Read a supplied transmission transformer chain
Apply voltage ratios stage by stage while distinguishing a conceptual network from real operating specifications.
Section 4.5.6 · The transformer
Exam scope and assessment notes
Core and Extended · Physics 0972, 2026–2028. Use the stated source, operating conditions and meter ranges. Written practice is self-checked. Human subject-teacher review, supervised practical competence and cumulative assessment remain pending. Cambridge states that IGCSE 0972 has the same subject content as IGCSE 0625, with 9–1 grading. This StudyForA pathway maps the 2026–2028 syllabus only. This 9–1 graded qualification is available only in a limited number of administrative zones. Confirm that your centre can enter you for this code and exam series with Cambridge International. Cambridge has published a separate syllabus for 2029. StudyForA has not reconciled that version yet; this page supports exams in 2026, 2027 and 2028 only.
Before you begin
- Convert kV to V.
- Use a simple voltage-turn ratio.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
How many volts are 10 kV?
What you will learn
- Apply voltage ratios stage by stage while distinguishing a conceptual network from real operating specifications.
- Use local transformer ratios through a supplied chain without converting voltage labels into unsupported performance claims.
Apply local ratios to a network diagram
A supplied chain uses a 20 kV to 200 kV step-up stage and a later 200 kV to 10 kV step-down stage. The first needs Ns/Np = 10 in the simple model; the second needs Ns/Np = 1/20. Each ratio belongs to its own transformer and is not a single turn ratio for the complete network.
If a final supplied stage changes 10 kV to 250 V, convert 10 kV to 10000 V before computing Ns/Np = 250/10000 = 1/40. Primary and secondary labels are assigned locally, and turn counts must be compatible with each ratio.
Keep what the values do and do not establish
The long-distance higher-voltage stage supports smaller current and reduced cable heating for the same transferred power. The numerical voltage chain alone does not state actual power, current, cable losses or overall efficiency. Those require further information.
These values are an original supplied exercise, not a claim about a particular country’s grid or permission to wire transformer stages. Voltage ratios are not wire, insulation, earthing or equipment ratings. Preserve the stated simple assumptions when interpreting the chain.
Pause and explain
A supplied stage changes 10 kV to 250 V. What is Ns/Np?
Worked example
For supplied 20 kV → 200 kV and 200 kV → 10 kV stages, find each secondary-to-primary turn ratio.
Show the worked solution
- Use Ns/Np = Vs/Vp for the first stage.
- 200/20 = 10.
- For the second stage, 10/200 = 1/20.
Answer 10 and 1/20 respectively.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Find output/input turn ratios for the supplied 20 kV → 200 kV → 10 kV changes.
Give me a hint
Treat the two arrows as separate transformers.
Compare my reasoning
- The first ratio is 200/20 = 10.
- The second is 10/200 = 1/20.
- Their functions are step-up and step-down.
10 and 1/20.
Look for these in your work
- Keep the stage order.
- Match each local input and output.
Find Ns/Np for 10 kV to 250 V.
Give me a hint
Convert the input into volts.
Compare my reasoning
- 10 kV = 10000 V.
- 250/10000 = 1/40.
- The final stage is step-down.
1/40; step-down.
Look for these in your work
- Use consistent units.
- State the ratio orientation.
A report infers cable current and 100% network efficiency from this voltage chain alone. Evaluate it.
Give me a hint
Identify missing transfer and loss information.
Compare my reasoning
- Power and load conditions are not supplied.
- Cable and transformer losses are not supplied.
- Voltage ratios alone do not establish current or overall efficiency.
The current and efficiency claims are unsupported by the voltage chain.
Look for these in your work
- Name missing quantities.
- Keep local voltage ratios separate from network performance.
Common mistakes
- Apply each ratio locally.
- Convert voltage units before comparing.
- Do not infer overall efficiency.
What can you explain now?
Which turn ratio equals Vs/Vp in the simple model?
Compare with the explanation
Ns/Np
The secondary-to-primary voltage ratio matches the secondary-to-primary turn ratio.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Use local transformer ratios through a supplied chain without converting voltage labels into unsupported performance claims.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.