Solution and Alternatives
The first method proposed consisting of only the existing 5th and 7th order filters because these two single-tuned filters alone could work normally. But the power factor is reduced to 0.89. There is no additional installation cost.
The second method is to tune the original 11th and 13th order filters to 17th and 35th order high-pass damped filters, and to remove 5th and 7th order filters. The only one parallel resonant frequency is located at 338Hz (5.63th order) and is far from harmonic frequencies. The amplification gain of the closest even-order harmonics is as low as 1.25. Furthermore, the THDs of voltages at all points are less than 5.0%. The additional losses of the damping resistors in 17th and 35th order high-pass damped filters are 0.61kW and 0.07kW per MVAR only.
Decision and Recommendation
The plant accepted the proposal of install two high-pass damped filters to replace the original single-tuned filters. The amplification problems at some even-order harmonics will be avoided.
