Case Studies

The penetration of wind energy has grown significantly in the past few years, resulting in the construction of large-scale onshore and offshore wind farms. The technical development of large wind turbine generators facilitates the connection of the large wind farm into the transmission network. Power system analysis study to design the grid connection and verify compliance with regulatory codes and international standards is required during the design stage.

In this paper a DFIG wind turbine is modelled using a power systems analysis software package (ERACS) to examine the voltage at the terminal of the wind turbine as a result of voltage dip on the grid. The fault ride through study allows verification that the WTG provides the reactive power during the fault and the voltage at the PCC is quickly restored to its initial value after the fault is cleared.

Another scenario discussed is determining the need for reactive power compensation. A wind farm with 24 2.3MW wind turbines was modelled. A reactive and power factor capacity study was conducted based on the model and the British grid code [1]. The results show that an 8.35MVAr of inductive compensation and a 10.9MVAr of capacitive compensation at PCC are required. If the compensation is applied at the 33kV bus, a 0.52MVAr of inductive compensation and a 0.68MVAr of capacitive compensation are required.

A harmonic study based on the Energy Networks Association Recommendation G5/4-1 was also conducted. Typical current harmonic injection data is used in this paper. The THD and harmonics with order 10 exceed G5/4-1 planning levels due to the high charging capacitance on underground cables used in wind farm collector systems. The harmonic study in this paper shows harmonic compliance is dependent on not only on the number of turbines operating and the power level, but also the configuration of the distribution circuits that are selected at any given time.

System studies to examine the impact and limiting levels of penetration for wind turbine generation. Many aspects of system performance were examined; wind energy integration, modelling of mixed gas turbine and diesel generation; incorporation of power factor correction capacitors. Technical support provided in establishing operating policies.

System studies conducted to establish safe and reliable site operations for the installation of 3 generating stations with regional electricity connection at 11kV.

Design of an islanding scheme for a 650km 220kV transmission line connecting two centres of generation. Factors considered included the high impedance of the line, relatively low inertia of one group of generators, limits on power transfer, and the speed of response necessary to meet the requirements of the regional electricity company and the mining company.

Provision of suitable protection settings for the 132/90kV and 90/33kV transformers, 22kV reactors and 90kV cable circuit to enable safe and reliable operation of the system. Back-up overcurrent and earth fault settings for transformers and cable, transformer differential protection, restricted earth fault relay settings for reactor circuits and neutral voltage displacement protection on the 22kV transformer tertiary side.

ERA conducted electrical power system analysis, including the provision of protection settings for all the protective devices from the 11kV Distribution Network Operator (DNO) intake point down to the main 415V distribution switchboards.

ERA conducted electrical power system analysis, including the provision of protection settings for all the protective devices from the 11kV Distribution Network Operator (DNO) intake point down to the main 415V distribution switchboards.

ERA provided protection settings for all overcurrent devices from the BT 11kV point down to the incomer to 415V distribution switchboards.