Thursday 23 May 2013

Full wave rectification

What is rectification?
"A rectifier is a device which is used to convert alternating current to direct current and this process is known as rectification".

The dc level obtained from a sinusoidal input can be improved by rectification. it is a process in which four diodes are connected in series in the form of closed loop called bridge configuration. A bridge rectifier provides full wave rectification from two wire AC input.




In the above circuit full wave bridge rectifier has shown. there are four diodes D1 to D4 arranged in bridge configuration. only two diodes conduct during each half cycle.
in the positive half cycle diodes D1 & D2 are conducting while D3 & D4 are reverse biased.


During negative half cycle diodes D1 & D2 are reverse biased and diodes D3 & D4 are conducting.



Output waveform:
Over one complete cycle the output voltages will appear as shown in fig





smoothing capacitor:
after rectification the dc voltage filtered through smoothing capacitor. the smoothing capacitor converts the full wave rippled output to the smooth DC output voltage.


where 
I load = the dc load current in amps.
f= frequency of ripple.

Sunday 19 May 2013

LCD

LCD stands for "Light Color Display".

It is a "flat panel display", "electronic visual display", "video display"that uses light modulating properties of liquid crystals.



Friday 17 May 2013

Feedback Concepts

TYPES OF FEEDBACK:
  • Negative feedback
  • Positive feedback.
Negative Feedback:
"If the feedback signal is out of phase with feedback signal then feedback is called as negative feedback."

Amplifiers always give negative feedback.

Disadvantages:
Negative feedback reduces overall gain of amplifiers.

Advantages:
  • Reduction in noise.
  • Greater bandwidth
  • Stability
  • Higher input impedance
  • Lower output impedance
  • Linear operation
Positive feedback:
"If the feedback signal is in phase with feedback signal then feedback is called as negative feedback."

Advantages:
Increases the gain of amplifiers.

Disadvantages:
  • Shorter bandwidth
  • Instability.
  • Lower input impedance
  • Higher output impedance


Applications:
Use for design of Oscillator.

Wednesday 15 May 2013

Pelamis Power Wave

This is one of the first facilities that convert effectively the power of the sea waves into electric power.
The device looks like a giant centipede floating on the water surface, and the more interesting here is that the project is already finished and running.
Richard Yemm is the founder of Pelamis Wave Power.
The Pelamis devices are 456 feet long,with a diameter of 12 feet nearly. these devices are made from 1.5 million pounds of carbon steel.
Bobbing up and down on the constant supply of waves in open sea, the devices convert this motion in to electricity.
Each of the converter has four articulated sections that moves up and down as waves pass along it.
Pelamis usually operates 2-10 km away from the shore and generates power of 750 kW, which is enough to supply electricity 500 households.









Sunday 12 May 2013

Crystal controlled oscillator

The most stable and accurate type of oscillator used crystal in feedback circuit to control the frequency.

there are three types of crystal used
  • Quartz
  • Tourmaline
  • Rochelle salt
but Quartz is one of the type of crystal which exhibits property of piezoelectric effect.

A great advantage of crystal oscillator is that it exhibits a very high Q.

crystal oscillator (Parallel resonant tank circuit)

Permanent magnet

  • Retain their magnetism for a long time.
  • Prepared from hardened steel and certain alloys of nickel and cobalt.
  • Alnico is widely used in electrical instruments, earphones, loud speakers, telephone reciever, small dc motor.
  • Permanent magnet should not be heated up or hammered. otherwise it will be demagnetized.
  • if a pair of magnets is kept, the keepers should be used and magnet should be kept facing the opposite polarity.

Improvement of Power factor

We can improve power factor by :
  • Static capacitors.
  • Synchronous condensor.
  • Use FACTS.
Static capacitors:
are used to generate reactive power and to improve the power factor. Capacitors compensate the reactive power absorbed by inductive loads.

Synchronous condenser:
Synchronous motor without load is also used to improve power factor.

