ADF Power Tuning

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Case Story: Gold Mining, Kalgoorlie

Australia

Kalgoorlie – The Big Pit

Industry: Mining
Local Partner: Toshiba International Corporation
Timeline: In operation since 2017

Background

A goldmine in Kalgoorlie had found a way of extracting more gold from the excavated ore. This required pumping water from another location, and a large variable speed drive was installed to control the pump.

Challenge

As is quite often the case in scarcely populated areas, the power grid here is very weak. In this case, adding a large variable speed drive would cause a large increase in harmonics. This was a concern as there is also another customer on the same transformer, and the mine operator had to comply with the very strict current distortion limits of the grid operator.

Further, due to the remoteness of this location, the end user had a preference for standardized equipment on site. This means that a standard 6-pulse rectifier type variable speed drive was selected. Therefore, harmonic distortion was also to be expected, unless a harmonic mitigation solution was installed.

Solution

Given the strict need for compliance to low current distortion limits, an active harmonic filter was the obvious choice. Passive AC line reactors would not be sufficient to meet the targets. Using other type of LC filters, such as matrix filters introduce side effects such as leading power factor at light loads. And an active front end (AFE) drive was considered nonstandard at this site and an increase risk for reliability. The AFE is in series with the mains while the active harmonic filter is in parallel with the drive. Should the filter be out of service for maintenance or inspection, the pump can continue operating.

Products used in this case:

Result

The active filter has achieved the required filtering. The drive and pump operate according to the specified requirements. All design goals were meet. THDi was reduced from 28% to 2,6%.

Current Harmonics without ADF

THDi Before

Current Harmonics with ADF

THDi After

Waveform diagrams show the THDi level before (28%) and after (2,6%) compensation with the ADF P300 activated.

 

The performance of the filter was a textbook case. With the variable speed drive running at nominal load, the harmonics in the line were clearly visible through the ADF P300 HMI. The VSD is the dominant load on the local grid. Then the ADF P300 was activated, and the harmonic distortion immediately decayed to virtually zero. The result was very clear with line currents returning to sinusoidal shape and voltage distortion disappearing. The end user’s expectations were easily met.

– Max Vechi, Project Manager

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