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Electrical Power Systems Quality, Second Edition phần 9

Điều này tránh các vấn đề kết nối và cung cấp một số hỗ trợ để điều chỉnh điện áp bằng cách giảm tải. Kiểm soát các nguồn phân phối phải được phối hợp với quản lý dòng hiện có và LTCs trạm biến áp một cách cẩn thận. Ngược lại quyền lực dòng chảy đôi khi có thể đánh lừa điều chỉnh điện áp vào chuyển động điều chỉnh điện áp sai | Distributed Generation and Power Quality 422 Chapter Nine Current of transformer rating Figure 9.32 Adjustable reverse-power characteristic. capability to electromechanical network relays. In the past these supplemental relays had minimum time delays of 1 s or more since their mission was to wait for the elevator to descend. However not all utilities endorse this low-current time-delay technique. Some feel that any time delay in opening the network protectors degrades the high service quality that the network system is intended to provide. The load-generation control and DG tripping schemes mentioned above are intended to ensure that the network protectors are never opened by exported power. As long as the schemes work properly the network protectors are never exposed to the out-of-phase voltage conditions that may exceed the switch capability. However because of the potentially catastrophic consequences of causing a network protector failure it is prudent to provide a backup. An interlocking scheme that trips the DG instantaneously when a certain number of network protectors have opened ensures that the network protectors will not be exposed to out-of-phase voltages for more than a few cycles. The decision as to how many protectors must open before the DG is tripped one two or all is a tradeoff between security of the protectors and nuisance tripping of the DG. Note that this scheme does not relieve the DG installer from the responsibility of providing stuck-breaker backup protection for the DG s switching device. An even more secure approach to avoiding overstressing the network protectors is to replace existing protectors with new designs that are capable of interrupting fault currents from sources with higher X R Downloaded from Digital Engineering Library @ McGraw-Hill www.digitalengineeringlibrary.com Copyright 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Distributed Generation and Power