we know i=p/v so if v is increased , i reduces for constant power...but as soon as supply voltage is increased ,the current and voltage across the distant load is going to change , so how can the power be constant?.
Also
From Kirchhoffs voltage law or directly applying ohms law ,the current is going to increase if source voltage is increased.
Pl. someone explain this to me.
Electrical power transmission network is divided into three parts, viz.
HV Transmission Network with 220-765kV
Subtransmission Network with 33-132kV
Distribution Network with 415V
These three parts are coupled by proper transformers. kVA rating of primary and secondary windings of a transformer is same. Hence if voltage increases, current decreases. So at transmission level current will be small. So also transmission losses. For a 11kV/415V, 500KVA transformer, primary current is 26.24A where as the secondary current is 695.62A. Your load is connected to this secondary winding. 26.24A flows in Subtransmission Network . Accordingly transmission losses will be small.
md Tauseef,
Ohm's law have some limitations. it is valid for concentrated system. it is not valid for system which are distributed in nature.
Design of machine , study of power system falls under the category of distributed system, that is why direct proportion of voltage and current doesn't hold good for power system ,electrical machines etc. constant power concept is applied for all these system.
your Question based on transformer theory: generation is done at low voltage and high current. generator output voltage is nothing but input voltage of step -up Tx. when voltage will step-up current goes down because generated power is constant.
here, the power you mentioned is based on the generation side. The generator generate constant power. As for the whole AC power system, it is more complicated. Because the power has real part and complex part and the power flow depends on many factors, including the distributed effects.
P is proportional to V^2. So if we double voltage , power that can be evacuated is quadrupled. So the main aim is to evacuate as much power as possible at higher and higher voltages. Reduced losses is an added advantage.
Reference: http://www.quora.com/For-transmission-system-R-X-ratio-is-low-to-reduce-power-loss-but-for-distribution-systems-R-X-ratio-is-high-it-causes-more-voltage-drop-What-is-the-advantage-of-designing-a-line-with-high-R-X-ratio
Poweer is proportional to current X voltage, Losses are proportional to the square of current. Then for tha same transmitted power lossess are inversely proportional to the sqeare of the voltage.
You have to apply transformers ratios to use Kirhoffs laws. On one side of the transformer you have V1 * I1 = P, on other side you have V2 * I2 = P. If you want to draw a voltage loop over the transformer you need to recalculate all voltages to the same level first by considering the transformers ratio.
The power transmitted is the same, but you trade copper losses for a need of greater insulation distances, which is necessary if you increase the voltage level. Therefore for long distance big towers are more optimal solution. On the other hand you have very low voltage at home (say 220 or 110V) and low power requirements (a few kW) thus small voltage is better as no high insulation is required and its much safer.
The advantage of using very high voltages and very low currents is that when currents are kept low, the amount of power lost in the form of heat through the transmission line is kept to a minimum, especially over very long distances.
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