問題一覧
1
A short circuit test was performed on a 15 kva, 2400/240 volts transformer yields the following results: Short circuit current =6.25 Amp, short circuit voltage 131 volts and short circuit power-214 watts. Determine the %VR at full load 80% power factor lagging
4.3%
2
A 250 KVA 20000/240 volts single phase transformer operates at Full-load 0.8 p.f. lagging for 11 hours. Half load at unity pf for 8 hours; 25% load at 95% pf leading for the rest of the day. The core loss is 1800 Watts and full load copper loss is 2500 Watts. What is the all-day efficiency?
97.9%
3
What should be the turn ratio of a three-phase transformer to transform 10 MVA from 230 kv to 4160 volts if the transformer is connected wye-delta
31.92
4
A single circuit, three phase 60 Hz transmission line consist of three conductors each of 250 mils in diameter arranged in triangular formation 5m, 5m and 8 m apart. Find the inductive reactance per km.
0.5858-ohm
5
A load of 10,000 KVA, 85% power factor lagging is connected to a 13,200-volt line. How much reactive power is needed to correct the power factor to 97% lagging?
3,138 kvar
6
One leg of a radio tuned circuit has a capacitance of one times ten to the minus nine farad. It is turned at 200 KHz, what is the inductance of the other leg in henry?
6.33x10^-7
7
A balanced three phase wye connected source has using negative phase sequence, Vca = 398 Vrms with 90 degrees angle. Determine Van.
-115 - j199 V
8
It is desired to measure the insulation resistance between the motor winding and the motor frame, a 300-volt 30,000-ohm voltmeter in making the measurement. The voltmeter connected across the source reads 230 volts and when connected in series with the insulation reads 5 volts. Find the insulation resistance?
1.35 Mohms
9
A wire has a resistance of 1.0 ohm per 1000 ft at diameter of 0.1 inch. Determine the resistance of a 200 ft long conductor if the diameter is 40 mils
1.25
10
Two coils in a network are positioned such that there is 80% coupling between them. If the inductance of one coil is 12 mH and the other is 6 mH, find the mutual inductance.
6.8 mH
11
A capacitor is charged at 100,000 micro-coulombs in 2 seconds. What is the current in mA ?
50
12
A coil of 50-ohm resistance and of 150 mH inductance is connected is parallel with a 50 micro-farac capacitor. The source voltage is 100 sin (wt +30deg). What is the equation of the line current?
1.25 sin (wt + 75.5deg)
13
Two current, 5 + j2 and 3 - j2 enter a junction. What is the outgoing current?
8 A
14
In a balanced three-phase system, the wye-connected impedances connected are 10 ohms with 30 degrees angle. If Vbc is equal to 416 V with 240 degrees angle, determine Icn. Assume the phase sequence is CAB.
12 + j20.8 A
15
A 10 kva, 440/110 volts 60 Hz 2-winding transformer is used as an autotransformer What is the kva rating if it is used as 550/110 volts autotransformer?
12.5
16
A 100 kva, 2300/230 volts 60 Hz 2-winding transformer is used as an autotransformer having a single winding to step up the voltage of a 2300 volts line by 10%. if the transformer has 3.3% impedance as 2- winding transformer, find the % impedance as autotransformer
0.3
17
A 500 hp, 2400V, 3-phase motor of 90 percent factor and 95 percent efficiency is to be operated from a 13.8 kV utility service through a wye-delta connected transformers. Compute the secondary winding current in ampere of the transformer.
60.6
18
What is the possible synchronous speed in rpm of a 10-pole induction motor used on 60 cycle line?
760
19
The two conductors of a transmission line carry equal current I in opposite direction. The force on each conductor is
proportional to I^2
20
A material which is slightly repelled by a magnetic field is known as
diamagnetic material
21
The ratio of intensity of magnetization to the magnetization force is known as
susceptibility
22
Paramagnetic materials have relative permeability
slinghtly > 1
23
The unit of magnetic flux is
weber
24
Permeability in a magnetic circuit corresponds to _______ in an electric circuit
conductivity
25
A three-phase generator with full load current of 450 at 12,400 volts has 0.08-ohm resistance, and a synchronous reactance of 2.8 ohms, what is the regulation in percent at 75 percent power factor lagging?
