WorksheetsEE 4-2
Total questions: 50
Worksheet time: 25mins
A sine wave has a frequency of 60 Hz. Its angular frequency is
120π
60π
30π
6π
In a loss-free RLC circuit, the transient current is
oscillating
square wave
sinusoidal
non-oscillating
What is the maximum flux in mWb of a transformer with 200 primary turns when connected to a 60 Hz, 200 V supply?
10.35
6.25
50.5
3.75
A 60 Hz, 4 pole, 3 phase induction motor has a slip of 2.5%. What is the slip speed in rpm?
55
40
60
45
A 15 hp, 460 V, 60 Hz, 6-pole, 3 phase induction motor has full-load slip of 4%. Find the full-load torque in N-m
85
88
93
90
At very low frequencies a series RC circuit behaves as almost purely
resistive
inductive
capacitive
none of these
A power plant gets water from a dam from a height of 122.45 m at the rate of 1,000 cubic meters per minute. If the output of the plant is 15,000 kW, what is the plant efficiency?
80%
75%
70%
65%
A 500 KVA, 34.5/13.8 kV, 3-phase transformer is delta-wye connected. The primary and secondary winding resistances are 35 ohms and 0.876 ohm per phase, respectively. Calculate the percent efficiency at full-load and unity power factor if core loss is 3 kW.
97.8
98.7
96.4
97.2
One of the advantages of distributing the winding in alternators is to
reduce harmonics
reduce the amount of copper
improve voltage waveform
decrease the value of the voltage
The effect of corona is
increased reactance
increased inductance
increased energy loss
all of these
The rms value of pure cosine function is
0.5 of peak value
0.707 of peak value
same as peak value
zero
Calculate the use factor of a power plant if the capacity factor is 35% as it operates 8,000 hours during the year.
38.32%
33.82%
36.82%
32.54%
How many commutator bars does a 6-pole dc generator with 4 coil elements per slot and 20 slots per pole have?
60
120
240
480
A coil having a resistance of 10 Ω and an inductance of 4 H is switched across a 20 V dc source. Calculate the rate of current change when the current reaches 50% of its final steady value.
2.5 A/s
3.5 A/s
4.5 A/s
5.5 A/s
Calculate the torque in N-m developed by a 440-V dc motor having an armature resistance of 0.25 Ω and running at 750 rpm when taking a current of 60 A.
240
285
325
342
In a 13.8 kV, 10 MVA base three-phase system, a phase to phase fault occurs. If the Thevenin’s equivalent impedance of the system is 2.63%, what is the per unit fault current?
19.01 pu
32.93 pu
57.03 pu
98.78 pu
A single-phase transmission line having a length of 15 miles is composed of two copper conductors spaced 7 ft apart having a diameter of 0.575 inch. Determine the line to line capacitance in farad if the system frequency is 60 Hz.
4.9 x 10⁻¹²
9.6 x 10⁻¹²
11.8 x 10⁻⁹
118 x 10⁻⁹
What is the equivalent IEEE device function number for directional power relay?
21
32
37
87
Energy radiated continuously in the form of lighting waves is called
luminous intensity
lumen
luminous flux
illumination
Efficiency is secondary consideration in case of
base load plants
peak load plants
both base load and peak load plants
none of these
A capacitor is charged with 10,000 μC. If the energy stored is 1 joule, find the capacitance.
5 μF
50 μF
500 μF
5,000 μF
To a series RLC circuit, a voltage of 10 V is applied. If Q of the coil at resonant frequency is 20, the voltage across the inductor at resonant frequency will be
200 V
100 V
75 V
50 V
A 75 kVA, 13,200/240, 60 Hz, single-phase transformer has 1% resistance and 3% reactance. Find the copper loss of the transformer at 3/4 of full-load and unity power factor.
185 W
422 W
368 W
508 W
The starting current of a 15 hp, 460 V, 3 phase induction motor is 130 A. What voltage in volts should be applied to the motor so that the starting current will not exceed 84.8 A?
238
295
300
310
The condition of a liquid electrolyte is measured in terms of its
current value
specific gravity
acid content
voltage output
If the field of a dc shunt motor is opened
it will continue to run at its rated speed
the speed of the motor will become very high
the motor will stop
the speed of the motor will decrease
An ideal full-wave rectifier with non-inductive load has zero transformation losses. What is the efficiency?
