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 – The 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 […]

Hopkinsons Test Hopkinsons Test – This is a regenerative test in which two identical dc shunt machines are coupled mechanically and tested simultaneously. One of the machines is made to act as a motor driving the other as a generator which supplies electric power to motor. The set therefore draws only loss-power from the mains […]

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 – Controlled 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 Method of Speed Control: Ward Leonard Method of Speed Control 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 […]

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 -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 – 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 […]

Armature Control: Armature Control – The main requirement of this control scheme is a variable voltage supply to the armature whose current rating must be somewhat larger than that of the motor. It is superior to the field control scheme in three respects, outlined below: 1.It provides a constant-torque drive. In the shunt motor case […]