12.8
26
A 500 kVA single phase transformer with 5% reactance is to share a load of 750 kVA at 80% pf lagging with a 333 kVA single phase transformer with 4% reactance. Calculate the kVA delivered by each transformer.
340 & 410
27
What is the slip in percent of a 6-pole synchronous motor running 1170 spm?
0
28
What is the slip in percent of an induction motor running 427 rpm?
5%
29
An AC generator 1500 kVA capacity has a full load efficiency of 91% at 100% power factor and 86% at 80% power factor lagging current. What engine drive in HP is required if the genset is to supply entirely motor loads?
1870
30
A delta connected motor with 6 leads, 20 hp, 3-phase, 60 Hz, 230 v, 1750 rpm, 54 amperes squirrel cage induction motor with starting current of 5 times its full load current with normal applied voltage and develops 1.5 times of its full load torque T. What is the starting current of the motor when wye connected?
90
31
Three 333 kVA transformers are delta connected, one connection has been cut, what is the maximum KVA that can be supplied by the remaining transformers?
577
32
What is the standard device number for overvoltage relay?
59
33
A three-phase wye-delta connected, 345/34.5 KV transformer has an the trency rating of 60 MVA Determine the CT ratio and CT connections required for the protection of the transformer secondary
1000:5 wye
34
A single phase 10 km transmission line has 16.65 mH total inductance. If the distance between the conductor is 1.0 m, what is the GMR of conductor?
1.558 cm
35
Two generator 50 MVA, 4 kV Xd"=25% are connected in parallel and are connected to a transformer 100 MVA 4.2 kV delta/115kV wye grounded with Xt^ prime prime = 10% What is the available short circuit MVA at the transformer secondary?
286
36
The per phase constants of a 345 kV, three phase, 150 km long transmission line has a resistance of 0.1 ohm per km, inductance of 1.1 mH per km and capacitance of 0.01 uF per km. The line supplies a 200MW load at 0.9 power factor lagging. Using nominal pi, calculate the Sending end line voltage.
366.6 kV
37
What is the standard device number for Directional Power Relay?
32
38
A short 3-phase transmission line has an impedance of 8+j11 ohm per phase. The sending end voltage is 120 kV when supplying a balanced load at 110 kV, 0.9 power factor lagging. What is the receiving end power in MW.
81.6 MW
39
A three phase, 13 kV transmission line delivers 8 MVA of load. The per phase impedance of the line is (0.01+j0.05) pu referred to a 13 kV, 8 MVA base. What is the voltage drop across the line?
663 volts
40
The per phase constants of a 345 kv. three phase, 150 km long transmission line has a resistance of 0.1 ohm per km, inductance of 1.1 mH per km and capacitance of 0.02 uF per km. The line supplies a 180MW load at 0.9 power factor lagging. Using nominal pi, calculate the B constant?
63.98 cis 76.44°
41
A 33 KV 3-phase generating station is to supply 10 MW load at 31 kV, 0.9 power factor lagging over a 3- phase transmission line 3 km long. For the efficiency of the line to be 96%, what must be the impedance of the line
3.24 + j5.9
42
The capacitance between any two conductors with the third connected to the sheath of a three phase, 3- conductor cable is 0.2 µF per km. What is total capacitance to neutral for 10km line?
