
28 Introduction to Electrical Power and Power Electronics
On the other hand, if the current and voltage are in phase—as in a pure resistor—
the power is always positive even when both the voltage and the current are negative
in one-half cycle. This results in the average power having the same positive value in
both one-half cycles and also over one full cycle.
1.8 THREE-PHASE AC POWER SYSTEM
The ac power is now universally adopted all over the world because of its easy con-
version from one voltage level to another using energy-efcient power transformers.
From a large ac power system (power grid), large power users are catered to at high
voltage, ...