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For a D.C. machines laboratory following type of D.C. supply will be suitable induction motor D.C. generator set.

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Satisfactory commutation of D.C. machines requires brushes should be of proper grade and size, brushes should smoothly run in the holders, smooth, concentric commutator properly undercut.

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Brushes of D.C. machines are made of carbon.

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The purpose of retardation test on D.C. shunt machines is to find out stray losses.

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What type of motor is used for drilling machines?

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universal motor also used in Handheld power tools, blowers, blenders, vacuum cleaners, polishers and kitchen appliances.universal motor is defined as a motor which may be operated either on direct or single phase AC supply at approximately the same speed and output

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Hopkinson's test on D.C. machines is conducted at full-load.

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In D.C. machines the residual magnetism is of the order of 2 to 3 percent.

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In D.C. machines fractional pitch winding is used to reduce the sparking.

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Write measures to be taken to maintain the insulation resistance of electrical machines to healthy levels.

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In dc machines, the armature windings are placed on the rotor because of the necessity for  (1) electromechanical energy conversion (2) generation of voltage (3) commutation (4) development of torque

Answer :

3  Commutation

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For protection of rotating machines against lightning surges _______ is used.  (1) lightning arrester (2) capacitor (3) combination of lightning arrester and capacitor (4) lightning conductor and arrester

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For protection of rotating machines against lightning surges combination of lightning arrester and capacitor is used. 

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The speed control of universal motor used for sewing machines is by varying the resistance.

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The inertia constants of two groups of machines which do not swing together are M1 and M2. The equivalent inertia constant of the system is

Answer :

The inertia constants of two groups of machines which do not swing together are M1 and M2. The equivalent inertia constant of the system is M1M2/M1+M2

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Laminated cores, in electrical machines, are used to reduce?

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Laminated cores, in electrical machines, are used to reduce eddy current loss.

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Silicon steel is used in electrical machines because it has?

Answer :

Silicon steel is used in electrical machines because it has low hysteresis loss.

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Exciters of synchronous machines are d.c. shunt machines.

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Losses which occur in rotating electric machines and do not occur in transformers are?

Answer :

Friction losses windage losses 

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Compare core type transformer and shell type transformer on the following parameters. (i) Types of winding used, (ii) Application

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Ans:

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Draw the connection diagram of long shunt differential D.C. compound generator.

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State any two conditions for parallel operation of 3-phase transformer.

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Conditions for Parallel operation of 3 phase transformer 1) Voltage ratings of both the transformers must be identical. 2) Percentage or p.u. impedance should be equal in magnitude. 3) X/R ratio ... between primary & secondary voltages must be same. 6) Phase sequence on both sides must be same.

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In case of D.C. machines, mechanical losses are primary function of speed.

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Cumulatively compounded D.C. motor will be suitable along with flywheel for intermittent light and heavy loads.

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Define: (i) Commercial efficiency of a transformer and  (ii) All day efficiency of a transformer.

Answer :

(i) Commercial Efficiency : It is the ratio of output power in watt to the input power in watt. (ii) All day efficiency of a transformer: It is the ratio of output energy in kWh to the input energy in kWh in the 24 hours of the day

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A 50 KVA transformer has iron loss 2 kW on full load. Calculate its iron loss at 75% of full load.

Answer :

Iron loss is dependent on voltage and independent of load. Hence iron loss at 75% of Load = Iron loss at full load = 2 kW

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Explain how in a 3 phase induction motor to a rotating magnetic field is developed. 

Answer :

Production of Rotating Magnetic Field in Three-phase Induction Motor: In three-phase induction motor, the three-phase stator windings are displaced in space by 120° and their three-phase currents are displaced ... time by 120°. Such fluxes give rise to the resultant rotating magnetic field.

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State any two applications of single phase autotransformer.

Answer :

Applications of single phase auto transformers: 1) Give small boost to distribution cable to correct the voltage drop. 2) As auto transformer starter for induction motors. 3) As furnace supply ... . 5) In control equipment for single phase locomotives. 6) As dimmer in lighting circuits.

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Define transformation ratio in terms of current and voltage.

Answer :

(i) Transformation Ratio (K) is defined as the ratio of the primary current to the secondary current.  (ii) Transformation Ratio (K) is defined as the ratio of the secondary voltage to the primary voltage.

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State any four properties of Ideal transformer.

Answer :

Properties of Ideal transformer: 1) No losses (iron and copper losses), hence no temperature rise. 2) No magnetic leakage i.e (Coefficient of coupling between primary and secondary windings is unity) 3) Zero winding ... drop i.e. E1 = V1, E2 = V2 5) Efficiency 100 %. 6) Regulation 0 %.

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List any four advantages and two disadvantages of 3 phase induction motor.

Answer :

Advantages of 3 phase induction motor: 1) Simple in construction. 2) Economical in cost. 3) Requires very less maintenance. 4) High efficiency. 5) Low maintenace cost. 6) Self starting. 7 ... operated below its full load capacity. 6) It takes a large current from line at instant of starting.