4uf
43
At a certain location in an electric system, the available fault MVA is 400 MVA A 15 MVA 34.5 kV/6.24kV, 2.5% impedance, wye-wye grounded transformer is installed at that location. Determine the short circuit MVA at the secondary
240 MVA
44
A 5 MVA, 13.8 kV/480 V, 5% impedance transformer is tapped at 13.8 kV line where the Thevenin's equivalent impedance is ½ ohm. Determine the fault current at the primary for a three-phase fault at the secondary
3300 amperes
45
The unit of capacitance is
coulombs/volts
46
"The total electric flux through any closed surface surrounding charges is equal to the amount of charge enclosed". The above statement is associated with
gauss law
47
Voltage across capacitor at any time t during charging from a DC source of voltage V is given by
v = V(1 - e ^ (- t / λ)
48
The breakdown voltage for paper capacitors is usually
200 tp 1600 volts
49
The initial rate of rise of current through a coil of inductance 10 H when suddenly connected to a DC supply of 200 V is ____ A/s
20
50
The property of a material which opposes the creation of magnetic flux in it is known as
reluctance
51
The coefficient of self-inductance for a coil is given as
NΦ/I
52
A 500 turns solenoid develops an average induced voltage of 60 V. Over what time interval must a flux change of 0.06 Wb occur to produce such a voltage?
0.5 s
53
A conductor carries 125 amperes of current under 60° to a magnetic field of 1.1 tesla. The force on the conductor will be nearly
120 N/m
54
The mass of an ion liberated at an electrode is directly proportional to the quantity of electricity. The above statement is associated with
faraday's law of electrolysis
55
The capacity of a lead-acid cell is measured in
ampere-hours
56
Five 2 V cells are connected in parallel. The output voltage is
2 V
57
The storage battery generally used in electric power station is
lead acid battery
58
The peak value of a sine wave is 200 V. Its average value is
127.4 V
59
The power consumed in a circuit element will be least when the phase difference between the current and voltage is
90°
60
The commutator segments are connected to the armature conductors by means of
copper lugs
61
For a DC generator when the number of poles and the number of armature conductors is fixed, then which winding will give the higher emf?
wave winding
62
Iron losses in a DC machine are independent of variation in
load
63
Brushes of DC machines are made of
carbon
64
No-load speed of which of the following motor will be highest
series motor
65
If a DC motor is to be selected for conveyors, which motor would be preferred
series motor
66
Small DC motors up to 5 H.P. usually have
2 poles
67
The mechanical power developed by a shunt motor will be maximum when the ratio of back emf to applied voltage is
0.5
68
The speed of a motor falls from 1100 rpm at no-load to 1050 rpm at rated load. The speed regulation of the motor
4.76%
69
The no-load current drawn by transformer is usually what per cent of the full-load current?
2 to 5 percent
70
The dielectric strength of transformer oil is expected to be
33 kV
71
The maximum efficiency of a distribution transformer is
at 50% full load
72
The frequency of the voltage generated in large alternators
50 hz
73
The number of poles in turbo-alternators is usually
2
74
Harmonic component of generated E. M.F. Will be more in
full pitch coil
75
The dark and bright lamp method is used for
synchronizing
76
If the certain conductor has an area of 336,400 cmils, what is the radius of this conductor in cm?
0.737
77
A 110 V dc motor draws current of 30 A and is located 500 ft from the power source. What is the supply voltage if the diameter of the copper wire is 0.25 inch? Resistivity is 10.4 ohm-cmil per ft
115 V
78
Two batteries are connected in parallel to feed a 12-ohm load. Battery A has open circuit emf of 6.3 V and internal resistance of 1.5 ohms. Battery B has an open circuit emf of 6 V and an internal resistance of 2.1 ohms. What is the load current?
0.48 A
79
Calculate the force in pounds upon each side of a coil of 50 tums carrying a current of 20 A if the axial length of the coil is 12 inch and the flux density is 25,000 lines per square inch. There are 4.448 * 10 dynes in a pound. The conductors are at right angles to the flux.
26.6 lbs
80
For a series RLC circuit with elements R = 50Omega, L L = 8mH and C = 2.22mu*F What is the equivalent impedance of the circuit if its frequency is 796 Hz?
