Increasing DG Capacity of Existing Networks through Reactive Power Control and Curtailment

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Summary, in English

Renewable energy sources (RES), especially wind turbines, have become more important

during the last years. An increasing number of distributed generation (DG) units are

connected to weak medium voltage distribution networks in rural areas where they have a large

influence on the voltage and the line losses. Voltage rise is in this case often a limiting factor for

the maximum amount of DG capacity. Already current wind turbines with a capacity of 2 MW

can often not easily be connected to existing 10 kV feeders.

To increase the DG capacity of existing networks without reinforcement DG units can be

controlled. This paper proposes abandoning unity power factor used today and letting the converters

used as network interface of many new wind turbine generators absorb reactive power

to reduce the voltage level. Since reactive power has great influence on losses in the network

the use of reactive power is limited. Line losses due to the transfer of reactive power are taken

into account in this study. Furthermore the use of curtailment is analysed.

Simulations of voltage change and line losses when using reactive power control by the connected

wind turbines and curtailment in a simple test system are presented. Without reinforcement

of the network it was possible to increase the DG capacity from 2;7MW to more than

4MW in the test network without violating voltage limits. Line losses increase but to a reasonable

extent and lost energy due to curtailment is insignificant.

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