Electrical engineering concepts

  📘 Unit‑5: Basics of PLC 5.1 Industrial Automation Definition: Use of control systems (computers, PLCs, robots) and information technologies to handle industrial processes with minimal human intervention. Block Diagram & Working: Sensors/Transducers → detect process variables (temperature, pressure, speed). Controller (PLC/DCS) → processes signals, applies logic/control algorithms. Actuators → execute commands (motors, valves, relays). Human–Machine Interface (HMI) → operator monitoring and control. Communication Network → links devices for data exchange. 5.2 Programmable Logic Controller (PLC) Definition: A digital computer used for automation of electromechanical processes. Block Diagram (PLC): Power Supply → provides DC power to PLC circuits. Processor (CPU) → executes control program, manages memory. Memory → stores user program and data. Input Module → receives signals from sensors/switches. Output Module → sends signals to actuators. Programming Device → us...

  Armature reaction is the effect of the magnetic field produced by the armature current on the main field flux of an alternator or synchronous machine. Its nature depends on the load power factor: at unity PF it distorts the flux (cross‑magnetizing), at lagging PF it weakens the flux (demagnetizing), and at leading PF it strengthens the flux (magnetizing). ⚙️ Definition When an alternator supplies load, the armature winding carries current . This current produces its own magnetic flux (armature flux). The armature flux interacts with the main field flux produced by the rotor poles. This interaction alters the distribution and magnitude of the resultant flux → called armature reaction . 🔄 Types of Armature Reaction (Based on Power Factor) Load Power Factor Effect on Flux Nature of Armature Reaction Result Unity PF (Resistive load) Flux distorted but magnitude unchanged Cross‑magnetizing Distortion of flux, small voltage drop Lagging PF (Inductive load) Armature flux opposes main ...

  Unit 4.0 Synchronous Motor 4.1 Working Principle & Starting of Synchronous Motor Working Principle: A synchronous motor runs at synchronous speed, i.e., speed is locked with supply frequency. Stator: supplied with 3‑phase AC → produces a rotating magnetic field. Rotor: excited with DC → produces constant magnetic poles. Synchronism occurs when rotor poles lock with stator’s rotating field. Starting: Synchronous motors are not self‑starting . Methods: Damper winding / squirrel cage winding → motor starts as induction motor, then DC excitation applied. Auxiliary motor starting → external motor brings rotor near synchronous speed. Variable frequency starting → supply frequency gradually increased until synchronism. 1 Understand Construction Rotor excited with DC, stator with 3-phase AC. Stator: 3-phase winding Rotor: DC excitation Produces constant poles 2 Starting Methods Motor requires external help to reach synchronous speed. Damper winding (induction start) Auxiliary moto...

  Unit 5.0 Special Electrical Machines 5.1 Construction, Working, Speed–Torque Characteristics, and Applications (i) AC Servo Motor Construction: Two‑phase motor with high resistance rotor; designed for precise control. Working: Operates on error‑signal amplification principle; responds quickly to control signals. Speed–Torque Characteristics: Linear torque vs. control voltage; high torque at low speeds. Applications: Robotics, CNC machines, aerospace control systems. (ii) Stepper Motor Construction: Stator with multiple windings; toothed rotor. Working: Rotates in discrete steps when windings are energized sequentially. Speed–Torque Characteristics: Torque decreases with speed; excellent for precise positioning without feedback. Applications: Printers, CNC machines, 3D printers, disk drives. (iii) Linear Induction Motor (LIM) Construction: Stator and rotor laid flat to produce linear motion. Working: Generates thrust instead of torque by creating a traveling magnetic fie...

  Unit‑3 Alternators (Synchronous Generators) 3.1 Construction – Salient and Cylindrical Rotor Salient Pole Rotor: Large diameter, short axial length. Poles project out; field windings wound on pole shoes. Suitable for low‑speed (100–400 rpm) hydro machines. Many poles (4–60). Diagram : Cylindrical Rotor Small diameter, long axial length. Smooth steel forging with slots for field windings. Suitable for high‑speed (1500–3000 rpm) turbo‑alternators. Few poles (2–4). Diagram : Smooth cylinder with slots along periphery. 3.2 Rotating Magnetic Field and Working Principle : Electromagnetic induction – EMF induced when flux cuts conductors. Rotating Magnetic Field : DC excitation on rotor → rotating flux → induces alternating EMF in stator. Synchronous Speed : N s = 120 f P Slip Speed : N s − N r . For synchronous machines, slip = 0. Diagram : Stator with 3‑phase windings, rotor field flux rotating. 3.3 Equivalent Circuit Model Internal EMF E in series with armature resistance R a and s...

  📘 AC Machines – Objective Questions  Unit 2 – Single‑Phase Induction Motor Single‑phase induction motors are not self‑starting ✅ Double revolving field theory explains: Starting of single‑phase induction motor ✅ Split‑phase motor uses: Auxiliary winding with resistance ✅ Capacitor start motor has: High starting torque ✅ Shaded pole motor is used in: Fans and small appliances ✅ Equivalent circuit of single‑phase induction motor is similar to: Transformer equivalent circuit ✅ Slip in induction motor is: ( N s − N ) / N s ✅ Applications of single‑phase induction motor: Ceiling fan, mixer, pump ✅ Capacitor start‑capacitor run motor has: Better efficiency and power factor ✅ Torque‑speed characteristic of single‑phase induction motor is: Non‑linear ✅ Unit 3 – Alternators Alternators are also called: Synchronous generators ✅ EMF equation of alternator: E = 4.44 f N Φ K c K b ✅ Salient pole alternators are used in: Hydro power plants ✅ Cylindrical rotor alternators are...

  📘 Control System & PLC – Objective Questions  Unit 2 – Control System Fundamentals A control system without feedback is called: Open loop ✅ A control system with feedback is called: Closed loop ✅ Transfer function is defined as: Output/Input in Laplace domain ✅ Poles on the right half of S‑plane indicate: Unstable system ✅ Negative feedback improves: Stability ✅ Root locus is plotted in: S‑plane ✅ The stability of a system can be checked using: Routh–Hurwitz criterion ✅ Time response of a system is analyzed in: Time domain ✅ Frequency response of a system is analyzed in: Frequency domain ✅ The steady‑state error decreases with: High gain ✅ Unit 3 – Stability Analysis Routh array is used to determine: System stability ✅ A system is stable if all poles lie: In LHS of S‑plane ✅ Gain margin is measured from: Bode plot ✅ Phase margin is measured from: Bode plot ✅ Nyquist plot is used for: Stability analysis ✅ A system is marginally stable if poles lie: On imag...

  Assignment – AC Machines  Course: Electrical Engineering Semester: 4 Subject: AC Machines **Assignment No.: 02 Maximum Marks: 20 Submission Date: 22/04/2026 Instructions Answer all questions neatly with proper diagrams wherever required. Use standard notation and units. Each question carries equal marks unless specified. Show all steps in derivations and numerical problems. Part A – Short Answer Questions (Any five) (2 Marks Each) Explain the construction and working principle of a single‑phase induction motor using the double revolving field theory. Classify single‑phase induction motors based on different starting methods (split‑phase, capacitor start, shaded pole). State the applications of single‑phase induction motors in domestic and industrial use. Explain with neat diagram the construction of a synchronous machine (salient pole and cylindrical rotor). Define synchronous speed and slip in alternators. Differentiate between turbo‑generators and hydro‑generato...