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Question:

Question about transformers and power transmission?

Two things:1.) Why when we're using an AC to step up the voltage the power has to remain constant?2.) Why is it if we increase the voltage by a factor of 100 we have to decrease the current by a factor of a hundred and therefore I^2R is decreased by a factor of 10,000

Answer:

The principle is simple. VI=constant. Energy loss is proportional to I^2. If you want transmit power over a long distance, then V should increase. So the current will be small and energy loss will less. You can not use it because, high voltage gives more shock. When bring it near the home, reduce the voltage so the items becomes less shock giving. Welder use very high current and very low voltage may be 6o volts so that they do not get unnecessary shock.
Power is generated at the power station and transferred to the end user your home by means of power cables. Unfortunately, some power is always lost in this transfer process. It's power NOT Voltage OR Current that is required to operate your home electrical appliance. Yes, current and voltages are involved ;but it is the PRODUCT of these two that makes up the power NOT the voltage or current individually. Power = Voltage x Current Power is lost in the cables as heat as given by your i^2R. To reduce the losses then we must reduce the current I. But, if I reduce the current and keep the voltage the same then the power will fall and my kettle/Xbox/curling tongs will no longer work at home. So, to keep the power up when reducing the current I must compensate by increasing the voltage and this means using a step up transformer. Near the homes, a step down transformer is used to reduce it back down again. Since the losses in a cable are a consequence of I^2R heating then it is important to reduce the current as much as possible when transferring power. If we assume the the resistance, R of the cable is constant, then a 10,000 reduction in power (power/10,000) gives P/10,000 = I^2 x R I^2 = Power/10, 000R I = square root of [const x 10,000] I = 100. Then using power = voltage x current reducing the current by 100 means increasing the voltage by 100 to keep the power the same.

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