Heat Generation in and Cooling of Transformers The losses in a transformer are small in relative terms, but they are appreciable in absolute terms, especially in large-size units. Therefore, a major task in transformer design is to provide for proper withdrawal of the heat generated in the core and coils to the surroundings. The task […]
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Electricity and Magnetism
Core and Winding Designs
Core and Winding Designs The service conditions in which transformers are used have a direct bearing on the design of their cores, coils, and (in the case of oil-immersed units), oil tanks. The core of a transformer is built up from electrical-sheet steel laminations 0.35 moo or 0.5 mm thick. The steel usually contains 4-5 […]
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Multiwinding Transformers
Multiwinding Transformers In many electrical installations it is desired to have an interconnection between several circuits (or networks) operating at different voltage levels. Most conveniently this can be done with a multi winding transformer which has one or several primary windings and several secondary windings. The simplest unit in this class is a three-winding transformer […]
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Autotransformers
Autotransformers In power transmission it is sometimes necessary to interconnect electric networks whose rated voltages differ in a 2-to-1 ratio at most. An example is an interconnection of a 110-kV network and a 220-kV network. This form of interconnection is effected with the aid of a transformer or, to be more specific, an autotransformer ‘which […]
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Transformers in Parallel
Transformers in Parallel When two (or more) transformers are used in parallel, their primary windings are energized from a common source (a common power line in Fig.23), and their secondary windings are connected across a common load (a common line in Fig 23). Transformers to be brought in for parallel operation should meet three conditions […]
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Phase Displacement (Reference Phasor) Groups
Phase Displacement (Reference Phasor) Groups Under normal operating conditions, the primary and secondary voltages v1 and v2 are practically in phase with the respective currents, il and i2, for the positive directions chosen in Fig.21. For the chosen positive directions of the load current iload and load voltage vload it follows that iload = i2 […]
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Three-Phase Transformers
Three-Phase Transformers All that has been said about a single-phase transformer may be carried over to each phase of a three-phase transformer operating into a balanced load. Let us take a closer look at how a three-phase transformer is arranged and operates. A three-phase system of currents or voltages might be handled by three single-phase […]
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Transformer Losses
Transformer Losses The ratio of the active power P2 at the output of a transformer to the active power P1 at its input (see Fig. 4) is called its efficiency ƞ = P2/ P1 or ƞ% = (P2/P1) X 100 (8.23) When a transformer is operating at its rated primary voltage, V1 = V1,rtd , […]
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External Characteristics of a Transformer
External Characteristics of a Transformer Consider the performance of a transformer for several values of the complex load impedance Z2 = z2 ∠ φ2 If the primary voltage is constant and equal to its rated value, V1 = V1.rtd,variations in the complex load impedance will bring about changes in the primary and secondary currents İ1 […]
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The Short-Circuit Condition of a Transformer
The Short-Circuit Condition of a Transformer This condition may arise as a result of a fault fraught with grave consequences (overheating and break-down), or it may be produced for testing purposes in which case it is called the short-circuit (or load loss and impedance) test. The short-circuit test is carried out by short-circuiting the secondary […]
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