AIR BLAST CIRCUIT BREAKERS

Circuit breakers are mechanical devices designed to close or open contact members, thus closing or opening of an electrical circuit under normal or abnormal conditions. Air blast circuit breakers are using compressed air or gas as the circuit breaking or interrupting medium. Gases such as nitrogen, carbon dioxide, hydrogen or Freon can be used as arc interrupting medium. But compressed air is the most accepted arc interrupting medium. The reasons are, nitrogen has circuit breaking properties similar to compressed air and there is no advantage of using it. Carbon dioxide has a draw back as it is difficult to control owing to freezing at valves and other restricted passages. Hydrogen has increased breaking capacity but it’s costlier.

Freon has high dielectric strength and good arc extinguishing properties, but it is expensive and it is decomposed by the arc into acid forming elements.

Desirable features of air blast circuit breakers are High speed operation, which is very necessary on large inter connected networks in order that system stability can be maintained and in the air blast circuit breaker this is achieved because the time interval between the receipt of a tripping impulse and contact separation is very short. Suitability for frequent operation, repeated switching by an air blast circuit breaker is possible simply because of absence of oil, which rapidly carbonizes with frequent operation, and because there is an insignificant amount of wear and tear at the current carrying contact surfaces. High speed reclosure by automatic means is an advantage on hv inter connected networks to assist and maintain system stability during the clearance of transient faults, a type of fault which is perhaps in majority on over head line. Negligible maintenance, the ability of the air blast circuit breaker to cope with repeated switching also means that negligible maintenance is required. Elimination of fire hazard, because of the absence of oil the risk of fire is eliminated.

Reduced size, the growth of dielectric strength is so rapid in air blast circuit breakers that final gap required for arc extinction is very small. This reduces the size of the device.

The air blast circuit breaker requires an auxiliary compressed air system which supplies air to the breaker air receiver. When opening is required compressed air is admitted to the arc extinction chamber. It pushes away the moving contacts. In doing so the contacts are separated and the air blast takes away the ionized gases along with it and assist arc extinction.

VACUUM CIRCUIT BREAKER

VACUUM CIRCUIT BREAKERS

Circuit breakers are devices which can automatically break a circuit under fault conditions and it can make the circuit manually after the fault. Circuit breakers are classified into different types. One of the main circuit breaker among them is Vacuum circuit breaker. Here vacuum is used to extinct the arc. Arc extinction is the main process of a circuit breaker

Before that, it is needy to explain how an arc is produced. Circuit breaker has two contacts- Fixed and movable, otherwise called as electrodes. Normally the contacts remain closed but if any fault occurs these contacts open automatically and of course can be opened manually.

We know that circuit breakers work under the instructions from relay. When the trip coils from relay energize, circuit breaker identifies fault occurred and hence the contacts are pulled apart. A high intensity current flows through the contacts of the circuit breaker before they are opened by the system. At the same instant contacts begin to separate and causes heavy heat and temperature in between the contacts. This is termed as an arc. This heat is highly dangerous and can cause heavy damage to the whole system. So it has to be extinguished in no time.

Vacuum is having superior qualities over other arc quenching medium. It has high insulating strength. When the contacts are opened in vacuum, the arc is produced in between them. It got extinguishes quickly since the metallic vapours and ions produced during the arc rapidly condense on the surface of the circuit breaker contacts, resulting in quick recovery of dielectric strength.

The contacts of Vacuum circuit breaker and arc shied is mounted inside a vacuum chamber. The chamber is connected to the control mechanism by means of stainless steel bellows. A glass vessel is used as the outer insulating body. This is all about its construction.

Vacuum circuit breaker is really the most reliable one with low cost, no fire hazards, no gas generation, low arc energy, little maintenance and low inertia.

What is an Actuator?

Actuator is a typical mechanical device used to move or control a mechanism or a system. This device gains energy for its working from air, electricity or liquid and then converts it into some kind of motion.

In engineering field actuators have many more applications in different sectors. In this field actuators are used as mechanisms to provide motion and are again used to stop the motion of that particular device. So it is clear that actuator just actuates the motion. May be start or stop, depends on the machine.

