SURGE MODIFIER

a small shunt capacitor between the line and the earth or a series air cored induct is incorporated which by storing temporary energy in them , reduces the steepness of the surge wave front, which otherwise can be detrimental to the apparatus  and this is known as surge modifier  

CRITICAL SPEED

critical speed is the speed at which the dc shunt generator just fails to build up with no external resistance in field circuit

Excitation

An electric generator or motor consists of a rotor spinning in a magnetic field. The magnetic field may be produced by permanent magnet or by field coil. In the case of a machine with field coils, a current must flow in the coils to generate the field, otherwise no power is transferred to or from the rotor. The process of generating a magnetic field by means of an electric current is called excitation.

Electrical Engineering Interview Questions and Answers

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Harmonic

In acoustics and telecommunication, a harmonic of a wave is a component frequency of the signal that is an integer multiple of thefundamental frequency. For example, if the fundamental frequency is f, the harmonics have frequencies f, 2f, 3f, 4f, etc. The harmonics have the property that they are all periodic at the fundamental frequency, therefore the sum of harmonics is also periodic at that frequency. Harmonic frequencies are equally spaced by the width of the fundamental frequency and can be found by repeatedly adding that frequency. For example, if the fundamental frequency is 25 Hz, the frequencies of the harmonics are: 25 Hz, 50 Hz, 75 Hz, 100 Hz, etc

NTPC PAPERS

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Tachometer

A tachometer (also called a revolution-counter, rev-counter, or RPM gauge) is an instrument that measures the rotation speed of a shaft or disk, as in a motor or other machine. The device usually displays the revolution per minute (RPM) on a calibrated analogue dial, but digital displays are increasingly common. The term comes from greek Ταχος, tachos, "speed", andmetron, "to measure"

History

The first mechanical tachometers were based on measuring the centrifugal force, similar to the operation of a centrifugal governer. The inventor is assumed to be the German engineer Dietrich Uhlhorn; he used it for measuring the speed of machines in 1817. Since 1840, it has been used to measure the speed of locomotive