Active Harmonic Filter With PFC Install at Recycling Plant
A recent catastrophic failure of a 200kVAr Power Factor Correction unit on the main incoming supply at Large Recycling Centre has raised concerns that the quality of the supply may in some way be compromised, resulting in this failure.
In order to determine the quality of the power on this site, including the levels of harmonics, general voltage levels and voltage stability, a week-long power analysis was commissioned on the main incoming supply, highlighting the fact that, due to the failure of the power factor correction on this supply, the load was operating power factor is slightly below the minimum target power factor of 0.95. In addition, it was found that the site loading is uncomfortably close to exceeding the limits of main supply.
Whilst the reinstatement of the power factor correction would restore the load operating power factor, the high level of load current harmonics means that even with harmonic detuning reactors fitted to the power factor correction, excessive 5th harmonic current absorption within the power factor correction capacitors could still result, possibly resulting in further failures in the future.
In addition to potentially reducing the longevity of the power factor correction capacitors, the high level of load current harmonics is producing elevated levels of voltage harmonics and is placing significant stress upon the supply transformer.
The results of the PQA also showed Voltage 5th, 33rd, 39th, 45th and 49th harmonic voltages and the voltage THD exceeded the G5/5 design limit. The 5th harmonic voltage dominates the voltage harmonic voltage distortion, which is to be expected given the proliferation of 6-pulse inverter drives within the load.
In order to prevent future power factor correction capacitor failures and to minimise the effects of the load harmonic currents, we have recommended that a 450Amp rated active harmonic filter be installed that can perform the combined harmonic filtration and power factor correction requirements in one device.
The APQF was designed and built in our workshop, fully tested, and then shipped to site where it was lifted up to the 1st floor of a container switchroom where we have already removed the failed PFC equipment ready for connection of the new Filter.
New C.T circuits were installed and the 630A MCCB previously used for the PFC was utilized for reconnection of the Active Filter. Once connected, a full commissioning was carried out and the unit showed a reduced Voltage distortion down from 3.9%VTHD to 1.5%VTHD and a reduced Current Distortion down from 9.2% iTHD to 5.2%iTHD
