DC Machine Applications

DC Machine Applications DC Machine Applications – Whenever the application of any machine is considered, its operating characteristics along with its economic and technical viability as compared to its competitors are the essential criteria. For a dc machine, of course, the main attraction lies in its flexibility, versatility and ease of control. This explains why […]

DC Machine Dynamics

DC Machine Dynamics DC Machine Dynamics –┬áThe DC machines are quite versatile and are capable of giving a variety of V-A and speed-torque characteristics by suitable combinations of various field windings. With solid-state controls their speeds and outputs can be controlled easily over a wide range for both dynamic and steady-state operation. By addition of […]

Efficiency and Testing

Efficiency and Testing: Efficiency of dc Machines Machine efficiency, in general, has been discussed in Sec. 5.9. The approach here will be to apply the general principles for the specific case of dc machines. The power flow diagrams for the generating and motoring modes of a dc machine are shown in Fig. 7.65(a) and (b). […]

Braking of DC Motors

Braking of DC Motors: Braking of DC Motors –┬áControlled slowing or stopping of a motor and its driven load is as important as starting in many applications (e.g. cranes, traction on a slope to avoid excessive speed, etc.). Braking methods based on friction, electromechanical action, eddy-currents, etc. are independent of the motor but sometimes electric […]

Ward Leonard Speed Control

Ward Leonard Speed Control Ward Leonard Speed Control – It is combined armature and field control and is therefore, operationally the most efficient method of speed control with a wide range. The dc motor armature is fed from a variable voltage and adjustable polarity supply whose current rating must be somewhat higher than that of […]

Series Parallel Control

Series Parallel Control: Here two identical motors are coupled together mechanically to a common load. Two speeds at constant torque are possible in this method one by connecting the motors armatures in series and the other by connecting them in parallel as shown in Fig. 7.60. When connected in series, the terminal voltage across each […]

Shunted Armature Control

Shunted Armature Control: Shunted Armature Control -It is a variation of rheostatic control. As is obvious from Fig. 7.59, the principle used in achieving control is that of voltage division. In the shunt motor armature control circuit of Fig. 7.59(a) the Thevenin equivalent as seen by motor armature is drawn. The no-load armature speed is […]

Rheostatic Control

Rheostatic Control Rheostatic Control – Series armature-resistance control Here the applied armature voltage is varied by placing an adjustable resistance Re in series with the armature as shown in Fig. 7.58 along with the speed-torque characteristics. Some of the limitations of the rheostatic control method are enumerated below: (i) Only speeds below the rated value […]

Speed Control of DC Motors

Speed Control of DC Motors The Speed Control of DC Motors are in general much more adaptable speed drives than ac motors which are associated with a constant-speed rotating field. Indeed one of the primary reasons for the strong competitive position of dc motors in modern industrial drives is the wide range of speeds afforded. […]

Starting of DC Motors

Starting of DC Motors Starting of DC Motors – At the time of starting (n = 0), the induced emf of a motor is zero such that the current drawn from rated voltage supply would be for a shunt motor. The series field resistance would be included in the denominator for a series motor. For […]

Compound Generator

Compound Generator The causes of voltage drop in the terminal voltage from no-load to full-load in a shunt generator can be partially/fully/over-compensated by use of an aiding series field (cumulative compound), which can be connected in a long- or short-shunt (long-shunt shown in. Fig. 7.34). The aiding ampere-turns of the series field automatically increase with […]

Predetermination of External Characteristic

Predetermination of External Characteristic The Predetermination of External Characteristic of a shunt generator can be predetermined from a knowledge of the OCC and armature and field resistances (which can be determined by simple dc test), without actually performing the load test which in fact is not feasible for a large generator. Assume for the time […]

Characteristics of DC Generators

Characteristics of DC Generators: With the advent of silicon-controlled rectifiers, the importance of the dc machine as a generator has considerably reduced as SCRs can be employed to draw dc power from standard ac supply and convert it to dc; also the dc voltage can also be varied with ease. For the sake of completeness […]