D.C generator working and construction

 DC Generator working and construction details:

A shunt-wound DC generator is constructed so that the field winding is in parallel with the armature winding. The voltage of a shunt-wound DC generator decreases with an increase in load current. A series-wound DC generator is constructed so that the field winding is in series with the armature winding. The voltage of a series-wound DC generator increases sharply with an increase in load. In a cumulatively-compounded DC generator, the series and shunt fields aid one another. In a differentially-compounded DC generator, the series and shunt fields oppose one another. The voltage of a flat-compounded DC generator changes less than 5 percent from no-load to full-load. The voltage of an over-compounded DC generator gradually rises with an increasing load.

Here is the construction diagram of dc generator

An electrical generator is a device that converts mechanical energy to electrical energy, generally using electromagnetic induction. The source of mechanical energy may be a reciprocating or turbine steam engine, water falling through a turbine or waterwheel, an internal combustion engine, a wind turbine, a hand crank, or any other source of mechanical energy.

The Dynamo was the first electrical generator capable of delivering power for industry. The dynamo uses electromagnetic principles to convert mechanical rotation into an alternating electric current. A dynamo machine consists of a stationary structure which generates a strong magnetic field, and a set of rotating windings which turn within that field. On small machines the magnetic field may be provided by a permanent magnet; larger machines have the magnetic field created by electromagnets.

The energy conversion in generator is based on the principle of the production of dynamically induced e.m.f. Whenever a conductor cuts magneticic flux , dynamically induced e.m.f is produced in it according to Faraday's Laws of Electromagnetic induction.This e.m.f causes a current to flow if the conductor circuit is closed. Hence, two basic essential parts of an electrical generator are (i) a magnetic field and (ii) a conductor or conductors which can so move as to cut the flux.

Generator Construction:

Simple loop generator is having a single-turn rectangular copper coil rotating about its own axis in a magnetic field provided by either permanent magnet or electro magnets.In case of without commutator the two ends of the coil are joined to slip rings which are insulated from each other and from the central shaft.Two collecting brushes ( of carbon or copper) press against the slip rings.Their function is to collect the current induced in the coil. In this case the current waveform we obtain is alternating current ( you can see in fig). In case of with commutator the slip rings are replaced by split rings.In this case the current is unidirectional.

Components of a generator:

Rotor: In its simplest form, the rotor consists of a single loop of wire made to rotate within a magnetic field. In practice, the rotor usually consists of several coils of wire wound on an armature.

Armature: The armature is a cylinder of laminated iron mounted on an axle. The axle is carried in bearings mounted in the external structure of the generator. Torque is applied to the axle to make the rotor spin.

Coil: Each coil usually consists of many turns of copper wire wound on the armature. The two ends of each coil are connected either to two slip rings (AC) or two opposite bars of a split-ring commutator (DC).

Stator: The stator is the fixed part of the generator that supplies the magnetic field in which the coils rotate. It may consist of two permanent magnets with opposite poles facing and shaped to fit around the rotor. Alternatively, the magnetic field may be provided by two electromagnets.

Field electromagnets: Each electromagnet consists of a coil of many turns of copper wire wound on a soft iron core. The electromagnets are wound, mounted and shaped in such a way that opposite poles face each other and wrap around the rotor.

Brushes:The brushes are carbon blocks that maintain contact with the ends of the coils via the slip rings (AC) or the split-ring commutator (DC), and conduct electric current from the coils to the external circuit.

How DC generator works?

The commutator rotates with the loop of wire just as the slip rings do with the rotor of an AC generator. Each half of the commutator ring is called a commutator segment and is insulated from the other half. Each end of the rotating loop of wire is connected to a commutator segment. Two carbon brushes connected to the outside circuit rest against the rotating commutator. One brush conducts the current out of the generator, and the other brush feeds it in. The commutator is designed so that, no matter how the current in the loop alternates, the commutator segment containing the outward-going current is always against the "out" brush at the proper time. The armature in a large DC generator has many coils of wire and commutator segments. Because of the commutator, engineers have found it necessary to have the armature serve as the rotor(the rotating part of an apparatus) and the field structure as the stator (a stationary portion enclosing rotating parts).

Motor inner parts

Motor inner parts 

Wave energy system

wave Energy System:

The wave Energy System developed in Australia by BioPower Systems, harnesses the power of ocean waves and converts it into smart grid-connected electricity.

