Four Quadrant Operation and Regenerative Braking of DC Motor The beauty of the separately excited d.c. motor is the ease with which it can be controlled. Firstly, the steady-state speed is determined by the applied voltage, so we can make the motor run at any desired speed in either direction simply by applying the appropriate […]
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Characteristics of DC Motor Before variable-voltage supplies became readily available, most d.c. motors were obliged to operate from a single d.c. supply, usually of constant voltage. The armature and Weld circuits were therefore designed either for connection in parallel (shunt), or in series. As we will see shortly, the operating characteristics of shunt and series
Current Surges in DC Motor The steady-state armature current depends on the small difference between the back e.m.f. E and the applied voltage V. In a converter-fed drive it is vital that the current is kept within safe bounds, otherwise the thyristors or transistors (which have very limited overcurrent capacity) will be destroyed. In order
Base Speed and Field Weakening of DC Motor When the field flux is at its full value the speed corresponding to full armature voltage and full current (i.e. the rated full-load condition) is known as base speed (see Figure 1). The motor can operate at any speed up to base speed, and at any torque
Motional EMF of DC Motor When the armature is stationary, no motional e.m.f. is induced in it. But when the rotor turns, the armature conductors cut the radial magnetic flux and an e.m.f. is induced in them. As far as each individual coil on the armature is concerned, an alternating e.m.f. will be induced in
Until the 1980s the conventional (brushed) d.c. machine was the automatic choice where speed or torque control is called for, and large numbers remain in service despite a declining market share that reflects the move to inverter-fed induction motors. Applications range from steel rolling mills, railway traction, to a very wide range of industrial drives,
Distinguishing Between Residential and Commercial Electricians Electricians are skilled professionals specializing in installing, maintaining, and repairing electrical systems. Although their work is the same, there are two distinct types of electricians: residential and commercial. While they share some similarities, fundamental differences between these two roles are worth understanding if you are considering pursuing an electrician
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Cooling of Power Switching Devices Thermal Resistance We have seen that by adopting a switching strategy the power loss in the switching devices is small in comparison with the power throughput, so the converter has a high efficiency. Nevertheless almost all the heat which is produced in the switching devices is released in the active
Inverter Switching Devices As far as the user is concerned, it does not really matter what type of switching device is used inside the inverter, but it is probably helpful to mention the four most important families of devices in current use so that the terminology is familiar and the symbols used for each device
A.C. FROM D.C. SP – SP INVERSION The business of getting a.c. from d.c. is known as inversion, and nine times out of ten we would ideally like to be able to produce sinusoidal output voltages of whatever frequency and amplitude we choose. Unfortunately the constraints imposed by the necessity to use a switching strategy