OPTIMISATION BASED REACTIVE POWER MANAGEMENT AT TRANSMISSION/DISTRIBUTION INTERFACE

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Abstract

The transition towards low carbon energy system requires increasing the volumes of renewable generation and low carbon technologies connected to distribution networks as well as encouraging the uptake of energy-efficient appliances. These new network participants and the corresponding expansion in distribution network assets required to meet the expected levels of demand/generation will change the traditional active and reactive power flows at the Transmission-Distribution grid interface. The changes in reactive power exchanges will place significant challenges on Transmission System Operator (TSO) to maintain voltages at the transmission networks within limits particularly during system minimum demand periods due to the injection of reactive power. For instance, National Grid, the Great Britain (GB) TSO has been facing the challenge of managing the reactive power injections through Grid Supply Points (GSPs).The frequency of voltage issues is expected to grow gradually due to the anticipated volumes of low carbon technologies and expansions in distribution networks. In this respect, adequate solutions should be in place to maintain voltages at the transmission networks within limits. However, the traditional methods adopted by TSO to manage reactive power by using VAr compensators such as shunt reactors may not be a cost-effective solution due to the volume and the frequency of network issues. The pace advancements of communications and the rolling of smart meters provide opportunity for TSO to manage reactive power injections by using the existing flexibility in demand to shift portion of their power consumption to the system minimum demand periods. Furthermore, controlling power factor of Distributed Generation (DG) can mitigate the reactive power issues. However, adequate planning framework is needed to assess the capability of demand response and power factor control to manage reactive power flows at the Transmission-Distribution grid interface. To do so, this thesis presents a multi-period AC Optimal Power flow (OPF) able to manage reactive power flows throughout the planning horizon by both the optimal scheduling of demand and the optimal control of DG power factor. To cater for uncertainty related to the potential flexibility in demand, multiple scenarios are created and incorporated in the OPF so that more robust conclusions can be drawn. To understand the effectiveness of demand response and DG power factor control solutions considering the design of distribution networks, the proposed optimisation-based planning approach have been investigated on both real rural Irish distribution network and urban distribution networks from the UK Generic Distribution System (GDS). The reactive power exchanges are assessed based on the European Demand Connection Code (ESTNO-E). The results show a significant reduction in the reactive power injections to the transmission system during the periods of minimum demand and the proposed schemes could be adopted as potential solutions for the management of reactive power injections at the transmission / distribution interface which could otherwise be very crucial from the investment perspective for the deployment of reactive power compensation devices at various interfaces between distribution and transmission networks to fulfil the future grid code requirements.

Keyword(s)

Distributed Generation; Optimal Demand Response; Optimal Power Factor Control; Optimal Power Flow; Reactive Power Management; Smart Grid

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