Current Cut-off Characteristics - Recovering voltage Characteristics of HRC fuse

How A Prime Movers Works In An Electic Power Plant....?

How A Prime Movers Works In An Electic Power Plant....?
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Electrical Power Plant today is more important than any other, that is because without those power plant operate we cannot do anything. From manufacturing plant, because we are all depend on Electricity. So therefore it a high time to know from the very beginning what is a prime movers, how it works or what is
all about.  To get the plant started, prime movers are typically Diesel Engines, Gas or Steam Turbines, or  Hydro and Wind Turbines. This Prime movers converts oil, gas, coal, wood, uranium, water, wind, etc. into mechanical energy. The mechanical energy is supplied to the shaft  of the generator and the generator in turn transform this mechanical energy to electrical energy. High quality electric power generating systems deliver precise voltage and frequency. The voltage regulator as noted earlier, provides the precise voltage regulation. The prime mover GOVERNOR, by accurately  controlling the speed, provides the precise frequency regulation.
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What is a Governor?
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Govers Define as a device which controls the speed or power of a prime mover in order to convert the power to useful work.When the governor senses the speed of a prime mover and controls the prime mover to maintain its speed (or load) at a desired output.Like for example if  you drive a car. You function as a governor when you control the car’s speed under a varying driving conditions. The driver adjust the accelerator that controls the fuel to maintain the desired speed at a certain level and adjust from time to time should the desired speed varies. Acutually the original  governors were entirely mechanical like a pair of centrifugal flyweights in most ballheads. It is known for its ruggedness, usefulness and sensitivity.
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The  flyweights are rotated by a drive from the prime mover that is directly related to the speed. As the speed changes, the flyweights move out at the top due to  centrifugal force. The centrifugal action causes the weights to increase the force on the thruster that control the pilot valve thereby changing the speed of  the prime mover due to applying or removing load.
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What a Governor Does?
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As the prime mover gets started or a speed of about 25%, a governor mechanism “comes to life”. The governor senses the prime mover rotation and begins to  regulate the linkages controlling the fuel/steam supply of the prime mover.
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But if the prime mover tends to increase speed above the set speed of the  governor, the governor mechanism decreases the controlling lever opening of the fuel/steam supply of the prime mover.Eventually, the prime mover speed will  be controlled so that only enough fuel/steam is being admitted, (power in) to hold the prime mover approximately the speed setting of the governor.

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What Happens as Load is Added to the System?
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As the customer load demand increases, the generator must supply the load instantaneously. The generator slows down as more power is being taken out from the  generator than what is being produced. But as soon as the shaft slows down, the governor mechanism senses and causes to increase the fuel/steam rack opening  it and increasing fuel/steam supply of the prime mover.The power produced by the prime mover will increase to match the generator demand. As the speed will  be a little less than before, since if the speed recover completely, the governor mechanism senses and causes to increase the fuel rack opening increasing
power for the prime mover.
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Therefore, the frequency of the AC produced by the generator will get lower as the generator slows down and load increases. What is a Governor Speed Setting Does? The speeder spring is the part that sets the “desired speed”. Applying more force down on the speeder spring causes the governor to increase fuel/steam supply to the prime mover. This initial force is usually set by the operator for the  desired or “reference’ speed.
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It can be set by an adjusting screw, a knob, a lever, a DC electric motor, an air pressure

Electrical machines interview questions and answers

[1] Define the term synchronous speed [Dec-2003]
For synchronous machines there exists a fixed relationship between number of poles P, frequency (f) and the speed of the machine. The speed of the synchronous machine for the given number of poles and the rated frequency is called the synchronous speed mentioned as NS.

[2] Write an expression for synchronous speed (Dec-2004)
An expression for synchronous speed is NS = 120f/P.
Where
f = frequency
P = No of poles of the machine.

[3] What does speed voltage mean? (Dec-2007)
When the magnetic flux is constant as well as stationary and the coil rotates to cut the flux then EMF gets induced due to relative speed between flux and coil. This EMF is called speed EMF, rotational EMF or dynamically induced EMF.