50 - j50 ohms
81
A transmission line has a horizontal spacing of 5ft, 5ft and 10 ft. The conductor is 336.4 MCM ACSR has an outside diameter of 0.721 in. What is the shunt capacitance in micro-farad per km per phase
0.00887
82
A series RC Circuit of 10 ohms resistance has a phase angle of 45 degrees at 500 rad/sec angular frequency. At what angular frequency is the total impedance be doubled?
189 rad/s
83
The primary winding of transformer has 2H inductarice while its secondary has 0.5H inductance. The coupling coefficient is 0.9. What is the ratio of primary turns to secondary turns?
2
84
The metallic conductor has a resistance of 7 ohms at 0oC. At 200C the resistance is 7.8 ohms, what is the temperature coefficient at OoC?
0.00571/°C
85
An electric motor operates at full load of 100kW for 10 minutes, at % full load for the next 10 min, % full load for the next 20 min, no-load on the next 20 min and this cycle repeats continuously. Find the continuous rating of the suitable motor
66 kW
86
A 230-volt long shunt compound motor has an armature whose resistance is 0.22-ohm, series resistance of 0.18. Assuming voltage across the brush contact is 2 volts, what armature current will flow when counter emf is 208 volts.
50 A
87
A symmetrical positive-sequence four-bus Z matrix Z11 =j 0.27, Z 12=j0.24 1 ,Z13=;0.17. Z * 14 = 10.2 Z 22=j 0.29, Z23 = j 0.20 Z 24= boxed 0.24 Z 33=j0.3, Z34-j 0.26, and 1 Z44=j0.38, all in p.u., what is the three-phase fault at Bus 3, if there is a fault impedance of 0.1 p.u.?
- j 2.5 p.u
88
Determine the CT ratio of current transformers for measuring current drawn of a three-phase load of 325kVA at 450 volts.
500:5
89
A certain 110-volt shunt generator has an armature and brush resistance of 0.06 ohm at full load of 85 amp. The resistance of the shunt field is 45 ohms, and the stray power losses are found to be 897 watt Calculate the full load efficiency.
85.2%
90
What is the ratio of the resistance of aluminum to that of copper conductor having the same length and diameter? The resistivity of aluminum is 2.83x10-8 ohm-meter and that of copper is 1.72 * 10 - 8 ohm-meter
1.645
91
Two single phase transformers are connected in parallel to supply a load of 225 kVA. Transformer A is rated 100 kVA with 2% impedance while transformer B is rated 125 kVA with 3% impedance. Calculate the load sharing of transformers in kVA.
122.7 & 102.3
92
The rotor of a 3-phase, 60 - Hz 4-pole induction motor takes 120 kW at 3 Hz. The motor has stator copper loss of 3 kW, a mechanical loss of 2 kW and a stator core loss of 1.7 kW. Determine the motor output at the shaft.
112 kW
93
A 2.5 kW single phase converter is operated inverted it converts dc to ac. If the output ac voltage is 240 volts. Find the d-c input voltage
339 volts
94
A transformer when it is operated as a conventional two winding transformer is rated 10 MVA, 12/1 2 KV. 60 Hz. Under these conditions, its series resistance and reactance are given as 2% and 7% pu respectively. This transformer is to be used as 13.2/12 kV step-down autotransformer in a power distribution system. What is the transformer's series impedance in pu in the autotransformer connection?
0.0018 +j0.006
95
A three-phase transposed distribution line is designed with equilateral spacing of 12 ft. It is decided to build the line with horizontal spacing D 31=2D12=2D23 What should be the spacing between adjacent conductors to obtain the same inductance as the original design?
9.5246 ft
96
An alternator driven by a Francis hydraulic turbine is alternator
low or medium speed
97
For low head and high discharge, the hydraulic turbine used is
Kaplan turbine
98
Which device is used to change the kW output of generators in parallet?
