51. The total number of possible phase sequences for a three phase AC system is ?
two
Phase rotation, or phase sequence, is the order in which the voltage waveforms of a polyphase AC source reach their respective peaks.
For a three-phase system, there are only two possible phase sequences: 1-2-3 and 3-2-1, corresponding to the two possible directions of alternator rotation.
52. Four types of power plants have been given, out of which three are alike in some manner and one is different. Select the odd one ?
Conventional Energy:- Those sources of energy, which have accumulated in nature over a period of millions of years and cannot be quickly replaced when exhausted are called non-renewable sources of energy.
This non-renewable source of energy is also called a conventional source of energy.
Conventional sources of energy include natural gas, coal, petroleum, electricity (Nuclear, Thermal & Hydro Power plants).
Non-Conventional Energy:- Non-conventional sources of energy are renewable resources of energy like biomass, solar energy, wind energy, tidal energy, etc.
53. For indoor lighting the range of space: height is ?
Spacing Height Ratio is defined as the ratio of the distance between adjacent luminaires (centre to centre), to their height above the working plane.
To have uniform illumination, the ratio of the spacing between the lamps and their height above the working plane (i.e., space-height ratio) should normally lie between 1 and 2.
54. A series magnetic circuit will have ?
The Series Magnetic Circuit is defined as the magnetic circuit having a number of parts of different dimensions and materials carrying the same magnetic field.
Consider a circular coil or solenoid having different dimensions.
55. In an electric traction the specific energy consumption is measured in ?
ENERGY CONSUMPTION
The energy input to the motor is called the energy consumption of the train as it is this energy which is utilized for movement of the train.<
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SPECIFIC ENERGY CONSUMPTION
It is defined as the energy consumed per Ton-metre.
It is the ratio of Specific energy output of driving wheels to the overall efficiency of transmission gear and motor.
It is measured in Watt-hour/ton-km.
FACTORS AFFECTING SPECIFIC ENERGY CONSUMPTION
1. DISTANCE COVERED
The greater distance covered between stops, the lesser will be the specific energy consumption.
Suburban service it is higher compared to the main line service.
Typical values for the two services are 60 and 25 per ton-km.
2. ACCELERATION AND RETARDATION
For a given run and a give schedule speed, the specific energy consumption is lower and for higher the acceleration and retardation since with a longer coasting period can be obtained and for a smaller period the supply is switched on.
3. TRAIN RESISTANCE
The specific energy consumption depends upon the train resistance which depends upon the nature of track, speed of the train and shape of the rolling stock.
The train resistance also depends upon the front and rear portion of the train.
4. GRADIENT
While going up steep gradients, more energy is needed through the specific energy consumption may be modified by regenerative braking.
5. MAXIMUM SPEED
The specific energy consumption increases with increase in maximum speed.
6. TRAIN EQUIPMENT
By using more efficient train equipment the specific energy consumption may be reduced.
SKIN FRICTION
The resistance of the air comes into play on front end of the locomotive known as head resistance and on the sides of the top and under sides of the coaches.
Head resistance may be streamlined the shape of the engine.
56. Which of the following is an important feature of a 3-phase synchronous motor ?
Synchronous motors contain electromagnets on the stator of the motor that create a magnetic field which rotates in time with the oscillations of the line current.
Hence, both MMFs cancel with each other and there is no starting torque because of the relative velocity between the stator and rotor MMFs are zero.
57. Observe the given figure. If the diode is an ideal diode, then what are the values of ID and VD respectively ?
Io = V/R = 20/100
Io = 0.2 A
Since the given diode is an ideal diode therefore there is no voltage drop across it.
Vo = Io × RD
Vo = 0.2 × 0
Vo = 0
Hence
Io = 0.2 A & Vo = 0
58. Identify the correct statement regarding a nuclear power plant ?
Moderator
Material in the core which slows down the neutrons released from fission so that they cause more fission.
It is usually water, but may be heavy water or graphite.
A substance that is used in a nuclear reactor to slow down the neutrons is a moderator. Examples of moderators used are water, beryllium, graphite, heavy water
59. The flux while crossing air gap tends to bulge outwards, thereby increasing the effective area of the gap, this effect is known as ?
Flux fringing - a phenomenon in which the magnetic flux flowing in a magnetic core spreads out (or fringes out) into the surrounding medium, for example in the vicinity of an air gap. Flux crowding is closely related to flux fringing, but flux leakage is usually treated as a different phenomenon
The fringing effect results from the presence of the air gap in the magnetic circuit.
The main consequence of the fringing effect is to make the magnetic flux density of the air gap different from the flux density of the core due to the path of the flux.
60. The residential distribution system employs ?
Electric power distribution is the final stage in the delivery of electric power; it carries electricity from the transmission system to individual consumers.
The primary distribution circuit delivers power to various substations, called distribution substations. The substations are situated near the consumers' localities and contain step-down transformers. At each distribution substation, the voltage is stepped down to 400 V and power is delivered by 3-phase, 4-wire system.
Secondary distribution systems. A low-voltage network or secondary network is a part of electric power distribution which carries electric energy from distribution transformers to electricity meters of end customers
The secondary distribution employs 400/230 V, 3-phase, 4-wire system.
An electric power distribution system can be classified according to its feeder connection schemes or topologies as follows -
1-Radial distribution system
2-Parallel feeders distribution
3-Ring main distribution system
4-Interconnected distribution
1 2 3 4 5 6 7 8 9 10
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