring).

Advantages: Simple construction, low maintenance, high efficiency, reliable, long life.

Applications: Pumps, Compressors, Textile industries, Factories, Fans, Crushers, Conveyors.

Slip: The difference between synchronous speed and rotor speed. Slip is essential for torque production.

21. Synchronous Motor

Rotor rotates exactly at synchronous speed. Characteristics: Constant speed, high efficiency, improves power factor. Applications: Power factor correction, Large industries, Compressors.

22. Alternator

Converts mechanical energy into alternating current based on Faraday's Law. Parts: Rotor, Stator, Exciter, Shaft. Applications: Thermal power plants, Hydro power plants, Diesel generators, Wind turbines.

23. Measuring Instruments

24. Electrical Wiring

• Cleat Wiring: Temporary wiring.
• Casing and Capping: Old system. Rarely used today.
• Batten Wiring: Suitable for small buildings.
• Conduit Wiring: Most common. Types: Surface conduit, Concealed conduit. Advantages: Safe, durable, neat appearance.

25. Earthing

Earthing protects people and equipment. Purposes: Prevent electric shock, protect equipment, provide low resistance path, protect against leakage current.

Types: Plate, Pipe, Rod, Strip earthing. Pipe earthing is the most commonly used method in India.

26. Fuse

A fuse protects electrical circuits based on the heating effect of electric current. Characteristics: Low melting point, connected in series, replaced after operation. Types: Rewirable Fuse, HRC Fuse, Cartridge Fuse.

27. Circuit Breaker

Automatically disconnects faulty circuits. Advantages over Fuse: Reusable, faster operation, better protection, remote control possible. Types: MCB, MCCB, ACB, OCB, VCB, SF₆ Circuit Breaker.

28. Relay

A relay senses abnormal conditions and sends a trip signal to the circuit breaker. Types: Overcurrent Relay, Earth Fault Relay, Differential Relay, Distance Relay.

29. Batteries

A battery stores electrical energy in chemical form.

• Primary Battery: Cannot be recharged. Examples: Dry Cell, Alkaline Cell.
• Secondary Battery: Rechargeable. Examples: Lead Acid, Lithium-ion, Nickel-Cadmium.

30. Power Generation

31. Transmission and Distribution

Transmission Voltage: Generated voltage is stepped up for long-distance transmission to reduce current and minimize I²R losses.

Distribution Voltage: Voltage is stepped down before supplying consumers. Typical supply in India: Single Phase: 230 V, Three Phase: 400 V.

32. Power Factor

Power factor is the ratio of real power to apparent power. Power Factor = cos φ.

Importance: Reduces line current, improves efficiency, reduces power losses, improves voltage regulation.

Methods of Improvement: Capacitor banks, Synchronous condensers, Phase advancers.

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Part 3 – Electronics Engineering, Digital Electronics, Control Systems & Communication

This part covers the Electronics portion of the TNPSC Combined Technical Services (CTS) syllabus.

33. Semiconductor Physics

A semiconductor is a material whose electrical conductivity lies between that of a conductor and an insulator.

Common Semiconductor Materials: Silicon (Si), Germanium (Ge). Silicon is preferred because it can withstand higher temperatures, has lower leakage current, and is inexpensive and widely available.

• Intrinsic Semiconductor: Pure semiconductor, no impurities added, number of electrons = number of holes. Examples: Pure Silicon, Pure Germanium.
• Extrinsic Semiconductor: Impurities added to improve conductivity. Types: N-type, P-type.
• N-Type: Pentavalent impurities (Phosphorus, Arsenic, Antimony). Majority carriers: Electrons. Minority carriers: Holes.
• P-Type: Trivalent impurities (Boron, Aluminium, Gallium). Majority carriers: Holes. Minority carriers: Electrons.

34. PN Junction Diode

A PN junction diode is formed by joining P-type and N-type semiconductors. It allows current in one direction only.

• Forward Bias: P to positive, N to negative. Current flows easily.
• Reverse Bias: P to negative, N to positive. Only a very small leakage current flows.

Applications: Rectifiers, Clippers, Clampers, Switching circuits.

35. Special Purpose Diodes

36. Rectifiers

A rectifier converts AC into DC.

• Half-Wave Rectifier: Uses one diode. Advantages: Simple, low cost. Disadvantages: Low efficiency, high ripple.
• Full-Wave Rectifier: Uses two diodes with center-tapped transformer OR four diodes in bridge rectifier. Advantages: Higher efficiency, less ripple, better output. Bridge rectifier is commonly used.

37. Filters

Filters remove AC ripple from rectifier output. Types: Capacitor Filter, Inductor Filter, LC Filter, π (Pi) Filter. Capacitor filter is the most common.