Governor
99
Which motor is used in food mixer
Universal motor
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32問 • 1年前問題一覧
1
A short circuit test was performed on a 15 kva, 2400/240 volts transformer yields the following results: Short circuit current =6.25 Amp, short circuit voltage 131 volts and short circuit power-214 watts. Determine the %VR at full load 80% power factor lagging
4.3%
2
A 250 KVA 20000/240 volts single phase transformer operates at Full-load 0.8 p.f. lagging for 11 hours. Half load at unity pf for 8 hours; 25% load at 95% pf leading for the rest of the day. The core loss is 1800 Watts and full load copper loss is 2500 Watts. What is the all-day efficiency?
97.9%
3
What should be the turn ratio of a three-phase transformer to transform 10 MVA from 230 kv to 4160 volts if the transformer is connected wye-delta
31.92
4
A single circuit, three phase 60 Hz transmission line consist of three conductors each of 250 mils in diameter arranged in triangular formation 5m, 5m and 8 m apart. Find the inductive reactance per km.
0.5858-ohm
5
A load of 10,000 KVA, 85% power factor lagging is connected to a 13,200-volt line. How much reactive power is needed to correct the power factor to 97% lagging?
3,138 kvar
6
One leg of a radio tuned circuit has a capacitance of one times ten to the minus nine farad. It is turned at 200 KHz, what is the inductance of the other leg in henry?
6.33x10^-7
7
A balanced three phase wye connected source has using negative phase sequence, Vca = 398 Vrms with 90 degrees angle. Determine Van.
-115 - j199 V
8
It is desired to measure the insulation resistance between the motor winding and the motor frame, a 300-volt 30,000-ohm voltmeter in making the measurement. The voltmeter connected across the source reads 230 volts and when connected in series with the insulation reads 5 volts. Find the insulation resistance?
1.35 Mohms
9
A wire has a resistance of 1.0 ohm per 1000 ft at diameter of 0.1 inch. Determine the resistance of a 200 ft long conductor if the diameter is 40 mils
1.25
10
Two coils in a network are positioned such that there is 80% coupling between them. If the inductance of one coil is 12 mH and the other is 6 mH, find the mutual inductance.
6.8 mH
11
A capacitor is charged at 100,000 micro-coulombs in 2 seconds. What is the current in mA ?
50
12
A coil of 50-ohm resistance and of 150 mH inductance is connected is parallel with a 50 micro-farac capacitor. The source voltage is 100 sin (wt +30deg). What is the equation of the line current?
1.25 sin (wt + 75.5deg)
13
Two current, 5 + j2 and 3 - j2 enter a junction. What is the outgoing current?
8 A
14
In a balanced three-phase system, the wye-connected impedances connected are 10 ohms with 30 degrees angle. If Vbc is equal to 416 V with 240 degrees angle, determine Icn. Assume the phase sequence is CAB.
12 + j20.8 A
15
A 10 kva, 440/110 volts 60 Hz 2-winding transformer is used as an autotransformer What is the kva rating if it is used as 550/110 volts autotransformer?
12.5
16
A 100 kva, 2300/230 volts 60 Hz 2-winding transformer is used as an autotransformer having a single winding to step up the voltage of a 2300 volts line by 10%. if the transformer has 3.3% impedance as 2- winding transformer, find the % impedance as autotransformer
0.3
17
A 500 hp, 2400V, 3-phase motor of 90 percent factor and 95 percent efficiency is to be operated from a 13.8 kV utility service through a wye-delta connected transformers. Compute the secondary winding current in ampere of the transformer.
60.6
18
What is the possible synchronous speed in rpm of a 10-pole induction motor used on 60 cycle line?
