Power Factor revisited

Power factor has been used for over a century as a rule of thumb to estimate the cost of the losses incurred in delivering reactive power. But it has been extremely troublesome to apply to three-phase systems. The same load might be penalized by some instruments, and not by others. There have been two noteworthy efforts at solution. In 1919 a committee was formed to solve the problem of its definition. The effort did not succeed at producing a single definition; two were recommended in the committee's final report in 1920, and more by individual committee members. In 2010, IEEE issued Standard 1459 to give definitions. In it, definitions of power factor appear under no less than seven different headings. Most of the 1920 definitions are retained. The problem still demands solution. The matter is of considerable economic importance to power producers, consumers, and instrument makers. This paper examines the history of the topic, and exposes the metrological reasons for the difficulty of definition. It is shown why power factor is not suited to purpose, and that no definition can exist that will define power factor usefully for its intended economic purpose. Some options are proposed.