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A separately excited dc motor is required to be controlled, from a 3-phase supply, for its operation in the first quadrant only. The most preferred converter would be 

(a) 3-phase fully controlled converter (b) 3-phase fully controlled converter with free wheel diode (c) 3-phase dual converter (d) 3-phase half wave converter 

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1 answer 16 views

A separately excited dc motor operating in first quadrant is fed from 3-phase semi -converter free -wheeling diode is open circuited, then the motor :  (A) can be operated in first quadrant (B) can be operated in first & second quadrants (C) can be operated in first & fourth quadrants (D) cannot be operated

asked Apr 30, 2018 in Electrical Engineering by Shimroz123
0 answers 11 views

A single-phase half-controlled rectifier is driving a separately excited dc motor. The dc motor has a back emf constant of 0.5 V/rpm. The armature current is 5 A without any ripple. The armature resistance is 2 Ohm. The converter is working from a 230 V, single-phase ac source with a firing angle of 30o . Under this operating condition, the speed of the motor will be  (A) 339 rpm (B) 359 rpm (C) 366 rpm (D) 386 rpm

asked May 18, 2018 in Bipolar Junction Transistor by Shimroz123
1 answer 33 views

A large dc motor is required to control the speed of the blower from a 3 -phase ac source. The suitable ac to dc converter is, 3 -phase (a) Fully controlled bridge converter (b) Fully controlled bridge converter with freewheeling diode (c) Half controlled bridge converter (d) Converter pair in sequence control

asked Apr 25, 2018 in Electrical Engineering by Shimroz123
1 answer 25 views

A DC chopper is used for regenerative braking of a separately excited DC motor. The DC supply voltage is 400V. The armature current during regenerative braking is kept constant at 300 A with negligible ripple. For a duty cycle of 60% the power return to the DC supply is  (a) 78 kW (b) 58 kW (c) 38 kW (d) 48 kW

asked May 13, 2018 in Power Electronic Controlled Drives by Shimroz123
1 answer 19 views

The supply both to field and armature circuits are disconnected simultaneously in a separately excited dc motor and it comes to a standstill in 5 sec. If the armature circuit of this motor is disconnected from supply with field circuit remaining energized, the motor would come to rest in (1) 5 sec (2) 7 sec (3) 4 sec (4) A very long time  

asked Apr 11, 2018 in Electrical Engineering by Shimroz123
1 answer 56 views

The no-load speed of a single-phase SCR bridge converter fed separately excited dc motor operating at a firing delay angle, α and flux, Φ (A) directly proportional to α and Φ (B) inversely proportional to α and Φ (C) directly proportional to α and inversely proportional to Φ (D) directly proportional to Φ and inversely proportional to α

asked Apr 28, 2018 in Power Electronic Controlled Drives by Shimroz123
0 answers 19 views

A separately excited d.c. motor fed from single phase full converter with firing angle 60° runs at 1000 r.p.m. If motor is connected to single phase semiconverter with the same firing angle of 60°, it would run at (a) 2000 rpm (b) 1850 rpm (c) 1500 rpm (d) 1000 rpm 

asked May 25, 2018 in DC motor by Shimroz123
0 answers 8 views

A separately excited dc generator is running at rated speed and at no load. If its field winding is suddenly connected to a dc source then rise in armature generated voltage is governed by (1) Armature time constant (2) Field time constant (3) Both (a) and (b) (4) Mechanical time constant

asked Apr 11, 2018 in Electrical Engineering by Shimroz123
1 answer 18 views

Three equal impedances are first connected in delta across a 3 -phase balanced supply. If the same impedances are connected in star across the same supply then,

asked Apr 23, 2018 in Electrical Engineering by Zeeshan
0 answers 20 views

If the supply frequency of a 3-phase induction motor is ‘f’, then frequency of rotor emf at motor slip ‘s’ will be   (a) sf (b) (1 – s)f (c) f/s (d) None of these 

asked Apr 10, 2018 in Electrical Engineering by Shimroz123
1 answer 28 views

A separately excited d.c. machine is coupled to a 50 Hz, three-phase, 4-pole induction machine as shown in the figure. The Dc machine is energized first and the machines rotate at 1 600 1pm. Subsequently the induction machine is also connected to a 50 Hz, three phase source, the phase sequence being consistent with the direction of rotation. In steady state

asked May 20, 2018 in DC machine by Shimroz123
1 answer 13 views

A 3-phase induction motor is running at slip ‘s’. If its two supply leads are interchanged, then the operating slip at that instant will be:

asked May 22, 2018 in Induction Machine by Shimroz123
0 answers 9 views

Two wattmeter method can be used in a three phase system excited with balanced three phase supply  A) To measure real power and power factor in a balanced load B) To measure reactive power in a balanced load C) To measure real power in an unbalanced load D) All of the above 

asked Apr 9, 2018 in Electrical Engineering by Zeeshan
1 answer 14 views

A solar cell of 350 V is feeding power to an ac supply of 440 V, 50 Hz through a 3-phase fully controlled bridge converter. A large inductance is connected in the dc circuit to maintain the dc current at 20 A. If the solar cell resistance is 0.5 Ohm ,then each thyristor will be reverse biased for a period of  (A) 125o (B) 120o (C) 60o (D) 55o

asked May 18, 2018 in Power electronics converters by Shimroz123
0 answers 41 views

