Electric motors alternating-current

EI6 - 150P, PROCESS ELECTRICAL EQUIPMENT - LOW VOLTAGE MOTORS, ALTERNATING CURRENT. 

Within these basic principles there are many types of electric motors. Each has its own individual operating characteristics peculiarly suited to specific drive applications. Equations (29-1) through (29-9), presented in Table 29-1, describe the general operating characteristics of alternating-current motors. When several types are suitable, selection is based on initial installed cost and operating costs (including maintenance and consideration of rehability). 

The electrical power supplied to electrical motors can be from a direct-current (dc) source or an alternating-current (ac) source. Because dc motors are more... 

Alternating-current motors are classified as induction motors or synchronous motors. Faraday found that a stationaiy wire in a magnetic field produced no current. However, when the wire continues to move across magnetic lines of force, it produces a continual current. When the motion stops, so does the current. Thus Faraday proved that electric current is only produced from relative motion between the wire and magnetic field. It is called an induced current—an electromagnetic induction effect. 

Italian-American physicist Nikola Tesla invents a motor that produces alternating current. This discovery changes the way electricity is transmitted over long distances. The first commercial, long-distance transmission of electricity takes place when a direct-current line provides power from Willamette Falls for street lights in Portland, Oregon. 

Figure 14-2A. Alternating current (AC) induction motor cross-sectional view of 220/440V, 3-phase, 60-cycle, totally enclosed fan-cooled standard motor. (Used by permission Reliance Electric Co., Div. Rockwell Automation.)...

This is a very good motor for direct connection to certain loads, particularly where constant speed is required. NEMA defines it as a synchronous machine which transforms electrical power from an alternating-current system into mechanical power. It usually has direct-current field excitation by a separately driven direct-current generator or one directly connected to the motor. This motor remains synchronous with the supply frequency and is not affected by the load. Proper application requires consideration of the following ... 

Many electrical problems, or problems associated with the quality of the incoming power and internal to the motor, can be isolated by monitoring the line frequency. Line frequency refers to the frequency of the alternating current being supplied to the motor. In the case of 60-cycle power, monitoring of the fundamental or first harmonic (60 Hertz), second harmonic (120 Hz), and third harmonic (180 Hz) should be performed. 

The running speed of electric motors, both alternating current (AC) and direct current (DC), varies. Therefore, for monitoring purposes, these motors should be classified as variable-speed machines. A narrowband window should be established to track the true running speed. 

Although at the time of his early inventions Dr. Schoop envisaged that an electric arc could be used to produce the molten metal for spraying, forty years passed before the method became commercially important. Then, in Germany, Russia and Japan tools were made based on the arc. Although in Japan alternating current is used, the noise is nearly intolerable and elsewhere direct current from motor generators is employed. The fundamental idea is simple two wires, carefully insulated from each other, are advanced to meet at a point where an arc is formed, immediately in advance of a Jet... 

A steam turbine is a machine with an ancient genealogy. It is a direct descendant of the overshot water wheel, used to kick off the industrial revolution in England, and the windmill still used in Portugal. Turbines are widely used in process plants to drive everything from 2-hp pumps to 20,000-hp centrifugal compressors. They are versatile machines, in that they are intrinsically variable-speed devices. Electric motors are intrinsically fixed-speed machines. It is true that there are a variety of ways to convert AC (alternating-current) motors to variable speed, but they are all expensive and complex. 

Next question The pump is driven by an ordinary alternating-current electric motor. It is running at 3600 rpm. When we switch from pumping water to naphtha, what happens to the speed of the pump ... 

MOTOR SHALL BE PROVIDED IN ACCORDANCE WITH DATA GIVEN ON STANDARD DATA SHEET FORM E242P1 ELECTRICAL ALTERNATING CURRENT MOTORS. 

Electrical System. The conductors in the hose-cable carry power and control signals down to the underwater vehicle and return information. The drive-pump motor is powered by three-phase, 220 V carried down three paired conductors. The solenoid valve, which controls the clean pump, is energized by 24 V direct current (DC), which is controlled on deck. The submersible pump that circulates water through in situ sensors uses 110 V alternating current (AC) power from the hose-cable. 

Most electronic equipment shares the television set s need for a number of differing voltages for the operation of individual components. This alone may be sufficient justification for the inclusion of a direct current to alternating current converter in fuel cell power systems. In addition, alternating current electric motors are more suitable in most applications. They tend to operate at a rotational speed controlled by the frequency of the current. If completely unloaded they speed up to this fixed velocity and accelerate no further. Many types of direct current motors, if operated unloaded, will continue to accelerate until they fail. A belt driven fan operated by an alternating current motor is undamaged by the failure of the belt. A direct current motor will require a special safety circuit to shut it down in case of belt failure. If the belt and the safety circuit both fail, the motor will speed up until it destroys itself. 

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