Use FACTS: 
"FLEXIBLE AC TRANSMISSION SYSTEM"  devices are used to improve power factor.

Advantages of high power factor

Disadvantages of Low power factor:

http://electricalengrz.blogspot.com/2013/05/disadvantages-of-low-power-factor.html
http://electricalengrz.blogspot.com/2013/05/power-factor.html

Advantages of high power factor:

  • Reduced copper losses.
  • Smaller conductor size.
  • Improved voltage regulation.
  • Increased system capacity.
  • Less energy bill.



Comparison between Electrical & Magnetic circuits:

Electric Circuits
Magnetic circuits
Current flows
Flux flows
Path of current is called electric circuit
Path of flux is called magnetic circuit
Current flows due to E.M.F
Flux flows due to M.M.F
Flow of current is opposed by resistance of circuit
Flow of flux is opposed by reluctane of circuit
Current = E.M.F / resistance
Flux = MMF/ reluctance

Saturday 11 May 2013

Special purpose diodes. . . !

Optical diodes:

Photo diode:
A photo diode is a p-n junction whose primary function is the detection of light.
It has small window that allows light to strike the PN junction.

A photodiode is always used in reverse bias conditions. Reverse bias only allows a small current to flow through it. this is known as reverse leakage current and is due to the action of the minority carriers. It conducts electric current directly propotional to the amount of light that falls upon it.
Photo Diode

Applications:
  • Communication:
Fiber optic links, optical remote control
  • Industry:
Bar code scanners, light pens, brightness controls.
  • Automotive:
Haed light dimmer, climate control sunlight detector

Friday 10 May 2013

Special Purpose diodes....!

Schottky diode:
It is also known as Hot Carrier Diode.
It is a semiconductor diode with a low forward voltage drop and a very fast switching action.

A schottky diode is formed by joining a doped semiconductor regio(usually N-type) with a metal such as Gold,Platinum, or Silver. So rather than P-N junction there is a metal semiconductor juction.

It operates with forward bias and only with majority carriers. This means that if the semiconductor body is doped n-type, only the n-type carriers play a significant role in normal operation of the device and same for p-type.

Applications:
It finds broad application in high speed computer circuits where the fast switching time equates to high speed capability, and the low forward voltage drop equates to less power dissipation when conducting.

Special purpose diodes....

Zener diode:

It is a special type of semiconductor diode designed to opearte in reverse breakdown region. it allows current to flow in opposite direction, but only when exposed to enough reverse voltage.

Special purpose diodes

Varactor diode:
It is also called as VARICAP.
It is a semiconductor device that behaves like a variable capacitor. when reverse biased it has a capacitance that varies with an applied voltage.

Applications:

  • commonly found in communication equipments where electronic tuning is necessity.
  • An important component of radio frequency or RF applications.
  • Found in radios, FM receivers, televisions and microwaves.

Special purpose diodes....!

Optical diodes:
  • LED (Light emitting diodes)
  • Optical diodes
Optical diodes:
LED is a type of semiconductor that emits light when it is forward biased. due to forward bias, electron across the PN junction from N-type material recombine with holes in P type material. the recombining electrons release energy in form of  light & heat.

Application:
LED'S are used for:
  • Indicator lamps
  • read out displays on wide variety of instruments.
  • Seven segment display.











Special purpose diodes...!

Tunnel diode:
It is a special type of diode which is capable of very fast operation by using the effect called tunneling. It exhibits negative resistance. That means when voltage is increased the current through it decreases. Tunnel diode is heavily doped N. It has very narrow depletion region.

Application:
Used in oscillator and microwave amplifier.









The D- flip flop has only one input terminal. The D flip flop may be obtained from an S-R flip flop by just putting one inverter between S & R terminals. In this figure it is positive edge triggered flip flop. negative edge triggered D flip flop operates in the same way as positive edge triggered except that the change of state takes place at the negative on going edge of the clock pulse.

