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 […]
DISADVANTAGES OF MANUAL CONTROL OF MACHINES Read More »
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
SYNCHRONOUS MOTOR STARTING BY USING DAMPER (AMORTISSEUR) WINDING Read More »
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
SYNCHRONOUS MOTOR STARTING WITH AN EXTERNAL MOTOR Read More »
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
SYNCHRONOUS MOTOR STARTING BY REDUCING THE SUPPLY FREQUENCY Read More »
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
METHODS OF STARTING SYNCHRONOUS MOTOR Read More »
Even though the basic functions of the oil used in transformers are (a) heat conduction and (b) electrical insulation, there are many other properties which make a particular oil eminently suitable. Organic oils of vegetative or animal origin are good insulators but tend to decompose giving rise to acidic by-products which attack the paper or
PROPERTIES OF TRANSFORMER OIL Read More »
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
THERMAL CONSIDERATIONS The losses in the windings and the core cause temperature rises in the materials. This is another important area in which the temperatures must be limited to the long-term capability of the insulating materials. Refined paper is still used as the primary solid insulation in power transformers. Highly refined mineral oil is still
THERMAL AND VOLTAGE CONSIDERATIONS OF PRACTICAL TRANSFORMER Read More »
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.
PERMANENT MAGNET DC MOTOR Read More »
1) DELTA DELTA CONNECTION 1. Suitable for both un-grounded and effectively grounded sources. 2. Suitable for a three-wire service or a four-wire service with a mid-tap ground. 2) DELTA WYE CONNECTION 1. Suitable for both un-grounded and effectively grounded sources. 2. Suitable for a three-wire service or a four-wire grounded service with XO grounded. 3. With
THREE PHASE TRANSFORMER WINDING CONNECTIONS Read More »