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 decrease is known as the alternating current decrement of the short-circuit current. Figure 4-2
shows a decreasing symmetrical short-circuit current.
(b) Most short-circuit currents are not symmetrical, but are offset from the
normal-current axis for several cycles. If the power factor is essentially zero until a steady-state
value is reached and the short circuit occurs at the zero point on the voltage wave, the current
starts to build up from zero, but cannot follow the normal-current axis because the current must
lag behind the voltage by 90. Although the current is symmetrical with respect to a new axis, it
is asymmetrical with respect to the original axis.
4-5
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