Accurate power factor definitions are of great importance for industries due to the fact that they affect the billing strategy. They also considerably affect the generation and distribution losses of the power system. At the moment, there are some ambiguities in power definitions to be used for this purpose. In recent years, because of a rapid growth in industry and the use of variable loads such as electrical furnaces and variable speed motors, there is a need for fast compensators that are capable of tracking load changes. One of these facilities is TSC, a capacitor bank that is controlled by static switches (thyristors). In this paper, the performance of these compensators in power factor correction for asymmetrical and variable loads in terms of PF-control capability, system losses and the THD of the input current based on various power factor definitions has been investigated, and a PF definition compatible with a commonly used control algorithm is proposed. Simulations have been carried out in PSCAD/EMTDC software environment.