Hidden causes of the failure of the hottest high-v

  • Detail

Abstract: combined with the statistics of high-voltage circuit breaker's non opening fault and the electric fire continuous operation accident and large-scale long-time power failure caused by the high-voltage circuit breaker, this paper analyzes the reasons for the relay protection setting and principle misunderstanding hidden in the non opening fault. Aiming at the time/current/selectivity/sensitivity and other factors of protection mode/protection setting, the details of its faults are quantitatively analyzed, and the update points of relay protection setting principle are sorted out and summarized. Simple, economical and practical

1 high voltage circuit breaker failure and cause decomposition

the failure of high voltage circuit breaker failure affects the control and protection of electricity, especially the failure of electrical short-circuit protection, which brings great losses to electricity, and even causes fire and continuous operation accidents, resulting in large-scale and long-term power failure. The performance of short-circuit protection is difficult to verify in actual combat exercises, which is easy to cause paralysis and fluke thinking. Usually, few short circuits are considered safe, and once the short-circuit protection is lost, something serious will happen. According to the data, nearly 100 switchgears are burnt out in the fire and camp accidents in China every year. In 2004, the fire and camp accidents increased again [2]. In recent years, many technically advanced developed countries in the world have also experienced large-scale and long-term power outages and burning accidents. This is not an accidental phenomenon. The reason is worth pondering and studying carefully. The author believes that the reasons for the deeper misunderstanding of relay protection setting and principle are not all attributed to the manufacturing quality of high-voltage circuit breaker manufacturers

according to the statistics of the State Grid Corporation of China, the failure of 6~500kv high voltage circuit breaker to open accounted for 14.5% of the total failures from 1998 to 2002, ranking the second among all kinds of failures [1]. In 2004, the failure of 6~500kv high-voltage circuit breaker to open accounted for 15.2% of the total failures, ranking the third among all kinds of failures [2]. In 2006, the non opening and non closing faults of high-voltage circuit breakers above 12kV accounted for 14.5% of the total faults, ranking first among all kinds of faults. The 40.5kV high-voltage circuit breaker refused to open fault accounted for 18.2% of the total faults in 2004 and 29.6% of the total faults in 2005 [3]. It can be seen that the failure rate is not small

in the accident statistics, the power department is generally used to attribute the reason of the failure of refusing to open to the circuit breaker, and sometimes classify it as the failure of refusing to operate, including the failure of refusing to open and the failure of refusing to close. For short-circuit protection, it has the greatest impact on the refusal to open, and it should be counted separately. Whether it is the failure of the circuit breaker or the failure of the main protection or the backup protection of the relay device. Backup protection also includes low-voltage lockout failure, differential protection failure, distance protection failure, and whether there is a fire and camp accident, etc. The proportion of each is convenient to analyze the real reason. In high-voltage electric protection, high-voltage circuit breakers and relay protection devices are manufactured and installed separately, and finally combined and set by the power department to form a complete protection system. These two parts may cause the failure of refusing to open. From the current statistics, we can't see the proportion of the non separation fault caused by the relay protection device's refusal to operate and the fire continuous operation fault, so we can't find the real culprit of the rise of the high-voltage electric fire continuous operation accident. There may be other internal statistics. Through careful analysis, we should be able to find out the problem

the failure of the circuit breaker to open and close is a problem of the switch manufacturer, which can be judged by whether the relay protection signal relay sends an action signal. If an action signal is sent, the circuit breaker refuses to open; No action signal is sent, that is, the relay protection device is set to fail to protect and refuse to operate, resulting in the failure of the circuit breaker to perform breaking. The two are essentially different and cannot be confused. Relay protection device failure includes main protection failure and backup protection failure, which is a problem of relay protection device and power station setting, and has nothing to do with the circuit breaker manufacturer. Failure of main/backup protection and long protection time often lead to fire and camp accidents. The probability of fire and continuous operation accident caused by the circuit breaker refusing to open is very small, because the breaking time of the circuit breaker is less than 0.1s, which is generally 0.06s, and it is unlikely that the upper and lower circuit breakers fail and refuse to open at the same time. The action time of the remote backup protection of the third level circuit breaker should be 0.5~0.7s to prevent continuous fire. Therefore, the fire and camp accidents are generally caused by the relay protection device refusing to operate and the protection action time is too long, which should be caused by the device setting problem of the power station. This may not even occur to the power stations and departments that refuse to divide the faults. The problem is actually in their own relay protection system

the breaking performance of the circuit breaker should be guaranteed by the manufacturer's type test and factory test, and the test report should be issued; The secondary circuit power on verification shall be carried out during the installation, setting and commissioning of relay protection devices and various main/backup protection time current ampere second action characteristics set, and the verification data report shall be issued. Strictly speaking, it must be ensured that the main protection can act within 0.1s when the end is the minimum single-phase short-circuit current, and the backup protection should act within 0.3~0.5s when the same current is applied. The preferred value of arcing time of switchgear recommended by International Electrotechnical iec:2003 internal fault arc test standard is 1s/0.1s[4], that is, the action time of remote backup protection cannot exceed 1s, and it is best to control it within 0.7s. Otherwise, it is very easy to cause the accident of burning the switchgear and burning the camp! In fact, many power stations in China and the world, including some developed countries, cannot meet this requirement at present. This is the result of the misunderstanding of relay protection setting principle [5]

