(1) By using a starting motor. This motor is directly coupled to the motor. It may be an induction motor which can run on a synchronous speed closer to the synchronous speed of the main motor. (2) Starting as an induction motor. This is the most usual method in which the motor is provided with […]
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1. Shunt generators with field regulators are used for ordinary lighting and power supply purposes. They are also used for charging batteries because their terminal voltages are almost constant or can be kept constant. 2. Series generators are not used for power supply because of their rising characteristics. However, their rising characteristic makes them suitable
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Following are the three most important characteristics or curves of a dc generator: 1. No-load saturation Characteristic (E0/If): It is also known as Magnetic Characteristic or Open-circuit Characteristic (O.C.C.). It shows the relation between the no-load generated MMF in armature, E0 and the field or exciting current If at a given fixed speed. It is just the
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Figure shows diagrammatically auto-transformer tap changing. Here, a mid-tapped auto-transformer or reactor is used. One of the lines is connected to its mid-tapping. One end, say a of this transformer is connected to a series of switches across the odd tappings and the other end b is connected to switches across even tappings. A short-circuiting
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The excitation control method is satisfactory only for relatively short lines. However, it is not suitable for long lines as the voltage at the alternator terminals will have to be varied too much in order that the voltage at the far end of the line may be constant. Under such situations, the problem of voltage
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External faults are those faults or hazards that occur outside the transformer. These hazards present stresses on the transformer that may be of concern and may shorten the transformer life. These faults include the following. • OVER LOADS Overloads cause the transformer to overheat and have the potential to cause permanent damage or loss of
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A three-phase transformer bank can be easily created by using three single-phase transformers. The two sides of these three transformers can be either connected in a wye or a delta configuration, thus allowing four possible types of connections. These are: • WYE WYE: With the wye-wye (Y-Y) connection, the secondary side is in phase with the
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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
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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
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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
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