Case Study:

India’s electricity demand has increased rapidly due to urbanization, industries, and digital infrastructure. Power stations such as thermal, hydroelectric, and solar plants generate electricity which must travel hundreds of kilometers to reach cities and villages. However, transmitting electricity directly from a generator would cause large energy losses.

In a typical power station, electricity is generated at a voltage of about 11-33 kV. Before the electricity is sent through transmission lines, it passes through a step-up transformer located in the power station switchyard. The transformer increases the voltage to extremely high values such as 132 kV, 220 kV, or even 400 kV. 

The reason for increasing the voltage is related to power transmission efficiency. Electric power is given by the relation P = VI, where P is power, V is voltage, and I is current. When the voltage is increased, the current decreases for the same amount of power. Since power loss in transmission lines is proportional to I²R, reducing current significantly lowers heat loss in the wires. 

For example, if electricity is transmitted at low voltage, the current would be very high and large amounts of energy would be lost as heat in the transmission lines. By stepping up the voltage using a transformer, the current becomes smaller and energy loss is minimized.

After the electricity reaches a city substation, step-down transformers reduce the voltage to safer levels for industrial and domestic use. This entire system allows electricity generated in remote power plants to efficiently reach homes, schools, hospitals, and industries across India.

This case demonstrates how electromagnetic induction and transformer technology play a crucial role in modern power transmission systems.

Questions

Section A - MCQs

1. In a power station, the main function of a step-up transformer is to:

A. Increase current and reduce voltage
B. Increase voltage and reduce current
C. Decrease both voltage and current
D. Convert AC to DC

2. If electric power remains constant, increasing voltage in transmission lines will:

A. Increase current
B. Decrease current
C. Not affect current
D. Stop the current

3. The main reason for transmitting electricity at high voltage is to:

A. Increase resistance of wires
B. Reduce energy loss during transmission
C. Produce more electricity
D. Increase the temperature of wires

4. A transformer works mainly on the principle of:

A. Ohm’s Law
B. Electromagnetic induction
C. Coulomb’s Law
D. Electrolysis

Section B - Short Answer Questions

1. Why is a step-up transformer used at a power station before electricity enters transmission lines?

2. Explain how increasing voltage reduces power loss in transmission lines.

3. What is the difference between a step-up transformer and a step-down transformer?

Section C - Long Answer Question

1. Electricity generated at a power station is 20 kV and must be transmitted through long-distance transmission lines.

a) Explain why a transformer is used before transmission.
b) If the voltage is stepped up to 220 kV, explain how this affects the current and transmission losses.
c) Describe the role of step-down transformers before electricity is supplied to homes.

Answer Key

MCQ Answers

1. B - It increases voltage and decreases current.
2. B - Current decreases when voltage increases for constant power.
3. B - High voltage reduces power loss in transmission lines.
4. B - Transformer operation is based on electromagnetic induction.

Short Answer Solutions

1. A step-up transformer increases the voltage of electricity generated at the power station so that the current becomes smaller, reducing energy loss during long-distance transmission.

2. Power loss in transmission lines is given by (P_{loss} = I^2R). Increasing voltage reduces current, which greatly reduces heat loss in the wires.

3.

• Step-up transformer: increases voltage and decreases current.
• Step-down transformer: decreases voltage and increases current for safe use.

Long Answer Solution

a) Purpose of transformer

• Electricity generated at low voltage causes high current.
• High current leads to large transmission losses.
• A transformer increases voltage before transmission.

b) Effect of stepping up voltage

• Voltage increases from 20 kV to 220 kV.
• Current decreases according to (P = VI).
• Reduced current lowers heat loss ((I^2R)) in transmission lines.

c) Role of step-down transformer

• Reduces high transmission voltage to safe levels such as 230 V for homes.
• Ensures electrical appliances operate safely.