AC Th, Lvl III - 3rd Ed. Lesson 8: An Introduction to 3-Phase Systems Quiz for Lesson 8
A 3-phase power source can be produced by rotating a magnetic field through three separate coils arranged ? apart.
120°
The horsepower rating of 3-phase motors and the kilovolt-ampere rating of 3-phase transformers are about ? of single-phase motors and transformers of about the same physical size.
150%
The delta connection requires ? conductors to connect the generator to a 3-phase load.
3
Most electrical power generated today is ? .
3-phase
The wye connection requires ? conductors to connect the generator to a 3-phase wye load when a neutral is required.
4
A balanced 3-phase system requires conductors of about ? the size of the conductors for a single-phase, two-wire system for the same kilovolt-ampere rating.
58%
Identify the type of connection in the figure.
Delta
Determine the line current of the circuit.
Eline = Ewinding x 1.73= 120 x 1.73= 208 V The correct answer is: 208 V
Determine the line voltage of the circuit.
Eline = Ewinding= 120 V The correct answer is: 120 V
Determine the line current of the circuit shown. (Round the FINAL answer to the nearest whole number.)
Iline = Iwinding x 1.73= 15 x 1.73= 26 A The correct answer is: 26 A
Determine the line current of the circuit.
Iwinding = Iline= 15 A The correct answer is: 15 A
? , as it applies to electrical distribution systems, means that power is transmitted using multiple wires utilizing voltages that are equal in magnitude but are separated in phase angle (or time).
Polyphase
In the figure, if a resistive load is connected phase to neutral on one winding, how much power is delivered by that winding?
Psingle phase = E x I= 120 x 15= 1,800 W The correct answer is: 1800 W
In the figure shown, if a 3-phase resistive load is connected to the generator, what is the total power supplied? (Round the FINAL answer to the nearest whole number.)
Pthree phase = Eline x Iline x 1.73= 120 x Iline x 1.73 Iline = x Iwinding x 1.73= 15 x 1.73= 26 A= 120 x 26 x 1.73= 5,398 W The correct answer is: 5398 W
In the figure shown, if a 3-phase resistive load is connected to the generator, what is the total power supplied? (Round the FINAL answer to the nearest whole number.)
Pthree phase = Eline x Iline x 1.73= 208 x 15 x 1.73= 5,398 W The correct answer is: 5398 W
In the figure, if three single-phase, purely resistive loads are connected line to neutral to the generator at 15 amperes, what is the total power supplied?
Ptotal = Pwinding x 3= 1800 x 3= 5,400 W The correct answer is: 5400 W
A single-phase power source can be generated by rotating a magnetic field through a single stationary coil.
T
There are two basic wiring schemes for 3-phase systems. These are wye and delta connections.
T
When two voltages are in-phase, they have the same frequency, and there is no time displacement between them. Both voltages cross the baseline at the same time, going in the same direction.
T
What is the time displacement between voltages on a 3-phase generator if the frequency is 60 hertz? (Round the FINAL answer to two decimal places of the unit shown.)
The correct answer is: 5.56
A machine shop has a delta-connected, 3-phase, 240-volt service with a balanced load of approximately 260 amperes and a power factor of 82%. How much power in kilowatts is being consumed? (Round the FINAL answer to one decimal place.)
The correct answer is: 88.5
Identify the type of connection in the figure.
Wye
Select the system connection that is described by each statement.
Wye, Delta, Delta, Wye, Wye
Identify the formulas as they apply to the delta or the wye connection.
Wye, → Delta, → Wye, → Delta, → Delta, → Wye
The word "phase" is often represented by the Greek letter ? , whose symbol is ? .
phi / ɸ
The voltage produced by a generator is zero for some period of time for the ? -phase power system. The voltage falls to zero ? each cycle.
single / twice
Another name sometimes used to refer to the wye connection is the ? connection.
star
Compare the power delivered by the wye armature feeding a 3-phase load, the delta armature feeding a 3-phase load, and the three equal single-phase loads connected to the wye armature in the previous questions. The power delivered is ? .
virtually the same in all three cases
