81. The resistive component of the rotor with resistance R2 offere to the backward rotating flux wave in a single-phase motor runs with slip s is given as ?
The flux rotating in the clockwise direction (i.e. the direction of spinning) is called the forward rotating flux (φf) and that in the other direction is called the backward rotating flux (φb). The forward rotating flux has synchronous speed Ns (= 120 f/P) and the synchronous speed of rotating backward flux (anticlockwise) is –Ns.
Slip in forward Direction-
Sf = (Ns – N)/Ns = s
Slip in backward Direction-
Sb = (–Ns – N)/–Ns = s
Sb = (2Ns + Ns + N)/Ns
Sb = (2 – s)
At standstill, N = 0 so that Sf = Sb = 1. For forward rotating flux, the slip is s (less than 1) and for backward rotating flux, the slip is 2 – s (greater than 1). We know that in a 3-phase induction motor, the torque developed is directly proportional to effective rotor resistance.
The effective rotor resistance for single-phase motor is R2/s in the forward direction and R2/2 – s in the backward direction.
82. Find the frequency of rotor induced EMF of a 3-phase, 440V, 50Hz induction motor having slip of 10% ?
Rotor frequency = slip × supply frequency.
Rotor frequency = 0.1 x 50 = 5 Hz
83. _ _ _ is a tube that brings water to turbines ?
The penstock takes water from the dam to the turbine.
A penstock is a sluice or gate or intake structure that controls water flow, or an enclosed pipe that delivers water to hydro turbines and sewerage systems.
84. The function of condenser in Thermal power plant is ?
In thermal power plants, the purpose of a surface condenser is to condense the exhaust steam from a steam turbine to obtain maximum efficiency, and also to convert the turbine exhaust steam into pure water (referred to as steam condensate) so that it may be reused in the steam generator or boiler as boiler feed water.
85. _ _ _ is NOT a component in a thermal power plant ?
A nuclear reactor produces and controls the release of energy from splitting the atoms of certain elements.
In a nuclear power reactor, the energy released is used as heat to make steam to generate electricity.
(In a research reactor the main purpose is to utilise the actual neutrons produced in the core.
86. Hysteresis loss is NOT a function of ?
Hysteresis loss is caused by the magnetization and demagnetization of the core as current flows in the forward and reverse directions. As the magnetizing force (current) increases, the magnetic flux increases.
hysteresis loss depends on Magnetic materials, its total volume, Maximum flux density and supply frequency.
Steinmetz's equation, sometimes called the power equation, is an empirical equation used to calculate the total power loss (core losses) per unit volume in magnetic materials when ... material parameters generally found empirically from the material's B-H hysteresis curve by curve fitting. ... with frequency as a parameter.
87. At f= _ _, R-L-C series circuit operates at unity power factor ?
At resonance frequency i.e.
f =1/ 2π √(LC)
circuit operates at unity power factor.
88. Lamp efficiency is measured in ?
lumens per watt
Luminous efficacy is a measure of how well a light source produces visible light. It is the ratio of luminous flux to power, measured in lumens per watt (lm/w) in the International System of Units (SI). According to how the power is measured, there are two different definitions for it.
A lumen is a measure of how much visible light is emitted by a source.
Lumens per watt (lm/W) refers to the energy efficiency of lighting.
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89. The law that explain about the economic size of a conductor is ?
"The Kelvin's law states that the most economical size of a conductor is that for which annual interest and depreciation on the capital cost of the conductor is equal to the annual cost of energy loss.".
90. A three phase induction machine, when it is operating like a motor, the range of slip 's' is given by ?
The value of slip in induction motor is can never be zero. As we know that, the speed of rotor cannot be equal to synchronous speed i.e. Ns > Nr, the value of slip s is always less than one.
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