Effects of phase-controlled switching on metering

In the common thyristor-controlled power ciicuit, the thyristor also functions as a convertor of power from the supply frequency to a very broad frequency spectrum. In general, a resistive load which is thyristor controlled has a inductive power factor, which approaches zero at large firing angles. Some of the harmonic power which is generated will be fed back to and redistributed by the supply network, and depending on their bandwidth this may or may not register on the users meters. If broadband meters are used, the harmonic power fed into the supply by a user will be subtracted from the fundamental power used. The power indicated by a broadband meter will depend on the mains supply impedance and on contributions of harmonic power from other users with similar nonlinear loads. The indicated power will therefore in general not be reproducible.