A centralized reactive power compensation system designed for small distribution systems
This author no longer works for DNV GL.
Reactive power planning of power systems provides the strategy of reactive power compensation so that the real power loss can be reduced and the system voltage profile and power factor can be improved. The current industry practice is to locally install reactive power compensation system to maintain the local bus voltage and power factor, which we called decentralized method.
During the planning of optimal reactive power compensation, decentralized methods only provide optimal capacitor placement for a particular load situation. If the load situation changes, a new set of optimal capacitor placement will be given by the decentralized method. However, during actual operation, it is not practical to keep moving capacitor banks from one location to another according to the load situation. Hence, the capacity of the reactive power compensation system at a location is fixed normally once it has been installed.
Two key issues have been identified for decentralized reactive power compensation system. First, the nature of the loads connected to the buses is time varying throughout the day. It is very difficult to decide the optimal locations and sizing of reactive power compensation. Second, reactive power compensation system at some buses with low load are unable to provide their excess capacity to other buses with heavy load once they have been placed.
To address this issue, DNV GL proposed a centralized reactive power compensation system. The reactive power compensation system is centralized and can be connected with selected buses where they need reactive power compensation. Then the total capacity of the centralized system can be shared by the connected buses. Although we know the truth—that the reactive power cannot travel in a very long distance—the centralized system is still possible for a small low voltage distribution power systems.
A study has been done for a small distribution network in Singapore. The results show that: 1) the power loss can reduce 14.3% compared with the current industry practice; 2) the total needed reactive power compensation capacity can reduce 20-30% compared with the current industry practice. Furthermore, it is also very easy to expand the capacity of centralize reactive power compensation system for future load increase.