A man grabs the high voltage wires above a train and electrocutes himself, he then bursts into flames.
There are three sets of independent components in a three-phase system: positive, negative and zero for both current and voltage. Positive sequence voltages are supplied by generators within the system and are always present. A second set of balanced phasors are also equal in magnitude and displaced 120 degrees apart, but display a counter-clockwise rotation sequence of A-C-B, which represents a negative sequence. The final set of balanced phasors is equal in magnitude and in phase with each other, however since there is no rotation sequence this is known as a zero sequence.
Under a no fault condition, the power system is considered to be essentially a symmetrical system and therefore only positive sequence currents and voltages exist. At the time of a fault, positive, negative and possibly zero sequence currents and voltages exist. Using real world phase voltages and currents along with Fortescue’s formulas, all positive, negative and zero sequence currents can be calculated. Protective relays use these sequence components along with phase current and/or voltage data as the input to protective elements.
This is an extract from a white paper circulated by APC!
A dedicated line is a power line, which runs from the circuit breaker panel to the critical load and has no other loads connected to it. Normally a circuit breaker feeds multiple receptacles; with a dedicated line, a single circuit breaker feeds only the one receptacle that the protected load is connected to. The advantages of a dedicated line are threefold:
First, the protected load is not subjected to input voltage variations that could be caused by other loads sharing the same circuit. Such variations could result from the voltage drops in the building wiring, which are caused by the currents drawn by the adjacent loads. These variations are prevented by the dedicated line since the adjacent loads no longer share the same building wiring. Second, the protected load is not subjected to variations in the voltage of the grounding wire, which might result from ground noise injection from adjacent loads. This reduces intersystem ground noise.
Third, the protected load is not subject to the potential hazard of having its source circuit breaker tripped by the malfunction of another load, since with a dedicated line no other load shares the same circuit breaker.
A dedicated line may be installed at any time. An electrician simply installs a new circuit breaker in the circuit breaker panel and runs a new wire to either a new or existing AC receptacle.
Energy Efficiency may be the most discussed words while shopping for electrical appliances. But since the terms are purely technical and there are several variations like capacity, speed and efficiency common man stand puzzled before the shop keeper. So some indications are required to easily identify the power efficiency of an electrical appliance. Here comes a BEE (Bureau of Energy Efficiency) label star rating. The BEE Star Energy Efficiency Labels have been created to standardize the energy efficiency ratings of different electrical appliances and indicate energy consumption under standard test conditions. BEE (Bureau of Energy Efficiency) label indicates the efficiency of the equipment with 1-5 stars. The more star the label bears the more efficient it will be. For example a 5 star rated AC or refrigerator is more energy efficient that an appliance bearing 4 stars. So go for maximum stars while you purchase an electrical appliance. The more stars means more energy efficiency and the more money it will save over the life. Energy saving is for your pocket and for the self reliance of our country.
There are several types of power problems. The standards define power problems under seven categories depending on their wave forms. They are as follows:
3. Sag / Under voltage
4. Swell / Overvoltage
5. Waveform distortion
6. Voltage fluctuations
7. Frequency variations
Learn more about these power problems at
Harmonics are integer multiples of fundamental frequency. For example if the line frequency is 50 Hz, the 2nd harmonic is 100 Hz, the 3rd harmonic is 150 Hz, and so on. Two hundred years ago the mathematician Joseph Fourier showed that any shape of distorted wave could be disaggregated into the series of a fundamental sine wave plus various sinusoidal harmonics of that wave at various amplitudes. This has proven very important in electrical theory because electrical conductors and devices respond to the various harmonic components as if they were indeed distinct frequencies. Harmonic frequencies are added to power frequency at generation, transmission or load levels. For perfect functions of the power electronic components it is important to eliminate unwanted power frequency harmonics.
Effect of electric current through the vital parts of human body depend on the duration, magnitude and frequency of this current. Most dangerous consequence could be ventricular fibrillation, a condition of inordinate action of main chambers of the heart, resulting in immediate arrest of blood circulation.
Currents at 50 Hz about 0.1 A can be lethal. But human can sustain larger currents at 25 Hz or DC or at frequencies in the range of 3,000 - 10,000 Hz.
Current depends on voltage applied and body resistance. Resistance is mainly offered by skin. Skin resistance increases with thickness and diminishes with moisture / perspiration. Except for skin; blood vessels, intravascular spaces etc. offer conduction system.
Earthing is a connection done through a metal link between the body of any electrical appliance, or neutral point, as the case may be, to the deeper ground soil. The metal link is normally of MS flat, CI flat, GI wire which should be penetrated to the ground earth grid. The purpose of earthing is to ensure a low resistance path between earth and metal body. Any short circuit or fault current that occur in the system will be dissipated to earth. The object of an earthing system is to provide as nearly as possible a surface under and around a station which shall be at a uniform potential and as nearly zero or absolute earth potential as possible. The purpose of this is to ensure that in general all parts of apparatus, other than live parts, shall be at earth potential, as well as to ensure that operators and attendants shall be at earth potential at all times. Also by providing such an earth surface of uniform potential under and surrounding the station, as nearly as possible, there can exist no difference of potential in a short distance big enough to shock or injure an attendant when short-circuits or other abnormal occurrence take place. Earthing associated with current-carrying conductor(neutral) is normally essential to the security of the system and is generally known as system Earthing, while earthing of non-current carrying metal work and conductor is essential to the safety of human life, of animals and of property and is generally known as equipment earthing.
