Dc electric motors

Efficient use of electric motors requires appropriate control systems. Typical control systems for AC and DC electric motor operations are now discussed [ 10]. 

GM built an electric vehicle (EV) called the Electrovette in 1980. It was a Chevette with a DC electric motor and zinc nickel oxide batteries. The Electrovette used a mechanical controller. The batteries were expensive and not much better than lead-acid power for extending the range of operation. The Electrovette had controller problems and GM let the project die. 

Developments by Chappell and Kyberd (1991) and others provide a fine example of the possibihties. A suitable mechanical configuration is shown in Figure 44.10. Four 12-V dc electric motors with gearboxes... 

Interaction with the real world is something current robotic and prosthetic actuators (dc electric motors with gear trains) do not do well. When a stiff robot arm comes into contact with a hard... 

By far the most common actuator for electrically powered prostheses is the permanent magnet dc electric motor with some form of transmission (Fig. 32.10). While there is much research into other electrically powered actuator technologies, such as shape memory alloys and electroactive polymers, none is to the point where it can compete against the dc electric motor. A review of the available and developing actuator technologies with their associated advantages and disadvantages as well as their power and force densities can be found in Hannaford and Winters (1990) and Hollerbach et al. 

With DC electric motors, power factor correction is sometimes used to improve the power factor of the drive [30]. This is done by incorporating capacitive components into the circuit. Capacitors produce leading reactive power whereas the phase-controlled rectifiers produce lagging reactive power. Thus, by adding appropriately sized capacitors, the power factor of the drive can be improved. 

A simplified dc electric motor is diagrammed in Fig. 20.1. A coil "stator" is stationary, and a steel magnet "rotor" can rotate around the axle signified by a black dot. The half-circle is a copper metal "commutator," so the electromagnet... 

As the harder stocks are generally more scorchy , because they increase in temperature more rapidly when being mixed, lower speeds are used. To get increased torque at lower speeds very often a DC motor which is slant rated using field weakening is specified. What this means is that it is possible to specify a DC electric motor so that it develops its full horsepower at 80% full speed as well as at full speed, e.g. 100 hp at 1200 rpm and 100 hp at 1500 rpm. This means that the torque up to 1200 rpm is constant, and it is reduced between 1200 and 1500 rpm. The slant rated or field weakened specification is ideal for a mixer drive, so as to have high torque at low speeds and reduced torque at high speeds. 

A relatively new innovation for use in electric motor compressor drives is the variable frequency power source. Fundamentally, the power source converts an existing three-phase source into DC then uses an inverter to convert back to a variable frequency supply. Thyristors or transistors are used to switch the output at the required frequency. 

The speed of an electric motor can be changed by altering the frequency of the electric current. This is because the ratio is the same as 60 or 50 f/p (f = the frequency of the current, p = the number of poles in the stator). Frequency converters are built of electronic components, frequently combined with microprocessors. They provide good motor protection and are superior to the traditional bimetal protection. The characteristic curve for a pump and fan motor is also quadratic, making lower demands to the frequency converters When the frequency of the electrical current is changed in the frequency converter, the main AC supply is transformed into DC. The DC is then treated... 

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... 

Energy Efficiency Electrical Motors, Arthur D. Little, Inc., Federal Energy Administration, Washington, DC. DOE/CS-0163, May 1980. 

The most common use of the gas turbine power system in the oil and gas industry is in combination with an electrical system (i.e., electric generators and electric motors). In 1965 such a system was used to power a rotary rig. This was a 3,000-hp rig developed by Continental-Ensco. The rig used three 1,100-hp Solar Saturn single-shaft gas turbines. These gas turbines operated at 22,300 rpm and were connected through double reduction gear transmissions to DC generators. 

Figure 4-10. The drive group of a large DC electric rig. Note that this rig may be equipped with either two or three traction motors.

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. 

The energy for driving all high-capacity electric motors is obtained from the AC network. AC motors can be supplied directly from the AC network, as long as the motor is to be operated at nominal speed. If variable speed is specified, AC motors are equipped with a frequency converter. In DC motors, power converters are used. 

The stack output voltage ranges from 34 V at open circuit to 22 V at full load, while the electric motor is supplied at 48 V DC. For this reason, a DC-DC converter (see Sect. 5.2) is used to match the stack output voltage with that required by the engine. In Table 6.3, the technical specifications of the DC-DC converter are shown. 

Every enpneer needs to understand the fimdamentak of electricity and mafftet-ism. Look around, and you tvill see all the devices, appliances, and machines that are driven by electrical power. The ol ective of this chapter is to introduce the fimdamentals of electricity. We will briefly discuss what is meant by electric charge, electric current (both akemating current, ac, and direct current, dc), electrical resistance, and voltage. We will ako define what is meant by an electrical circuit and its components. We will then look at the role of electric motors in our everyday lives and identify the factors that enpneers consider when selecting a motorfor a specific application. 

One method of feeding material into an entry loop is by simply driving the payoff mandrel with an electric motor (see Fig. 11). Normally, this is accomplished with a DC motor, but on slow speed lines, an AC motor with an on-off -type operation may be adequate. When a DC motor is utilized, the loop position is usually automatically controlled with a set of photocells and flood lights or an ultrasonic sensor. This method of paying off material from the master coil is quite acceptable provided there are no stickers from the annealing furnace or any dents or damage to the sides of the coil. These defects would cause the material to stick to itself and not pay off with the force of gravity as it is uncoiled. 

Extruder motors are usually electric, but some systems utilize hydraulic motors. For example, injection molding machines use hydraulics to develop clamp tonnage. Electric motors may be of the direct current (DC) or alternating current (AC) types. Traditionally, DC motors, which regulate speed through voltage control, have been more popular because they could provide the necessary power at a lower cost. However, recent advances in frequency control - the technique used to regulate speed in AC motors - have caused this type of motor to become more widely used. 

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