A 0.5 Hp, 6 pole wound rotor induction motor is excited by a 3 phase 60 Hz source. Calculate the frequency of the rotor current at standstill.  (A) 50 Hz (B) 30 Hz (C) 60 Hz (D) 120 Hz 

asked Apr 5, 2018 in Electrical Engineering by Shimroz123
0 answers 57 views

If a self excited d.c. generator after being installed, fails to build up voltage on its first trial run, the first thing to do is (a) reverse the field winding connections (b) increase the field resistance (c) decrease the speed of prime mover (d) increase the speed of prime mover  

asked May 25, 2018 in DC generator by Shimroz123
0 answers 24 views

A 750 Hp, 250 V, 1200 r/min DC motor is connected to a 208 V, 3 phase, 60 Hz, line using a 3 phase bridge converter. The full load armature current is 2500 A and the armature resistance is 4 m ohm. Calculate the required firing angle under rated full load conditions.  (A) 45 deg (B) 208 deg (C) 27 deg (D) 32 deg 

asked Apr 5, 2018 in Electrical Engineering by Shimroz123
2 answers 140 views

Separately Excited DC motor

asked Aug 9, 2017 in Electrical Machine by Zeeshan
1 answer 15 views

In a 2 kW, 200 V, 1000 rpm. DC series motor the torque at full load was found to be 0.3 N -m. The torque at half full load in N -m is :

asked Apr 29, 2018 in Electrical Machine by Shimroz123
1 answer 41 views

A 3 -phase, fully controlled, converter is feeding power into a DC load at a constant current of 150 A, the rms value of the current flowing through each thyristor of the converter is

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During 3-phase short circuit on a unloaded alternator, the dc component may be zero in (1) One phase only (2) Any two phases (3) All three phases (4) None of the above 

asked Apr 11, 2018 in Electrical Engineering by Shimroz123
0 answers 58 views

To enable dc series motor work satisfactory with an AC supply, the following modifications should be done (1) The yoke and poles should be completely laminated (2) The poles should be made of laminated steel (3) The air gap between stator and rotor be reduced (4) Compensating poles should be introduced  

asked Apr 11, 2018 in Electrical Engineering by Shimroz123
1 answer 18 views

A 3-phase fully controlled bridge converter with free wheeling diode is fed from 400 V, 50 Hz AC source and is operating at a firing angle of 60o. The load current is assumed constant at 10 A due to high load inductance. The input displacement factor (IDF) and the input power factor (IPF) of the converter will be  (A) IDF IPF = = 0.867; 0.828 (B) IDF IPF = = 0.867; 0.552 (C) IDF IPF = = 0.5; 0.478 (D) IDF IPF = = 0.5; 0.318 

asked May 18, 2018 in Power electronics converters by Shimroz123
0 answers 13 views

If supply voltage decreases by 4% the torque in 3-phase induction motor would decrease by (1) 4% (2) 16% (3) 8% (4) 7.84%  

asked Apr 11, 2018 in Electrical Engineering by Shimroz123
1 answer 25 views

A capacitor-start single phase induction motor is switched on to supply with its capacitor replaced by an inductor of equivalent reactance value. It will?

asked Mar 20, 2018 in Induction Machine by Shimroz123
0 answers 18 views

A coherent QPSK demodulator is required on ground for receiving data from a LEO satellite. What should be optimum order of PLL in the carrier phase tracking loop?  A) 1st order B) 2nd order C) 3rd order D) None of the above

asked Apr 9, 2018 in Electrical Engineering by Shimroz123
0 answers 12 views

In the equivalent circuit of a 3-phase induction motor, the mechanical load on the motor can be represented by a resistance of value (1) R2 (2) R2/S (3) R2(1-S)/S (4) (R2/S)+1 

asked Apr 11, 2018 in Electrical Engineering by Shimroz123
1 answer 9 views

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How much resistance is required to limit the current from a 12 V battery to 3.6 mA? A.3.3 k ohms B.33 k ohms C.2.2 k ohms D.22 k ohms

asked May 15, 2018 in Basic concepts by Shimroz123
0 answers 54 views

A 1-phase, 7.46 kW motor is supplied from a 400 V, 50 Hz A.C mains. Its efficiency is 85% and power factor is 0.8 lagging. Calculate the KVA input (1) 9.56 kVA (2) 5.4 Kva (3) 10.97 kVA (4) 8.6 kVA 

asked Apr 11, 2018 in Electrical Engineering by Shimroz123
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The method of speed control used for increasing the speed of a dc shunt motor above its rated speed is  1) armature resistance control 2) field control (3) armature voltage control (4) series parallel control 

asked Apr 10, 2018 in Electrical Engineering by Shimroz123
0 answers 76 views

A 3-phase circuit breaker is rated at 1250 A, 2000 MVA, 33 kV, 4s. Its making current capacity will be   (a) 35 kA (b) 89 kA (c) 79 kA (d) 69 kA

asked Apr 10, 2018 in Electrical Engineering by Shimroz123
1 answer 223 views

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asked Apr 28, 2018 in Electrical Engineering by Shimroz123
1 answer 15 views

