tailieunhanh - Electrical Power Systems Quality, Second Edition phần 7

hải đảo. Vì vậy, một số phương tiện của chuyến đi chuyển giao trực tiếp là cần thiết để đảm bảo rằng máy phát điện ngắt kết nối từ hệ thống khi một số bộ phận ngắt tiện ích hoạt động. Một kết nối bình thường của DG là sử dụng quyền lực và kiểm soát hệ số công suất. Điều này giảm thiểu nguy cơ islanding. | Long-Duration Voltage Variations 316 Chapter Seven island. Therefore some means of direct transfer trip is generally required to ensure that the generator disconnects from the system when certain utility breakers operate. A more normal connection of DG is to use power and power factor control. This minimizes the risk of islanding. Although the DG no longer attempts to regulate the voltage it is still useful for voltage regulation purposes during constrained loading conditions by displacing some active and reactive power. Alternatively customer-owned DG may be exploited simply by operating off-grid and supporting part or all of the customer s load off-line. This avoids interconnection issues and provides some assistance to voltage regulation by reducing the load. The controls of distributed sources must be carefully coordinated with existing line regulators and substation LTCs. Reverse power flow can sometimes fool voltage regulators into moving the tap changer in the wrong direction. Also it is possible for the generator to cause regulators to change taps constantly causing early failure of the tap-changing mechanism. Fortunately some regulator manufacturers have anticipated these problems and now provide sophisticated microcomputer-based regulator controls that are able to compensate. To exploit dispersed sources for voltage regulation one is limited in options to the types of devices with steady controllable outputs such as reciprocating engines combustion turbines fuel cells and battery storage. Randomly varying sources such as wind turbines and photo-voltaics are unsatisfactory for this role and often must be placed on a relatively stiff part of the system or have special regulation to avoid voltage regulation difficulties. DG used for voltage regulation must also be large enough to accomplish the task. Not all technologies are suitable for regulating voltage. They must be capable of producing a controlled amount of reactive power. Manufacturers of devices .