Series-wound motor

Series-Wound Motor. A series-wound motor is a motor in which the field circuit and armature circuit are connected in series. 

Universal Motors. A universal motor is a series-wound motor designed to operate at approximately the same speed and output on either direct current or single-phase alternating current of a frequency not greater than 60 cycles/s and approximately the same rms voltage. There are two types ... 

Series-Wound Motors. These motors are inherently varying-speed motors with charges in load. On light or no loads, the speed may become dangerously high. These motors should be employed only where the load is never entirely removed from the motor. They should never be connected to the driven machine by belt. 

DC methods mostly use shunt or compound wound motors. Occasionally series wound motors are used when high torque at low speeds is required. These machines are fed with DC voltage derived from a three-phase AC source using a thyristor converter. The thyristor converter rectifies the AC into DC but with control over the magnitude of the average DC voltage. Thyristors are also called silicon controlled rectifiers . 

Equip motor-driven electrical equipment used in a laboratory where volatile flammable materials may be present (e.g., a hydrogenation room) with either nonsparking induction motors that meet Class 1, Division 2, Group C-D electrical standards (U.S. DOC, 1993) or air motors instead of series-wound motors that use carbon brushes, such as those generally used in vacuum pumps, mechanical shakers, stirring motors,... 

Because series-wound motors cannot be modified to make them spark-free, do not use kitchen appliances (refrigerators, mixers, blenders, and so on) with such motors in laboratories where flammable materials may be present. 

When bringing ordinary electrical equipment such as vacuum cleaners and portable electric drills having series-wound motors into the laboratory for special purposes, take specific precautions to ensure that no flammable vapors are present before such equipment is used (see Chapter 5, section G). 

Series-Wound Motors. In series-wound motors, the field flux is created by coils that are electrically in series with the armature (Fig. 5.119). When the motor starts, the current and, consequently, the magnetic field are at maximum values, producing a large starting torque. As the motor speeds up and the current is reduced, the field flux also becomes smaller. With no external load on the shaft, the field flux drops nearly to zero and motor speed becomes dangerously high. For this reason, series-wound motors should be used only where the load is directly connected or geared to the shaft. 

Compound-wound dc motors have both series and shunt fields. The addition of a small series field helps provide the proper amount of no-load to fuU-load speed regulation or droop. Shunt or compound-wound motors are apphed widely to many adjustable-speed drives. They are important for drives requiring accurate speed regulation and adjustment. 

Direct-current motors are of three general types, shunt wound, series wound, and compound wound, and are defined as follows ... 

Stabilized Shunt-Wound Motor. A stabilized shunt-wound motor is a direct-current motor in which the shunt field circuit is connected either in parallel with the armature circuit or to a separate source of excitation voltage, and which also has a light series winding added to prevent a rise in speed or to obtain a slight reduction in speed with increase in load. 

Compound-Wound Motors. Compound-wound motors combine both series and shunt fields (Fig. 5.120). The disadvantage of series-motor overspeeding at light loads is avoided since there is so httle current in the series field at no load that speed is determined by the shunt field alone. At higher loads, speed depends on the sum of the two fields, making speed reduction similar to that of a series motor. 

Tapered horsepower motors develop the maximum rated horsepower at three times the minimum speed, the horsepower decreasing in direct proportion to the decrease in speed down to the horsepower rating at 150% of the minimum speed. Figure 3-12 plots characteristics of shunt, series, and compound-wound direct-current motors. 

With this technique the motor has a wound rotor brought out to slip rings and an external resistance is connected into the rotor circuit. This resistance usually consists of a series of resistor banks, which are switched out progressively in a number of steps as the motor accelerates. The number and rating of each step is chosen so that starting current and motor torque are within requirements. 

Medial prefrontal and orbitofrontal regions are known to be associated with reward circuits. The HI and H2 coils are designed to stimulated deep prefrontal structures, with minimal undesired side effects such as pain, motor stimulation, and facial muscles activation. The coils are wounded with a double 14 AWG (American Wire Gauge) insulated cupper wire winded into several windings, connected in series. Detailed illustration of the wiring pattern of HI is shown in Figure 37.13, and of H2 is shown in Figure 37.14. 

Practical motors are constructed as shown in Fig. 10.14. All d.c. motors contain a field winding wound on pole pieces attached to a steel yoke. The armature winding rotates between the poles and is connected to the commutator. Contact with the external circuit is made through carbon brushes rubbing on the commutator segments. Direct current motors are classified by the way in which the field and armature windings are connected, which may be in series or in parallel. 

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