Jacek F. Gieras Izabella A.Gieras Electrical Energy Utilisation Wydawnictwo Adam Marszalek Contents Preface ........................................................VII 1 ENERGY AND DRIVES .................................. 1 1.1 Electrical energy . 1 1.2 Conservation of electrical energy . 2 1.3 Classification of electric motors . 4 1.4 Applications of electric motor drives . 5 1.5 Trends in the electric-motor and drives industry . 11 1.6 How many motors are used in affluent homes ? . 11 1.7 Fundamentals of mechanics of machines . 12 1.7.1 Torque and power . 12 1.7.2 Simple gear trains . 12 1.7.3 Efficiency of a gear train . 14 1.7.4 Equivalent moment of inertia . 14 1.8 Torque equation . 18 1.9 Mechanical characteristics of machines . 19 Problems . 21 2 D.C. MOTORS ............................................ 23 2.1 Construction . 23 2.2 Fundamental equations. 24 2.2.1 Terminal voltage . 24 2.2.2 Armature winding EMF . 25 2.2.3 Magnetic flux . 25 2.2.4 Electromagnetic (developed) torque . 25 2.2.5 Electromagnetic power . 26 2.2.6 Rotor and commutator linear speed . 26 2.2.7 Input and output power . 26 2.2.8 Losses . 27 2.2.9 Armature line current density . 28 2.3 D.c. shunt motor . 28 VI Contents 2.4 D.c. series motor . 30 2.5 Compound-wound motor . 31 2.6 Starting . 32 2.7 Speed control of d.c. motors . 34 2.8 Braking . 36 2.8.1 Braking a shunt d.c. motor . 37 2.8.2 Braking a series d.c. motor . 37 2.9 Permanent magnet d.c. commutator motors . 38 2.9.1 Permanent magnet materials . 38 2.9.2 Construction of d.c. permanent magnet motors . 40 2.9.3 Slotted-rotor PM d.c. motors . 44 2.9.4 Slotless rotor PM motors . 44 2.9.5 Moving-coil cylindrical motors . 45 2.9.6 Disc motors . 45 Problems . 47 3 THREE-PHASE INDUCTION MOTORS . 51 3.1 Construction . 51 3.2 Fundamental relationships . 52 3.2.1 Slip . 52 3.2.2 Rotor speed . 53 3.2.3 Input power . 53 3.2.4 Electromagnetic power . 53 3.2.5 Electromagnetic (developed) torque . 54 3.2.6 Mechanical power . 54 3.2.7 Rotor winding losses . 54 3.2.8 Voltage induced in the stator winding . 55 3.2.9 Stator winding factor . 55 3.2.10 Voltage induced in the rotor winding . 56 3.2.11 Induced rotor voltage referred to the stator system . 56 3.2.12 Rotor current referred to the stator system . 56 3.2.13 Rotor impedance . 57 3.2.14 Rotor impedance referred to the stator system . 57 3.2.15 Output power . 57 3.2.16 Rotational (mechanical) losses . 57 3.2.17 Stray losses . 58 3.2.18 Slip, electromagnetic power, and mechanical power . 58 3.2.19 Efficiency . 58 3.2.20 Shaft torque . 58 3.3 Equivalent circuit . 59 3.4 No-load and blocked-rotor tests . 61 3.4.1 No-load test . 61 3.4.2 Blocked-rotor test . 61 3.5 Torque-speed characteristics . 64 3.6 Starting . 72 Contents VII 3.6.1 Slip{ring motors . 72 3.6.2 Cage{rotor motors . 73 3.7 Induction motors that use skin effect in the rotor winding . 79 3.7.1 Double-cage motors . 79 3.7.2 Deep bar motors . 81 3.7.3 Comparison of torque{slip and input-current curves of cage induction motors.. 84 3.8 Speed control . 84 3.8.1 Frequency changing for speed control . 85 3.8.2 Pole changing for speed control . 87 3.8.3 Speed control by voltage variation . 88 3.8.4 Changing the resistance in the rotor circuit . 88 3.9 Braking . 88 3.9.1 Direct current injection (dynamic) braking . 88 3.9.2 Plugging . 89 3.9.3 Regenerative braking . 90 3.10 Connection of a three-phase motor to a single-phase power supply . 91 3.11 Abnormal operating conditions . 92 3.11.1 Increase in voltage, Pout = const . 92 3.11.2 Decrease in voltage Pout = const . 92 3.11.3 Change in frequency . 93 Problems . 93 4 SYNCHRONOUS MOTORS .............................. 97 4.1 Construction . 97 4.2 Fundamental relationships . 98 4.2.1 Speed. 98 4.2.2 Induced voltage . 98 4.2.3 Electromagnetic power . 99 4.2.4 Synchronous reactance . 99 4.2.5 Electromagnetic (developed) torque . 99 4.3 Phasor diagram . 100 4.4 Characteristics . 105 4.5 Starting . 105 4.5.1 Starting by means of an auxiliary motor . 105 4.5.2 Frequency-change starting . 106 4.5.3 Asynchronous starting . 107 4.6 Comparison with induction motors . 107 4.7 Permanent magnet synchronous motors . 108 4.8 Synchronous reluctance motors . 112 4.9 Hysteresis motors . ..