General Structure of Electrical Protection for Power Transmission Lines-ساختار حفاظت الکتريکي خطوط انتقال نيرو

Distance protection of transmission lines is a reliable and selective form of protection for lines where the line terminals are relatively far apart. The most accurate form of comparison for relay quantities is to compare the current entering a circuit with the current leaving that circuit. For many transmission circuits, because of the line length, it is costly to compare the currents at both line terminals since this requires communications circuits suitable for protection applications that are at least as long as the transmission line. An alternative method compares the voltage and the current at each line terminal. Their ratio is the apparent impedance seen at the relay location, looking into the line, and therefore measures the distance to a fault along the line. This may not be as accurate as directly comparing the currents entering the circuit, since both the voltage and current undergo violent changes during a fault, but the method has advantages that outweigh the disadvantages.

عواملي مانند بازار غيرقانوني برق، عوامل اقتصادي، رعايت حريم ها و الزامات زيست‌محيطي، شرکت‌هاي برق را مجبور کرده  است تا خطوط انتقال نيرو را با در نظر گرفتن اين محدوديت‌ها بهره برداري و نگهداري نمايند.

هر خطا، اگر به سرعت شناسايي و برطرف نشود، به يک اختلال گسترده در شبکه تبديل مي‌شود و باعث قطعي گسترده در شبکه برق مي‌گردد. سيستم هاي حفاظتي انتقال براي شناسايي محل خطاها و جداسازي تنها بخشي که دچار خطا شده است، طراحي شده­ اند. چالش اصلي براي سيستم حفاظت خطوط انتقال نيرو، شناسايي و قطع مطمئن خطاهايي است که امنيت شبکه را به خطر مي اندازند.