EE 71--80

71: What is the principle of motor?

Whenever a current carrying conductor is placed in an magnetic field it produce turning or twisting movement is called as torque.

72: Why Negative Feedback is preffered in the Control System?

The role of Feedback in control system is to take the sampled output back to the input and compare output signal with input signal for error (deviation from the desired result). Negative Feedback results in the better stability of the system and rejects any disturbance signals and is less sensitive to the parameter variations. Hence in control systems negative feedback is considered.

73: What is a feedback in Control System?

The Feedback in Control System in one in which the output is sampled and proportional signal is fed back to the input for automatic correction of the error (any change in desired output) for futher processing to get back the desired output.

74: Why skin effect exists only in Ac and not in DC?

Because DC frequency is zero hertz and therefore its inductive reactance will be zero (XL= 2* pi * f *L). No inductive reactance means no opposition to current and current flows through both outer and inner part easily i.e. there is no skin effect in DC. 

75: What is Chain reaction and how it is controlled in Nuclear reactor? 

In fission reaction during every stage two or more daughter nuclei is released, two or more neutrons and vast energy is released. Each neuron produced further participate in fission reaction and results in release of more neutrons, this reaction continues results in nuclear explosion. However in nuclear reactor the excess neutrons produced will be absorbed using moderator and control rods allowing only one neutron per fission to carryout further chain reaction.

76: What is the relation between applied voltage and emf induced with respect to flux wave?

Under no load condition and considering no losses
Induced emf in both primary and secondary lags behind the main flux by 900.
Applied voltage to primary winding leads the main flux by 900 and is in phase opposition with the induced emf in the primary winding (V1=-e1)
Secondary voltage V2-e2 as there is no voltage drop in the secondary

77: What are the different substation components?

Circuit Breakers, Disconnecting switches, Grounding switches, Current Transformers, Potential Transformers or Capacitor voltage Transformers, Line Traps, Lightning Arrestors, Power Transformers, Shunt Reactors, Current limiting reactors, Station Buses and Insulators, Grounding system, Series capacitors and shunt capacitors.

78: What is the purpose of Pulverizes?

Pulverizers serve two purposes, to dry the coal and to grind the coal. They crush the coal to size of 74microns. 

79: For distribution network which type of Switching scheme is employed?

For distribution network Ring Main busbar scheme is employed. It has the provision that if power interruption occurs to one bus section due to maintenance or fault, power can be fed the bus from other side of the power system.

80: What are the particles used in nuclear fission?

High energy alpha particles, protons, deuterons, X-rays as well as neutrons can be used for the fission process. However neutrons are chosen because neutrons are electrically neutral in nature and thus they do not require high kinetic energy to overcome electrical repulsion from the positively charged nuclei and can participate in fission reaction.