760
19
The two conductors of a transmission line carry equal current I in opposite direction. The force on each conductor is
proportional to I^2
20
A material which is slightly repelled by a magnetic field is known as
diamagnetic material
21
The ratio of intensity of magnetization to the magnetization force is known as
susceptibility
22
Paramagnetic materials have relative permeability
slinghtly > 1
23
The unit of magnetic flux is
weber
24
Permeability in a magnetic circuit corresponds to _______ in an electric circuit
conductivity
25
A three-phase generator with full load current of 450 at 12,400 volts has 0.08-ohm resistance, and a synchronous reactance of 2.8 ohms, what is the regulation in percent at 75 percent power factor lagging?
12.8
26
A 500 kVA single phase transformer with 5% reactance is to share a load of 750 kVA at 80% pf lagging with a 333 kVA single phase transformer with 4% reactance. Calculate the kVA delivered by each transformer.
340 & 410
27
What is the slip in percent of a 6-pole synchronous motor running 1170 spm?
0
28
What is the slip in percent of an induction motor running 427 rpm?
5%
29
An AC generator 1500 kVA capacity has a full load efficiency of 91% at 100% power factor and 86% at 80% power factor lagging current. What engine drive in HP is required if the genset is to supply entirely motor loads?
1870
30
A delta connected motor with 6 leads, 20 hp, 3-phase, 60 Hz, 230 v, 1750 rpm, 54 amperes squirrel cage induction motor with starting current of 5 times its full load current with normal applied voltage and develops 1.5 times of its full load torque T. What is the starting current of the motor when wye connected?
90
31
Three 333 kVA transformers are delta connected, one connection has been cut, what is the maximum KVA that can be supplied by the remaining transformers?
577
32
What is the standard device number for overvoltage relay?
59
33
A three-phase wye-delta connected, 345/34.5 KV transformer has an the trency rating of 60 MVA Determine the CT ratio and CT connections required for the protection of the transformer secondary
1000:5 wye
34
A single phase 10 km transmission line has 16.65 mH total inductance. If the distance between the conductor is 1.0 m, what is the GMR of conductor?
1.558 cm
35
Two generator 50 MVA, 4 kV Xd"=25% are connected in parallel and are connected to a transformer 100 MVA 4.2 kV delta/115kV wye grounded with Xt^ prime prime = 10% What is the available short circuit MVA at the transformer secondary?
286
36
The per phase constants of a 345 kV, three phase, 150 km long transmission line has a resistance of 0.1 ohm per km, inductance of 1.1 mH per km and capacitance of 0.01 uF per km. The line supplies a 200MW load at 0.9 power factor lagging. Using nominal pi, calculate the Sending end line voltage.
366.6 kV
37
What is the standard device number for Directional Power Relay?
32
38
A short 3-phase transmission line has an impedance of 8+j11 ohm per phase. The sending end voltage is 120 kV when supplying a balanced load at 110 kV, 0.9 power factor lagging. What is the receiving end power in MW.
81.6 MW
39
A three phase, 13 kV transmission line delivers 8 MVA of load. The per phase impedance of the line is (0.01+j0.05) pu referred to a 13 kV, 8 MVA base. What is the voltage drop across the line?
663 volts
40
The per phase constants of a 345 kv. three phase, 150 km long transmission line has a resistance of 0.1 ohm per km, inductance of 1.1 mH per km and capacitance of 0.02 uF per km. The line supplies a 180MW load at 0.9 power factor lagging. Using nominal pi, calculate the B constant?
63.98 cis 76.44°
41
A 33 KV 3-phase generating station is to supply 10 MW load at 31 kV, 0.9 power factor lagging over a 3- phase transmission line 3 km long. For the efficiency of the line to be 96%, what must be the impedance of the line
3.24 + j5.9
42
The capacitance between any two conductors with the third connected to the sheath of a three phase, 3- conductor cable is 0.2 µF per km. What is total capacitance to neutral for 10km line?
