Electrical transformer pdf file

 

    properly ground a transformer, and the secondary electrical system Figure Control transformers are common in appliances and electrical equipment. technical details are included in other documents and are referenced in this document. .. load is connected to a transformer and electrical currents exist in both. The Transformer. The principle parts of a transformer and their functions are: path for the most lines of flux with the least loss in magnetic and electrical energy.

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    Electrical Transformer Pdf File

    What is Electrical Transformer? Construction of a Transformer - Parts of a Transformer Operation & Working Principle of a Transformer. Types of Transformer. three-phase transformer is shown in Figure 1. Since these transformers are ideal, the secondary voltages are electrical displacement in the voltages. There is no electrical connection between the primary and secondary windings. In a transformer there are two or more coils linked together by a common.

    Therefore, it is important to know the working principle, construction and types of transformers used in different analog circuits. What is a transformer? A transformer can be defined as a static device which helps in the transformation of electric power in one circuit to electric power of the same frequency in another circuit. The voltage can be raised or lowered in a circuit, but with a proportional increase or decrease in the current ratings. A basic transformer consists of two coils that are electrically separate and inductive, but are magnetically linked through a path of reluctance. The working principle of the transformer can be understood from the figure below. The core laminations are joined in the form of strips in between the strips you can see that there are some narrow gaps right through the cross-section of the core. Both the coils have high mutual inductance. A mutual electro-motive force is induced in the transformer from the alternating flux that is set up in the laminated core, due to the coil that is connected to a source of alternating voltage. Most of the alternating flux developed by this coil is linked with the other coil and thus produces the mutual induced electro-motive force. The alternating current supply is given to the first coil and hence it can be called as the primary winding. The energy is drawn out from the second coil and thus can be called as the secondary winding.

    Hence, wattmeter reading practically gives the iron losses in the transformer. It is reminded that iron losses are the same at all loads. In this test, the secondary usually low-voltage winding is short-circuited by a thick conductor and variable low voltage is applied to the primary as shown in Fig. The low input voltage is gradually raised till at voltage VSC, full-load current I1 flows in the primary. Under such conditions, the copper loss in the windings is the same as that on full load.

    There is no output from the transformer under short-circuit conditions. Therefore, input power is all loss and this loss is almost entirely copper loss.

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    It is because iron loss in the core is negligibly small since the voltage VSC is very small. Hence, the wattmeter will practically register the full- load copper losses in the transformer windings.

    Why Transformer Rating in kVA An important factor in the design and operation of electrical machines is the relation between the life of the insulation and operating temperature of the machine. Therefore, temperature rise resulting from the losses is a determining factor in the rating of a machine.

    Electrical Transformer, Construction, Working, Types and Application

    We know that copper loss in a transformer depends on current and iron loss depends on voltage. Therefore, the total loss in a transformer depends on the volt-ampere product only and not on the phase angle between voltage and current i.

    For this reason, the rating of a transformer is in kVA and not kW. All-Day or Energy Efficiency The ordinary or commercial efficiency of a transformer is defined as the ratio of output power to the input power i.

    There are certain types of transformers whose performance cannot be judged by this efficiency. It means that a constant loss i. Thinner laminations reduce losses, [27] but are more laborious and expensive to construct.

    Laminating the core greatly reduces eddy-current losses One common design of laminated core is made from interleaved stacks of E-shaped steel sheets capped with I-shaped pieces, leading to its name of 'E-I transformer'. The cut-core or C-core type is made by winding a steel strip around a rectangular form and then bonding the layers together.

    It is then cut in two, forming two C shapes, and the core assembled by binding the two C halves together with a steel strap. A steel core's remanence means that it retains a static magnetic field when power is removed. When power is then reapplied, the residual field will cause a high inrush current until the effect of the remaining magnetism is reduced, usually after a few cycles of the applied AC waveform.

    Transformer, Construction, Working, Types Application & Limitations

    On transformers connected to long, overhead power transmission lines, induced currents due to geomagnetic disturbances during solar storms can cause saturation of the core and operation of transformer protection devices. The higher initial cost of the core material is offset over the life of the transformer by its lower losses at light load.

    These materials combine high magnetic permeability with high bulk electrical resistivity. For frequencies extending beyond the VHF band , cores made from non-conductive magnetic ceramic materials called ferrites are common.

    Toroidal cores[ edit ] Small toroidal core transformer Toroidal transformers are built around a ring-shaped core, which, depending on operating frequency, is made from a long strip of silicon steel or permalloy wound into a coil, powdered iron, or ferrite.

    The closed ring shape eliminates air gaps inherent in the construction of an E-I core. The primary and secondary coils are often wound concentrically to cover the entire surface of the core. This minimizes the length of wire needed and provides screening to minimize the core's magnetic field from generating electromagnetic interference. Toroidal transformers are more efficient than the cheaper laminated E-I types for a similar power level. Other advantages compared to E-I types, include smaller size about half , lower weight about half , less mechanical hum making them superior in audio amplifiers , lower exterior magnetic field about one tenth , low off-load losses making them more efficient in standby circuits , single-bolt mounting, and greater choice of shapes.

    The main disadvantages are higher cost and limited power capacity see Classification parameters below. Because of the lack of a residual gap in the magnetic path, toroidal transformers also tend to exhibit higher inrush current, compared to laminated E-I types. Ferrite toroidal cores are used at higher frequencies, typically between a few tens of kilohertz to hundreds of megahertz, to reduce losses, physical size, and weight of inductive components.

    A drawback of toroidal transformer construction is the higher labor cost of winding. This is because it is necessary to pass the entire length of a coil winding through the core aperture each time a single turn is added to the coil.

    As a consequence, toroidal transformers rated more than a few kVA are uncommon. Small distribution transformers may achieve some of the benefits of a toroidal core by splitting it and forcing it open, then inserting a bobbin containing primary and secondary windings. An air-core transformer eliminates loss due to hysteresis in the core material.

    Transformer

    Air-core transformers are unsuitable for use in power distribution, [12] but are frequently employed in radio-frequency applications. Windings are usually arranged concentrically to minimize flux leakage. Cut view through transformer windings. Legend: White: Air, liquid or other insulating medium Black: Primary winding Red: Secondary winding The electrical conductor used for the windings depends upon the application, but in all cases the individual turns must be electrically insulated from each other to ensure that the current travels throughout every turn.

    For small transformers, in which currents are low and the potential difference between adjacent turns is small, the coils are often wound from enamelled magnet wire.