The National Grid

This question is about transformers.

The diagram shows a step‑down transformer.

The table gives some data for the step‑down transformer.

State the formula linking input (primary) voltage, output (secondary) voltage and the turns ratio for a transformer.

Use data from the table to calculate the output (secondary) voltage of the transformer.

This transformer is not 100% efficient.

The efficiency of a transformer can be calculated using the formula

Calculate the efficiency of the transformer.

Explain how transformers are used in the efficient, large‑scale transmission of electrical energy.

You may draw a diagram to help your answer.

The photograph shows transmission cables used for long-distance transmission of electricity.

The diagram shows a power station and a school.

Add to the diagram by drawing the structures needed to efficiently transfer energy from the power station to the school using electricity.

Power station
School

Explain how the amount of current in the transmission cables increases the efficiency of the transmission of electricity.

The National Grid is used in the United Kingdom for the large-scale transmission of electricity. The photograph shows solar panels connected to the National Grid.

Solar panels provide direct current to a device that outputs an alternating current so that the energy from the solar panels can be supplied to the National Grid.

Explain why a step-up transformer is used to supply the National Grid.

This is the label on the step-up transformer.

State the formula linking input voltage, output voltage and turns ratio for a transformer.

Calculate the number of turns on the secondary coil of the step‑up transformer.

Solar panels produce constant direct current (d.c.).

Explain why a transformer will not work when connected to constant direct current.

The diagram shows part of the National Grid.

There is a step-up transformer at the power station end of a transmission line and a step-down transformer at a distant town.

Explain why step-up transformers and step-down transformers are used in this way.

State the formula linking the input voltage, the output voltage and the turns ratio for a transformer.

The primary coil on a step-up transformer has 3300 turns.

Calculate the number of turns required on the transformer’s secondary coil to step up the voltage from 15 kV to 340 kV.

Transformers in the National Grid have efficiencies less than 100%.

Suggest which energy store of the transformer increases as a result of the efficiency being less than 100%.

The iron core of a transformer is an electrical conductor.

When the transformer is in use, the primary coil causes a changing magnetic field in the iron core. This causes a small current to be induced in the core.

Explain how a current is induced in the core of the transformer.

Transformers are useful in the transmission of electricity.

The diagram shows a step‑down transformer.

Give the name of a suitable metal that could be used in the core of the transformer.

State the formula linking input power and output power for a transformer.

The step‑down transformer has an input voltage of 275 kV and an output voltage of 230 V.

The transformer has an output current of 95 A.

Calculate the input current to the transformer.

Assume the transformer is 100% efficient.

Explain how transformers are useful in the large‑scale transmission of electricity.

You may draw a diagram to support your answer.

The diagram shows the first stages in a method of transferring energy electrically through long distances.

The table shows data about the step-up transformer.

State the formula linking input voltage, output voltage, number of primary turns and number of secondary turns for a transformer.

Calculate the number of turns on the secondary coil.

Explain why step-up and step-down transformers are used in the large-scale transmission of electricity.

You may draw a diagram to support your answer.