Investigation of harmonics in relation to 150 kV capacitor banks at PPC's Philippi substation

As result of some frequent capacitor unit failures at the 150 kV Philippi substation, an investigation of harmonics as relate to 150 kV capacitor banks was undertaken to determine as to whether harmonics were the cause of the capacitor failures and at the same time to determine the influence of harmonics on capacitors at the 150 kV level in general. This paper presents the measured voltage harmonics at the 150 kV capacitor bus and by utilizing these measurements establishes as to whether they are within acceptable limits as defined by IEEE Std. 519 1992. In addition, NEMA Std. CP1, the applicable standard for the Philippi substation capacitors, is used to calculate the maximum capacitor voltage harmonic levels for comparison with the measured harmonic levels. Furthermore, the resonant frequency of the circuit involved is calculated and, along with the THD, is used for determining if harmonic problems exist or not. Finally, the influence of the measured harmonics on capacitor inrush current is established and the resulting inrush current is compared with the limitation posed by NEMA Std. CP1.