ELEN236_SocraticTransformers_short.pdf - Questions Question 1 Explain why transformers are used extensively in long-distance power distribution systems

ELEN236_SocraticTransformers_short.pdf - Questions Question...

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Questions Question 1 Explain why transformers are used extensively in long-distance power distribution systems. What advantage do they lend to a power system? file 02213 Question 2 Are the transformers connecting power plant generators to high-voltage power lines considered step-up or step-down ? Explain your answer. file 02214 Question 3 Explain how the construction of a step-down transformer differs from that of a step-up transformer. file 02205 Question 4 Explain how the construction of an isolation transformer differs from that of a step-up or step-down transformer. file 02209 1
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Question 5 If we energize an inductor’s coil with an oscillating (AC) voltage, we will generate an oscillating magnetic flux in the inductor core: Oscillating current Oscillating flux If we wrap a second coil of wire around the same magnetic core as the first (inductor) coil, we set up a situation where mutual inductance exists: a change of current through one coil induces a voltage in the other, and visa-versa. This, obviously, will result in an AC voltage being induced in the second wire coil: Oscillating current Oscillating flux Induced voltage What name is given to such a device, with two coils of wire sharing a common magnetic flux? Also, plot both the magnetic flux waveform and the secondary (induced) voltage waveform on the same graph as the primary (applied) voltage waveform: Time φ = ??? v p v s = ??? file 01876 2
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Question 6 Shown here is a schematic diagram of a transformer powering a resistive load, at the exact moment in time where the primary winding’s voltage is at its positive (+) peak: + - + - This moment in time + - Identify the polarity of voltage across the load resistor at this exact moment in time, as well as the direction of current in each of the windings. file 00490 Question 7 Calculate the voltage output by the secondary winding of a transformer if the primary voltage is 35 volts, the secondary winding has 4500 turns, and the primary winding has 355 turns. V secondary = file 02206 Question 8 Calculate the voltage output by the secondary winding of a transformer if the primary voltage is 230 volts, the secondary winding has 290 turns, and the primary winding has 1120 turns. V secondary = file 02207 Question 9 Calculate the number of turns needed in the secondary winding of a transformer to transform a primary voltage of 300 volts down to a secondary voltage of 180 volts, if the primary winding has 1150 turns of wire. N secondary = file 02215 3
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Question 10 If an isolation transformer (a transformer with the same number of ”turns” in the primary and secondary coils) is connected between an AC source and an AC load, we will measure the same voltage and the same current at both source and load terminals: A A V V 120 VAC 120 VAC 3.5 A 3.5 A If we calculate power output by the source and power dissipated by the load, the value is the same: 420 Watts ( P = IV ).
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