A 3-phase induction motor under locked rotor condition and with stator supply, induces (A) small voltage at slip frequency (B) large voltage at rotor frequency (C) zero voltage at zero frequency (D) large voltage at slip frequency

asked Apr 25, 2018 in Electrical Engineering by Shimroz123
0 answers 17 views

The starting torque of a V/f controlled inverter-fed 3-phase induction motor operating at 25 Hz as compared with the same motor operating at 50 Hz is (A) more (B) double (C) equal (D) less 

asked Jun 4, 2018 in Electrical Machine by Shimroz123
0 answers 17 views

DC ammeter has a resistance of 0.1 Ω and its current range is 0-100 A. If the range is to be extended to 0-300 A, what shunt resistance need to be connected?  A) 0.025 Ω B) 0.05 Ω C) 0.015 Ω D) 0.03 Ω

asked Apr 9, 2018 in Electrical Engineering by Shimroz123
1 answer 22 views

A minimum clearance of 6.3 m to ground is required for overhead lines when operating voltages are :  (A) less than 66 kV (B) lie between 66 kV and 110 kV (C) more than 165 kV (D) lie between 110 kV and 165 kV

asked Apr 30, 2018 in Electrical Engineering by Shimroz123
0 answers 371 views

Internal resistance of a micro-ammeter is 500 ohm. Shunt resistance required to increase its range from 0-100 µA to 0-10 A will be approximately (a) 0.05 Ω (b) 0.005 Ω (c) 0.5 Ω (d) 5.0 Ω

asked May 26, 2018 in Electrical Measurements and Instrumentation by Shimroz123
1 answer 14 views

The main application of delta/zig-zag connected 3-phase transformer is to supply (A) balanced loads (B) unbalanced loads (C) furnace loads (D) single-phase loads

asked Apr 25, 2018 in Electrical Engineering by Shimroz123
2 answers 74 views

The sum of product expression for a Boolean function can be derived from its truth table by (a) AND operation of the product terms. (b) NOR operation of the product terms. (c) OR operation of the product terms. (d) NAND operation of the product terms.

asked Apr 14, 2018 in Electrical Engineering by Shimroz123
1 answer 23 views

A 10A DC Ammeter has a resistance of 0.1 Ω is to be extended to 50 A, the required shunt wire is A) Manganin wire of 20 m Ω B) Constantan wire of 20 m Ω C) Manganin wire of 25 m Ω D) Constantan wire of 25 m Ω

asked Jun 4, 2018 in Electrical Measurements and Instrumentation by Shimroz123
1 answer 12 views

In dc choppers for chopping period T, the output voltage can be controlled by FM by varying   (A) T keeping Ton constant (B) Ton keeping T constant (C) Toff keeping T constant (D) None of the above

asked May 17, 2018 in Power Electronics by Shimroz123
0 answers 21 views

If the back emf of a dc motor is doubled and its speed is also doubled, the torque developed in the machine will  (1) get doubled (2) become 4 times (3) get halved (4) remain unaltered

asked Apr 10, 2018 in Electrical Engineering by Shimroz123
1 answer 34 views

A balanced three-phase, 50 Hz voltage is applied to a 3 phase, 4 pole, induction motor. When the motor is delivering rated output, the slip is found to be 0.05. The speed of the rotor m.m.f. relative to the rotor structure is: (A) 1500 r.p.m. (B) 1425 r.p.m. (C) 25 r.p.m. (D) 75 r.p.m

asked Apr 11, 2018 in Electrical Engineering by Shimroz123
1 answer 20 views

what is separately excited motor ?

asked Aug 15, 2017 in Electrical Machine by Zeeshan
0 answers 46 views

In order to recover the original signal from the Sampled one, what is the condition to be satisfied for sampling frequency ωs and highest frequency component ωm?  (A) ωm < ωs ≤ 2 ωm (B) ωs ≥ 2 ωm (C) ωs < ωm (D) ωs = ωm

asked Apr 5, 2018 in Electrical Engineering by Zeeshan
0 answers 14 views

Pick up the false statement from the choices given below : (A) In a 3 -ph balanced delta circuit, phase voltage is same as line voltage (B) In a 3 -ph balanced delta circuit, phase current is same as line current (C) In a 3 -ph balanced star circuit, line voltage is 1.73 times phase voltage (D) In a 3 -ph balanced star circuit, phase current is same as line current 

asked Apr 14, 2018 in Electrical Engineering by Shimroz123

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