Which method can bring the locomotive to dead stop

# which method can bring the locomotive to dead stop.

(a) Plugging braking
(b) Rheostatic braking
(c) Regenerative braking
(d) None of the above

 

Answer : plugging for dc motor except for dc series motor

            for d.c series motor dynamic breaking is used

Difference between ground and neutral

What is the main difference between Ground and Neutral?

Answer:
The difference between Ground and Neutral? NEUTRAL is the origin of all current flow. In a poly-phase system, as its phase relationship with all the three phases is the same, (i.e.) as it is not biased towards any one phase, thus remaining neutral, that’s why it is called neutral. Whereas, GROUND is the EARTH on which we stand. It was perceived to utilize this vast, omnipresent conductor of electricity, in case of fault, so that the fault current returns to the source neutral through this conductor given by nature which is available free of cost. If earth is not used for this purpose, then one has to lay a long. long metallic conductor for the purpose, thus increasing the cost. Ground should never be used as neutral. The protection devices (eg ELCB, RCD etc) work basically on principle that the phase currents are balanced with neutral current. In case you use ground wire as the neutral, these are bound to trip if they are there – and they must be there. at least at substations. And these are kept very sensitive i.e. even minute currents are supposed to trip these. One aspect is safety – when someone touches a neutral, you don’t want him to be electrocuted – do you? Usually if you see the switches at home are on the phase and not neutral (except at the MCB stage). Any one assumes the once the switch is off, it is safe (the safety is taken care of in 3 wire system, but again most of the fixtures are on 2 wire) – he will be shocked at the accidental touching of wire in case the floating neutral is floating too much.

Transformer rating in kva

Why transformer rating is in KVA?

A transformer is basically rated in Kilovolt-amperes (kVA). An example is a 10 kVA Single phase Transformer, by which, the rating is 10 kVA. Have you wondered why transformers are rated in kVA and not in Kilowatts (kW)?
If we dig deeper into the study of transformers, we will see that the copper loss of a transformer depends on the current, while its iron loss depends on its voltage. Therefore, the total transformer loss, which is the copper loss and the iron loss, depends on the volt-ampere and not on the phase angle between current and voltage. Thus, the transformer losses are independent on the load power factor. It is the main reason why transformers are rated in kVA and not in kW.

Single phase transformer

CLEAR EXPLANATION OF SINGLE PHASE TRANSFORMER

Basic Parts of the Distribution transformer

In Transformers Part 1, a transformer was defined as a stationary equipment which transforms power from one voltage level to another through electromagnetic induction. After learning the theory of operation of transformers, it is necessary to know the basic parts of an electrical transformer. Take note that the transformer used in my example is a single phase distribution transformers. These are transformers mostly mounted on pole to deliver power to residential and commercial establishments.
As shown in the figure, the basic parts of a distribution transformer are as follows:
A.  Hand Hole –The hand hole, as the name implies, serves as an access point of a technician to tap changers/mechanisms located  inside the tank without the need of opening the cover. Most modern transformers have tap changers located outside the tank for convenience.
B. Lifting Lugs – This is used, where the hook/rope is connected, for lifting, either using a hoist or a crane.
C. Terminal Markings (Secondary) – The markings provide identification about the terminals of a transformer.
D. LV Bushing – The bushing is made of porcelain. It serves as the output and is the low voltage side of the transformer, which usually supplies power on residential/commercial establishments.
E. Ground Tap – As the name implies, this is where the grounding of the transformer is connected.

F. Transformer Markings – Are markings which indicate the capacity (in Kilovolt-amperes) of a transformer and its voltage output.
G. Radiator Fins –This is the cooling mechanism of a transformer. The cooling mechanism of a transformer depends on the size or rating of the transformer. The bigger the rating, the more cooling mechanisms are used. Take note that in order to maintain operation of the transformer for a long period of time, it is necessary to keep the temperature to be stable.
H. Casing (Tank) – It is generally made of steel. It encloses the core-coil and is the container for the liquid coolant/insulant.
I. HV Bushing – This is the bushing for the high voltage side of the transformer. It is usually made of solid porcelain. This is the input of the transformer.
J. Pressure Relief Device – This is a spring loaded device which releases excess pressure.
K. Mounting Lugs – This is usually used if the transformer is mounted on poles. It is connected on a transformer cluster which is connected on a pole.
L. Tap Changer – This sets the ratio of the HV and LV windings. Most distribution transformers have taps ± 5%, ± 2.5% and 0.
M. Nameplate – Contains all data about the distribution transformer it is connected to.
N. Core – Part of a transformer that serves as a path for the flow of magnetic flux. There are two types of transformer core, the Shell type and the Core type. The core is inside the tank.
• Core Type – The core is in the form of a rectangular frame with coils placed on two vertical sides. They are divided, part of each primary and secondary on each of the two vertical legs.
• Shell Type – The core surrounds the coils, instead of the coils surrounding the core.
O. Windings – Arrangement of conductors wound on an insulating form with each turn insulated from all the other turns. This usually determines the rating of the transformer as the winding is designed by the amount of current it can carry.