4uf
43
At a certain location in an electric system, the available fault MVA is 400 MVA A 15 MVA 34.5 kV/6.24kV, 2.5% impedance, wye-wye grounded transformer is installed at that location. Determine the short circuit MVA at the secondary
240 MVA
44
A 5 MVA, 13.8 kV/480 V, 5% impedance transformer is tapped at 13.8 kV line where the Thevenin's equivalent impedance is ½ ohm. Determine the fault current at the primary for a three-phase fault at the secondary
3300 amperes
45
The unit of capacitance is
coulombs/volts
46
"The total electric flux through any closed surface surrounding charges is equal to the amount of charge enclosed". The above statement is associated with
gauss law
47
Voltage across capacitor at any time t during charging from a DC source of voltage V is given by
v = V(1 - e ^ (- t / λ)
48
The breakdown voltage for paper capacitors is usually
200 tp 1600 volts
49
The initial rate of rise of current through a coil of inductance 10 H when suddenly connected to a DC supply of 200 V is ____ A/s
20
50
The property of a material which opposes the creation of magnetic flux in it is known as
reluctance
51
The coefficient of self-inductance for a coil is given as
NΦ/I
52
A 500 turns solenoid develops an average induced voltage of 60 V. Over what time interval must a flux change of 0.06 Wb occur to produce such a voltage?
0.5 s
53
A conductor carries 125 amperes of current under 60° to a magnetic field of 1.1 tesla. The force on the conductor will be nearly
120 N/m
54
The mass of an ion liberated at an electrode is directly proportional to the quantity of electricity. The above statement is associated with
faraday's law of electrolysis
55
The capacity of a lead-acid cell is measured in
ampere-hours
56
Five 2 V cells are connected in parallel. The output voltage is
2 V
57
The storage battery generally used in electric power station is
lead acid battery
58
The peak value of a sine wave is 200 V. Its average value is
127.4 V
59
The power consumed in a circuit element will be least when the phase difference between the current and voltage is
90°
60
The commutator segments are connected to the armature conductors by means of
copper lugs
61
For a DC generator when the number of poles and the number of armature conductors is fixed, then which winding will give the higher emf?
wave winding
62
Iron losses in a DC machine are independent of variation in
load
63
Brushes of DC machines are made of
carbon
64
No-load speed of which of the following motor will be highest
series motor
65
If a DC motor is to be selected for conveyors, which motor would be preferred
series motor
66
Small DC motors up to 5 H.P. usually have
2 poles
67
The mechanical power developed by a shunt motor will be maximum when the ratio of back emf to applied voltage is
0.5
68
The speed of a motor falls from 1100 rpm at no-load to 1050 rpm at rated load. The speed regulation of the motor
4.76%
69
The no-load current drawn by transformer is usually what per cent of the full-load current?
2 to 5 percent
70
The dielectric strength of transformer oil is expected to be
33 kV
71
The maximum efficiency of a distribution transformer is
at 50% full load
72
The frequency of the voltage generated in large alternators
50 hz
73
The number of poles in turbo-alternators is usually
2
74
Harmonic component of generated E. M.F. Will be more in
full pitch coil
75
The dark and bright lamp method is used for
synchronizing
76
If the certain conductor has an area of 336,400 cmils, what is the radius of this conductor in cm?
0.737
77
A 110 V dc motor draws current of 30 A and is located 500 ft from the power source. What is the supply voltage if the diameter of the copper wire is 0.25 inch? Resistivity is 10.4 ohm-cmil per ft
115 V
78
Two batteries are connected in parallel to feed a 12-ohm load. Battery A has open circuit emf of 6.3 V and internal resistance of 1.5 ohms. Battery B has an open circuit emf of 6 V and an internal resistance of 2.1 ohms. What is the load current?
0.48 A
79
Calculate the force in pounds upon each side of a coil of 50 tums carrying a current of 20 A if the axial length of the coil is 12 inch and the flux density is 25,000 lines per square inch. There are 4.448 * 10 dynes in a pound. The conductors are at right angles to the flux.
26.6 lbs
80
For a series RLC circuit with elements R = 50Omega, L L = 8mH and C = 2.22mu*F What is the equivalent impedance of the circuit if its frequency is 796 Hz?
