Question 1: Define the term 'National Grid' in the context of electricity supply in the UK.

Answer: The National Grid is a network of high-voltage power lines and substations that transports electricity from power stations to homes and businesses across the UK.

Question 2: Explain why high voltage is used for electricity transmission in the National Grid.

Answer: High voltage reduces the current for a given power, which minimises energy loss due to resistance in the transmission cables.

Question 3: What material is commonly used for the conductors in high-voltage transmission lines and why?

Answer: Aluminium is commonly used because it is lightweight, conducts electricity well, and is cost-effective.

Question 1: Calculate the power loss in a transmission cable if the current is 200 A, the resistance of the cable is 0.5 Ω, and the voltage is 400 kV. Use the formula P = I^2 R.

Answer: Power loss = (200)^2 × 0.5 = 40,000 W or 40 kW

Question 2: If the supply voltage is increased from 400 kV to 500 kV while maintaining the same power transmission, what is the new current assuming power remains constant? Use P = V × I.

Answer: Original power P = 400,000 V × I; I = P / 400,000. New current I' = P / 500,000. Since P is constant, I' = (400,000 / 500,000) × I = 0.8 × I.

Question 1: Describe two safety precautions that must be considered when working with high-voltage transmission lines.

Answer: Maintaining a safe distance from live wires and wearing appropriate personal protective equipment (PPE).

Question 2: Identify one key variable that affects the efficiency of electricity transmission in the National Grid and explain its impact.

Answer: The resistance of the transmission cables; higher resistance increases energy loss as heat, reducing efficiency.

Question 1: A section of the National Grid transmits 1 GW of power at a voltage of 400 kV. The resistance of the transmission line is 0.3 Ω. Calculate the current flowing through this section and the approximate power lost as heat in the line.

Answer: Current I = P / V = 1,000,000,000 W / 400,000 V = 2500 A. Power loss = I^2 R = (2500)^2 × 0.3 = 1,875,000 W or 1.875 MW.

Question 1: Explain how the use of transformers in the National Grid helps to minimise energy losses during transmission. (6 marks)

Answer: Transformers are used to step up the voltage for transmission and step down the voltage for distribution. Increasing the voltage reduces the current for a given power, which significantly decreases energy lost as heat in the transmission cables, improving efficiency. The use of high-voltage transformers at substations ensures minimal energy loss over long distances, making electricity transmission more economical and effective.

Question 1: Describe how the development of smart grids enhances the efficiency and reliability of electricity supply compared to traditional National Grid systems.

Answer: Smart grids use digital communication and automation to monitor and manage electricity flow, allowing for real-time adjustments, integrating renewable energy sources, reducing wastage, and improving reliability and efficiency of supply.