38. Transistor (BJT)

A transistor is a three-terminal semiconductor device used for amplification and switching. Terminals: Emitter, Base, Collector. Types: NPN, PNP.

A small base current controls a large collector current. Thus, a transistor acts as an amplifier. Applications: Amplifiers, Switching, Oscillators, Logic circuits.

39. Field Effect Transistor (FET)

A voltage-controlled device. Types: JFET, MOSFET. Advantages: High input impedance, low power consumption, low noise. Applications: Integrated circuits, Amplifiers, Switching circuits.

40. MOSFET

MOSFET stands for Metal Oxide Semiconductor Field Effect Transistor. Advantages: Very high switching speed, high efficiency, low heat generation. Applications: SMPS, Computer motherboards, Inverters, Power electronics.

41. Operational Amplifier (Op-Amp)

An operational amplifier is a high-gain differential amplifier. Popular IC: IC 741. Characteristics: Very high gain, high input impedance, low output impedance. Applications: Comparator, Integrator, Differentiator, Summing amplifier, Instrumentation.

42. Oscillator

An oscillator produces AC signals without an external input signal. Types: RC Oscillator, LC Oscillator, Crystal Oscillator. Crystal oscillator provides the highest frequency stability. Applications: Clocks, Microprocessors, Communication equipment.

43. Digital Electronics

Digital electronics deals with binary numbers. Only two logic levels: 0 (LOW) and 1 (HIGH). Advantages: High reliability, high speed, better noise immunity.

44. Number Systems

• Decimal: Base = 10, Digits: 0–9.
• Binary: Base = 2, Digits: 0 and 1.
• Octal: Base = 8, Digits: 0–7.
• Hexadecimal: Base = 16, Digits: 0–9 and A–F.

Important Binary Conversions: Decimal 10 = Binary 1010; Decimal 15 = Binary 1111; Decimal 16 = Binary 10000; Decimal 25 = Binary 11001.

45. Logic Gates

46. Boolean Algebra

Basic Laws: Commutative Law, Associative Law, Distributive Law, De Morgan's Theorem. De Morgan's theorem is frequently asked in TNPSC.

47. Flip-Flops

Flip-flops store one binary bit. Types: SR, JK, D, T Flip-Flop. Applications: Memory, Registers, Counters.

48. Counters

Counters count pulses. Types: Ripple, Synchronous, Up, Down, Up/Down Counter. Applications: Digital clocks, Frequency counters, Traffic control.

49. Registers

Registers temporarily store binary information. Types: SISO, SIPO, PISO, PIPO. Applications: Data storage, Data transfer.

50. Microprocessor

A microprocessor is the CPU on a single integrated circuit. Main Units: ALU, Control Unit, Registers. Common Processor: 8085. Applications: Computers, Automation, Embedded systems.

51. Microcontroller

A microcontroller contains CPU, RAM, ROM, I/O Ports, Timers. Popular Controllers: 8051, PIC, AVR. Applications: Washing machines, Traffic lights, Home automation, Robotics.

Difference: Microprocessor needs external memory and peripherals; Microcontroller integrates them on a single chip.

52. Communication Systems

A communication system transfers information from transmitter to receiver. Main Blocks: Information Source, Transmitter, Channel, Receiver, Destination. Types: Wired, Wireless.

Modulation: The process of varying a carrier wave according to the information signal. Types: AM, FM, PM. FM has better noise immunity than AM.

53. Optical Fiber Communication

Uses light signals for communication. Advantages: High bandwidth, low attenuation, high speed, immune to electromagnetic interference. Applications: Internet, Cable TV, Telephone networks.

54. Control Systems

• Open Loop System: No feedback, simple, low cost, less accurate. Example: Electric toaster.
• Closed Loop System: Uses feedback, more accurate, better performance. Examples: Automatic voltage regulator, Air conditioner thermostat, Speed control system.

55. Sensors and Transducers

A sensor detects a physical quantity such as temperature, pressure, or light. A transducer converts one form of energy into another. Examples: Thermocouple, LVDT, Strain Gauge, RTD, Thermistor. Applications: Industrial automation, Robotics, Medical instruments.

56. Power Electronics

Power electronics deals with the control and conversion of electrical power using semiconductor devices. Important Devices: SCR, TRIAC, DIAC, IGBT. Applications: Motor speed control, Inverters, UPS, Electric vehicles.

57. PLC (Programmable Logic Controller)

A PLC is an industrial digital controller used for automation. Advantages: Reliable, flexible, easy troubleshooting, compact. Applications: Manufacturing plants, Conveyor systems, Packaging industries, Process control.

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