Electrical Energy and Electrical Tariffs

Abstract

The amount of heat energy, W joules or watt seconds, produced by a current of I amperes flowing in a resistor R ohms for t seconds is

$$W = {I^2}Rt{\rm{ joules(J) or watt seconds}}$$

Thus, if 1 A flows for 1 second in a resistance of 1 Ω, the energy dissipated is

$$W = {I^2} \times 1 \times 1 = 1{\rm{J}}$$

However, if 100 A flows for the same length of time in the same resistor, the energy dissipated is

$$W = {100^2} \times 1 \times 1 = 10000{\rm{J}}$$

The electrical power rating of an item of electrical plant is related to its ability to dissipate the energy which is created within the apparatus. Since the heat energy is related to I², the rating of an electrical machine depends on its ability to dissipate the heat generated (I²R) within it; the rating therefore depends on the current which the apparatus consumes.