Electric Transformers

Topics: Transformer, Electricity, Alternating current Pages: 10 (3536 words) Published: February 28, 2013
Chapter 1 The History of Electric Transformer

INTRODUCTION:

Transformer is a device that transfers electric energy from one circuit to another, usually with a change in voltage. Transformers work only with a varying electric current, such as alternating current (AC). Transformers are important in the distribution of electric power. They raise the voltage of the electricity generated at a power plant to the high levels needed to transmit the electricity efficiently. Other transformers reduce the voltage at the locations where the electricity is used. Many household devices contain transformers to raise or lower house-current voltage as needed. Television sets and stereo equipment, for example, require high voltages; doorbells and thermostats, low voltages. A simple transformer consists essentially of two coils of insulated wire. In most transformers, the wires are wound around an iron-containing structure called the core. One coil, called the primary, is connected to a source of alternating current that produces a constantly varying magnetic field around the coil. The varying magnetic field, in turn, produces an alternating current in the other coil. This coil, called the secondary, is connected to a separate electric circuit. The ratio of the number of turns in the primary coil to the number of turns in the secondary coil—the turns ratio—determines the ratio of the voltages in the two coils. For example, if there is one turn in the primary and ten turns in the secondary coil, the voltage in the secondary coil will be 10 times that in the primary. Such a transformer is called a step-up transformer. If there are ten turns in the primary coil and one turn in the secondary the voltage in the secondary will be one-tenth that in the primary. This kind of transformer is called a step-down transformer. The ratio of the electric current strength, or amperage, in the two coils is in inverse proportion to the ratio of the voltages; thus the electrical power (voltage multiplied by amperage) is the same in both coils. The impedance (resistance to the flow of an alternating current) of the primary coil depends on the impedance of the secondary circuit and the turn’s ratio. With the proper turn’s ratio, the transformer can, in effect, match the impedances of the two circuits. Matched impedances are important in stereo systems and other electronic systems because they permit the maximum amount of electric power to be delivered from one component to another. In an autotransformer, there is only one coil and both circuits are connected to it. They are connected at different points, so that one circuit contains a larger portion of the coil (that is, has more turns) than the other. The name itself offers a simple definition. Electrical transformers are used to transform electrical energy. How electrical transformers do so is by altering voltage, generally from high to low. Voltage is simply the measurement of electrons, how many or how strong, in the flow. Electricity can then be transported more easily and efficiently over long distances. While power line electrical transformers are commonly recognized, there are other various types and sizes as well. They range from huge, multi-ton units like those at power plants, to intermediate, such as the type used on electric poles, and others can be quite small. Those used in equipment or appliances in your home or place of business are smaller electrical transformers and there are also tiny ones used in items like microphones and other electronics. Probably the most common and perhaps the most necessary use of various electrical transformers is the transportation of electricity from power plants to homes and businesses. Because power often has to travel long distances, it is transformed first into a more manageable state. It is then transformed again and again, or “stepped down,” repeatedly as it gets closer to its destination. When the power...