[4] Mention the factors on which hysteresis loss depends (Dec-2008)
The hysteresis loss is directly proportional to the area under the hysteresis curve ie area of the hysteresis loop.
It is directly proportional to frequency ie number of cycles of magnetization per second.
It is directly proportional to volume of the material.

[5] Distinguish between statically induced and dynamically induced EMF (Dec - 2010, 2011, 2009)
How is EMF induced dynamically ( May-2010)
An induced EMF which is due to physical movement of coil, conductor with respect to flux or movement of magnet with respect to stationary coil, conductor is called dynamically induced EMF or motional induced EMF.
The change in flux lines with respect to coil can be achieved without physically moving the coil or the magnet. Such induced emf in a coil which is without physical movement of coil or a magnet is called statically induced EMF.

[6] Define torque (May-2010)
A turning or a twisting force about an axis is called as torque.

[8] What are the three types of basic rotating electric machines? (May-2011)
DC machines
Induction Machines
Synchronous Machines

[9] What are the causes of core loss? what are the components of core loss?
When a core is subjected to an alternating flux then it undergoes the cycles of magnetisation and demagnetisation. This produces hysteresis effect which causes hysteresis loss in the core.
Similarly core is under the influence of the changing flux and under such condition according to the Faraday's law of electromagnetic induction, EMF gets induced in the core. Such currents in the core which are due to induced emf in the core are called as eddy current loss. Thus eddy current and hysteresis are the two components of the core loss.

Electrolysis and Storage of Batteries - MCQ and answers

Electrolysis and Storage of Batteries - MCQ and answers

1. "The mass of an ion liberated at an electrode is directly proportional to the quantity of electricity".
The above statement is associated with
(a) Newton's law
(b) Faraday's law of electromagnetic
(c) Faraday's law of electrolysis
(d) Gauss's law
Ans: c

2. The charge required to liberate one gram equivalent of any substance is known as ______ constant
(a) time
(b) Faraday's
(c) Boltzman
Ans: b

3. During the charging of a lead-acid cell
(a) its voltage increases
(b) it gives out energy
(c) its cathode becomes dark chocolate brown in colour
(d) specific gravity of H2SO4 decreases
Ans: a

4. The capacity of a lead-acid cell does not depend on its
(a) temperature    
(b) rate of charge
(c) rate of discharge
(d) quantity of active material
Ans: b

5. During charging the specific gravity of the electrolyte of a lead-acid battery
(a) increases
(b) decreases
(c) remains the same
(d) becomes zero
Ans: a

6. The active materials on the positive and negative plates of a fully charged lead-acid battery are
(a)     lead and lead peroxide
(b)     lead sulphate and lead
(c) lead peroxide and lead
(d) none of the above
Ans: c

7. When a lead-acid battery is in fully charged condition, the colour of its positive plate is
(a) dark grey
(b) brown
(c) dark brown      
(d) none of above
Ans: c

8. The active materials of a nickel-iron battery are
(a)     nickel hydroxide
(6)     powdered iron and its oxide
(c) 21% solution of KOH
(d) all of the above
Ans: d

9. The ratio of ampere-hour efficiency to watt-hour efficiency of a lead-acid cell is
(a) just one
(b) always greater than one
(c) always less than one
(d) none of the above.
Ans: b

10. The best indication about the state of charge on a lead-acid battery is given by
(a) output voltage
(b) temperature of electrolyte
(c) specific gravity of electrolyte
(d) none of the above
Ans: c

11. The storage battery generally used in electric power station is
(a) nickel-cadmium battery
(b) zinc-carbon battery
(c) lead-acid battery
(d) none of the above
Ans: c

12. The output voltage of a charger is
(a) less than the battery voltage
(b) higher than the battery voltage
(c) the same as the battery voltage
(d) none of the above
Ans: b

13. Cells are connected in series in order to
(a)     increase the voltage rating
(6)     increase the current rating
(c) increase the life of the cells
(d) none of the above
Ans: a

