Hitachi ABB Power Grids was contracted to provide engineering services for Nyrstar, which generates the energy for its El Toqui zincgold mine (formally owned by Breakwater Resources Ltd) in southern Chile. The company wanted to create a power system concept design that would solve frequency and power stability issues in its combined wind/diesel/hydro power system.
The primary focus was on maximizing energy from the installed wind farm capacity while maintaining system stability, as well as adding a planned hydro plant extension to the existing power system.
The existing system was not connected to the main distribution network. Power was provided by four diesel generators (5.6 megawatts (MW) in total), six small wind turbines (1.5 MW in total), and two hydropower generators (2.3 MW in total), plus a planned additional hydro generator (1.9 MW).
Operationally, there is no automated dispatch control; station operators control the system. The goal of the concept design was to maximize energy production from the wind farm and the planned hydro plant, to overcome the stability issues and to meet performance requirements. Nyrstar rejected full automation of the system but agreed some level of automation was necessary.
In 2010, a wind farm with six wind turbine generators was commissioned near the mine which introduced stability issues into the system, caused by power output fluctuations. Cyclical variance of up to 800 kilowatts (kW) equaled 50 percent of the system load during low demand periods. The fluctuations were causing large frequency variations, and power dispatch issues due to the generator over- and under-loading. The diesel generators and hydropower turbine generators could not cope with the rapid changes in power output.
To avoid stability issues wind power was limited to 1.3 MW, and wind turbines had to be switched offline occasionally, resulting in a large amount of excess energy not being utilized, which led to increased fuel consumption. To improve power system performance and reliability, ABB considered various control systems/methodologies to determine the best integration concept.
Without an additional hydro plant, a 1 megavolt ampere (MVA) PowerStore grid stabilizing system together with a PowerStore controller was the proposed solution, to smooth wind power fluctuations causing stability issues. It was estimated a PowerStore system would increase the energy yield from the wind farm by about 7 percent.
With an additional hydro plant, the microgrid controller (MGC 600) was needed to solve fluctuation issues by managing the control and dispatch of the wind/diesel/hydropower system. The MGC 600 combined with the PowerStore enables the system to operate without any diesel generators online. If diesel power is required, the MGC 600 minimizes the input to ensure the renewable contribution is maximized, while maintaining system stability. Estimates found the energy yield from the wind farm and additional hydro plant could be increased by about 29 percent with a PowerStore and an MGC 600.