A typical grid uses 110..500 kilovolts lines to deliver electricity to substations which lower that to 6..20 kilovolts and then lines with that lower voltage get to consumers where yet other substations are located which finally lower those 6-20 kilovolts to consumer voltage (100 or 230 volts or whatever the local standard is).
Those 110..500 kilovolt lines often pass through areas where those consumers are located. Consumers could be connected to those lines via transformers accepting say 110 kilovolts and outputting consumer voltage. Instead those lines run to faraway somewhere and then another powerline runs back with some lower voltage and a consumer is hooked to the latter. That's a lot of extra wiring.
What's the reason for this design? Why not hook consumers to the closest powerline?
If your house is adjestant to high way, yet to reached to house, you have to come out from highway following exit, then to drive to your house by following local roads and street roads, similarly the H.V line transmitting power in MW, are like highway. The power received at distributing sub station, step down to distributing voltage by high rating step down transformers, and send to load area by respective feeders, using proper switch gear(circuit breaker, isolator and protecting relays) needed, and would be more efficient, economical and reliable.
If your house is adjestant to high way, yet to reached to house, you have to come out from highway following exit, then to drive to your house by following local roads and street roads, similarly the H.V line transmitting power in MW, are like highway. The power received at distributing sub station, step down to distributing voltage by high rating step down transformers, and send to load area by respective feeders, using proper switch gear(circuit breaker, isolator and protecting relays) needed, and would be more efficient, economical and reliable.
Container Trucks carrying consumables pass through highways near our home every while, but we have to go to the super market to get things cheap or at the local shop to get it at a higher cost. It would appear to be cheap if these Trucks stopped near our home and delivered things. But in practice this would be costlier considering the manpower, space and storage needs.
It would be similar in the case of Electricity too. The very High voltage lines are usually taken at greater heights along uninhabited area (Nobody wants to live near a high voltage line; may be it is unhealthy) and building and operating and maintaining transformers near these will be uneconomical in many ways.
Narayanan
hi
Because most Homemade consumers need low voltage electrical equipment needed to launch and high voltages suitable for industrial use.
Transmission lines uses high voltage and low current for less loss during transmission, also it is not suitable for household applications. So before it can be used in our houses, it is down converted to suitable voltage.
Regards,
Nitish
Transmission lines carry power at 110kV/132kV / 220kV / 400kV / 765kV (values may vary a bit from country to country) voltage levels. Home appliances are generally rated to operate at 110V / 230V (single phase) or 400V / 415V / 440V (3phase). A Transformer to step down the voltage will be too big to accommodate in the residential areas and its highly uneconomical. And we can't simply hook to the line... in addition to the transformer to reduce the voltage, we need an array of equipment (breakers, isolators, surge arrestors... put it differently, a small switchyard itself) required for bringing the line to transformer inputs & taking it out from the LV terminals.
As explained in the above replies, it is economics coupled with engineering, that decides the transmission voltage. Transmitting huge power (from remote generating stations to load centres), with lower losses & with smaller conductors (transmission line), requires high voltage (thus reducing the current which flows in the line).
Basically, the electricity network/gird is hierarchical: transmission, distribution and end user, to optimize the operation in terms of technical and commercial. We can not step down the voltage from 500kV to 220V or 110V by one step, due to technical issue and economic issue.
Maybe another way to say it is this. Other engineering concerns - such as economics - don't allow it. The grid (or any other expensive system) is optimized for and must balance multiple design criteria, such as cost, control, efficiency, reliability, safety, serviceability, expandability, fault tolerance, etc. rather than just proximity. I'll speculate that the cost of stepping that high transmission voltage down to more useful levels is such that a few strategically located facilities are far more economical and technically feasible than numerous smaller ones, after all costs have been considered.
Also, I bet that having very limited, controllable connections to those transmission lines holds other technical advantages for the power generator, e.g., in fault tolerance & recovery.
Think of troubleshooting, for example. If a large transmission line goes down, which situation would you rather troubleshoot and correct: The one with a few well-documented, well-monitored, well-controlled distribution stations connected, or the one with tens of thousands of connections, and orders of magnitude more variables to consider?
Clearly there are more factors to consider, but these are a few that typically come to mind in large design challenges.
Very simple answer. Because the household appliances can't withstand such a huge power. And also they are designed for almost 230V(+ -)6% rated value. And if a consumer take connection from those HV lines , he should have to make suitable arrangemnets for making that high voltage to possible usage level.
Imran Riaz,
First, understand about the basics of voltage, current, power, their relations and such other fundamentals.
Mr. Mohsen,
The main reason is the cost and reliability. The cost of the transformer and the associated switch gear largely depends on the insulation level required. As Lowell Ramsey rightly pointed, limited controllable connections to a transmission line always has the advantages of lesser faults, faster recovery rates and higher reliability.
Industries settle near HV line for economical reason, land is cheaper. The power required is not ready available nearby, it needs to go to a transformation facility and then distributed to houses and industries. If an industry or group of industries needs a large amount of power, the distributor can arrange a transformation facility near-by to supply thèses consumers.
if that is made possible just think how many transformers would be required and installing transformers for meagre loads is not economical
And to clarify a little further - it is more difficult and expensive to make transformers and insulation that stand up to high voltage. Even though every couple of houses will still need a transformer, (sometimes known as a "pole pig") these are much more affordable transformers, because they don't have to withstand the high transmission line voltage levels, and can be sized appropriately for their load. It's a little bit like drinking out of a water fountain, as opposed to a 50 inch high pressure water main. Not the perfect analogy, but sorta works.
You don't need a High Voltage supplied into your house. Therefore, a voltage suitable for you has to be. Made available through a lower voltage service point.
The high Voltage lines are transmission lines and operates at very high voltages that are not compatible with the distribution level voltages- so it can be used directly without the required step down transformers.
most Homemade consumers need low voltage electrical equipment needed to launch and high voltages suitable for industrial use.
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