Question 1: Define the purpose of the National Grid in the UK electricity supply system.

Answer: The National Grid distributes electricity from power stations to homes and industries across the country efficiently and reliably.

Question 2: Explain why high voltages are used for transmitting electricity over long distances in the National Grid.

Answer: High voltages reduce the current for a given power, which decreases energy lost as heat in the transmission cables.

Question 3: Describe the role of transformers in the National Grid.

Answer: Transformers increase (step-up) voltage for transmission and decrease (step-down) voltage for safe use in homes.

Question 1: A power station supplies electricity at a voltage of 400,000 V with a current of 500 A. Calculate the power transmitted. (Use P = V × I)

Answer: P = 400,000 V × 500 A = 200,000,000 W or 200 MW

Question 2: If a household appliance uses 1.5 kW of power and operates at 230 V, what is the current flowing through the appliance? (Use I = P / V)

Answer: I = 1500 W / 230 V ≈ 6.52 A

Question 1: Outline the steps involved in safely performing maintenance on high-voltage transmission lines.

Answer: Maintenance involves isolating sections of the grid, wearing appropriate PPE, using insulated tools, following safety protocols to prevent electric shocks, and coordinating with control centres to ensure power is safely shut down before work begins.

Question 2: Identify at least three variables that must be controlled during the testing of transformers in the National Grid.

Answer: Voltage input, current flow, and temperature of the transformer.

Question 1: A section of the transmission line carries a current of 600 A at a voltage of 400,000 V. The resistance of the cable is 0.2 Ω. Calculate the power loss as heat in the cable.

Answer: Power loss, P_loss = I² × R = (600)² × 0.2 = 72,000 W or 72 kW

Question 1: Explain how the use of step-up transformers at power stations and step-down transformers at substations helps in reducing energy loss during transmission. Include relevant calculations to support your explanation.

Answer: Step-up transformers increase voltage to reduce current, decreasing I²R losses in transmission lines. At substations, step-down transformers reduce voltage for safe domestic use. For example, increasing voltage from 230 V to 400,000 V reduces current for the same power, thus reducing heat loss. Calculations show that power loss in cables decreases with higher transmission voltages due to lower current.

Question 1: Discuss the importance of the National Grid in supporting renewable energy sources such as wind and solar power. Include the challenges involved.

Answer: The National Grid allows the transmission of electricity generated from renewable sources over large distances, supporting a sustainable energy mix. Challenges include variability in power output, need for flexible grid management, and maintaining voltage stability during fluctuating supply.