Power Quality Problems Always Exist

The Philippine Distribution Code (PDC) has Power Quality (PQ) performance regulation for Distribution Utilities. In Section 3.2 of the PDC, it provides generalities and specific limitations for quality regulation. I have copied section 3.2.1.2 from the PDC for the purpose of this article, see below.

In this section, the PDC points to the identification of a PQ problem in the distribution system by classifying presence of quality parameters. Going beyond this section are specified limits of the parameters stated above which clearly identifies the existence of a PQ problem. It is interesting that this PDC section identifies PQ problems where some of the classifications always exist in operating a distribution system. My rationale are the following:

• Power system frequency is seldom at its nominal value of 60 Hz. The continuous variation of loads impact the maintenance of frequency at 60 HZ. Item (a) of the said section implies that a PQ problem due to frequency deviation always exists.
• Harmonic frequencies always exist in distribution systems. The issue if these harmonics are acceptable or not is another facet. But voltage harmonics and current harmonics are always present in a power system due to the popular usage of electronic-based devices and equipment. Item (c) of the said section above implies that a PQ problem exist due to the presence of harmonic frequencies, whether tolerable or not.
• Items (c) and (d) of the said section are combined definitions for voltage unbalance. In a practical distribution system, voltage unbalance exist at all nodes due to the two-phase and single-phase laterals in the three-phase distribution feeder and unequal loading of the three-phase distribution lines. If this unbalance in voltage is acceptable of not is about the magnitude of the unbalance. If we follow the thesis of the said items, then a PQ problem exist even at acceptable levels of voltage unbalance.

The PDC definition for the existence of a PQ problem, with respect with the section above, gives us an understanding that a PQ problem exist not withstanding the magnitude of frequency deviations, harmonic frequencies and voltage unbalance magnitudes.