14. Five 2 V cells are connected in parallel.
The output voltage is
(a) 1 V
(6) 1.5 V
(c) 1.75 V
(d) 2 V
Ans: d

15. The capacity of a battery is expressed in terms of
(a)     current rating
(b)     voltage rating
(e) ampere-hour rating
(d) none of the above
Ans: c

16. Duringthe charging and discharging of a nickel-iron cell
(a) corrosive fumes are produced
(b) water is neither formed nor absorbed
(c) nickel hydroxide remains unsplit
(d)     its e.m.f. remains constant
Ans: b

17. As compared to constant-current system, the constant-voltage system of charging a lead acid cell has the advantage of
(a) reducing time of charging
(b) increasing cell capacity
(c) both (a) and (b)
(d) avoiding excessive gassing
Ans: c

18. A dead storage battery can be revived by
(a) adding distilled water
(6) adding so-called battery restorer
(c) a dose of H2SO4
(d) none of the above
Ans: d
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19. As compared to a lead-acid cell, the efficiency of a nickel-iron cell is less due to its
(a) compactness
(b) lower e.m.f.
(c) small quantity of electrolyte used
(d) higher internal resistance
Ans: d

20. Trickle charging of a storage battery helps to
(a)     maintain proper electrolyte level
(b)     increase its reserve capacity
(c) prevent sulphation
(d) keep it fresh and fully charged
Ans: d

21. Those substances of the cell which take active part in chemical combination and hence produce electricity during
charging or discharging are known as______materials.
(a) passive
(b) active
(c) redundant
(d) inert
Ans: b

22. In a lead-acid cell dilute sulphuric acid (electrolyte) approximately comprises the following
(a) one part H2O, three parts H2SO4
(b) two parts H2O, two parts H2SO4
(c) three parts H2O, one part H2SO4
(d) all H2S04
Ans: c

23. It is noticed that durmg charging
(a)     there is a rise in voltage
(6)     energy is absorbed by the cell
(c) specific gravity of H2SO4 is increased
(d) the anode becomes chocolate brown in colour (PbCfe) and cathode be¬comes grey metallic lead (Pb)
(e) all of the above
Ans: e

24. It is noticed that during discharging the following does not happen
(a)     both anode and cathode become PbS04
(b)     specific gravity of H2SO4 decreases
(c) voltage of the cell decreases
(d) the cell absorbs energy
Ans: d

25. The ampere-hour efficiency of a leadacid cell is normally between
(a) 20 to 30%
(b) 40 to 50%
(c) 60 to 70%
(d) 90 to 95%
Ans: d

26. The watt-hour efficiency of a lead-acid cell varies between
(a) 25 to 35%
(b) 40 to 60%
(c) 70 to 80%
(d) 90 to 95%
Ans: c

27. The capacity of a lead-acid cell is measured in
(a) amperes
(b) ampere-hours
(c) watts
(d) watt-hours
Ans: b

28. The capacity of a lead-acid cell depends on
(a) rate of discharge
(b) temperature
(c) density of electrolyte
(d) quantity of active materials
(e) all above
Ans: e

29. When the lead-acid cell is fully charged, the electrolyte assumes _____ appearance
(a) dull
(b) reddish
(c) bright
(d) milky
Ans: d

30. The e.m.f. of an Edison cell, when fully charged, is nearly
(a) 1.4 V
(b) 1 V
(c) 0.9 V
(d) 0.8 V
Ans: a

31. The internal resistance of an alkali cell is nearly _____ times that of the lead-acid cell.
(a) two
(b) three
(c) four
(d) five
Ans: d

32. The average charging voltage for alkali cell is about
(a) 1 V
(b) 1.2 V
(c) 1.7 V
(d) 2.1 V
Ans: c

33. On the average the ampere-hour efficiency of an Edison cell is about
(a) 40%
(b) 60%
(c) 70%
(d) 80%
Ans: d

34. The active material of the positive plates of silver-zinc batteries is
(a) silver oxide      
(b) lead oxide
(c) lead
(d) zinc powder
Ans: a

