How Does A Step-up Transformer or Step-down Transformer Work?

Dry-type Transformer

Step-up vs step-down transformers

Step-up transformers definition

A transformer where the output (secondary) voltage is greater than the input (primary) voltage is called a step-up transformer. Step-up transformers reduce the output current to keep the input and output power of the system equal.

The number of turns in the secondary transformer is greater than the number of turns in the primary transformer, i.e. T 2 > T 1. The voltage turns ratio of a step-up transformer is therefore 1:2. The primary winding of a step-up transformer consists of thickly insulated copper wire, as low amplitude currents flow through it.

Applications - Boost transformers are used in transmission lines for converting the high voltage generated by alternators. The power loss of a transmission line is proportional to the square of the current flowing through it.

The output current of a step-up transformer is low and is therefore used to reduce power losses. Step-up transformers are also used to start electric motors, microwave ovens, X-ray machines, etc.

Dry Type Transformer     

Step-down transformer definition

A transformer where the output (secondary) voltage is less than the input (primary) voltage is called a step-down transformer. The number of turns in the primary transformer is greater than the number of turns in the secondary transformer, i.e. T 2 < T 1.

The voltage turns ratio of a step-down transformer is 2:1. The voltage turns ratio determines the magnitude of the voltage transformation from the primary winding to the secondary winding of the transformer.

A step-down transformer consists of two or more coils wound on the transformer core. It works on the principle of magnetic induction between the coils. The voltage applied to the primary of the coils magnetises the core, which in turn induces the secondary winding of the transformer. As a result, the voltage is converted from the primary winding of the transformer to the secondary winding.

Applications - for electrical isolation, power distribution networks, control of household appliances, doorbells, etc.

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What "rated" transformer do I need?

This depends entirely on the product you will be using it for. Provide the electrical retailer with a detailed list of all the products you will be using - and their maximum output. Based on this information, he/she will be able to advise on the correct transformer rating required.

A transformer converts alternating current (AC) from one voltage to another. It has no moving parts and works on the principle of magnetic induction; it can be designed as a "step-up" or "step-down" voltage. Thus, a step-up transformer increases the voltage, while a step-down transformer decreases it.

How does a step-up transformer or step-down transformer work?

A transformer consists of two or more insulated wire coils wound around an iron core. When voltage is applied to one coil (usually called the primary or input), it magnetizes the core, which induces a voltage in the other coil (usually called the secondary or output). The ratio of the number of turns in the two sets of windings determines the amount of variable voltage.

For step-up or step-down transformers, the voltage ratio between the primary and secondary will reflect the "turns ratio" (except for single-phase less than 1 kva with a compensated secondary). A practical application of this 2 to 1 turns ratio is a step-down of 480 to 240. Please note that if the input is 440 volts, the output will be 220 volts. The ratio between input and output voltage will remain the same. Transformers should not be operated at voltages higher than the nameplate rated voltage but can be operated at voltages lower than the rated voltage. It is therefore possible to use standard transformers for some non-standard applications.

Single-phase transformers of 1 kva and larger can also be connected in reverse to step-down or step-up voltages. (Note: Single-phase step-up or step-down transformers of sizes smaller than 1 KVA should not be connected in reverse because the secondary winding has extra turned to overcome the voltage drop when a load is applied. If connected in reverse, the output voltage will be less than desired.)