DC Machines and Drives . Books Principle Of Electrical Machines (V.K. Mehta, Rohit Mehta) Electric Machinery Fundamentals (CHAPMAN J STEPHEN) Electrical Technology Volume II (B.L.Theraja) Basic Concepts Lecture # 01
Basic Quantities and Definitions Energy? Types of Energy? Conversation of Energy What is electricity /electrical Energy? - flow of electric charge. Charge . (atom, Electrons Protons, Neutrons) 1- Current 2- Voltage 3-Resistance
Electric Machines “Electromechanical device that converts electrical energy into mechanical energy is called motor ” while “A device that converts mechanical energy into electrical energy is called generator” We need electric machines in almost every field of our life today. From transportation to construction. Cars, Clocks, Drills, Fans, Fridges, Vacuum Cleaners,Water pumps, Washing Machines, Computers, Lifts, lathes, robots etc.
Machines are categorized or classified on the basis of input supply, construction and operation principles. Input supply ? In electrical system there are two kinds of supply systems means power source are provided. 1. AC system. 2. DC system. Alternating Current (AC). An electric current that reverses direction sinusoidally. Concept of phases and frequency. Direct Current (DC). Current flow is unidirectional and of constant magnitude . Negative and positive terminals (battery, cells)
Electric machines Alternating Current (AC) Machines Direct Current (DC) Machines Synchronous Induction Separately Excited Self Excited Single-Phase Three-Phase Series Compound Shunt Type of Electric Machines Classification of Machines
Construction and working of Electric machines An electric motor consists of many parts. Stator : The stationary part of an electric motor is called the stator. The stator will be provided with permanent magnets or windings. Rotor: The rotor is the part that actually converts electrical energy into mechanical energy. The rotor is connected to the mechanical load through the shaft. These come in various designs. For Example if we are talking about Induction or asynchronous motor, (a) Squirrel cage rotor, (b) Slip ring rotor or wound rotor or phase wound rotor. Or if we are talking about synchronous motors (a) Salient pole (100 to 1500rpm.) (b) non salient pole(>1500rpm).
Field windings: conductors used to produce electromagnetic field. Armature windings: conductors in which output voltage is produced (or input is provided) Electromagnetic Induction It is the fundamental operating principle of transformers, inductors, and many types of electricalmotors, generators and solenoids. Faraday (1831): An emf is induced in a conductor if a magnetic field passes by a conductor Whenever in a conductor if change in current occurs it "induces”a voltage (electromotive force) in both the conductor itself (self-inductance) and in any nearby conductors (mutual inductance).
Electromagnetic Induction • Magnitude of induced current can be increased by: • Increasing strength of magnetic field • Increasing speed of relative motion • Positioning of field & conductor to increase number of magnetic lines of flux cut • Magnetic field usually produced by electromagnet
Electromagnetics Rotor Stator • How motors work • Electricity supplied to stator • Magnetic field generated that moves around rotor • Current induced in rotor • Rotor produces second magnetic field that opposes stator magnetic field • Rotor begins to rotate
Overview of Direct Current Machines Direct-current (DC) machines are divided into dc generators and dc motors. Most DC machines are similar to AC machines: i.e. they have AC voltages and current within them. DC machines have DC outputs just because they have a mechanism converting AC voltages to DC voltages at their terminals. This mechanism is called a commutator; therefore, DC machines are also called commutating machines. DC generators are not as common as they used to be, because direct current, when required, is mainly produced by electronic rectifiers. While dc motors are widely used, such automobile, aircraft, and portable electronics, in speed control applications…