EPO460 - Three phase system

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