# Network Theory Questions and Answers – Inter Connection of Three-Phase Sources and Loads

This set of Network Theory Quiz focuses on “Inter Connection of Three-Phase Sources and Loads”.

1. In a three phase alternator, there are __________ independent phase windings or coils.
a) 1
b) 2
c) 3
d) 4

Explanation: In a three phase alternator, there are 3 independent phase windings or coils. So, 3 independent phase windings or coils. The end connections of the three sets of the coils may be brought out of the machine to form three separate single phase sources to feed three individual circuits.

2. Each coil in three phase alternator has ________________ number of terminals.
a) 2
b) 4
c) 6
d) 8

Explanation: Each coil in three phase alternator has 2 number of terminals, viz. start and finish. So, 2 number of terminals. the coils are inter connected to form a wye or delta connected three phase system to achieve economy and reduce the number of conductors and thereby the complexity of the circuit.

3. In wye or star connection _____________ of the three phases are joined together within the alternator.
a) similar ends
b) opposite ends
c) one similar end, two opposite ends
d) one opposite end, two opposite ends

Explanation: In wye or star connection, similar ends of the three phases are joined together within the alternator. The common terminal so formed is referred to as the neutral point or neutral terminal.

4. The voltage between __________ and ___________ is called phase voltage.
a) line and line
b) line and reference
c) neutral point and reference
d) line and neutral point

Explanation: In a three phase four wire star connected system, the terminals R, Y and B are called the line terminals of the source. The voltage between line and neutral point is called phase voltage. And the voltage between line and line is called line voltage.

5. The voltage between ______________ is called line voltage.
a) line and neutral point
b) line and reference
c) line and line
d) neutral point and reference

Explanation: The voltage between line and line is called line voltage. And the voltage between line and neutral point is called phase voltage. The currents flowing through the phases are called the phase currents, while those flowing in the lines are called the line currents.
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6. Figure below represents three phases of an alternator. The phase voltage for the star connection among the options given below is?

a) VRY
b) VRN
c) VYB
d) VBR

Explanation: If the neutral wire is not available for external connection, the system is called a three phase,three wire star connected system. Phase voltage = VRN. And VRY, VYB and VBR are not phase voltages.

7. In the figure shown below, what will be the line voltage?

a) VBR
b) VBN
c) VRN
d) VYN

Explanation: The star connected system formed will supply equal line voltages displaced 120 from one another and acting simultaneously in the cicruit like three independent single phase sources in the same frame of a three phase alternator. Line voltage = VBR. And VRN , VYN and VBN are not line voltages.

8. In the Delta or Mesh connection, there will be __________ number of common terminals.
a) 1
b) 2
c) 3
d) 0

Explanation: The three line conductors are taken from the three junctions of the mesh or delta connection to feed the three phase load. This constitutes a three phase, three wire, delta connected system. In the Delta or Mesh connection, there will be zero number of common terminals. Number of common terminals = 0.

9. The relation between line voltage and phase voltage in Delta or Mesh connection is?
a) Vphase > Vline
b) Vphase < Vline
c) Vphase = Vline
d) Vphase >= Vline

Explanation: When the sources are connected in delta, loads can be connected only across the three line terminal. The relation between line voltage and phase voltage in Delta or Mesh connection is Vphase = Vline.

10. Which of the following voltage is a phase voltage in the delta connection?
a) VRN
b) VBR
c) VYN
d) VBN

Explanation: A balanced three phase source is one in which the three individual sources have equal magnitude with 120 phase differences. VBR is a phase voltage in delta connection. And VRN, VYN and VBNare not phase voltages.

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