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WorksheetsPower System
Total questions: 24
Worksheet time: 12mins
In a series RLC circuit, what is the nature of the power factor of the circuit if the frequency is very high
unity
leading
lagging
cannot be determined
Which of the following is not a unit of electrical energy?
W
Ws
J
kWh
What does a positive power in an electrical element indicate?
Element may absorb or supply powe
The sign of the power does not matter
The element is supplying power
The element is absorbing power
In three phase system, the three voltages (or currents) differ in phase by ____ electrical degrees from each other in a particular sequence.
30
120
60
90
Which of the following elements of electrical engineering cannot be analyzed using Ohm’s law?
capacitors
resistors
inductors
transistors
______ states that the total electric flux through any closed surface is equal to the charge enclosed by that surface.
Faraday's law
Gauss' law
Lenz's law
Maxwell's law
What part of an electric machine will the temperature rise mainly affect?
speed of the machine
conductance of the windings
insulation of the machine
output voltage of the machine
Transformer ratings are always given in:
VA
VAR
W
HP
An ideal transformer will have maximum efficiency at a load when ______.
Pcu=Pco
Pcu>Pco
Pcu<Pco
cannot be determined
For a star connected three phase AC circuit:
None of these
Line voltage is square root three times phase voltage and phase current is equal to line current
Phase voltage is equal to line voltage and phase current is three times the line current
Phase and line voltages and currents are equal
Resonance occurs when:
Xl=Xc
Xl = Xc
Xl<Xc
Xl>Xc
In a DC circuit, inductive reactance would be:
extremely high
zero
high
equal as in AC circuits
What is the number of primary turns in a 200:5 V current transformer if the EMF per turn is 10 V?
2 turns
10 turns
20 turns
2000 turns
Which of the following is a correct representation of peak value in an AC circuit?
RMS value times the square root of 3
RMS value times the square root of 2
RMS value divided by the square root of 3
RMS value divided by the square root of 2
In superposition theorem, while considering a source, all other voltage sources are?
removed from the circuit
changed in position
short circuited
open circuited
Which of the following materials is generally used in the design of electromagnetic machines?
Paramagnetic materials
Diamagnetic materials
Ferromagnetic materials
Core-magnetic materials
The name of the Induction motor comes from the fact that:
Operation of the motor depends upon the inrush current in the motor conductors
Operation of the motor depends upon the induced voltage in the stator
Operation of the motor depends upon the value of coil windings
Operation of the motor depends upon the induced voltage in the rotor conductors
What value of direct current must flow through a resistor to produce the same heating power as an alternating current with a peak value of 4 A?
4 A
5.66 A
1.05 A
2.83 A
If the phasors are drawn to represent the maximum values instead of the RMS values, what would happen to the phase angle between the quantities?
becomes zero
increases
remains constant
decreases
The purpose of the transformer core is to provide ______ for magnetic flux linkage.
high capacitive path
low capacitive path
high reluctance path
low reluctance path
The equivalent Thevenin resistance (or impedance) is found by:
Shorting all voltage sources
Opening all voltage sources and shorting all current sources
Shorting all voltage sources and opening all current sources
Opening all current sources
The total number of possible phase sequences for a three-phase AC system is ___.
1
2
3
4
For a polyphase system, phase sequence depends on the:
rotation of the field
armature
field
rotation of the armature
How many cycles will an AC signal make in 3 seconds if its frequency is 150 Hz?
300 cycles
50 cycles
450 cycles
200 cycles