Basic flip flop using NAND gate


SR flip flop using nor gates


Wednesday 8 May 2013

Wind turbine components


Rotor blades: captures wind energy and convert it in to rotational energy of shaft.

Shaft: transfer rotational energy in to generator.

Nacelle: that holds gear box, generator, electronic control unit, yaw controller, brakes.
-> Gear box: increases speed of shaft between rotor hub and generator.
-> Generator: Use rotational energy of shaft to convert to electricity using electromagnetism/
-> Yaw controller: moves rotor to align with direction of wind.
-> Brakes: stop rotation of shaft in case of power overload or system failure.

Tower: supports rotor and nacelle and lifts entire set up to higher elevation where blades can safely clear the ground.

Electrical equipment: Carries electricity from generator down through tower and controls many safely elements of turbine.







Question. . .!

Question: why, when birds sit on transmission lines or current wires doesn't get shock?
Answer:
Its true that if birds sit on single phase transmission line they do not get sock but is they touch two lines then the circuit is closed and they get electrical shock.

so if a human touch a single one line then he doesn't get shock if he is standing in the air. if he is standing on the ground then touching the line he will get a shock because the ground on what we standing is like a neutral and in the most electric lines neutral is grounded so that means that human who touch the line closes the circuit between phase and neutral.

Relay

A relay is an electrically operated switch. Many relays use electromagnet to operate a switching mechanism mechanically but other operating principles are also used,

Use of relay:
Relays are used where it is necessary to control the circuit by a low power signal( with complete electrical isolation between control and controlled circuit), or where several circuits must be controlled by one signal.

Contactor:
a type of relay that can handle the high power required to directly control an electric motor or other loads is called a contactor.

Solid state relays control power circuits with no moving parts instead using a semiconductor device to perform switching.

Relays with calibrated operating characteristics and sometimes multiple operating coils are used to protect electrical circuits from overload or faults. in modern electrical power systems these functions are performed by digital instrument still called protective relays.

AOI logic to NAND or NOR logic



Methods to increase Efficiency of transformer...

"The ratio of output power to input power is called as efficiency of transformer"

efficiency = power output/ power input

Methods to increase efficiency of transformer:
  • Loop area
  • Insulation.
  • Resistance of primary & secondary coil
  • Flux coupling
Loop area:
Insulation:  The insulation between sheets of core should be perfect to stop eddy currents.
Resistance of primary & secondary coil:  The material of primary and secondary coils must be such that their electrical resistance is very small as may possible.
Flux coupling:  The primary and secondary coils should be wound in such a way that flux coupling between them is maximum because power transfer from primary to secondary coil takes place through flux linkages.

Monday 6 May 2013

SWG TO mm conversion table

Sometimes you need to convert SWG (standard wire guage) to mm (millimeter) unit. For converting SWG to mm, you can use two tables below.



MOST USED VALUES:



Questions. . . !

Question:How tube light circuit is connected and how it works?

Answer: A choke is connected in one end of the tube light and a starter is in series with the circuit. When supply is provided ,the starter will interrupt the supply cycle of AC. Due to the sudden change of supply the chock will generate around 1000volts . This volt will capable of to break the electrons inside the tube to make electron flow. once the current passes through the tube the starter circuit will be out of part. now there is no change of supply causes choke voltage normalized and act as minimize the current.

Octocoupler


Capacitor Voltage Transformer

A capacitor voltage transformer (CVT), or capacitance coupled voltage transformer (CCVT) 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. In its most basic form the device consists of three parts: two capacitors across which the transmission line signal is split, an inductive element to tune the device to the line frequency, and a transformer to isolate and further step down the voltage for the instrumentation or protective relay. The tuning of the divider to the line frequency makes the overall division ratio less sensitive to changes in the burden of the connected metering or protection devices. 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. CVTs are typically single-phase devices used for measuring voltages in excess of one hundred kilovolts where the use of wound primary voltage transformers would be uneconomical. In practice, capacitor C1 is often constructed as a stack of smaller capacitors connected in series. This provides a large voltage drop across C1 and a relatively small voltage drop across C2.


