CONCEPT OF SWITCH GEAR

What is meant by switch gears in electrical engineering?

Answer:Switchgear is the generic name for transmission and distribution equipment designed control, disconnect, and protect an electrical system. Switchgear includes circuit breakers, fuses, and isolators (US term: disconnectors). As well as being used to control circuits by opening or closing those circuits, circuit breakers are designed to interrupt and to close onto electrical faults so must incorporate means of extinguishing the arcing associated with such faults. Circuit breakers, therefore, have a essential role in responding to protection systems. Isolators are non-load breaking switches, designed to isolate equipment (including circuit breakers) from high voltages, so that the equipment can be maintained. 

INVENTION AND INVENTOR

Invention	Inventor	Year	Patent No.
Alternating Current Calculations	Charles Proteus Steinmetz	1897
Alternator	Nikola Tesla	1891	US447,921
Battery (Voltaic Pile)	Alessandro Volta	1800
Cell Phone	Martin Cooper	1973	US3,906,166
Microphone	Emile Berliner	1877	US224,573

BASIC QUESTIONS FOR EEE

                               TODAY QUESTION  FOR CHALLENGERS:

1) Resistivity of a wire depends on
A. material

B. length

C. cross section area

D. all of above

ANS:Resistivity is a basic property of any materials. It is defined as the resistance offered by a cube of unit volume of the materials. Hence resistivity of a wire depends on its material.

2) Resistance of a wire is r ohms. The wire is stretched to double its length, then its resistance will be

A. r/2 

B. 4r

C. 2r 

D. r/4

ANS:Resistance r = ρl/a. When the wire of length l is stretched to 2l, then the cross – sectional area of the wire becomes a/2. Now new value of resistance, r’ = ρ2l/(a/2) = 4ρl/a = 4r.

3) Kirchhoff’s second law is based on law of conservation of

A. charge

B. energy

C. momentum

D. mass

ANS:Kirchhoff’s voltage law (KVL) is also called Kirchhoff’s second law. The principle of conservation of energy implies that the directed sum of the electrical potential differences (voltage) around any closed network is zero. 

4) A circuit contains two un equal resistor in parallel

A. voltage drops across both are same

B. currents in both are same

C. heat losses in both are same

D. voltage drops are according to their resistive value

ANS:Whatever may be the value of resistance the voltage drops, across all the resistors connected in parallel, are always same

QUESTIONS WITH ANSWERS

      1.Can harmonic produce in the dc circuit?
                                                          A harmonic can exist on both AC and DC power.
     2.Which motor is used in electric train and traction?

                            Motor  3phase induction motor and dc series motor is used in electric train because both                 motors provide high starting torque

     3.What is B.H.P in 3 phase induction motor?

                             BHP stands for 'brake horsepower', and simply means it is describing the output, rather than the input, power of the machine. Although a motor's output power is expressed in horsepower in North... 

       

      4.Why is 3 phase motor neutral not used?

                                A three phase motor does not need a neutral because it has two 'phase' leads running it at any given point in time. The electricity comes in on one phase lead and goes out on the other phase...

  

QUESTION FOR CHALLENGERS

                                       QUESTIONS FOR ELECTRICAL ENGINEER
                                                  THI IS FOR CHALLENGERS
                                  
                  1.Can harmonic produce in the dc circuit?

                        2.Which motor is used in electric train and traction?

                         3.What is B.H.P in 3 phase induction motor?

                         4.Why is 3 phase motor neutral not used?

FUNCTION OF CHOKE IN TUBELIGHT

                                               Today  concept
FUNCTION OF  CHOKE IN  TUBELIGHT

     The choke has two main functions. It (in conjunction with the starter if it has one) causes the tube to ignite by using the back emf to create a plasma in the tube and it controls the current through the tube when it is ignited.

In a gas discharge, such as a fluorescent lamp, current causes resistance to decrease. This is because as more electrons and ions flow through a particular area, they bump into more atoms, which frees up electrons, creating more charged particles. In this way, current will climb on its own in a gas discharge, as long as there is adequate voltage (and household AC current has a lot of voltage). If the current in a fluorescent light isn't controlled, it can blow out the various electrical components.

A fluorescent lamp's ballast works to control this. The simplest sort of ballast, generally referred to as a magnetic ballast, works something like an inductor. A basic inductor consists of a coil of wire in a circuit, which may be wound around a piece of metal. If you've read How Electromagnets Work, you know that when you send electrical current through a wire, it generates a magnetic field. Positioning the wire in concentric loops amplifies this field.

This sort of field affects not only objects around the loop, but also the loop itself. Increasing the current in the loop increases the magnetic field, which applies a voltage opposite the flow of current in the wire. In short, a coiled length of wire in a circuit (an inductor) opposes change in the current flowing through it. The transformer elements in a magnetic ballast use this principle to regulate the current in a fluorescent lamp.

A ballast can only slow down changes in current -- it can't stop them. But the alternating current powering a fluorescent light is constantly reversing itself, so the ballast only has to inhibit increasing current in a particular direction for a short amount of time.

Magnetic ballasts modulate electrical current at a relatively low cycle rate, which can cause a noticeable flicker. Magnetic ballasts may also vibrate at a low frequency. This is the source of the audible humming sound people associate with fluorescent lamps.

Modern ballast designs use advanced electronics to more precisely regulate the current flowing through the electrical circuit. Since they use a higher cycle rate, you don't generally notice a flicker or humming noise coming from an electronic ballast. Different lamps require specialized ballasts designed to maintain the specific voltage and current levels needed for varying tube designs.

Fluorescent lamps come in all shapes and sizes, but they all work on the same basic principle: An electric current stimulates mercury atoms, which causes them to release ultraviolet photons. These photons in turn stimulate a phosphor, which emits visible light photons. At the most basic level, that's all there is to it!

                                                      ALL  IS  VEL

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