50 - j50 ohms
81
A transmission line has a horizontal spacing of 5ft, 5ft and 10 ft. The conductor is 336.4 MCM ACSR has an outside diameter of 0.721 in. What is the shunt capacitance in micro-farad per km per phase
0.00887
82
A series RC Circuit of 10 ohms resistance has a phase angle of 45 degrees at 500 rad/sec angular frequency. At what angular frequency is the total impedance be doubled?
189 rad/s
83
The primary winding of transformer has 2H inductarice while its secondary has 0.5H inductance. The coupling coefficient is 0.9. What is the ratio of primary turns to secondary turns?
2
84
The metallic conductor has a resistance of 7 ohms at 0oC. At 200C the resistance is 7.8 ohms, what is the temperature coefficient at OoC?
0.00571/°C
85
An electric motor operates at full load of 100kW for 10 minutes, at % full load for the next 10 min, % full load for the next 20 min, no-load on the next 20 min and this cycle repeats continuously. Find the continuous rating of the suitable motor
66 kW
86
A 230-volt long shunt compound motor has an armature whose resistance is 0.22-ohm, series resistance of 0.18. Assuming voltage across the brush contact is 2 volts, what armature current will flow when counter emf is 208 volts.
50 A
87
A symmetrical positive-sequence four-bus Z matrix Z11 =j 0.27, Z 12=j0.24 1 ,Z13=;0.17. Z * 14 = 10.2 Z 22=j 0.29, Z23 = j 0.20 Z 24= boxed 0.24 Z 33=j0.3, Z34-j 0.26, and 1 Z44=j0.38, all in p.u., what is the three-phase fault at Bus 3, if there is a fault impedance of 0.1 p.u.?
- j 2.5 p.u
88
Determine the CT ratio of current transformers for measuring current drawn of a three-phase load of 325kVA at 450 volts.
500:5
89
A certain 110-volt shunt generator has an armature and brush resistance of 0.06 ohm at full load of 85 amp. The resistance of the shunt field is 45 ohms, and the stray power losses are found to be 897 watt Calculate the full load efficiency.
85.2%
90
What is the ratio of the resistance of aluminum to that of copper conductor having the same length and diameter? The resistivity of aluminum is 2.83x10-8 ohm-meter and that of copper is 1.72 * 10 - 8 ohm-meter
1.645
91
Two single phase transformers are connected in parallel to supply a load of 225 kVA. Transformer A is rated 100 kVA with 2% impedance while transformer B is rated 125 kVA with 3% impedance. Calculate the load sharing of transformers in kVA.
122.7 & 102.3
92
The rotor of a 3-phase, 60 - Hz 4-pole induction motor takes 120 kW at 3 Hz. The motor has stator copper loss of 3 kW, a mechanical loss of 2 kW and a stator core loss of 1.7 kW. Determine the motor output at the shaft.
112 kW
93
A 2.5 kW single phase converter is operated inverted it converts dc to ac. If the output ac voltage is 240 volts. Find the d-c input voltage
339 volts
94
A transformer when it is operated as a conventional two winding transformer is rated 10 MVA, 12/1 2 KV. 60 Hz. Under these conditions, its series resistance and reactance are given as 2% and 7% pu respectively. This transformer is to be used as 13.2/12 kV step-down autotransformer in a power distribution system. What is the transformer's series impedance in pu in the autotransformer connection?
0.0018 +j0.006
95
A three-phase transposed distribution line is designed with equilateral spacing of 12 ft. It is decided to build the line with horizontal spacing D 31=2D12=2D23 What should be the spacing between adjacent conductors to obtain the same inductance as the original design?
9.5246 ft
96
An alternator driven by a Francis hydraulic turbine is alternator
low or medium speed
97
For low head and high discharge, the hydraulic turbine used is
Kaplan turbine
98
Which device is used to change the kW output of generators in parallet?
Governor
99
Which motor is used in food mixer
Universal motor