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. This forms a carrier communication network throughout the transmission network.




configurations of three phase transformers




Sunday 5 May 2013

Working principle of Induction motor

A Machine is a device which is used to change the level of energy.
e.g: Motors, generators and transformer..

The machine which converts electrical to mechanical energy is called as motor & which converts mechanical to electrical is called as generator.

AC motors & DC motors.
Induction motor is one of the type of AC motors.

In induction motor rotor does not receive any power from conduction but only by induction similar to transformer's secondary which receives power from primary that is why it is named as induction motor....


when 3 phase AC supply is given to the stator of machine then a rotating magnetic field is produced which rotates around the rotor at synchronous speed .
the rotating magnetic field passes through air gap and cuts the rotor conductors which are yet stationary due to relative speed between rotating magnetic field and stationary rotor emf is induced in the rotor conductor and as the rotor conductors are short circuited so current starts to flowing.
so mechanical force acts on the rotor conductor and torque is produced which rotates the rotor in the same direction as the rotating field.


Disadvantages of low power factor


Disadvantages of Low power Factor:
  • Large KVA rating of equipment:
KVA= KW / cosθ
If equipment has low power factor  then KVA rating of the equipment greater making the equipment larger and expensive
  • Greater conductor size.
  • Larger copper losses, grater the KVA rating, greater the current, due to large current copper losses also increases
  • Poor voltage regulation.
  • High energy bill:
Low power factor  increases the KVA demand which in turn increases the energy bill.
Energy bill = KVA demand charges + energy charges

Power Factor

What is power Factor?

  • Ratio between real and apparent power is known as power factor.
PF = KW/ KVA

OR
  • Cosine of phase angle between Real and apparent powers is known as power factor.
PF = cos θ

Disadvantages of Low power Factor:
  • Large KVA rating of equipment:
KVA= KW / cosθ
If equipment has low power factor  then KVA rating of the equipment greater making the equipment larger and expensive
  • Greater conductor size.
  • Larger copper losses, grater the KVA rating, greater the current, due to large current copper losses also increases
  • Poor voltage regulation.
  • High energy bill:
Low power factor  increases the KVA demand which in turn increases the energy bill.
Energy bill = KVA demand charges + energy charges

Concept of solar powered refirigrator


Saturday 4 May 2013

Question. . !

Question: Why we use a capacitor in electric fan?

Answer:
  • Capacitor is used for both starting the fan and improving power factor.
  • The voltage taken by the fan during running has lagging power factor and in order to run the fan we need leading power factor. The capacitor increases the power factor so we use capacitor in fan to increase power factor.
  • To give a start up for any instrument, capacitor is used in electronics by using capacitor in start up there is a charge accumulation in between the plates of capacitor, which is discharged again and gives a start to instrument otherwise we have to use a very high voltage to the instrument.


Friday 3 May 2013


Thursday 2 May 2013

Characteristics of DELTA-DELTA connection


  • In delta-delta connection, dissimilar ends join together.
  • The system is three phase, 3 wire system.
  • In delta-delta connection line current is given by IL = IP√3.
  • In star-star connection line voltage and phase voltage are equal  VL = VP.
  • Line currents are 120 degree apart.
  • Line currents are 120 degree ahead w.r.t phase current.
  • Zero sequence current and circulating current can not be avoided.
  • As phase voltage is greater so large number of turns are required and hence more insulation is required.
  • Due to low currents winding must have small cross sectional area.
  • This connection is suitable for low voltage transformers.

