# STEP-UP TRANSFORMERS & STEP-DOWN TRANSFORMERS

Step-Up Transformers:

Step-up transformers have a higher number of turns in the secondary winding compared to the primary winding. They are used to convert low voltage (high current) electricity to high voltage (low current) electricity. The voltage is stepped up in this process. Step-up transformers are commonly used in power plants, X-ray machines, and microwave ovens.

Step-Down Transformers:

Step-down transformers have a lower number of turns in the secondary winding compared to the primary winding. They are used to convert high voltage (low current) electricity to low voltage (high current) electricity. The voltage is stepped down in this process. Step-down transformers have various applications:

(i) High Voltage (6.6 kV) to High Voltage (3.3 kV) – Step-Down Transformers: They are used to supply high voltage (3.3 kV) electrical loads such as propulsion converters and motors.

(ii) High Voltage (>1 kV) to Low Voltage (440 V) – Step-Down Transformers: They are used to supply low voltage (440 V) electrical loads such as pump motors and heaters.

(iii) Low Voltage (440 V) to Low Voltage (220 V) – Step-Down Transformers: They are used to supply low voltage (220 V) electrical loads such as lighting and sockets.

Transformer Equation:

The transformer equation relates the voltages, currents, and number of turns in the windings of a transformer. It states that the ratio of voltages is equal to the ratio of turns:

V1/V2 = N1/N2

where V1 and V2 are the voltages in the primary and secondary windings, and N1 and N2 are the number of turns in the primary and secondary windings, respectively.

The efficiency of a Transformer:

The efficiency of a transformer is the ratio of output power to input power, expressed as a percentage. Typically, transformers have an efficiency ranging from 95% to 99%. The efficiency is calculated using the formula:

Efficiency = Output Power / Input Power = 1 – Losses / Input Power

Transformers have no mechanical losses such as windage loss (air resistance) or friction loss. They only have electrical losses:

(i) Iron Losses (Core Losses): These losses include eddy current loss and hysteresis loss, which depend on the magnetic properties of the core material (usually steel/iron).

(ii) Copper Losses (Winding Losses): These losses occur due to the resistance of the windings and depend on the current flowing through them.

Copper losses vary with load since the current changes with the load.