In electronics engineering, actuators are subdivisions of transducers. They are used to transform input signal into motion. Normally input signal would be electrical. E.g. electrical motors, pistons, relays, pneumatic actuators, piezo electric actuators etc. Actuators can be sometimes used as hardware components. Different types of actuators are available like plasma actuators, pneumatic actuators, electric actuators, linear actuators.

It’s a type of tool used to put something into automatic action. Actually actuators are used with number of sources. Depending on the type of actuator we are using, different tools will be assisting us to put the device to motion. Mostly they are used in office work area since most of them are used to move valve door in systems.

Sometimes they are used to maneuver certain mechanical devices on work. Depending on the shape and style actuators are divided into different classes. Linear actuators, valve actuators, hydraulic actuators are the best known and used among them. Each of them has assigned functions e.g. hydraulic actuators are used to allow more pressure, size and movement with the object.

All of these different types of actuators are best when knowing what type of motion control you need. They also provide speed, Belt drive, acceleration and accuracy with linear motion No matter what type of actuator is needed, there is a tool that makes it easier to maneuver a certain object or space in your work area.

VARISTORS

What is a VARISTOR?

The name varistor came from variable resistor. Varistor is a pure electronic component used to protect circuits from transient over voltages making the circuit triggered. The function of a varistor is to provide increased current when voltage becomes excessively high. Varistor is also known as Voltage Dependent Resistor (VDR) since it depends on voltage.

The most common type we are dealing with now days is Metal Oxide Varistor (MOV). It is just like a Unijunction Transistor, since it allows current flow only in one direction. It contains mass of ceramic grains enclosed between two metal plates. The boundary between and its neighbour forms a diode junction. So when a small voltage is applied across the electrodes, only a small current passes due to the reverse break down at the junctions. Similarly when a large voltage is applied, due to thermionic emission large current passes through the junction. This behavior results in nonlinear current voltage characteristic.

Varistor can absorb surge in some ways but to some to extent. A typical surge protector power strip can be made using MOV’s. A varistor provides no equipment protection from inrush surge current. A varistor doesn’t control such events. Varistors have many applications on different electronic circuits. It can replace ordinary resistor in almost all functions, basically it can vary its resistance. So using varistors we can control voltage and current to the circuit. Thus we can protect the circuit from internal damage and severe short circuits.

What is a neural network?

What are NEURAL NETWORKS?

The term neural network refers to be a club of biological neurons. But now this term is referred as artificial neural network which is composed of artificial neurons. So first of a comparison is needed between both the terms.

Biological neural network (BNN) is composed of natural and is connected in central nervous system or peripheral nervous system. They are destined to perform specific functions as ordained. Artificial neural network are fabricated with a group of artificial neurons. The name is so given because we know a neuron is the basic functional unit of our body which is capable of doing specific functions. These artificial ones are used to solve artificial intelligence problems. The artificial neural network (ANN) focuses on the detailed coverage of two types.

In BNN a single neuron is connected to other neurons and finally forms an extensive connection. These connections are called synapses and are connected with axons to dendrites. As such neural networks are extremely complex. Scientists need to melt the properties of BNN artificially in different areas. They ended up in the formation of ANN. The ANN concentrated in the solving of particular assigned tasks. It is successfully applied to speech recognition, face recognition, image analysis, adaptive control, to construct robots etc. Mostly now they are employed in the fields of statistical estimation, optimization and control theory. All neural networks take numeric input and numeric output.

The concept of neural networks emerged in the late 18th century. In the early 1950’s Friedrich Hayek was the one to posit this idea to the world.

The utility of ANN lies in the fact that it can be used to observe variety of functions. It can be used to determine the significance of seating arrangement in a class room. In real life it deals with function approximation, time prediction, blind signal production, data processing etc. Neural network software is used to research, stimulate, develop and apply ANN and BNN. Neural networks, with their remarkable ability to derive meaning from complicated or imprecise data, can be used to extract patterns and detect trends that are too complex to be noticed by either humans or other computer techniques. A neural network is not something that can be categorized in a single feature. It’s a day by growing branch of science. In all the ways above said neural network is a typical notable area that can produce drastic changes in technologies.

