N2 Electrical Trade Theory|The Easy Way!


7


Te current “I” is the current which actually flows through the conductors and is also the current for which one pays. Te larger the phase angle ϕ, the smaller the power factor cos ϕ and consequently the larger the actual current “I” will have to be to deliver a certain power.


With a power factor of 0,8 (which can be considered to be quite good), the current flowing through the conductors of the cable will actually be 25% higher, in order to supply a given amount of power, than it would have been, had the power factor been unity (cos ϕ = 1). With a power factor of 0,6 the actual current through the conductors will be a staggering 67% higher.


At a power factor of 0,6 one pays at least 67% more for electricity than one would if the power factor were to be unity. Te cross-sectional area of the conductors would also have to be increased by at least 67%.


• Power at a low power factor costs the consumer more.


Te cables supplying a load have to be large enough to carry the actual current “I” and therefore the lower the power factor, the larger the diameter of the supply conductors has to be.


• Thicker cables cost considerably more. 1.3.4 Reactive power in a single-phase circuit


Te component of the current, I x sin ϕ, which is in quadrature with the voltage, does no useful work and causes energy loss in the form of heat. I × sin ϕ is also known as the reactive component of the current and since it results in energy loss, it is said to produce reactive power (Q) which is expressed in reactive volt-amperes (VAr ), therefore;


Q = VI sin ϕ VAr


In a three-phase circuit; Q = 3 × Vph


............................................................................................... (1.4) Iph sin ϕ = 3 VL IL sin ϕ watts


• Power at a low power factor causes energy losses which result in unwanted heat and overheating.


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