70%
80%
90%
100%
In an ACB sequence balanced 3φ system, the angle between the line voltage and the line current is 50°. What is the lagging power factor of the system?
0.30
0.50
0.64
0.94
A power station supplies 60 kW to a load over 2,500 ft of 000 2-conductor copper feeder the resistance of which is 0.078 Ω per 1,000 ft. The bus-bar voltage is maintained constant at 600 volts. Determine the maximum power which can be transmitted.
60 kW
230.7 kW
120 kW
150 kW
If a certain conductor has an area of 336,400 circular mils, what is the radius of this conductor in cm?
0.663
0.810
0.737
0.921
In a laboratory experiment, the impedance of a coil was obtained at 60 Hz and 30 Hz. These are 75.48 ohms and 57.44 ohms, respectively. What is the inductance of the coil?
150 mH
182.5 mH
42.5 mH
2.1 mH
The dummy coil in dc machines is used to
eliminate reactance voltage
eliminate armature reaction
bring about mechanical balance of armature
eliminate harmonics developed in the machine
A half wave rectified sine wave has an average value of 100 amperes. What is its effective value?
157 A
70.71 A
100 A
141.4 A
A 3φ transmission line has two aluminum conductors in bundle. The self GMD of each conductor is 8.90 mm and the distance between the conductors and phases is 40 cm and 9 m, respectively. What is the inductance of the line per phase?
1 μH/m
2 μH/m
3 μH/m
4 μH/m
The purpose of insulating oil when used on power circuit breaker are the following, EXCEPT:
Interrupter
Coolant
Insulation
Quencher
A wind generator with an efficiency of 80% has a blade diameter of 20 m. If the wind velocity is 30 km/hr, how much power in kW is obtained from the generator?
58.47
45.78
48.75
54.87
The field system of a 50 Hz alternator has a sinusoidal flux per pole of 0.1 Wb. Calculate the emf generated in one turn which spans two-thirds of a pole pitch.
17.4 V
19.2 V
12.2 V
9.6 V
A dc shunt motor develops 15 hp at 120 V. If the effective armature resistance is 0.061 ohm and the field winding draws 2 amperes, what is the overall efficiency?
93%
94%
95%
90%
A 8-pole triplex wave-wound armature carries a total of 660 amperes. If there are 8 brush arms, calculate the current in each armature conductor.
110 A
66 A
22 A
11 A
Inside a hollow spherical conductor
electric field is zero
electric field is constant
electric field changes with distance from the center of the sphere
electric field is unity
Residual magnetism is necessary in a
separately excited generator
self-excited generator
both of these
none of these
Three impedances Z_ab = 4 - j3 ohms, Z_bc = 3 + j4 ohms and Z_ca = 10 + j0 ohms are connected in delta across a 220 volts, three-phase balanced source. What is the total power of the circuit?
1,839 W
1,936 W
6,130 W
18,392 W
A light source located 2.75 m from a surface produces an illumination of 528 lux on that surface. Find the illumination if the distance is changed to 1.55 m.
298 lux
1,662 lux
937 lux
168 lux
In case of delta connected circuit, when one resistor is open, power will be
unaltered
reduced to 1/9
reduced to 1/16
reduced by 1/3
Two similar poles, each of 1 Wb, placed 1 m apart in air will experience a repulsive force of
63,000 N
796 N
8 x 10⁻² N
63 x 10⁻³ N
In a transformer, the core loss is found to be 60 watts at 30 Hz and 90 watts at 40 Hz measured at the same maximum flux density. Compute the eddy current and hysteresis losses at 60 Hz in watts.
90, 75
85, 60
95, 69
88, 72
Transient current in an RLC circuit is oscillatory when
R = 0
R = 2√(L/C)
R > 2√(L/C)
R < 2√(L/C)
The current from neutral to ground connection is 12 A. What is the zero sequence component in phases?
12 A
36 A
4 A
3 A
With reference to armature windings, wave windings are often called ________ windings.
cascade
series
parallel
ring
This is the compact arrangement of switching devices.
Circuit protector
Switchboard
Switchgear
Panelboard