35. Lead-acid cell has a life of nearly charges and discharges
(a) 500
(b) 700
(c) 1000
(d) 1250
Ans: d

36. Life of the Edison cell is at least
(a) five years
(b) seven years
(c) eight years
(d) ten years
Ans: a

37. The internal resistance of a lead-acid cell is _____ that of Edison cell
(a)    less than
(b)    more than
(c) equal to
(d) none of the above
Ans: a

38. Electrolyte used in an Edison cell is
(a) NaOH
(b) KOH
(c) HC1
(d) HN03
Ans: b

39. Electrolyte used in a lead-acid cell is
(a) NaOH
(b) onlyH2S04
(c) only water        
(d) dilute H2SO4
Ans: d

40. Negative plate of an Edison cell is made of
(a) copper
(b) lead
(c) iron
(d) silver oxide
Ans: c

41. The open circuit voltage of any storage cell depends wholly upon
(a) its chemical constituents
(b) on the strength of its electrolyte
(c) its temperature      
(d) all above
Ans: d
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Admin :- Bellapuri saikumar
                  ( Sai Saikumar Jn)

Electrical shock (Sai saikumar jn)

                                                                    Electrical shock

Q:If one lamp connects between two phases it will glow or not? ( sai saikumar jn )

Q:If one lamp connects between two phases it will glow or not? 

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 A:If the voltage between the two phase is equal to the lamp voltage then the lamp will glow. When the voltage difference is big it will damage the lamp and when the difference is smaller the lamp will glow depending on the type of lamp. 

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Q:What is the power factor of an alternator at no load? ( sai saikumar jn )

Q:What is the power factor of an alternator at no load? 

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 A:At no load Synchronous Impedance of the alternator is responsible for creating angle difference. So it should be zero lagging like inductor. 

Q:- what is meant by knee point voltage...? ( sai saikumar jn )

Q: What is meant by knee point voltage? 

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 Ans: Knee point voltage is calculated for electrical Current transformers and is very important factor to choose a CT. It is the voltage at which a CT gets saturated.(CT-current transformer).

Q: Explain the operation of variable frequency transformer? ( sai saikumar jn )

Q: Explain the operation of variable frequency transformer? 

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 Ans :A variable frequency transformer is used to transmit electricity between two asynchronous alternating current domains. A variable frequency transformer is a doubly-fed electric machine resembling a vertical shaft hydroelectric generator with a three-phase wound rotor, connected by slip rings to one external ac power circuit. 

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A direct-current torque motor is mounted on the same shaft. Changing the direction of torque applied to the shaft changes the direction of power flow; with no applied torque, the shaft rotates due to the difference in frequency between the networks connected to the rotor and stator. The variable frequency transformer behaves as a continuously adjustable phase-shifting transformer. It allows control of the power flow between two networks . 

Q: What is the function of interposing current transformer? ( sai saikumar jn )

Q:What is the function of interposing current transformer?

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 Ans:The main function of an interposing current transformer is to balance the currents supplied to the relay where there would otherwise be an imbalance due to the ratios of the main current transformers.

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 Interposing current transformer are equipped with a wide range of taps that can be selected by the user to achieve the balance required. 

Q: What is rated speed? ( sai saikumar jn )

Q:What is rated speed? 

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 Ans: At the time of motor taking normal current (rated current)the speed of the motor is called rated speed. It is a speed at which any system take small current and give maximum efficiency. 

Q:Why we use ac system in India why not dc ? ( sai saikumar jn )

Q:Why we use ac system in India why not dc ? 

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:Ans:- Firstly, the output of power stations comes from a rotary turbine, which by it's nature is AC and therefore requires no power electronics to convert to DC. Secondly it is much easier to change the voltage of AC electricity for transmission and distribution. thirdly the cost of plant associated with AC transmission (circuit breakers, transformers etc) is much lower than the equivilant of DC transmission AC transmission provides a number of technical advantages. 

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When a fault on the network occurs, a large fault current occurs. In an AC system this becomes much easier to interupt, as the sine wave current will naturally tend to zero at some point making the current easier to interrupt. 

Q:What's electric traction? ( sai saikumar jn )

Q:What's electric traction?

