Current and Heat

Why do power companies use ultra-high voltage transmission? Because after the voltage is increased, the current will be reduced for transmission. According to Joule's law, in high-voltage wires, the voltage is increased, the current is reduced, and the resistance on the line will reduce heat loss.

In Taiwan, most old houses have aging wires, so if the power company keeps reducing the voltage, the wires could be on fire easily. If the power company lowers the voltage on its high-voltage line by 3%, it will increase the heat on the high-voltage line by 6.28%. It is also because the transmission current on the high voltage is large, the heat value (Q) is larger, and the high-voltage wire is hotter, which is easy to cause the high-voltage wire body on fire first, and eventually cause the substation to explode.

Electric power formula P=V·I

Voltage V, electric current I, multiply the two. If the transmitted power P remains fixed and if the voltage of Taipower drops by 3%, according to the electric power formula, the current will increase by 3.09%. According to Joule's law Q=I·I·R, the heat generated by the resistance R on the wire Q=I·I·R, the heat will increases by 6.28% and the plastic material on the wire is prone to heat increase, resulting in high temperature aging, and the wire is prone to fire.

In addition, the current and heat increase are only linear consequences, however it may be more serious non-linear consequences.

The increase in heat can cause the electrical resistance of wires, transformers and appliances to increase, which in turn

1. Increasing the temperature, even if it does not cause burns, will further increase the resistance...,

2. Reduce the natural frequency of the power system, causing…

a) The difference in the drive frequencies of the power generation systems increases, reducing the resonant currents...,

b) The difference between the frequency and the original design of the appliance, the difference between the three will affect its operation...

Author Professor Wei-Keng Lin Education｜Ph.D., University of Maryland Occupation｜Professor, National Tsing Hua University  Specialty｜Electronic package heat dissipation, Heat pipe, Loop heat pipes(CPL，LHP，PHP), Energy-saving design, Solar heat storage and cooling, Heat flow system, Cooling of electronic components, Two-phase flow, Heat transfer elements of artificial satellite and high-altitude flying object