transformer

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Transformer

A transformer is an electrical device that changes, or transforms, an alternating current (AC) signal from one level to another. The device typically consists of two sets of insulated wire, coiled around a common iron core. Electrical power is applied to one of these coils, called the primary coil, and is then magnetically transferred to the other coil, called the secondary. This magnetic coupling of electrical power occurs without any direct electrical contact, and allows transformers to change AC voltage level and to completely isolate two electrical circuits from one another.

There are two types of transformers based on the relationship between the primary and secondary coils. A voltage in the secondary coil that is greater than the voltage in the primary coil is called a step-up transformer. The reverse situation is called a step-down transformer. The power in a transformer is constant in each set of coils; that is, the product of current (I) and voltage (V), or power (P) is constant. For example, in a step-up transformer, an increase in voltage in the secondary coil results in a corresponding decrease in the current.

When a voltage is applied to a coil of wire, an electrical current flows (just as water flows through a pipe when pressure is applied.) The flowing electrical current, however, creates a magnetic field about the coil. This principle can be demonstrated by simply wrapping insulated wire around a nail, and attaching a battery to the ends of that wire. A sufficient number of loops and ample electrical power will enable this electromagnet to lift small metal objects, just as an ordinary magnet can attract metals. If, however, the battery is replaced by a varying power source such as AC, the magnetic field also varies. This changing magnetic field is essential for the operation of a transformer.

Because the two coils of a transformer are very close to each other, an electric current through the primary coil generates a magnetic field that is also around the secondary coil. When this magnetic field varies with time (as it does when AC is applied), it combines with the secondary coil to form a type of generator. (Recall that a generator produces electrical power by moving coils of wire through a stationary magnetic field, the converse of the transformer situation.) At any rate, electrical power in the primary coil is converted into a magnetic field which then generates electrical power in the secondary coil.

The main point of a transformer is that, although the power is neither increased nor decreased in this transfer (except for minor losses), the voltage level can be changed through the conversion. The ratio of the voltages between the two coils is equal to the ratio of number of loops in the two coils. Changing the number of windings allows a transformer to step-up or step-down voltages easily. This is extremely useful as the voltage level is converted many times between a power station, through transmission lines, into a home, and then into a household appliance.

views updated

Transformer

A transformer is an electrical device which changes or transforms an alternating current (AC) signal from
one level to another. The device typically consists of two sets of insulated wire, coiled around a common iron core. Electrical power is applied to one of these coils, called the primary coil, and is then magnetically transferred to the other coil, called the secondary. This magnetic coupling of electrical power occurs without any direct electrical contact, and allows transformers to change AC voltage level and to completely isolate two electrical circuits from one another.

When a voltage is applied to a coil of wire, an electrical current flows (just as water flows through a pipe when pressure is applied.) The flowing electrical current, however, creates a magnetic field about the coil. This principle can be demonstrated by simply wrapping insulated wire around a nail, and attaching a battery to the ends of that wire. A sufficient number of loops and ample electrical power will enable this electromagnet to lift small metal objects, just as an ordinary magnet can. If, however, the battery is replaced by a varying power source such as AC, the magnetic field also varies. This changing magnetic field is essential for the operation of a transformer.

Because the two coils of a transformer are very close to each other, an electric current through the primary coil generates a magnetic field which is also around the secondary coil. When this magnetic field varies with time (as it does when AC is applied), it teams-up with the secondary coil to form a type of generator . (Recall that a generator produces electrical power by moving coils of wire through a stationary magnetic field, the converse of the transformer situation.) At any rate , electrical power in the primary coil is converted into a magnetic field which then generates electrical power in the secondary coil. The beauty of a transformer is that, although the power is neither increased nor decreased in this transfer (except for minor losses), the voltage level can be changed through the conversion. The ratio of the voltages between the two coils is equal to the ratio of number of loops in the two coils. Changing the number of windings allows a transformer to step-up or step-down voltages easily. This is extremely useful as the voltage level is converted many times between a power station, through transmission lines, into a home, and then into a household appliance.

views updated

Transformer

A transformer is an electrical device used to change the voltage in an electric circuit. It usually consists of a soft iron core with a rectangular shape. An incoming wire (the primary coil) is wrapped around one side of the core, and an outgoing wire (the secondary coil) is wrapped around the opposite side of the core. Each wire is wrapped around the core a different number of times.

A transformer works on the principle of inductance. An alternating electric current entering the transformer through the primary coil creates a magnetic field within the iron core. The strength of the magnetic field depends on the strength of the electric current.

Once the magnetic field is established in the iron core, the reverse effect occurs in the secondary coil at the opposite side of the core. The oscillating (vibrating) magnetic field within the core creates an electric current in the secondary coil. The strength of the electric current is determined by the number of times the outgoing wire is wrapped around the iron core.

A transformer can be used either to increase or decrease the voltage in a circuit. A transformer of the former type is known as a step-up transformer; one of the latter type is known as a step-down transformer.

Applications

Transformers are used widely in everyday situations. The transmission of electric current from its source (such as a hydroelectric dam) to the consumer can be accomplished most efficiently at high voltages. The high-tension wires one sees overhead in the open country carry electric current at high voltage. But most household appliances operate at much lower voltages. It is necessary, therefore, to install transformers near the point where electric current enters a house or within appliances themselves.

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trans·form·er / transˈfôrmər/ • n. 1. an apparatus for reducing or increasing the voltage of an alternating current. 2. a person or thing that transforms something.

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transformer Device for converting alternating current at one voltage to another voltage at the same frequency. It consists of two coils of wire coupled together magnetically. The input current is fed to one coil (the primary), the output being taken from the other coil (the secondary).

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