Electrical Design Tutor is one beautiful site that help beginners and electrical engineers learn the basics of Electrical Engineering and practice theory and practice together. This site has been designed for electrical engineers, electricians, students and anyone else that is interested in learning about how to design electrical engineering systems. Students can start from the basics and they will get information on Ohm’s law and start their learning process. There are detailed sections on Motors, Generators, Electrical Panels, Transformers etc. The article section deals with some interesting subjects. Read about NEC etc here. For a real time experience please visit http://www.electrical-design-tutor.com/
It is very important for every electrical engineer to keep up to date by gathering information after his/her graduation. There are many online education sites offer quality education for professional electrical engineers. Recently I have found one interesting site while browsing. This site offer distance education for electrical engineers after hi8s/her graduation while on-going job. These courses are very specific to subject and offer in depth information on the subject. Some courses are as listed below:
Fault and Disturbance Analysis Conference (ELEC 9190P): Join fellow power systems professionals to examine recent electrical disturbances and possible solutions in this annual Georgia Tech conference.
Grounding, EMI, and Power Quality (ELEC 3501P): Understand design practices for grounding and electromagnetic compatibility of industrial, commercial, and residential systems with linear and distorting loads.
Find more of such programs and courses at http://www.pe.gatech.edu/subjects/electrical-engineering
Nice audio of the 50 Hz inrush. 110kV / 33kV 60MVA transformer Sorry for the poor quality as it was drizzle and some water hit the camera lens.
the NEC 2011 Handbook combines solid, thorough, research-based content with the tools you need to build an in-depth understanding of the most important topics. It provides the full text of the updated code regulations alongside expert commentary from code specialists, offering code rationale, clarifications for new and updated rules, and practical, real-world advice on how to apply the code. New to the 2011 edition are articles including first-time Article 399 on October, Overhead Conductors with over 600 volts, first-time Article 694 on Small Wind Electric Systems, first-time Article 840 on Premises Powered Broadband Communications Systems, and more. This winning combination has created a valuable reference for those in or entering careers in electrical design, installation, inspection, and safety.
Author: National Fire Protection Association
Publisher: National Fire Protection Association
Please download your copy from: http://www.pdfbooksdownload.net/national-electrical-code-2011-handbook/
Earth faults are common fault condition in an electrical system. This will get noticed suddenly on a raining day. Once earth fault is detected it is Electrical Engineers headache to find the cause of earth fault. It can be a faulty device or a loose wire or wet terminal block. It is very important to locate the position of the earth fault and the reason for it.
In my experience a live line checking is easy. It is easy to go from the higher end. Go to the main distribution board and switch off all loads on by one. When you switch off one load the earth fault indication will vanish. (If it is not vanishing after switching off all individual feeders then the cause can be inside the panel or there can be multiple faults. To locate multiple faults you have to switch off all feeders and switch on loads one by one).
Once you have identified one feeder go down with that feeder. If it is a sub distribution board repeat the exercise and find out the affected feeder. If it is a motor starter check the starter without motor and later the motor. Once you have pin pointed the location it is easy to find the reason for the fault. For complicated systems you have to isolate individual systems and locate the location. Make groups of three or four items and remove supply to that line.
Remember it is important for any system to clear off earth faults before a second fault occur. So be fast in tracing the fault.
Current Transformers are transformers that produce proportional current in the secondary. The open-circuit voltage of a CT has absolutely nothing to do with the system voltage of the primary. For a given core secondary winding design, the secondary open-circuit voltage is the same, whether the CT is on a 400V circuit or an 110kV system. The voltage developed on the secondary of an open-circuited CT is a function of the current flowing in the primary and the inductance properties of the secondary windings. If the secondary is open-circuited, that is seen as infinite impedance, so all of the primary current is forced through the magnetizing branch. The voltage seen on the secondary is this primary current times the magnetizing impedance.
Energy Surveillance System (ESS) will monitor alarms send by Energy Management System (EMS) and inform the operator about Energy Leakages. Let us see how the GE Energy Surveillance System (ESS) works. Energy Surveillance System (ESS) will monitor the alarms issued by the company’s Energy Management System and will relay that information by means of email. Each alarm will be tagged with a name according to your preference. All information will be stored on a dedicated server which will be located at your location. The Energy Surveillance System (ESS) will monitor alarms from 8 -16 loads. When the ESS notices any alarm issued by your Energy Management System, it will send out an alert to the proper personnel.