Questions
Question 1
Explain why transformers are used extensively in longdistance power distribution systems.
What
advantage do they lend to a power system?
file 02213
Question 2
Are the transformers connecting power plant generators to highvoltage power lines considered
stepup
or
stepdown
? Explain your answer.
file 02214
Question 3
Explain how the construction of a
stepdown
transformer differs from that of a
stepup
transformer.
file 02205
Question 4
Explain how the construction of an
isolation
transformer differs from that of a
stepup
or
stepdown
transformer.
file 02209
1
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 visaversa. 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
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
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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 Spring '20
 Vsecondary, Iprimary