6. (a) Draw a labelled diagram of a transformer suitable for transforming from \( 240 \mathrm{~V} \) a.c to \( 12 \mathrm{~V} \) a.c. Give details of the materials used in its structure and reasons for their choice. [ 8 marks] (b) A step up treasformer connected to a \( 240-\mathrm{V} \) r.m.s a.c line is to supply \( 18 \mathrm{kV} \) r.m.s. for a neon sign as shown in Figure VII. To reduce shock hazard, a fuse is to be inserted in the primary circuit; the fuse is to blow when the current in the secondary circuit exceeds \( 10 \mathrm{~mA} \). Figure VII Calculate, assuming the transformer is ideal. (i) the peak value of the primary voltage (ii) the tums ratio \( \frac{N_{p}}{N_{s}} \) of the transformer (iii) the power that must be supplied to the transformer when the secondary current is \( 10 \mathrm{~mA} \) (iv) the current rating of the fuse that is to be used in the primary circuit. \[ \text { [ } 8 \text { marks] } \] (c) The transformer al a power station has an output of \( 15 \mathrm{MW} \) at \( 60 \mathrm{kV} \). This power is transmitted to a sub-station some distance away along cables which have a total resistance of \( 12 \Omega \). What percentage of the power transmitted is lost in the cables? \[ \text { [ } 4 \text { marks] } \]
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### Part (a) - Drawing and Describing a Transformer ** Show more…
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31.38. A Step-Up Transformer. A transformer connected to a $120-\mathrm{V}(\mathrm{rms})$ ac line is to supply $13,000 \mathrm{V}(\mathrm{ms})$ for a neon sign. To reduce shock hazard, a fuse is to be inserted in the primary circuit; the fuse is to blow when the ms current in the secondary circuit exceeds 8.50 $\mathrm{mA}$ (a) What is the ratio of secondary to primary turns of the transformer? (b) What power must be supplied to the transformer when the rms secondary current is 8.50 $\mathrm{mA} ?(\mathrm{c})$ What current rating should the fuse in the primary circuit have?
A transformer connected to a $120 \mathrm{~V}$ (rms) ac line is to supply $13,000 \mathrm{~V}$ (ms) for a neon sign. To reduce shock hazard, a fuse is to be inserted in the primary circuit; the fuse is to blow when the rons current in the secondary circuit exceeds $8.50 \mathrm{~mA}$. (a) What is the ratio of secondary to primary turns of the transformer? (b) What power must be supplied to the transformer when the $\mathrm{rms}$ secondary current is $8.50 \mathrm{~mA} ?$ (c) What current rating should the fuse in the primary circuit have?
A step-up transformer. A transformer connected to a 120 $\mathrm{V}$ (rms) ac line is to supply $13,000 \mathrm{V}$ (rms) for a neon sign. To reduce the shock hazard, a fuse is to be inserted in the primary circuit and is to blow when the rms current in the secondary circuit exceeds 8.50 $\mathrm{mA}$ (a) What is the ratio of secondary to primary turns of the transformer? (b) What power must be supplied to the transformer when the rms secondary current is 8.50 $\mathrm{mA}$ ? (c) What current rating should the fuse in the primary circuit have?
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