Amount Of Transmission Line Transient High-speed Protection

Transmission line corridor along the geographical environment is complex, and Transmission line often subjected to bad weather, so the transmission line fault account for a significant proportion in the power system faults. At present, the traditional power frequency protection were overwhelmingly dominant in high voltage and EHV transmission line protection, It discriminated if the faults occurred by steady-state vector of fault. Before the fault was eliminated, the fault information always existed, so it had stable action performance. But it was relational that power frequency message and high-frequency message caused by faults. To the traditional protection, it can attain power frequency component through time delay process. To the EHV transmission line, it has little resistance, and larger reactance, making it is that decay time is long and the electromagnetic transient process is long. With the constant development of power system, the stable operation require higher to the movement speed of the relay protection, But the traditional protection of that is close to the limit.It will produce power frequency and transient high-frequency fault component when the EHV transmission line fault, which contains more fault information than power frequency fault component. The ultra high-speed transient protection can implement by detecting transient high-frequency fault component. This article describes the transient protection principles, and the applicable was analyses and improved based on the digital test, as follows:Travelling wave directional protection can be divided into the polarity directional protection and the amplitude directional protection according to the information of wave-head. The polarity directional protection utilizes the Catastrophe direction of the wave-head, and the amplitude directional protection which is implement by the ratio utilizes the Catastrophe strength of the wave-head. So the directional protection has a strong adaptability to the transition resistance and the initial angle of fault. As long as the signal can be detected and identified as a fault travelling wave, it can determine the fault direction correctly.It was analyzed that the adaptability of differential protection of the traveling wave, to improve its sensitivity of internal fault and reliability of external fault, it was proposed that the differential protection of the traveling wave with the braking current. It can exactly action in the condition of the large transition resistance and small faults initial angle.The difficulties of Distance protection based on travelling wave were summarized. The method was proposed that be use to identify the property of the second wave head, considering the stopband characteristic of the wave trapper. This method which improved the distance protection based on travelling wave could adapt to three kinds of bus and all fault type. The method could also be used to identify the property of the second wave head for single-ended traveling wave fault location.The basic principle of boundary protection was introduced and two forms of the criterion which were the ratio of high-frequency energy and low-frequency and the rise time of the head wave were given. The voltage transfer function of the wave trapper, the amplitude-frequency characteristic of the function was given using sweep signal in the condition of the closed loop. The amplitude-frequency characteristic provided the theoretical basis of the choice for the high-frequency energy band and the low-frequency. Through large volumes of digital test, the adaptability whose boundary of two different criterion protection was analyzed including the fault location, the transition resistance, the faults initial angle and the fault types. The result was the form of the rise time of the head wave has the better adaptability than the form of the ratio in the condition of the small faults initial angle.The basic composition of the auxiliary components was introduced in the AC transmission line transient protection. Through large volumes of digital test, the adaptability was analyzed including the starting element, the phase selector, the recognition element for the weak fault initial angle, the recognition element for the interference of lightning and the recognition element for the switch-on fault. The new transient phase selector was proposed, whose criterion was simpler. The phase selector can correctly identify the fault type for the most faults. The phase selector can still provide the reliable basis for the composite recloser at the specific or weak fault initial angle.