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Can you guys explain the advantages of frequency converter against the star delta or soft starter?

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¬Soft starters  A soft starter is, as you would expect, a device which ensures a soft starting of a motor. A softstarter has different characteristics to the other starting ... at rated current from zero to full speed. Frequency converters are becoming cheaper all the time.

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Answer :

The efficiency of transformer is Greater than electrical Machine because there is no rotational losses in transformer and there is no air gap losses in transformer so losses is less in transformer compare to electrical machine so efficiency is higher in case of transformer.

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If residual magnetism is present in a D.C. generator, the induced e.m.f. at zero speed will be?

Answer :

If residual magnetism is present in a D.C. generator, the induced e.m.f. at zero speed will be zero.

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A 220 V D.C. generator is run at full speed without any excitation. The open circuit voltage will be about 2 V.

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In a D.C. generator the number of mechanical degrees and electrical degrees will be the same when number of poles is 2.

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If brushes of a D.C. generator are moved in order to bring these brushes in magnetic neutral axis, there will be crossmagnetisation as well as demagnetising.

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Answer :

In case of a 4-pole D.C. generator provided with a two layer lap winding with sixteen coils, the pole pitch will be 8.

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The total losses in a well designed D.C. generator of 10 kW will be nearly 500 W.

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You have to sort a list L, consisting of a sorted list followed by a few ‘random’ elements. Which of the following sorting method would be most suitable for such a task ? (A) Bubble sort (B) Selection sort (C) Quick sort (D) Insertion sort

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(D) Insertion sort

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The most accurate statement about teaching machines is that Options: A) b. f. skinner Began The Movement For Their Use. B) They Were Designed As A Economy Measure To Replace Teachers. C) They Are Not As Efficient As Teachers In Reinforcing Responses D) They Can Be Used For All earning Programmes

Answer :

A) b. f. skinner Began The Movement For Their Use. 

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Images tend to be very large collection of data. The size of memory required for a 1024 by 1024 image in which the colour of each pixel is represented by a n-bit number, (in an 8 bit machines) is (A) n × 8 MB (B) n / 8 MB (C) (1024 × 1024) / 8 MB (D) 1024 MB

Answer :

(B) n / 8 MB

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Calculate quantity of water to be added for casting cubes in laboratory by 12.5 kg cement if w/c ratio 0.45. 

Answer :

As w/c = (weight of water / weight of cement)  w/c = (Ww / Wc)  0.45 = (Ww / 12.5)  Ww = (0.45x12.5)  Ww = 5.625 kg or 5.625 Litres

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Identify type of BJT configuration having following features : (i) BJT configuration having the least current gain. (ii) KIT configuration called as voltage follower. (iii) BJT configuration having current gain less than one. (iv) BJT configuration suitable for impedance matching. (v) BIT configuration suitable for voltage amplification. (vi) BJT configuration having the least output impedance.  

Answer :

(i) BJT configuration having the least current gain : Common Base Configuration  (ii) KIT configuration called as voltage follower: Common Collector Configuration  (iii) BJT ... Emitter Configuration  (vi) BJT configuration having the least output impedance: Common Collector Configuration

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Hay bridge is suitable for measuring following type of inductance (a) having Q greater than 10. (b) having Q less than 10. (c) having any value of Q. (d) having phase angle of reactance very large. 

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Given two jugs of capacities 5 litres and 3 litres with no measuring markers on them. Assume that there is endless supply of water. Then the minimum number of states to measure 4 litres water will be (A) 3 (B) 4 (C) 5 (D) 7

Answer :

(D) 7

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Answer :

When a D.C. series motor is connected to A.C. supply, the power factor will be low because of high inductance of field and armature circuits.

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Which of the following methods of teaching encourages the use of maximum senses? Options: A) Problem-solving method B) Laboratory method C) Self-study method D) Team teaching method

Answer :

B) Laboratory method 

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Description :

Which of the following methods of teaching encourages the use of maximum senses? (A) Problem-solving method (B) Laboratory method (C) Self-study method (D) Team teaching method

Answer :

(B) Laboratory method

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Answer :

For high value of diversity factor, a power station of given installed capacity will be in a position to supply more number of consumers.

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for the voltage built-up a self-excited D.C. generator, which of the following is not an essential condition.  1.there must be some residual flux  2.field winding mmf must aid the residual flux  3.total field circuit resistance must be less than t critical value  4.armature speed must be very high

Answer :

for the voltage built-up a self-excited D.C. generator, which of the following is not an essential condition.  1.there must be some residual flux  2.field winding mmf must aid the ... .total field circuit resistance must be less than t critical value  4.armature speed must be very high

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The National Educational Policy of 1979, recommended also about the public schools Options: A) their uniquencies and traditions have to preserved the interests of the best talents of the country B) they should be brought under laws and regulations of the government public education system C) they must be allowed the autonomy that was bestowed on the by the past system of education D) suitable ratio has to be maintained for admission of middle class and poor student also.

Answer :

D) suitable ratio has to be maintained for admission of middle class and poor student also.

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