# When high voltage leads to low current in power transmission system how its not applicable for household voltages?

When high voltage leads to low current in power transmission system using transformers,how increase in voltage in household circuits from 220 volts makes the current increase damaging the appliances,

I understand the power transmission this way that when a battery of 1.5 volt that can work for maximum 2 hours when connected to a resistor drawing current of 10 amp,its power is vit = 1.5 x 10 x 2 = 30 watt hour,

What i do not understand is how in the power generation system the voltage increases but current decreases and when this is true,

when the voltage of the household supply using 220 volt alternating current supply increases,the current should decrease enabling the appliances work safer in high voltages as the appliances get damaged not by the voltage but by the current that flows through them,

but the opposite happens in household system that is when voltage increases current increases damaging the appliances.

• The high voltage lines are designed to be higher impedance so that the appropriate current is maintained to maximize power distribution, i.e. you could damage older power lines with the newer higher voltages. Your appliance's impedance is only designed for 120 or 220. – PhysicsDave May 2 '19 at 20:48

for power transmission, the high voltage/low current conversion is performed using transformers. Their purpose is to minimize current flow in the transmission lines, and thereby minimize power losses.

However, once in the house, there are no transformers in the power lines- and an increase in the 220VAC mains voltage will force too much current through the appliances, ruining them.

• does it mean the current in power lines in "higher voltage and lower current in power transmission" means the current inside the inductor of the transformer and the current inside the house is the current inside the loads of the house when connected to the ends of the secondary inductor of the transformer ? that way can we say the primary and secondary inductors in transformers are connected in some kind of parallel combinations ? – sachin May 3 '19 at 13:49
• I am not sure what you mean here. – niels nielsen May 3 '19 at 16:36

when the voltage of the household supply using 220 volt alternating current supply increases,the current should decrease enabling the appliances work safer in high voltages as the appliances get damaged not by the voltage but by the current that flows through them,

That assumption could possibly hold, if you assumed that the device received the same amount of power, regardless of voltage.

I don't think you would expect unsophisticated devices to operate that way. Instead, consider if the devices were set at a fixed resistance.

Knowing Ohm's law, we can see that $$V = IR$$, and therefore $$I = \frac V R$$. If we assume that the device has a fixed resistance, then you can see that increasing the voltage will lead to an increase in current.

This can be an issue in devices that assume you will only ever provide it one current, and have no overcurrent protections. This could also lead to problems in the wires that you are feeding the additional current through. Wires have internal resistance, so increasing the voltage increases the current, which can increase the temperature and even set fire if the voltage were high enough and the wires were thin enough.

the opposite happens in household system that is when voltage increases current increases damaging the appliances.

If you have a particular resistive appliance (for example an incandescent light bulb or a space heater) and increase the AC voltage you provide it, this is correct.

But if you can re-design the appliance for use on the higher voltage, you may be able to design it to use less current. For example, electric kettles made for sale in 230-V countries can use less current than ones made for 120-V countries while heating water equally quickly.

Or if you have an appliance that is internally run on DC and uses a switching supply to generate that DC (for example, a phone charger), then it's not true. If you take your phone charger from the US to a 230-volt country, it will draw less current. This is because the switching supply can adjust how much current it draws from its input side in order to provide the needed amount of power to its DC load.