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When electrical quantities are monitored over large observation times the measurement time is divided in equal small time windows (intervals). For each window the harmonic voltages and currents as well as the active and nonactive powers are recorded. The recorded values are treated as statistics. The total active and nonactive powers, calculated for the entire observation time, equal the arithmetic mean (expectation) of the respective values measured for each interval. The total apparent power, however, has a value larger than its mean value. This condition proves that a new type of nonactive power, characteristic only to power systems with randomly time varying voltages and currents, should be introduced to complete the resolution of apparent power.