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Regenerative method of braking is based on that back e.m.f. is equal to the applied voltage.

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The braking retardation is usually in the range 10 to 15 km phps.

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The main disadvantage of the Ward-Leonard control method is high initial cost, high maintenance cost, low efficiency at light loads.

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For constant torque drive armature voltage control speed control method is preferred.

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Types of Triggering: 1) Forward voltage triggering 2) Thermal triggering (Temperature triggering) 3) Radiation triggering (Light triggering) 4) dv/dt triggering 5) Gate triggering ... generated leakage current increases. This current gets multiplied internally and thyristor is turned on. 

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A parallel RLC circuit has the node equation Determine v(t) using the phasor method.

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Merits of two wattmeter method

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State any two disadvantages of one wattmeter method of measurement of 3 phase power.

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The power consumed by a balanced 3-ph load is measured by two-wattmeter method. The meter readings are 8 kW and 4 kW. The power factor of the load is between 0.5 and unity

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Compared to Gauss-Seidel method, Newton-Raphson method takes : A. less number of iterations and more time per iteration B. less number of iterations and less time per iteration C, more number of iterations and more time per iteration D. more number of iterations and less time per iteration

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Compared to Gauss-Seidel method, Newton-Raphson method takes : A. less number of iterations and more time per iteration B. less number of iterations and less time per iteration ... of iterations and more time per iteration D. more number of iterations and less time per iteration

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Explain regenerative braking for D.C. series motor.

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Schematic diagram of regenerative braking of D.C. series :-  Explanation of regenerative braking: During normal running, motors are connected in parallel with field winding in series ... For final stop mechanical braking is applied. External Resistances are connected to limit the current.

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In a regenerative braking, which of the following is generally true?  (a) Back e.m.f. in the motor exceeds the applied voltage (b) Back e.m.f. is less than the applied voltage (c) Kinetic energy of the motor is dissipated in a resistance (d) Kinetic energy of the motor is dissipated through free wheeling diode across the motor 

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In a regenerative braking, which of the following is generally true?  (a) Back e.m.f. in the motor exceeds the applied voltage (b) Back e.m.f. is less than the applied voltage ... in a resistance (d) Kinetic energy of the motor is dissipated through free wheeling diode across the motor 

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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

Answer :

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  48 kW

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Regenerative braking can: (A) be used for stopping a motor (B) not be easily applied to DC series motors (C) be easily applied to DC shunt motors (D) not be used for heavy duty -cycle motors

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Regenerative braking can: not be easily applied to DC series motors

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The nodal method of circuit analysis is based on  (A) KVL and ohms law (B) KVL and KCL (C) KCL and ohms law (D) Thevenins theorem

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 The nodal method of circuit analysis is based on KCL and Ohm’s law

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School based assessment is primarily based on the principle that Options: A) teachers know their learners’ capabilities better than external examiners B) students should at all costs get high grades C) schools are more efficient than external bodies of examination D) assessment should be very economical

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A) teachers know their learners’ capabilities better than external examiners 

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Given below are some characteristics of reasoning. Select the code that states a characteristic which is not of deductive reasoning: (A) The conclusion must be based on observation and experiment (B) The conclusion should be supported by the premise/premises (C) The conclusion must follow from the premise/premises necessarily (D) The argument may be valid or invalid

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(A) The conclusion must be based on observation and experiment

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A calendar stick carved centuries ago by the Winnebago tribe may provide the first evidence that the North American Indians have developed advanced full-year calendars basing them on systematic astronomical observation. (A) that the North American Indians have developed advanced full-year calendars basing them ... American Indians and their development of advanced full-year calendars based (E) that the North American Indians developed advanced full-year calendars based

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In a P-N diode, assume that P-side is lightly doped and N-side is heavily doped. Based on this information, which of the following statement is true ? (A) Depletion region is more extended in P-side than N-side (B) Depletion region is more extended in N-side than P-side (C) Depletion region would be equal on both sides (D) Not enough information provided to give answer

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In a P-N diode, assume that P-side is lightly doped and N-side is heavily doped. Based on this information, which of the following statement is true ? (A) Depletion region is more extended ... (C) Depletion region would be equal on both sides (D) Not enough information provided to give answer

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 Which braking system on the locomotives is the costliest among the following? A) Vacuum braking on diesel locomotives B) Vacuum braking on steam locomotives C) Regenerative braking on electric locomotives D) All braking systems are equally costly

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Which braking system on the locomotives is the costliest among the following? A) Vacuum braking on diesel locomotives B) Vacuum braking on steam locomotives C) Regenerative braking on electric locomotives D) All braking systems are equally costly

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Research is based upon Options: A) Scientific method B) Experiments C) Scientists D) Genera principles

Answer :

A) Scientific method

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Which combination of methods of teaching is likely to optimise learning ? (A) Lecturing, discussions and seminar method (B) Interactive discussions, planned lectures and PowerPoint based presentations (C) Interactive lecture sessions followed by buzz sessions, brainstorming and projects (D) Lecturing, demonstrations and PowerPoint based presentations

Answer :

Answer: C 

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The chief advantage of Ward-Leonard system D.C. motor speed control is that is  1. Can be used even for small motors 2. has high overall efficiency at all speeds 3. Gives smooth, sensitive and wide speed control 4. Uses a flywheel to reduce fluctuations in power demand

Answer :

The chief advantage of Ward-Leonard system D.C. motor speed control is that is Gives smooth, sensitive and wide speed control 

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Why shouldn’t a DC shunt motor start on the heavy load setting?

Answer :

A series motor never started at no load and a shunt motor is never started at on load.

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Retardation test on d.c. shunt motors is performed for (a) frictional losses (b) stray losses (c) copper losses (d) iron loss  

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