Extremely long—hundreds of kilometers—untransposed high and extra-high voltage transmission lines with a flat, horizontal conductor configuration significantly contribute to negative-sequence voltages and, to a lesser extent, zero-sequence voltages. The incidence of negative-sequence voltages rises with increasing electrical load. In the late 1970s and early 1980s, Eskom operated two 400kV transmission lines to the Western Cape:

In a balanced three-phase network, the magnitudes of the voltages and currents in all three phases are the same and these voltages and currents phase are shifted symmetrically by 120 degrees to each other. If the magnitudes are not the same and phase-shifts are different from the 120 degrees, the network is unbalanced. Eskom strive

When switchgear is poorly maintained and operated continuously, it is only a matter of time before something significant occurs. However, if these extreme events go unnoticed, the consequences can be long-lasting. During load-shedding, circuit-breakers should be opened when load-shedding starts and closed when load-shedding ends. Unfortunately, the contacts of these circuit-breakers are often concealed. As