Transformer Basics

Transformer Basic Voltage Transformer Basics

One of the main reasons that we use alternating AC voltages and currents in our homes and workplace's is that it can be easily generated at a convenient voltage, transformed into a much higher voltage and then distributed around the country using a national grid of cables over very long distances. The reason for transforming the voltage is that higher distribution voltages implies lower currents and therefore lower losses along the grid.

These high AC transmission voltages and currents are then reduced to a much lower, safer and usable voltage level were it can be used to supply electrical equipment in our homes and workplaces, and all this is possible thanks to the basicVoltage Transformer.

A Typical Voltage Transformer

The transformer is very simple static (or stationary) electro-magnetic passive electrical device that works on the principle of Faraday's law of induction by converting electrical energy from one value to another. It does this by linking together two or more electrical circuits using a common oscillating magnetic circuit which is produced by the transformer itself. A transformer operates on the principals of "electromagnetic induction", in the form of  Mutual Induction.

Mutual induction is the process by which a coil of wire magnetically induces a voltage into another coil located in close proximity to it. Then we can say that transformers work in the "magnetic domain", and transformers get their name from the fact that they "transform" one voltage or current level into another. Transformers are capable of either increasing or decreasing the voltage and current levels of their supply, without modifying its frequency, or the amount of electrical power being transferred from one winding to another via the magnetic circuit.

A single phase voltage transformer basically consists of two electrical coils of wire, one called the "Primary Winding" and another called the "Secondary Winding" that are wrapped together around a closed magnetic iron circuit called a "core". This soft iron core is not solid but made up of individual laminations connected together to help reduce the core's losses. These two windings are electrically isolated from each other but are magnetically linked through the common core allowing electrical power to be transferred from one coil to the other.

In other words, for a transformer there is no direct electrical connection between the two coil windings, thereby giving it the name also of an Isolation Transformer. Generally, the primary winding of a transformer is connected to the input voltage supply and converts or transforms the electrical power into a magnetic field. While the secondary winding converts this magnetic field into electrical power producing the required output voltage as shown.

Transformer Construction (single-phase)

• Where:
•   VP  -  is the Primary Voltage
•   VS  -  is the Secondary Voltage
•   NP  -  is the Number of Primary Windings
•   NS  -  is the Number of Secondary Windings
•   Φ (phi)  -  is the Flux Linkage

Notice that the two coil windings are not electrically connected but are only linked magnetically. A single-phase transformer can operate to either increase or decrease the voltage applied to the primary winding. When a transformer is used to "increase" the voltage on its secondary winding with respect to the primary, it is called a Step-up transformer. When it is used to "decrease" the voltage on the secondary winding with respect to the primary it is called a Step-down transformer.