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Control of a machine can be semi-automatic or fully automatic. There are probably more machines operated by semi-automatic control than by manual or fully automatic controls. Consider, for example, an over-head tank which supplies drinking water to a factory. If we provide a manual switch near the pump motor and depute an operator to switch […]

Having discussed the starting and stopping of a motor by using control devices like push buttons, contactors and over-load relays, we are in a position to discuss the advantages of magnetic control over the manual control. The various advantages are listed as follows: 1) Magnetic control permits installation of power contacts close to motor whereas

When electric motors were first introduced, simple manual switches were used to start and stop the motor. The only protective device used was the fuse. Progress was subsequently made along the lines of improving the reliability, flexibility and make-break performance of the manual switches. In those days one large motor was used to drive a

Most of the large synchronous motors are provided with damper windings, in order to nullify the oscillations of the rotor whenever the synchronous machine is subjected to a periodically varying load. Damper windings are special bars laid into slots cut in the pole face of a synchronous machine and then shorted out on each end

The second method of starting a synchronous motor is to attach an external starting motor (pony motor) to it and bring the synchronous machine to near about its rated speed (but not exactly equal to it, as the synchronization process may fail to indicate the point of closure of the main switch connecting the synchronous

If the rotating magnetic field of the stator in a synchronous motor rotates at a low enough speed, there will be no problem for the rotor to accelerate and to lock in with the stator’s magnetic field. The speed of the stator magnetic field can then be increased to its rated operating speed by gradually

Basically there are three methods that are used to start a synchronous motor: 1) To reduce the speed of the rotating magnetic field of the stator to a low enough value that the rotor can easily accelerate and lock in with it during one half-cycle of the rotating magnetic field’s rotation. This is done by

Insulating media in high voltage transformers consists of paper wrapped around the conductors in the transformer coils plus mineral oil and pressboard to insulate the coils from ground. From the moment a transformer is placed in service, both the solid and liquid insulation begin a slow but irreversible process of degradation. 1) SOLID INSULATION: PAPER

A permanent magnet dc motor (PMDC) is a dc motor whose poles are made of permanent magnets. PMDC motor offer a number of benefits compared with shunt dc motors in some applications. A PMDC motor is basically the same machine as a shunt dc motor, except that the flux of a PMDC motor is fixed.

When considering the design of an electrical distribution system for a given customer and facility, the electrical engineer must consider alternate design approaches that best fit the following overall goals. 1. SAFETY The No. 1 goal is to design a power system that will not present any electrical hazard to the people who use the