What is meant by step down and step up transformer?

Step down transformer, the transformer whose input ac voltage is more than that of output ac voltage is called step down transformer. Hence number of turns in secondary coil is less than that of primary coil. 

Step down transformer : 

The transformer whose output ac voltage is more than that of input ac voltage is called step up transformer. Here number of turns in primary coil is less than that in secondary coil. 

A transformer designed to reduce the voltage from primary to secondary is called a step-down transformer. The transformation ratio of a transformer will be equal to the square root of its primary to secondary inductance (L) ratio.The concept of a step down transformer is actually quite simple. The transfer has more turns of wire on the primary coil as compared to the turns on the secondary coil. This reduces the induced voltage running through the secondary coil, which ultimately reduces the output voltage.A Step down Transformer is a type of transformer, which converts a high voltage at the primary side to a low voltage at the secondary side. If we speak in terms of the coil windings, the primary winding of a Step down Transformer has more turns than the secondary winding.Step-down transformers are used to decrease or 'step-down' voltages. These are used when voltages need to be lowered for use in homes and factories. A step-down transformer has fewer turns of wire on the secondary coil than on the primary coil. This transformer steps down the voltage by increasing the current.

A transformer that increases the voltage from primary to secondary (more secondary winding turns than primary winding turns) is called a step-up transformer. ... As a step-down unit, this transformer converts high-voltage, low-current power into low-voltage, high-current power.Step-up transformers are used in central power stations. They allow the stations to increase the voltage to the necessary level to produce electricity. The electricity is then transmitted through power lines. However, high voltages are very dangerous for commercial or residential use.

This increase in voltage for transmission and decrease in voltage for utilization can only be achieved by using a step-up and step-down transformer. The major difference between step-up and step-down transformer is, step-up transformer raises the output voltage, whereas step-down transformer reduces the output voltage.Although the voltage increases in a step-up transformer, the current is reduced proportionately. ... In other words, power equals voltage times current. A transformer transfers power from the primary coil to the secondary coil. Since the power must stay the same, if the voltage increases, the current must decrease.