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WorksheetsEPO460 - Three phase system
Total questions: 10
Worksheet time: 8mins
Which of the following is true for a balanced three-phase system?
All three phase voltages are unequal
Voltages equal in magnitude & 120° differ in phase, and
identical loads
Phase currents vary with load only
Voltages equal in magnitude & 120° differ in phase, and
unidentical loads
In a star-connected three-phase system, the phase voltage is:
Equal to the line voltage
√3 times the line voltage
1/√3 times the line voltage
Independent of line voltage
What is the phase difference between each phase of a balanced three-phase system?
60 degrees
90 degrees
120 degrees
180 degrees
In a three-phase power system, the total power is given by:
P=3⋅Vline⋅Iline⋅cosϕ
P=3⋅Vphase2⋅Iphase⋅cosϕ
P=Vline⋅Iline.cosϕ
P=√3⋅Vline⋅Iline⋅cosϕ
Which of the following is a benefit of using a three-phase system over a single-phase system?
Higher voltage drop
Lower efficiency
More power per unit of conductor material
Less stable operation
In a delta-connected system, the line current is related to the phase current by:
Iline=Iphase
Iline=√3⋅Iphase
Iline=Iphase/√3
Iline=3⋅Iphase
What is the primary reason for using a neutral wire in a star-connected system?
It provides ground connection for all phases
It balances out unequal phase voltages
It carries the return current when there is an unbalanced load
It is used only in delta-connected systems
A three-phase induction motor connected in star configuration operates at a line voltage of 400V. What is its phase voltage?
230V
400V
690V
200V
For a three-phase system, the power factor is:
Always leading
Defined as the ratio of active power to apparent power
Always 1
Equal to the phase difference between line currents
The relationship between line voltage and phase voltage in a delta-connected system is given by:
Vline=√3⋅Vphase
Vline=Vphase
Vline=3⋅Vphase
Vline=Vphase/√3
