A.C. Machines - I

Features Includes:

  • 152 - 3D/2D Animation
  • 757 Pages of Content
  • 90 Lecture Hours
  • 53 Solved Problems
  • 150 Quiz
  • Suitable for All Technical University Syllabus

Course Description

This learning solution provides an exhaustive coverage of the constructional details, the principle operation, prediction of performance, the methods of testing the transformers, three phase transformer connections and parallel operation of alternators.


  • Understand the working of single phase transformer and 3 phase transformers
  • Understand Three Phase Transformers
  • Understand the classification, construction, working and testing of alternators
  • Comprehend the procedure for voltage control and synchronisation

Single phase transformer - Definition of transformer - Transformer and its principle - Step-up and step-down transformer. Types of transformer - Based on construction - Types of transformers according to the magnetic core - Difference between core type and shell type transformer. Construction of transformer - Essential parts of a transformer - Construction of transformer. E.M.F. equation of a transformer - E.M.F. equation of transformer - Problems. Transformation ratio - Voltage transformation ratio - Problems. Ideal transformer - Elementary theory of ideal transformer. Transformer on No load - Transformer on No load - Importance in the study of transformer - Problems. Transformer On load - Transformer On load - Problems based on transformer on load. Transformer with winding resistance - Parameters referred to HV/LV windings - Magnetic leakage. Transformer with resistance and leakage reactance - Transformer with resistance and leakage reactance - Problem based on transformer with resistance and leakage reactance. Equivalent circuit - Equivalent circuit – Problems. Testing of transformers - Transformer test - Open circuit or no load test - Short circuit (or) impedance test. Voltage regulation - Regulation of transformer - Problems on voltage regulation. Losses in a transformer - Losses in a transformer - Problem based on losses in a transformer. Efficiency of a transformer - Transformer efficiency - Condition for maximum efficiency - Problems. All-day efficiency - All-day efficiency of a transformer - Problems. Sumpner’s test - Comparison between power transformer and distribution transformer - Sumpner's or back to back test. Parallel operation of transformers - Parallel operation of transformers - Parallel transformers on No-load - Division of load between transformers in parallel - Problems on parallel operation of transformers - Problems on load sharing.


Introduction - Three phase transformers advantages, types. Three phase transformer connections and condition for parallel operation - Three phase transformer connections - Connections of primary and secondary windings of 3-phase transformers - Types of 3-phase transformer winding connections - Delta/Delta Connection - Wye/Delta Connection - Delta/Wye Connection - Open delta connection - Conditions for parallel operation of three phase transformers. Special purpose transformer - Special purpose transformer - Saving of copper - Welding transformer. Instrument transformer - Necessity of instrument transformers - Types of instrument transformers - Current transformers - Ring type current transformer - Precautions in using C.T. Power measurement with the help of instrument transformer - Single phase power measurement - Three phase power measurement. Scott connection - Scott connection or T - T connection. Cooling of transformer - Necessity of cooling of power transformer - Methods of Cooling - OFN: Oil forced natural cooling (O-Oil, F-Forced, N-Natural) - Specifications of oil for cooling. Transformer tap changing - Necessity of tap changer - OFF-Load tap changing - ON-Load tap changing. Functions of Transformer Accessories - Function of breather, explosion vent, conservator, and oil level indicator - Buchholz relay. Maintenance of transformer - ISI 1886-1967 Recommended maintenance - ISI 1886-1967 Recommended Maintenance - BIS specifications for cooling system.


Introduction to alternators - Types of alternators - Advantages of polyphase alternator - Working operation of simple loop generator - Difference between D.C. generator and alternator. Construction of alternator - Construction and classification of alternators - Stator - Rotor - Difference between salient pole and non-salient pole rotor - Advantages of stationary armature - Mechanical and electrical angle - Frequency of induced E.M.F - Synchronous speed (Ns). Three phase windings in A.C. machines - Armature windings - Coil or winding element - Pole Pitch. Types of three phase windings - Types of armature windings - Coil span - Pitch factor - Chording of winding. EMF equation of alternator - E.M.F. equation - Problems - Exciter - Methods of excitation. Armature reaction - Armature reaction of alternators on load at various power factor - Power factors. Voltage variation of alternator on load - Alternator on load - Armature leakage reactance - Synchronous reactance - Synchronous impedance. Vector diagram of a loaded alternator - Vector diagram of alternators on load (for lag, lead and unity power factor). Voltage regulation - Determination of regulation by direct load test - Regulation for large machines - E.M.F. method or alternator test - Synchronous impedence method - Example using synchronous method/EMF method. Vector diagram and regulation for lagging, leading and unity power factor load - Vector diagram and regulation for lagging power factor load.


Necessity of parallel operation of alternators - Parallel operation of alternator - Three-phase alternators. Conditions for parallel operation of alternators - Parallel operation of alternators. Synchroscope - Dark lamp method - Bright lamp method - Dark and bright lamp method - Synchroscope method. Synchronizing current, synchronizing power - Synchronizing current, synchronizing power. Load sharing - Load sharing between two alternators - Alternators connected to infinite bus-bars - Alternative expression for synchronizing power - Effect of unequal voltages - Effect of change in steam supply. Problems on load sharing - Problems.