Probabilistic Reactive Power Capability Charts at DSO/TSO Interface

Hosting an increasing share of distributed generation and flexible consumers, distribution systems are being more often considered as providers of ancillary services among which are reactive power support and voltage control. For the purpose of reliable and efficient planning and operation of a transmission system, information about reactive power capabilities of connected distribution systems would be beneficial. These capabilities are subject to uncertainties especially with a presence of intermittent distributed generation and stochastic loads. To capture these uncertainties, this paper introduces probabilistic capability charts using the concept of probabilistic curves. These curves analytically represent reactive power support limits of distribution systems as a family of random variables with their associated probabilistic density functions. As such, they carry more information about states of the system than deterministic curves. The proposed capability charts can be easily applied in probabilistic studies of the overlaying transmission system. By providing analytical expressions of stochastic power injections of connected distribution systems, the use of these charts can speed up time and memory demanding probabilistic calculations of transmission systems planning and operation studies. Not containing sensitive system information, the charts can be used to exchange data between distribution and transmission system operators.