Electricity and Magnetism

Synchronous Machines General Synchronous machines are called “Synchronous” because in a steady state their rotors are running at the angular velocity of the rotating magnetic field set up by the currents in the phase windings of a stator similar to that of an induction machine. ,This synchronism is achieved owing to the fact that the […]
Continue reading…

The Induction Tachogenerator Induction tachogenerators are employed in automatic control systems and electric drives as angular-rate transducers. One form of induction tachogenerator known as the drag-cup type is shown in Fig 42. When the rotor is at a standstill (ɷrot = 0), the alternating magnetic flux Φt excited by the current traversing a field coil, […]
Continue reading…

The Induction Regulator and the Phase Shifter An induction regulator is essentially a booster transformer constructed in the same way as a three-phase wound-rotor induction motor except that the rotor is not free to rotate; it can, however, be set in a range of orientations with respect to the stator. The winding connections in an […]
Continue reading…

Two-Phase and Single-Phase Induction Motors In an induction motor with only one single-phase winding on the stator (Fig 33), the applied alternating current would excite an alternating magnetic field whose axis would remain stationary so long as its rotor remains stationary, too. This field would induce an emf in the rotor winding, giving rise to […]
Continue reading…

Speed Control of Induction Motors In many cases three-phase induction motors are used in drives where speed control is not required. However, induction motors have valuable advantages to offer, namely reliability, low cost, simple design, high efficiency, and a relatively small weight. For this reason, it is only natural that efforts have been made to […]
Continue reading…

The Universal Torque-Slip Curve of an Induction Machine As is the case with any electric machines, induction machines are reversible. This means that one and the same induction machine can operate as a motor, that is, convert electricity into mechanical energy (motoring action), or as a generator, that is, convert mechan­ical energy into electricity (generating […]
Continue reading…

The Operating Characteristics of an Induction Motor The speed-torque characteristic of an induction motor is a con­venient indicator of its properties as a part of an electric drive. A deeper insight into its performance, however, can be gleaned from what we call its operating characteristics which relate its speed n , its torque T, its […]
Continue reading…

Starting of an Indudion Motor The starting performance of induction motors is an important consideration in their evaluation. This performance is basically determined by the following quantities: the starting current Istart . the starting torque Tstart . the starting time, and the economy of operation at starting. Makers’ data sheets usually quote the start­ing-to-rated ratio […]
Continue reading…

The Torque-Slip Curve and Speed-Torque Characteristic of an Induction Motor For an induction motor to run steadily, it is essential that its torque should balance the applied load automatically-as the load applied to the shaft of a motor is increased, the torque developed by the motor must go up in proportion. In a running induction […]
Continue reading…

The Torque of an Induction Motor An expression for the torque of an induction motor may be deri­ved from the equation of the mechanical power, Pm , available at. its shaft T = Pm/ɷrot                              (14.22) where ɷrot is the angular velocity of the rotor. Since the angular velocity of the rotor is ɷrot = 2πn/60 […]
Continue reading…