Electric Shock On Train Live

A man grabs the high voltage wires above a train and electrocutes himself, he then bursts into flames.

Symmetrical components - Positive, Negative and Zero Sequence Components

Wikipedia says that In electrical engineering, the method of symmetrical components is used to simplify analysis of unbalanced three phase power systems under both normal and abnormal conditions.

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.

What is a dedicated line?

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.

BEE (Bureau of Energy Efficiency)

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.

The Seven Types of Power Problems

There are several types of power problems. The standards define power problems under seven categories depending on their wave forms. They are as follows:

1. Transients
2. Interruptions
3. Sag / Under voltage
4. Swell / Overvoltage
5. Waveform distortion
6. Voltage fluctuations
7. Frequency variations

Learn more about these power problems at

The Seven Types of Power Problems

by APC

What are harmonics?

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 current through human body

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.