Electric Motors

HOW TO IMPROVE THE POWER (Electric Motor)

4.4 FACTOR To improve the power factor for a given load, the reactive load component (kvar) must be reduced. This component of reactive power lags the power component (kW input) by 90 electrical degrees, so that one way to reduce the effect of this component is to introduce a reactive power component that leads the […]

THE POWER FACTOR WITH NONLINEAR LOADS (Electric Motor)

4.5 The growing use of power semiconductors has increased the complexity of system power factor and its correction. These power semiconductors are used in equipment such as Rectifiers (converters) DC motor drive systems Adjustable-frequency AC drive systems Solid-state motor starters Electric heating Uninterruptible power supplies Computer power supplies In the earlier discussion about the power […]

HARMONICS AND THE POWER FACTOR (Electric Motor)

4.6 How do you know if you have a harmonic distortion problem? A single adjustable-frequency drive or DC drive is usually not a problem. However, if over 20% of the plant load contains power semiconductors, there is a good possibility of problems. Some of these problems are Transformer overheating and noisy Electric motors overheating and […]

POWER FACTOR MOTOR CONTROLLERS (Electric Motor)

4.7 In recent years, solid-state control devices have been developed that, when connected between a power source and an electric motor, FIGURE 4.17 Graphic and harmonic analysis of current of a DC motor drive. (Courtesy of Dranetz Technologies, Inc., Edison, NJ.) FIGURE 4.18 System line current before harmonic suppression. FIGURE 4.19 System line current after […]

Applications of Induction Motors (Electric Motor)

5.1 GENERAL DISCUSSION The AC induction motor is used more than any other means to power industrial equipment. This is confirmed by the U.S. Department of Energy report on electric motors, which states that 53-58% of the electric energy generated is consumed by electric motors (see Table 5.1). Because there are so many applications, it […]

VARYING DUTY APPLICATIONS (Electric Motor)

5.2 In many applications the load imposed on the driving motor varies from no load to a peak load. When the motor load fluctuates, the temperature rise of the motor fluctuates. When there is a definite repeated load cycle, the motor size selection can be based on the rms value of motor losses for the […]

VOLTAGE VARIATION (Electric Motor)

5.3 NEMA Standard MG1 recognizes the effect of voltage and frequency variation on electric motor performance. The standard recommends that the voltage deviation from the motor rated voltage not exceed ±10% at the rated frequency. A certain degree of confusion may exist in regard to the rated motor voltage since the rated motor voltage and […]

VOLTAGE UNBALANCE (Electric Motor)

5.4 Voltage unbalance can be more detrimental than voltage variation to motor performance and motor life. When the line voltages applied to a polyphase induction motor are not equal in magnitude and phase angle, unbalanced currents in the stator windings will result. A small percentage voltage unbalance will produce a much larger percentage current unbalance. […]

OVERMOTORING (Electric Motor)

5.5 In many instances, the practice has been to overmotor an application, i.e., to select a higher-horsepower motor than necessary. The disadvantages of this practice are Lower efficiency Lower power factor Higher motor cost Higher controller cost Higher installation costs One example of overmotoring is illustrated by the case of the varying duty applications discussed […]

POLYPHASE INDUCTION MOTORS SUPPLIED BY ADJUSTABLE-FREQUENCY POWER SUPPLIES (Electric Motor)

5.6 When applying polyphase induction motors to adjustable-frequency power supplies, it must be remembered that the induction motor nameplate rating is based on a fixed-frequency, fixed-voltage, sine-wave voltage source. Therefore, the application of polyphase induction motors with adjustable-frequency power supplies requires consideration of additional features that are not considered for fixed-frequency motor applications. 5.6.1 Types […]

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