ELECTROSTATIC GENERATOR

In electromagnetic generators, current carrying conductors are moved against the electromagnetic forces acting upon them. In contrast to the generator, electrostatic generators convert mechanical energy into electric energy directly. The electric charges are moved against the force of electric fields, thereby higher potential energy is gained at the cost of mechanical energy . The basic principle of operation is explained with the help of Fig. 2.7. An insulated belt is moving with uniform velocity ν  in an electric field of strength  E  (x ). Suppose the width of the belt is b  and the charge density  σ  consider a length dx  of the belt, the charge dq = σ  bdx.

The force experienced by this charge (or the force experienced by the belt). 

Assuming no losses, the power output is also equal to VI.Fig. 2.8 shows belt driven electrostatic generator developed by Van deGraaf in 1931. An insulating belt is run over pulleys. The belt, the width of which may vary from a few cms to metres is driven at a speed of about 15 to 30 m/sec, by means of a motor connected to the lower pulley. The belt near the lower pully is charged electrostatically by an excitation arrangement. The lower charge spray unit consists of a number of needles connected to the controllable d.c source (10 kV–100 kV) so that the discharge between the points and the belt is maintained. The charge is conveyed to the upper end where it is collected from the belt by discharging points connected to the inside of an insulated metal electrode through which the belt passes. The entire equipment is enclosed in an earthed metal tank filled with insulating gases of good dielectric strength viz. SF 6  etc. So that the potential of the electrode could be

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GENERATION OF HIGH VOLTAGES | AC AND DC VOLTAGE GENERATION

HVDC is used for testing HVAC cables of long lengths as these have very large capacitance and would  require very large values of currents if tested on HVAC voltages. Even though D.C. tests on A.C cables is convenient and economical, these suffer from the fact that the stress distribution within the insulating material is different from the normal operating condition.

In industry it is being used for  electrostatic precipitation of ashing in thermal power plants, electrostatic painting, cement industry, communication systems etc. HVDC is also being used extensively in physics for particle acceleration  and in medical equipment's (X-Rays).

The most efficient method of generating high D.C. voltages is through the process of rectification employing voltage multiplier circuits. Electrostatic generators have also been used for generating

high D.C. voltages.

According to IEEE standards 4-1978, the value of a direct test voltage is defined by its arithmetic mean value   and is expressed mathematically as 

where T  is the  time period  of the voltage wave having a frequency f = 1/ T.  Test voltages generated using rectifiers are never constant in magnitude. These deviate from the mean value periodically and this  deviation is known as  ripple . The magnitude of the ripple voltage denoted by  δV  is defined as half the difference between the maximum and minimum values of voltage  i.e.,

and ripple factor is defined as the ratio of ripple magnitude to the mean value  V d

  i.e.,   δV/V d .  The  test voltages should not have ripple factor more than 5% or as specified in a specific standard for a particu-lar equipment as the requirement on voltage shape may differ for different applications.

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WHY AC SYSTEM ARE PREFERRED OVER DC

We (Usually all over the world), In all the countries, We use AC voltage for consuming and for use electricity. Why not DC voltages?
It may ask you in an interview so it's better to know it first.
There are some factors for using AC rather than DC.

• From powerhouse/power plant, we produce AC voltages so it's better to use AC rather than convert it from AC to DC (because there is extra no benefit to using DC). We need to change transformers, breakers and other devices that we are using at the powerhouse.
• It is easy to maintain AC voltages and step up & step down AC voltages as compared to DC.
• The cost of power-plant is much lower than the DC generation plant (transformers, circuit breakers etc).

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WHAT IS THE DIFFERENCE BETWEEN GENERATOR AND ALTERNATOR

Generator and Alternator.

Generator convert mechanical energy into electrical energy, Alternator also converts mechanical energy into electrical energy but there is the difference between both.

Generator and alternator are functionally same but the only difference in construction.  Generator persists stationary magnetic field and rotating conductor which rolls on the armature with slip rings and brushes.

Hence it converts the induced emf into dc current for external load whereas an alternator has a stationary armature and rotating magnetic field for high voltage and for low voltage it has vice versa.

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WHAT ARE THE BASIC COMPONENTS REQUIRED FOR GENERATOR ACTION TO EXITS?

Generator is an electrical machine use to generate Electrical energy, Or it also can be define as "Generator is a machine that change mechanical energy into electrical energy.
A generator has following given basic components.

• Conductor or Coil
• Flux or Magnetic field / Magnetics lines of forces.
• Relative motion between conductor and flux.

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WHY GENERATORS ARE OPERATED IN PARALLEL, NOT IN SERIES.

The generators are not operated usually in series, it operated in parallel beacuse to get these following things,

1. It is in parallel, so maintenance and repair will be easy.
2. It is in parallel, so in plant capacity will be increased.
3. It is not in series so we get, Continuity and reliability of service without interruption.
4. It is in parallel so we get efficient operation of each generator.

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