ELECTRICAL EQUIPMENTS

ELECTRICAL EQUIPMENTS

Electrical equipment is an appliance powered by electricity. This includes an enclosure, several electrical components, power switch etc. A machine which is the part of an electrical distribution system can be put under the category of electrical equipment. The components in this include switch board, distribution board, circuit breakers, energy meters, transformers etc

Let’s have a look at some significant electrical equipment. Electrical switch board is a major appliance. It directs electricity from one form to another. These switch boards contain large number of panels and each of it contains switches to redirect electricity. Actually the control of electricity to this switch board is carried out by electrical generators. As the power law defines the amount of power entering and leaving the switch must be equal. So generators make this stable. While going to the technical side of switch boards, it contains bus bars inside the case to isolate the switch board from the connections before it gets opened.

Distribution board is key electrical equipment. The main function of a distribution board is to divide the electric power feed into subsidiary circuits. It provides a safety breaker and fuse for each circuit in a common enclosure and hence the distribution board is sometimes called as power breaker.

An unavoidable part in electrical equipment section is circuit breakers. Basically it is an electric switch. It is designed to protect a device from over current or short circuit. It detects the fault if any and stops the flow of current to it. It incorporates manual as well as automatic control for switching operations. The latter control employs relays and operates only under fault conditions.

Its known to every one, transformer holds the top slot in the priority list. It’s a static piece of apparatus by means of which electric power from one circuit is transformed into electrical power of the same frequency in another circuit. It can raise and lower the voltage according to the need with the increase or decrease in current. The physical basis of a transformer is mutual induction and it works under the principle of Faraday’s laws of electromagnetic induction.

The above explained are some of the main electrical equipments which hold the key place in this section.

BASIC ELECTRICAL RULES

BASIC ELECTRICAL RULES

To protect all while working under electric apparatus from hazardous conditions some rules are to be strictly followed. They are made and proposed for the safety of users. These rules are listed under several sections.

Make sure that the equipment used is safe and check its working conditions properly. If the equipment is watered by some means, do avoid contact with it. Use the appliance only for the purpose for which it is made. Before using the device, check whether it has passed the entire requirement prescribed. Avoid direct contact from fuses. The equipments that are made to use in wet conditions may only used in that condition, ensure it. Before using identify its working and disconnecting methods. Equipments with out the mark of manufacturer can’t be used. Maintenances should be done in a proper way. The cases, cables, fuses all should be fixed as prescribed. Another important thing is the equipment should be perfectly grounded and is over current protected. Several different rules are to be used in different working conditions. The devices are to be classified under type, voltage, power rating and several other factors. Replace the fuse only after rectified the mistake of the blown fuse. Avoid using wires with poor insulation. Don’t touch the circuit with fingers. Proper safety measures are to be followed in each case.

National Electrical Code - NEC

National Electrical Code (NEC)

National Electrical Code is the United States standard for the installation of electric wiring safely; it is the most approved American national standard. Actually it is a series of codes issued by National Fire Protection Association (NFPA). This NEC consists of 19 code making panels and technical correlating committee. NEC work is sponsored by NFPA. It is formally identified as ANSI/NFPA 70.

This code was published in 1897 and is getting updated every three years. The 2008 code is the most recent version. Most states adopt the most recent edition within a couple of years of its publication. As with all national codes some of the portions or sections are omitted usually, but NEC is the least amended model code

NEC can be accessed to the public as a book in early periods but now available in the electronic version. NEC is composed of introduction, nine chapters. The introduction contains purpose, scope, enforcement and rules or information. These chapters deal with voltages, connections, markings, wiring devices, conductors, cables, cords, switches, heaters etc. In general all the chapters enclose numbered articles, parts, sections (or lists or tables) italicized exceptions, and fine print notes (FPN) -- explanations that are not part of the rules. Each code article is numbered based on the chapter which is in.

For eg; Article 210 addresses branch circuits and receptacles. This says about the minimum number of branches, placement of receptacles etc. NEC also has laws about how many circuits and receptacles are to be placed in a residential dwelling. It has separate law enforcement sections on conduit and cable protection, temperature rating etc

NEC consists of codes covering all the sections in electrical field. So in general NEC is the most accepted and least amended electrical code.

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