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Category: Electrical Eng.

Principles of DC Machines

Principles of DC Machines

DC Machines are the electro mechanical energy converters which work from a d.c source and generate mechanical power or convert mechanical power into a d.c. power. These machines can be broadly classified into two types, on the basis of their magnetic structure. They are, Homopolar machines Heteropolar machines Homopolar Machines :- Homopolar Generators – A homo-polar generator is a DC electrical generator comprising an electrically conductive disc or cylinder rotating in a plane perpendicular to a uniform static magnetic field. A potential difference is…

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Interconnected Synchronous Generators

Interconnected Synchronous Generators

The study of interconnection of several synchronous generators is important because of the following main reasons: 1. Since the demand of electricity varies during a day, also during the various seasons in a year, a modern power station employs two or more units so that one or more alternators can supply power efficiently according to the need. Installation of a single generator of capacity equal to the installed capacity of a station will be uneconomic, as such a generator will…

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Parallel Operation Of Two Generators

Parallel Operation Of Two Generators

When two synchronous generators are connected in parallel, they have an inherent tendency to remain in step, on account of the changes produced in their armature currents by a divergence of phase. Consider identical machines 1 and 2, in parallel and working on to the same load. With respect to the load, their e.m.fs are normally in phase: with respect to the local circuit formed by the two armature windings, however, their e.m.fs are in phase-opposition. Suppose there to be…

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Synchronous Generator Operation

Synchronous Generator Operation

Cylindrical Rotor Machine:-   The synchronous generator, under the assumption of constant synchronous reactance, may be considered as representable by an equivalent circuit comprising an ideal winding in which an e.m.f. Et proportional to the field excitation is developed, the winding being connected to the terminals of the machine through a resistance ra and reactance  (Xl + Xa) = Xs all per phase. The principal characteristics of the synchronous generator will be obtained qualitatively from this circuit. Generator Load Characteristics:- Consider…

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Armature Winding

Armature Winding

Winding Types:- Concentrated three-phase,half-coil wave winding with one slot per phase(one coil side per slot and instantaneous polarity and phase relation of coils). A three phase winding, in extremely simplified form. The start and finish of all the coils in phase A are designated, respectively, as SA and FA. Phase A is shown as a solid line in the figure, phase B as a dashed line, and phase C as a dotted line. Note that each winding does not start…

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Synchronous Machines

Synchronous Machines

Introduction:- With the development of the technology and the way in which human labour is getting minimized and the comforts increasing tremendously the use of electrical energy is ever increasing. Basically electric power is the main source of energy for carrying out many functions, as it is a clean and efficient energy source, which can be easily transmitted over long distances. With the availability of Transformer for changing the voltage levels to a very high value (of say 132kV to…

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Parallel Operation of 1 & 2 Phase Transformers

Parallel Operation of 1 & 2 Phase Transformers

By parallel operation we mean two or more transformers are connected to the same supply bus bars on the primary side and to a common bus bar/load on the secondary side. Such requirement is frequently encountered in practice. The reasons that necessitate parallel operation are as follows. Non-availability of a single large transformer to meet the total load. The power demand might have increased over a time necessitating augmentation of the More transformers connected in parallel will then be pressed…

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Phasor Diagrams & Testing Transformer

Phasor Diagrams & Testing Transformer

  The  resulting equivalent  circuit is known  as the exact equivalent circuit. This circuit can be used for the analysis of the behavior of the transformers. As the no-load current is less than 1% of the load current a simplified circuit known as ‘approximate’ equivalent circuit is usually used, which may be further simplified to the one. On similar lines to the ideal transformer the phasor diagram of operation can be drawn for a practical transformer also. The positions of the…

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Three Phase Transformer

Three Phase Transformer

It is the three phase system which has been adopted world over to generate, transmit and distribute electrical power. Therefore to change the level of voltages in the system three phase transformers should be used. Three number of identical single phase transformers can be suitably connected for use in a three phase system and such a three phase transformer is called a bank of three phase transformer. Alternatively, a three phase transformer can be constructed as a single unit. Introducing…

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Poly Phase Connections and Transformers

Poly Phase Connections and Transformers

The individual transformers are connected in a variety of ways in a power system. Due to the advantages of polyphase power during generation, transmission and utilization polyphase power handling is very important. As an engineering application is driven by techno-economic considerations, no single connection or setup is satisfactory for all appli- cations. Thus transformers are deployed in many forms and connections. Star and mesh connections are very commonly used. Apart from these, vee or open delta connections, zig zag connections…

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