Key Benefits
Large Variable Speed Drives suffer from one issue. Being non-linear loads – that is, as their currents are not proportional to voltages, they tend to distort the voltages and currents in the supply lines and can affect nearby electronic equipment. Further, these disturbances can also affect an adjacent facility’s power supply through no fault of theirs! Hence, electricity authorities impose very strict regulations on how much distortion is permitted when someone uses VSDs in their plants.
As the magnitude of these distortions – called Harmonics, depend on the strength of the supply network, careful analysis is required to ensure that after installation of VSDs the impact of these distortions will be within the permissible limits. If for some reason such as a weak network, the harmonics exceed the permissible levels, then additional measures are necessary to mitigate the issue.
One such measure is the use of Active Harmonic Filter connected in parallel to VSD.
Overview
One of Toshiba’s mining customers (name withheld for privacy reasons) needed to upgrade a pumping station in a remote location in Western Australia. Electricity supply to this mine is fed via a main overhead line with several branches, one of which feeds the mine and goes further to feed another user several kilometres away.
As Variable Speed Drives (VSDs) save a considerable amount of energy for pumping applications, the customer decided to use a large 450 kW Toshiba VSD for running a pump, however quickly realised that using a VSD would lead to supply network distortion issues as the relevant supply authority had imposed strict harmonic limits covering all harmonics up to the 40th level.
After a discussion with Toshiba, the customer decided to build a new substation for the 450 kW VSD where the VSD was the primary load and used > 90% of the capacity. This ensured that other electronic equipment was not on the same network in the immediate vicinity.
However, analysing the site conditions, it was quickly realised that this isolation was not sufficient. When Toshiba engineers were given all the site-related supply data, it become clear that without the additional measures, the harmonics generated by 450 kW network would exceed supply authority limits. Keeping the focus on the imposed limits, the engineers came up with a solution to use an Active Harmonic Filter adjacent to the VSD for compensating the generated harmonics. This compensation ensured that the generated harmonics were absorbed by the Active Harmonic Filter locally and thus prevented them from entering the supply network. Once, all the simulations were confirmed, the engineers agreed on the filter parameters to select the proper Active Harmonic Filter.
After supplying and installing the VSD and the filter at the site, the commissioning started. Fine-tuning the parameters of both the equipment along with measurement of the harmonic performance, final settings were completed to ensure that the supply authority limits were complied with.
It was the application of the Active Harmonic Filter that allowed the customer to use a 450 kW Variable Speed Drive for his pumping application while saving a significant amount of energy and also meeting all their obligations under their power supply agreements.
The plant is currently running without any issues.