Construction details of single phase transformer

CLEAR EXPLANATION OF SINGLE PHASE TRANSFORMER

# The major cause of creeping in an energymeter is

A. over compensation for friction
B. excessive voltage across potential coil
C. mechanical vibrations
D. stray magnetic field

A future where the whoosh of passing cars power highway lights

#‎In‬ distribution transformer which winding is used

A. helical
B. sandwitched
C. circular
D. cylindrical

 

# Swinburne’s test is applicable to

A. DC series motor
B. DC shunt motor
C. DC compound motor
D. None of the above

Extra high Voltage Oil filled Cable (110kV/500kV)

Constructional differences between rotors

why do transformers make a humming sound??

Answer:

Iron or ferrite core transformers if operate at frequency between 20- 20,000 Hz of the applied ac voltage,
the core material's length is extended & contracted in length by very small amount at that frequency known as magnetostriction process.
Magnetostriction causes air being pushed back & forth at that frequency causing sound generation which is hummung sound.
Transformers without core do not generate that sound

How the engineer see the society

how the engineer see the society
v

Temperature sensor

Temparature sensor

Capacitor voltage transformer

Capacitor Voltage Transformers/ Coupling Capacitors

What is reverse power relay?

Answers:-
Reverse Power flow relay are used in generating stations's protection. A generating stations is supposed to fed power to the grid and
in case generating units are off, there is no generation in the plant then plant may take power from grid.
To stop the flow of power from grid to generator we use reverse power relay.

interview question:

Two bulbs of 100w and 40w respectively connected in series across a 230v supply which bulb will glow bright and why?

Answers:-
Since two bulbs are in series they will get equal amount of electrical current but as the supply voltage is constant across the bulb(P=V^2/R).
So the resistance of 40W bulb is greater and voltage across 40W is more (V=IR) so 40W bulb will glow brighter

Capacitor Voltage Transformer(CVT):

A capacitor voltage transformer (CVT) is a transformer used in power systems to step down extra high voltage signals and provide a low voltage signal, for measurement or to operate a protective relay.
The device has at least four terminals: a terminal for connection to the high voltage signal, a ground terminal, and two secondary terminals which connect to the instrumentation or protective relay.

The CVT is also useful in communication systems. CVTs in combination with wave traps are used for filtering high frequency communication signals from power frequency.

Capacitor

Q : How do capacitors store a charge?

Answer: Capacitors act like tiny storage batteries made of two plates separated by a thin insulator or air. When one plate is charged negative and the other positive, they build up a charge that remains when the current is removed. When its power is required, the circuit is switched to conduct current between the two plates, and the capacitor releases its charge. AnswerCapacitors don't really store charge at all. They allow negative charge to be transferred from one plate to the other, thus establishing an electric field between their plates. But there is no net increase in charge -the amount of charge on the capacitor's plates, after 'charging', is exactly the same as there was before 'charging' -it's just moved around! What capacitors 'store' is energy, not charge.

interview question:

Why synchronous generators are used for the production of electricity?

Answers:-
synchronous machines have capability to work on different power factor (or say
different imaginary power varying the field emf.)
Hence syn. generators r used for the production of electricity.

New technology:

Marine Solar Cells (MSC) by Phil Pauley are conceptual hybrid solar and wave energy generators designed to generate renewable energy off shore.
The solar wave unit captures wave energy through natural buoyancy displacement and solar energy through photovoltaic cells, taking advantage of natural light reflecting off the ocean’s surface to increase solar capture by 20%.
This ability contrasts with conventional solar farms or wave power designs which only harvest one form of power

# If the no. of rotor slots is equal to no.of stator slots, then motor refuses to start.
Hence it is known as

A. crawling
B. cogging
C. air gap
D. relative speed




Answer : cogging

Grounding transformer

Grounding Transformer:

A Grounding Transformer is used to provide a physical neutral for a power transformer with a delta connected downside.
The Grounding Transformers neutral point has low impedance and is suitable for different system groundings such as solid earthing, NER earthing (resistor) and resonance earthing (Arc Suppression Coils).

