Wind generating facilities often require significant reactive power support to maintain voltage and power factor within operating limits prescribed by the transmission grid entity. Many installations include multiple stages of switched capacitor and reactor banks for this purpose. Coordinated control of these capacitor and reactor banks, which are often connected to the point of interconnection via multiple step-up transformers, requires a centralized control system. This paper discusses a reactive power control system that utilizes a central automation controller to regulate both power factor and voltage at the point of utility interconnection. This controller includes the capabilities of a complete communications processor to exchange voltage, power flow, and status information along with control commands to microprocessorbased relays throughout the system. It also includes a powerful IEC 61131-3-compliant soft programmable logic controller (PLC) logic engine to execute the control algorithms. The system is easily adaptable and scalable to nearly any configuration.The challenge when controlling both power factor and voltage is to prevent hunting due to conflicts between the two control requirements. An adaptive algorithm is utilized to deal with this challenge. The controller also includes a sophisticated sequencing algorithm to ensure that both reactors and capacitors are not in service at the same time, to optimize power factor through multiple step-up transformers to reduce losses, and to even out switching operations between reactive banks.
For completely islanded industrial facilities, a stable and robust power system is absolutely essential. Such facilities are not able to rely on an interconnection to a utility grid to provide stability or act as a safety net in the event of large, on-site generation disturbances. Knowing the ramifications of operating an islanded facility, Saudi Aramco has taken great care to help design a complete power management system for its new Gas Oil Separation Plant (GOSP) in Saudi Arabia. This power management system performs automatic, intelligent generation and voltage control to keep the on-site generation operating within its ideal range under normal conditions and within range in abnormal conditions, where the plant may be separated into individual islands. In addition to the voltage and generation control, which is used to keep the system running optimally for day-to-day operations, a high-speed load-shedding system provides dynamic, intelligent, protection-speed corrective action, based on user-defined load priority tables, for any major system contingency that could occur. Together, these systems provide a complete solution for power system management.
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