Apparent Power, Power Factor, and Current Factor in Single-phase Circuits with Non-negligible Line Impedances

摘要

The first part of this article reviews the concepts of apparent power and power factor in single-phase circuits with non-negligible line impedances. The study is based on the well-known definition that the apparent power is the maximum load power subject to constant line losses and constant load voltage. In reality, however, all transmission/distribution lines have some finite impedance, and thus, the constant voltage condition cannot be maintained at the load terminals. In this article, the constant load voltage condition is relaxed and allowed to change, as long as it remains within acceptable range of application. This is a scenario that better reflects the realistic situations. Modified expressions for the apparent power and power factor are derived and discussed. The second part of the article presents a new concept called the current factor as the ratio of the minimal current to the actual current while keeping the load power constant. The current factor coincides with the power factor when the line impedances are neglected. The article explains how the current factor can be superior to the power factor when the line impedances are not negligible. The current factor is then extended to non-sinusoidal current factor for a non-linear load and is examined.