The Grounding Transformer can also be equipped with a low voltage auxiliary winding to be used as local power supply to the substation.

# The direction of rotation of a D.C. series motor can be changed by

A. Interchanging supply terminals
B. Interchanging field terminals
C. both (A) and (B)

Answer : c but one only at a time

# To improve the efficiency of thermal power plant ————————is placed between boiler and turbine.

A. ash handling point.
B. air pre-heater.
C. economizer.
D. super heater.



Answer : super heater

Latest Invention:
"Wind Lens - Structure" that Triples the Power of Wind Turbines

The Wind Lens functions similar to a magnifying glass that increases the light from the sun.
the structure features a hoop that is used to increase wind power, and a turbine that rotates by making use of the wind captured from the hoop.

 Wind turbine and its internal parts

● Ques: What is 2 phase motor?

● Ans: 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.

● Ques:What is slip in an induction motor?

● Ans:Slip can be defined as the distinction between the flux speed (Ns) and the rotor speed (N). Speed of the rotor of an induction motor is always less than its synchronous speed. It is usually expressed as a percentage of synchronous speed (Ns) and represented by the symbol ‘S’.

Ques:Why we can’t store AC in Batteriesinstead of DC.or Can we store AC in batteries instead of DC?

Ans:We cannot store AC in batteries because AC changes their polarity upto 50 (When frequency = 50 Hz) or 60 (When frequency = 60 Hz) times in a second. Therefore the battery terminalskeep changing Positive (+ve) becomes Negative (-Ve) and vice versa, but the battery cannot change their terminals with the same speed so that’s why we can’t store AC| in Batteries.
Also when we connect a battery with AC Supply, then It will charge during positive half cycle and discharge during negative half cycle because the Positive(+ve) half cycle cancel the negative (-Ve) half cycle, so the average voltage or current in a complete cycle is Zero. Sothere is no chance to store AC in the Batteries.
Also note that Average Voltage x Average Current ≠ Average Power

Difference between AC & DC power supply




Ques:Why we can’t store AC in Batteriesinstead of DC.or Can we store AC in batteries instead of DC?

Ans:We cannot store AC in batteries because AC changes their polarity upto 50 (When frequency = 50 Hz) or 60 (When frequency = 60 Hz) times in a second. Therefore the battery terminalskeep changing Positive (+ve) becomes Negative (-Ve) and vice versa, but the battery cannot change their terminals with the same speed so that’s why we can’t store AC| in Batteries.
Also when we connect a battery with AC Supply, then It will charge during positive half cycle and discharge during negative half cycle because the Positive(+ve) half cycle cancel the negative (-Ve) half cycle, so the average voltage or current in a complete cycle is Zero. Sothere is no chance to store AC in the Batteries.
Also note that Average Voltage x Average Current ≠ Average Power

# What will happen when power factor is leading in distribution of power?

Answers:-
If their is high power factor, i.e if the power factor is close to one:

1.losses in form of heat will be reduced,
2.cable becomes less bulky and easy to carry, and very
cheap to afford, &
3. it also reduces over heating of tranformers.

Comment If you Are Genius !!!!

*In a network made up of linear resistors and ideal voltage source values of resistors are doubled. Then the voltage across each resistor is

A. doubled
...

Sodium vapour lamps

Difference between electronic regulator and ordinary regulator for fan

interview question:
what is the diff. btwn. electronic regulator and ordinary rheostat regulator for fans?

Answer:-

The difference between the electronic and ordinary regulator is that in electronic reg. power losses are less because as we decrease the speed the electronic reg. give the power needed for that particular speed but in case of ordinary rheostat type reg. the power wastage is same for every speed and no power is saved.In electronic regulator triac is employed for speed control by varying the firing angle speed is controlled but in rheostatic control resistance is decreased by steps to achievespeed control

Electrical interview questions

Electrical interview question:

What is the difference between Isolator and Circuit Breaker?
Answer:-
:Isolator is a off load device which is used for isolating the downstream circuits from upstream circuits for the reason of any maintenance on downstream circuits. it should not be operated while it is having load. first the load on it must be made zero and then it can safely operated. its specification only rated current is given.
But circuit breaker is onload automatic device used for breaking the circuit in case of abnormal conditions like short circuit, overload etc., it is having three specification
1 is rated current and
2 is shortcircuit breaking capacity and
3 is instantaneous tripping current.