Application of Four Common Relay Protection Technologies in HVDC Transmission Lines

Relay protection technology is very important for the safe and stable operation of HVDC transmission lines. As the current commonly used technical means have certain deficiencies, we should increase research efforts and develop a relay protection scheme that is more suitable for my country's DC transmission requirements , Thereby promoting the long-term development of the power system. Here are four common relay protection technologies. Traveling wave protection In the process of HVDC transmission, the main protection measure is traveling wave protection. The protection principle is as follows: When the line fails, the fault point will propagate the anti-traveling wave to both ends of the line, and the traveling wave protection can pass the reading Identify and judge the situation of the fault-related area. At this stage, when using traveling waves to protect HVDC transmission lines, two more schemes are adopted. One is the ABB scheme. The fault detection of this scheme is carried out by pole waves, and at the same time, the fault pole is determined by ground model waves; the other is Siemens In the scheme, the starting criterion of the scheme is voltage differentiation, but the fault determination method is to observe the sudden change of the reverse traveling wave within 10MS. The above description shows that the two schemes adopt different detection methods, and there are certain differences in effect. Because the differential link exists in the Siemens scheme, the detection speed is relatively slower than the ABB scheme, but it is precisely because of this link. Makes the Siemens solution has better anti-interference ability. However, these two schemes have certain shortcomings, such as insufficient resistance to excessive resistance, high sampling requirements, and lack of good anti-interference ability. Since many problems exist in the traveling wave protection technology, a traveling wave directional protection scheme based on wavelet changes is proposed; another example is to optimize the sensitivity and study the principle of polarity comparison equation.

Differential undervoltage protection In DC transmission lines, differential undervoltage protection belongs to the main protection. At the same time, when using traveling wave protection, it also acts as a backup protection. The main way to realize protection is to detect the voltage differential value and voltage amplitude level. From the protection principle, the differential undervoltage protection is the same as the ABB scheme and the Siemens scheme. Both are the determination of the polar voltage differential and amplitude, and the voltage differential setting is consistent with the traveling wave protection. The difference is that the original 6ms is extended. It becomes 20ms. As a result, when the traveling wave protection exits or there is no sufficient rising edge width, the differential undervoltage protection can fully exert its backup protection function. Compared with traveling wave protection, differential undervoltage protection has a slower operating speed, and its accuracy is significantly improved. However, it is still not ideal in terms of resistance to excessive resistance and is very limited.

Low-voltage protection For the first two protection technologies, low-voltage protection is a backup protection method, and the relay protection function of the fault pole is determined by voltage amplitude detection. According to its design, after a high-impedance fault occurs, when the traveling wave protection and differential under-voltage protection fail to act, the low-voltage protection will cut it off. However, from the actual application situation, the low-voltage protection mirror is equipped in the extreme In a small number of HVDC transmission lines, there are two types of low-voltage protection, one is line low-voltage protection, and the other is pole-controlled low-voltage protection. Compared with the latter, the former has a higher protection rating, and the former acts After that, the line restart procedure will start, and after the latter action, the fault will be blocked. Although the low-voltage protection has a relatively simple principle, it also has many problems, such as poor selectivity and inaccurate discrimination of high resistance faults. Pilot current differential protection In HVDC transmission lines, pilot current differential protection is a backup protection scheme. The principle is to promote insulation selectivity through double-ended electrical quantities. According to the design, high-resistance faults can be cut off. Judging from the existing longitudinal current differential protection, because the capacitive current problem has not been fully considered, the differential criterion only uses the sum of the two ends of the power, which leads to a relatively long waiting time and relatively slow action speed. For example, the Siemens scheme of longitudinal current differential protection has large current fluctuations at the beginning of the fault, and the differential protection will have a delay of 600ms. At the same time, the delay of the differential criterion itself is 500ms, that is, the differential The action will not appear until at least 1100ms after the fault occurs, and during this period, accidents where the fault is directly blocked may occur many times, causing the equipment to fail to start, and the backup actions of the longitudinal current differential protection can not be fully performed. . In order to enhance the effect of this protection technology, improvements can be made from multiple aspects, including compensation capacitor currents to promote the sensitivity of differential protection; upgrading high-frequency channels to fiber channels to speed up the protection action.