Abstract
In Japan, limit values on the harmonic current emitted by customers with 6.6 kV and higher power supplies were specified in 1994. Because the limit values are applied to large pieces of equipment (those drawing currents of more than 20A), they generally apply to three-phase equipment. Most three-phase transformers have a star-delta connection. Many home appliances are considered to be equivalent to three-phase equipment with a delta-delta connection transformer, because single-phase equipment is connected phase-to-phase. This means that the harmonic currents created by three-phase equipment and single-phase equipment can cancel each other out.
The authors reached the following conclusions by analyzing harmonic voltage and current data measured at the supply points for customers with a 6.6kV power supply. (1) The 5th harmonic voltage in the electric power-supply system in Japan is produced mainly by single-phase equipment. (2) The limit values for customers with a middle- or high-voltage power supply are unnecessary, because the 5th harmonic current generated by three-phase equipment reduces the 5th harmonic voltage. (3) Connecting a reactor in series with the capacitors to improve the power factor is a necessary and sufficient method for suppressing the 5th harmonic voltage.