foreign data shows that the cost of switchgear will increase by 10% every time the arcing time of switchgear increases from 0.1s to 0.1s. When it is increased to 1s, the cost of the switchgear will be increased by 100%. If the electric short-circuit protection time is required by the current 4S, the cost of the switchgear will be unbearable and the user will not accept it. If the protection time is extended, the cost will be astronomical! It is impossible to achieve. Therefore, using long time delay as short-circuit main protection in relay protection principle is fundamentally a subjective misleading and naive assumption! The principle of short-circuit protection should minimize the action time, so that the burning loss of fault arc is small, and the recovery time of power supply is short, which is beneficial to the country, the people and the industry. The past short-circuit protection principle lacked the concept of system economy combined with actual manufacturing

since the low-voltage circuit breaker is manufactured and set as a whole with the relay protection device, the manufacturer has found a practical solution: setting a simple and practical three-stage protection to avoid the fire and continuous operation accident of the low-voltage system. However, the high-voltage circuit breaker and relay protection device are manufactured separately, which leads to the misunderstanding that the power department is too rigid in trusting the setting principle of relay protection. Its protection method is cumbersome, complex and impractical, and the setting value is broad and inaccurate, which leads to the high number of continuous fire accidents. At present, developed countries have not walked out of this strange circle, from the International Electrotechnical Standard IEC, British standard bs142, American Standard ansic37.112 and Chinese national standard gb/t14598 This can be illustrated by the fact that the simulation characteristic of the long time-delay turntable is also applied to the microcomputer controlled short-circuit protection. Such microcomputer protection can only be called crisis protection. Don't think that with microcomputer protection, everything will be fine and you can rest easy. Microcomputer control is not an omnipotent fairy. Its principle is also designed by people, and it still needs to be set by people, so that it can play its due protective role. The objective reality is that the cold fire and camp accidents and large-scale long-time power outages should be seriously and resolutely put an end to it. The most fundamental change is the change of concept. Foreign technology should be analyzed, digested and discarded

2 hidden factor of high-voltage circuit breaker failure

when the relay protection device and setting cannot reach the minimum single-phase short-circuit current at the end, the main protection <0.1s/backup protection 0.3~0.5s/remote backup protection 0.5~0.7s action characteristics are required because the relay protection setting principle has been using long time delay as short-circuit main protection and backup protection, resulting in too long time; The instantaneous protection and short-time delay protection are set according to the maximum short-circuit current, resulting in a protection dead zone equal to no instantaneous/short-time delay protection and backup protection. This results in the loss of short-circuit protection from both time and current parameters [5]. Unfortunately, at present, universities related to this are still teaching these contents, which is misleading to children. Microcomputer protection devices at home and abroad also do not have this clear protection function. It is not surprising that a short circuit causes a fire and camp accident and a large area of long-term power failure

for example [6 October this year]: on March 21, 2008, the power failure accident of 220kV Caoqiao substation of Beijing Electric Power Co., Ltd. led to the complete shutdown of the station and its three subordinate 110kV substations, and the switching of power supply for the other two 220kV substations and four 110kV substations. Involving 16 switching stations and 2 important users, large-scale power outage, loss of load 78mw. The accident was caused by the grounding flashover of the circuit breaker on the right power side running in parallel. The distance protection and zero sequence protection of the full microcomputer system protection in the upper a station and N station were used to remove the fault. The action time was 0.546s + Post reclosing acceleration protection 0.0. With the development of sensor technology 61S, the reclosing interval was 1.117s. That is, the switch burns for 0.607s, causing the switch to burn seriously and can only be replaced. Why is the first action time of distance protection and zero sequence protection 0.546s (longer than 0.3s of short delay backup protection)? 0.061s for post acceleration protection? What's the significance of post acceleration after the main protection lasts so long? Whether the two sets of protection operate correctly? It is reasonable that the time of two actions should be instantaneous 0.06s, and the switch burning time should be 0.12s. Compared with 0.607s, the burning loss can be reduced by 4/5! Maybe it can be used with a little repair, and there is no need to replace it. This is also beneficial for users to reduce losses and restore power supply. Although the cause of the accident is attributed to the improper manufacture and installation of the manufacturer, the degree of burning loss should be related to the setting principle of the power station protection system. Imagine which manufacturer's switch design can withstand an internal fault arc of 0.607s without being burned? Is there no problem with the setting principle of modern microcomputer protection in recent years? It is worth pondering

the function of relay protection setting principle on long time delay/short time delay/instantaneous protection, that is, who cares about short-circuit protection and overload protection, who should be the main protection and backup protection, the basis for the value of protection sensitivity is not clear, and there is no way to solve the problem of protection selectivity of circuit breakers at the beginning and end of the same line, which leads to the distortion of protection setting principle

long time delay protection takes a long time, generally> 1s, which is not suitable for short-circuit protection at all. It can only be used for overload protection to avoid the starting time of the motor. The current setting is 1 times the rated current in, and the action multiple is 1.2~6 times. It has the function of backup protection, but it has no effect on the quick break of short-circuit protection

short time delay protection the function of 0.2/0.4/0.6s delay is to ensure the selectivity of the upper and lower levels. It can only be used for short-circuit backup protection, not as the main protection. It should be set according to the rated current, and failure to set according to the short-circuit current will cause the protection dead zone. The line is generally set at 3-4 times of in to avoid peak inrush current (generally 2-3 times of in). The upper and lower current setting values should be staggered by at least 1.1 times to have selectivity, plus a short time delay to cooperate with the backup selectivity

the instantaneous protection should be the main short-circuit protection only when its quick break time is less than 0.1s, and it should also be set according to the rated current to eliminate the protection dead zone. The line is generally set at 5 times of in to avoid peak inrush. The upper and lower current setting values shall be staggered by at least 1.25 times to ensure the selectivity of the upper and lower levels and the head and tail circuit breakers of the same line


Copyright © 2011 JIN SHI