Assessment of the operating conditions of coordinated Q-V controller within secondary voltage control system

Abstract

The paper, discusses the possibility to use coordinated Q-V controller (CQVC) to perform secondary voltage control at the power plant level. The CQVC performs the coordination of the synchronous generators' (SG) reactive power outputs in order to maintain the same total reactive power delivered by the steam power plant (SPP), while at the same time maintaining a constant voltage with programmed reactive droop characteristic at the SPP HV busbar. This busbar is the natural pilot node for secondary voltage control at HV level as the node with maximum power production and maximum power consumption. In addition to voltage control, the CQVC maintains the uniform allocation of reactive power reserves at all SGs in the power plant. This is accomplished by setting the reactive power of each SG at given operating point in accordance to the available reactive power of the same SG at that point. Different limitations imposed by unit's and plant equipment are superimposed on original SG operating chart (provided by the manufacturer) in order to establish realistic limits of SG operation at given operating point. The CQVC facilitates: i) practical implementation of secondary voltage control in power system, as it is capable of ensuring delivery of reactive power as requested by regional/voltage control while maintaining voltage at system pilot node, ii) the full deployment of available reactive power of SGs which in turn contributes to system stability, iii) assessment of the reactive power impact/contribution of each generator in providing voltage control as ancillary service. Furthermore, it is also possible to use CQVC to pricing reactive power production cost at each SG involved and to design reactive power bidding structure for transmission network devices by using recorded data. Practical exploitation experience acquired during CQVC continuous operation for over two years enabled implementation of the optimal setting of reference voltage and droop on daily, monthly and seasonal basis. Finally, the paper suggests and elaborates on studies related to application of several coordinated Q-V controllers in power system to facilitate secondary voltage control. It is shown that the CQVC can be used to maintain desired voltage at assigned pilot node in the power system with predefined reactive droop characteristic, and such maintain the required voltage profile across the transmission network based on commands received from upper hierarchical control level.

Keywords

• coordinated reactive power - voltage control
• secondary voltage control
• reactive power
• reactive power reserves