Examples of harmonics-related malfunctions in electrical installations : case of “Overloads of power factor correction capacitors”
Harmonics-related malfunctions are fortunately few in number nowadays. The main reason lies in the importance given to harmonics analysis in installation design. International standardisation has been tackling these phenomena for many years, and the standards and recommendations in force have produced results.
The other reason is the fact that harmonics are phenomena whose effects are felt in the long term and difficult to distinguish from the natural ageing of equipment.
There are, however, some more or less spectacular cases of malfunctions, linked essentially to the following phenomena:
- Overloads of power factor correction capacitors leading to the tripping of protection devices, shutdowns and even damage,
- Overloads in neutral conductors by third-order harmonics created by single-phase loads, leading to tripping, overheating and even cable damage,
- Overloads on transformers or generators, leading to tripping,
- High harmonic distortion, disturbing sensitive electronic loads.
This article will concentrate on the first case of Overloads of power factor correction capacitors.
Overloads of power factor correction capacitors may occur when there is resonance. This phenomenon is linked to the presence in the same system of capacitors and sources of harmonic currents (most frequently, variable speed drives).
A few examples:
- In Japan, in March 1994, a fire broke out in a museum dedicated to young visitors. A museum technician was injured. Following an in-depth investigation, the accident was attributed to harmonics. A reactor connected to the power factor correction capacitors exploded, as a result of temperature build-up caused by the continuous flow of fifth-order harmonic current. The accident received wide coverage by the media and all the parties concerned, including the Regulator, manufacturers, large companies and Energy suppliers, realized the importance of harmonic reduction measures. This is the only presently known example of harmonics-related injuries and it is at the origin of the strict harmonic emission limitation standards in Japan.
- United Parcel Service freight processing centre, Louisville, Kentucky airport. The total installed power is in the vicinity of 100MVA. About 10,000 variable speed drives are in operation. Several capacitor banks had to be replaced prematurely in 2007 as a result of harmonics-related overloads.
in about 20 days i will come back to illustrate other cases