Characteristics of STAR-STAR connection


  • In star-star connection, similar ends join together to form a neutral or star point.
  • If neutral is taken outside then the system will be three phase, 4 wire system.
  • In star-star connection line voltage is given by VL = VP√3.
  • In star-star connection line current and phase current are equal  IL = IP.
  • Line voltages are 120 degree apart.
  • Line voltages are 120 degree ahead w.r.t phase voltage.
  • Zero sequence current can be avoided due to neutral.
  • As phase voltage is less so less number of turns are required and hence less insulation is required.
  • Due to high currents winding must have large cross sectional area.
  • This connection is economical for high voltage transformers and is seldom used.

Solid conductors vs stranded conductors

Solid Conductor:
It consists of single piece of metal wire. It is cheap for manufacturing.Skin effect is higher in solid conductors as at higher frequencies current flow on the surface of the conductors results in the increase in the effective resistance. The main disadvantage of the solid wire is its more rigid property. It cannot be bent easily.

Stranded Conductors:
Stranded wire consists of sub conductors touch each other. It is costlier to manufacture compared to solid wire. For the given current carrying capacity the size of the stranded conductor is large compared to solid wire. Different elements of strands can be wound together to get the transmission line of desired property (eg: ACSR conductor contains Aluminum and Steel stands wound together). Proximity and skin effect is reduced using stranded conductors.

Silica gel in transformer

Question:
Why Silica gel is used in transformer ?

Answer:
When load on transformer increases current flowing the transformer windings increases. Heat generated by the rise in the current will be dissipated in to the transformer oil. Heated transformer oil becomes less denser compared to the normal transformer oil and moves up in to the conservator. This heat will be dissipated in to the atmosphere from hot transformer oil.

When load on transformer increases, transformer breather breathes air in. Air contains moisture when come in contact with the oil will affect the purity of the transformer oil. Moisture and impurity level in the transformer oil increases results in the damage of insulation property of the transformer oil.

To avoid entry of moisture air in to the transformer silica gel crystals are used. Silica gel will absorb the moisture in the air and allows dry air in to the transformer. Silica gel will be blue when they are installed or dry. When the crystals absorb the moisture they turn to pink color.

Thus silica gel protects the insulation strength of the transformer oil by absorbing the moist air entering in to the transformer.

Skin effect

Question: What is skin effect?

Answer:
When the AC passed through the conductor the density of the current is not uniform over the cross-section of the conductor, the density of the current is very high near the surface of the conductor and very low at middle this effect is called skin effect. this effect is only in the ac.

Questions. . !

Question: Why three-phase power is superior to single-phase power for many applications ?

Answer:
1st Reason :
Three-phase machines and controls can be smaller, lighter in weight, and more efficient than comparable single-phase equipment. More power is supplied to them in the same period than can be supplied by a single-phase power circuit.

2nd Reason :
Only about 75 percent as much copper wire is required for distributing three-phase power as is required for distributing the same amount of single-phase power.

Single-Phase Power vs Three-Phase Power:

Single-Phase Power vs Three-Phase Power:

Both three-phase and single-phase devices can be powered from a three-phase supply. A three-phase circuit is a combination of three single-phase circuits. The current, voltage, and power relations of balanced three-phase AC circuits can be studied by applying the rules that apply to single-phase circuits.

The sine waves of three-phase voltage are separated by 120 electrical degree because they are generated by three separate sets of armature coils in an AC generator. These three sets of coils are mounted 120 electrical degrees apart on the generator’s armature. The coil ends could all be brought out of the generator to form three separate single-phase circuits, but they are conventionally interconnected so that only three or four wires are actually brought out of the generator.

Single-phase AC voltage with zero power factor has both voltage and current sine waves in phase, so they cross the zero line together twice in each cycle. Similarly, a plot of three-phase voltage sine waves, also with zero power factors as shown in the Figure, has all three voltage and current waves crossing the zero line twice each cycle together. Each of its three phases, V1, V2, and V3, is separated by 120 electrical degrees.

Sag:
The difference in level between points of supports and the lowest point on the conductor.

Space:
The distance between the conductors on the same tower.

Span:
The distance between two towers.

Clearance:
The minimum distance between the conductor and ground.