Three-phase induction motor

The calihration curve (three-phase induction motor) of Figure 14-5 is essential to determine the load change based on the current change for motors helow 200 hp or with load variations of more than 5-10%. 

Table 2-1 yields ballpark motor efficiencies. The table applies to three-phase induction motors only. For singlephase, multiply by about 0.8. Single-phase motors are not generally recommended above 10 HP. 

Three-phase induction motors operating at a fixed speed are used industrially. By using permanent magnets in the induction motors, it is possible to attain reduction in size and weight and improved efficiency. 

In addition to the above, NEMA designates a special class of Premium Efficiency Electric Motors (2003) for three-phase induction motors applied to municipal or industrial applications for operation on voltages of 600 V or less, rated 500 HP or less, operating more than 2000 hr/yr at more than 75% of full load. For details, please refer to NEMA MG 1-1998 Table 12-12. For each HP rating, that table defines nominal and minimum efficiencies for 2-, 4-, and 6-pole open motors. 

AC electric drives require more sophisticated converters when they are supplied with DC sources, because electric machines requires periodic voltage and current waves with a variable frequency depending on the load requirements. In Fig. 5.8, the scheme of an example of three-phase induction motor driven by a pulse-width-modulated inverter is reported. In this scheme a three-phase bridge connection with six power modules is shown to form the so-called inverter. Each power module can be composed by a number of power switches connected in parallel to carry higher currents. Across each power switch (IGBT) a parallel diode is connected to provide a return path for the phase current when the power module is switched off. 

Fig. 5.8 Scheme of a three-phase induction motor driven by inverter... 

Some rule-of-thumb methods are often stated in the purchasing specifications of the motor-machine unit, see for example Table 1.11, which applies to low voltage three-phase induction motors. 

A cage rotor is used on single-phase a.c. motors, the turning force being produced in the way described previously for three-phase induction motors and shown in Fig. 2.49. Because both windings carry currents which are out of phase with each other, the motor is known as a split-phase motor. The phase... 

B. C. Ghosh and S.N. Bhadra. Bond graph simulation of a current source inverter driven induction motor (csi-im) system. Electric Machines and Power Systems, 21(l) 51-67, 1993. B. Umesh Rai and L. Umanand. Bond graph model of doubly fed three phase induction motor using the axis rotator element for frame transformation. Simulation Modelling Practice and... 

Electric motors. The PF of an induction motor varies with the load, as shown in Fig. 10.207. Unloaded or lightly loaded motors exhibit a low PF. Figure 10.208 illustrates the variation of PF and reactive power for varying loads on a three-phase induction motor. Synchronous motors provide good PF when their excitation is adjusted properly. Synchronous motors also can be overexcited to exhibit a leading power factor and, therefore, may be used to improve the power factor of a facility. 

FIGURE 10.208 The relationship of reactive power and power factor to percentage of load for a 100-kW, three-phase induction motor. 

Evolution and standardization within the motor industry have resulted in five fundamental types of three-phase induction motors known by NEMA design letters (discussed later in... 

Today, energy-efficient three-phase induction motors, both open and TEFC, are available in ratings from 1 to 500 hp (0.7 kW to 373 kW). In many locations the cost of electric power is high and energy-efficient motors can be justified on loads operating a high percentage of the time. 

Reversed-Phase Protection. Phase-failure and phase-reversal relays are used to prevent the operation of elevators and industrial machinery to protect motors, machines, and personnel from potential hazards when phase reversal or loss occurs. Interchanging two phases of the supply of a three-phase induction motor will reverse its direction of rotation. 

Fig. 9.14 Mercedes-Benz zero emission class A EV. The car uses a 40 kW (54 hp)—three-phase induction motor developing a rated torque of 155 Nm which can accelerate the ear to 100 km/h in 17 s with a top speed of 120 km/h and a normal usage range of 150 km. Recharging can be made in 6-12 h using normal household sockets. The battery system is sodium/nickel chloride with an energy storage capacity of 100 Wh/kg and a life of over 100,000 km...

Onel, l.Y, Dalci, K.B. Send, 1. 2006. Detection of bearing defects in three-phase induction motors using Park s transform and radial basis function neural networks. Sadhana 31(3) 235-244. 

For tests, this model was conveniently operated by a submerged, three phase induction motor. This was of a type specially designed and built by Pesco for cryogenic applications. 

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