They wished to reduce the harmonic load on their internal 11/0.4kV distribution transformers. There were three transformers where the harmonic load was high, so GES provided three bespoke manufactured Active Harmonic Filter units (AHFs) to tackle the problem. These were installed beside each of the three LV Switchboards, which were fed from the transformers.
With the AHFs switched off the THDi figures were in the order of 10-50% depending on the transformer and amount of equipment running. When the AHFs were switched on the THDi on the transformer side was reduced to approximately 5%. It should be noted that the load continues to inject harmonic current into the distribution system. However, since the harmonic current is now cancelled by the AHF, it is not seen by the transformer.