CRCMining’s Power Management program is based at the School of Electrical Engineering at the University of Newcastle and is working to enable autonomous operation of equipment supplied from stiff, weak or islanded sources including conventional, renewable or hybrid generation.
Current work is focused on three main areas:
- Developing a range of predictive condition monitoring tools (DC and AC Motor Duty Meters and novel Power Quality measuring tools).
- Identifying power supply and reticulation weakness to understand their effect on production and equipment, then providing voltage support and harmonic correction solutions.
- Extending the interoperability capability of the CRCMining Power Management group by using mine precinct data to determine the key elements of mixed energy generation, with a view to optimising operational cost, power delivery capacity and power quality. Mine planners will be able to draw metrics for the development of power systems, and researchers can focus on issues effecting operational capabilities to provide new and innovative solutions to optimise energy delivery and cost.
The second area aims to understand mine precinct power requirements driven by diurnal, shift, week/weekend, seasonal, and product impacts and matching this varied demand with grid supply options. This includes an assessment of interoperability between conventional, renewable and hybrid supply solutions.
The project has recently seen advances in this understanding through the collection of voltage and current information in an underground offshore coal mine at the substation (power centre) level into which the mine’s continuous miners are connected.
The data collection device, designed and built in Australia by the University of Newcastle research team, collected information over the 100th harmonic in an attempt to capture transients associated with switched power factor correction capacitors and harmonics associated with variable speed AC drive units not fitted with active front end filters.
Modelling of a target mine in CRCMining’s “Statcom” based voltage stabilisation project had indicated significant voltage transients would be found as a side effect of using switched capacitors. Field measurements have now confirmed the modelled transient effects.
However, the level of harmonic distortion in both the current and voltage signals was substantially higher than had been anticipated, and is now the subject of further studies.
A quick analysis of the collected data indicates very high levels of 5th, 7th and 11th harmonics which can considerably decrease the life of power system components such as transformers, and connected motors due to heating.
Contributing components to these harmonics may include variable speed AC drives as well as core saturation of transformers in the system, which was previously not considered in the mix of potential issues.
Over voltage transients of 1.6PU (600V at 1kV nominal) were measured, associated with capacitor switching, and under voltage issues associated with line impedances have been verified, validating the mine model developed by the University for the “Statcom” project.
An interesting question raised by the results is whether a “Stiff Supply” would have any effect on the data. While heavy dynamic loading of weak supplies will cause voltage fluctuations for equipment, the observed harmonic distortion could be generally unaffected by the stiffness of the connecting supply considering the line impedances between miners and their grid interconnect.
Electrical engineers in mining have welcomed the results which they believe are very timely given the industry’s rate of adoption of variable speed AC drives.
It is believed increased nuisance tripping of conveyor belt drives and earth leakage detection failures are possible outcomes of not fully understanding the dynamics of the underground mining power distribution system as well the obvious maintenance and life cycle issues of equipment.
CRCMining conducts projects within a number of key research, development and demonstration programs with its members. The programs currently span the areas of Automation, Power & Equipment Management, Rock Fragmentation & Handling; and Coal Technology & Fugitive Emissions.
CRCMining members come from mining end-users (Anglo American, AngloGold Ashanti, Barrick Gold Corporation, BHP Billiton, Newcrest Mining, Newmont Mining, Peabody Energy and Xstrata Coal), original equipment manufacturers and service providers (Caterpillar, CSC, Herrenknecht, Joy Global, and Sandvik) and from the research providers at the Universities of Newcastle, Queensland, Western Australia and Curtin University.