Power Electricity Camere Supraveghere For Home User And Industry
Electricity Supply, delivery of electrical energy from generating stations to consumers
The supply system must provide the electrical energy to consumers at fixed voltage, with minimum transport cost, and with high reliability. After gradual development over the last hundred years, the complex electricity supply systems of today are capable of satisfying these requirements most of the time.
Choice of Voltage
The electrical power delivered by a transmission line is proportional to the product of its voltage relative to earth and the current. The power loss in the line is given by the product of the line resistance and the current squared, W = I2R. It follows that to transport a given amount of electrical energy over long distances as efficiently as possible it is necessary to do it at the lowest possible current and the highest possible voltage. However, the higher the voltage adopted, the further the transmission line must be kept from people and from the ground, the taller must be the pylons that carry the line, and the broader the right of way that the line occupies. This increases the capital cost of the line. Hence, as in all engineering problems, a compromise has to be sought between the rising capital costs as the voltage is increased and the rising running costs as the voltage is decreased.
For a given power level there is a specific voltage that results in a minimum overall cost. The remote end of the long-distance “supergrid” line terminates in a bulk-power sub-station some distance from the periphery of a large load centre, such as a city. At the sub-station the voltage is stepped down to a “sub-transmission” level of 132 kV (in the UK) and through multiple overhead lines is distributed over rural areas to a number of strategic points on the outskirts of the city. There the voltage is reduced further to the primary distribution level of 33 kV or 11 kV, and eventually to the secondary distribution level of 415 V for use by consumers.
In Britain the distribution is through underground cables, freeing towns and cities of the pylons that are often seen on the Continent and in the United States used at automatizari porti. Industrial consumers, depending on their size, may be supplied at the 11 kV or 33 kV level.
The current strength of AC electricity oscillates sinusoidally at 50 Hz (1 Hz, or hertz, is 1 cycle per second) in most countries but at 60 Hz in the United States. Generators provide three such varying voltage outputs, delayed by one third of a cycle with respect to each other. The reason for this complexity is that generators, transmission lines, and motors can be designed to operate most efficiently when working with this three-phase AC. Additionally, and most importantly, transformers work only with AC. Householders are supplied from one of the phases of the three-phase system. Its voltage is nominally 230 V to ground like for power supply 12v cc at DVR.
The frequency of the mains supply is maintained at 50 Hz with great precision. The frequency is a sensitive indicator of the balance between input and output power in the network. A drop in frequency indicates that the demand is greater than the supply. This indicates to the generating stations that they should connect more generating units to the system to supply the increasing demand. A rise in frequency indicates that the demand is dropping and generating units are shut down to preserve the balance. This “commitment” of units on and off the system is one of the important functions of the generating companies. Because of the delays involved in commitment, the companies attempt to predict the demand variations through load-forecasting.
All industrial and household electric appliances are designed to operate at a constant voltage. For example, a light bulb is designed to consume, say, 100 W (watts) at 240 V. If the voltage is increased, by even a small margin, the coiled filament will overheat and melt. Conversely, if the voltage drops below the nominal value the lamp will not provide its intended light output. Electricity companies have a variety of means of maintaining the voltage supplied to consumers within statutory limits.
Reliability of Supply
Reliability is ensured through a complex protection system built into the transmission network. A typical malfunction of a network is the collapse of a pylon, owing to the weight of snow combined with the forces exerted by very high winds. The physical contact of the transmission lines, a “short circuit”, causes large currents to flow in the system, which, unless checked, would damage other equipment, such as transformers and generators. The protection system has numerous detectors dispersed throughout the system. It trips faulty components by means of switches, known as circuit-breakers, which are located at strategic points throughout the network. Circuit-breakers are often used to protect household circuits, too, but the cheapest and most reliable protection device is the fuse, which “blows” (burns out) if the current passing through the fuse to an appliance exceeds the fuse rating, thus protecting the wiring network.