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 A:Traction implies with the electric power for traction system i. e. for railways, trams, trolleys etc. electric traction implies use of the electricity for all these. 

 

 Now a day, magnetic traction is also utilised for bullet trains. Essentially dc motors are utilized for electric traction systems. 

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 From ur's :- Bellapuri saikumar ( sai saikumar jn )

Q: What is 2 phase motor? ( sai saikumar jn )

Q: What is 2 phase motor? 

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 A: A two phase motor is often a motor with the the starting winding and the running winding have a phase split. e. g; ac servo motor. where the auxiliary winding and the control winding have a phase split of 90 degree. 

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 From ur's :- Bellapuri saikumar ( sai saikumar jn )

How to test insulators....? ( sai saikumar jn )

Q:-How to test insulators?

Must read & share to all electrical & electronics engineer's...

Ans:-Always remember to practice safety procedures for the flash-over voltage distance and use a sturdy enclosure to contain an insulator that may shatter, due to steam build-up from moisture in a cavity, arcing produces intense heat, an AM radio is a good RFI/arcing detection device, a bucket truck AC dielectric test set (130KV) is a good test set for most pin and cap type insulators.


A recent article said the DC voltage required to “search out defects can be 1.9 times the AC voltage.

*.Insulators have a normal operating voltage and a flash-over voltage. Insulators can have internal flash-over that are/are not present at normal operating voltage. If the RFI is present, de-energize the insulator (line) and if the RFI goes away, suspect the insulator (line).

Then there can be insulators that have arcing start when capacitor or other transients happen, stop when the line is de-energized or dropped below 50% of arc ignition voltage.

Using a meg-ohm-meter can eliminate defective insulators that will immediately arc-over tripping the test set current overload.

From ur's # sai saikumar jn
                                ( Bellapuri saikumar )

What is a battery...? ( sai saikumar jn )

Hello ... Engineer's

Q:- What is a Battery....?

MUST READ & SHARE

Ans:- A true battery consists of two or more cells connected together in series or parallel. But the term is more commonly used for a single cell.
A cell consists of a negative electrode, an electrolyte, a separator, and a positive electrode. Both the electrolyte and separator conduct ions.

The electrolyte can be composed of water or something that is not water and can be in liquid, paste, or solid form. When you connect the cell to an external load or a device you want to power, the negative electrode supplies a current of electrons that flow through the load and are accepted by the positive electrode. When you remove the load the reaction stops.

 -- Bellapuri saikumar
 sai saikumar jn

Advantages and Disadvantages of nuclear power plant. ( sai saikumar jn )

Hello .... Engineer's


Q:- What are the advantages and disadvantages of nuclear power plant?

MUST READ & SHARE WITH YOUR FRIEND'S

Ans:- Advantages:
(i) The amount of fuel required is quite small.
(ii) It requires less space so it can be located near to the load centre.
(iii) Huge deposits of nuclear fuels available all over the world. So supply of electricity can be ensured.
(iv) It ensures reliability of operation.

Disadvantages:
(i) The fuel used is expensive and is difficult to recover.
(ii) The capital cost on a nuclear plant is very high as compared to other types of plants
(iii) The disposal of the by-products is a big problem. They are radioactive in nature.
(iv) The maintenance charges are high.

-- Bellapuri saikumar
 sai saikumar jn

Difference Between Electric motor and Electrical Generator..? ( sai saikumar jn )

 Hello ..... Engineer's

MCQ:- What is the difference between Electric Motor and Electric Generator?

MUST READ & SHARE WITH YOUR FRIEND'S

Ans:- • Generator converts mechanical energy to electrical energy, while motor converts electrical energy to mechanical energy.

• In a generator, shaft attached to the rotor is driven by a mechanical force and electrical current is produced in the armature windings, while the shaft of a motor is driven by the magnetic forces developed between the armature and field; current has to be supplied to the armature winding.

• Fleming's left-handrule (for motors), and Fleming's right-handrule (for generators ).

Donot forget to  share it.

-- Bellapuri saikumar
 sai saikumar jn