[b]1. Decomposition of High Voltage Circuit Breaker Failure to Open and Causes[/b] The failure of high voltage circuit breakers to open affects the control and protection of the power grid. In particular, the failure of short circuit protection of the power grid causes great losses to the power grid. In severe cases, it can even cause a fire that spreads to the entire grid, resulting in a large-scale and long-term power outage. It is difficult to verify the performance of short circuit protection in actual combat exercises. It is easy to become complacent and take chances. People often think that there is nothing to worry about when there are few short circuits. Once a short circuit fails, a major accident will occur. Data shows that nearly 100 switch cabinets are burned down in the national power grid every year due to fire. In 2004, the number of fire accidents increased again[2]. In recent years, many developed countries in the world, which are supposed to be technologically advanced, have also experienced large-scale and long-term power outages and fire accidents. This is not an accidental phenomenon. The reasons are worth pondering and investigating. The author believes that there are deeper reasons for the misconceptions in relay protection settings and principles. It is not simply due to the manufacturing quality of high voltage circuit breaker manufacturers. According to statistics from the State Grid Corporation of China, from 1998 to 2002, the failure of 6-500kV high-voltage circuit breakers to open accounted for 14.5% of the total faults, ranking second among all types of faults [1]. In 2004, the failure of 6-500kV high-voltage circuit breakers to open accounted for 15.2% of the total faults, ranking third among all types of faults [2]. In 2006, the failure of 12kV and above high-voltage circuit breakers to open or close accounted for 14.5% of the total faults, ranking first among all types of faults. The failure of 40.5kV high-voltage circuit breakers to open accounted for 18.2% of the total faults in 2004 and 29.6% in 2005 [3]. It can be seen that its failure rate is not small! In accident statistics, the power sector generally attributes the failure to open to the circuit breaker, and sometimes classifies it as failure to operate, including failure to open and failure to close. For short-circuit protection, failure to trip has the greatest impact. Failures to trip and failure to close should be statistically analyzed separately. Is the failure due to a circuit breaker fault, or is it caused by the main protection or backup protection failing to operate? Backup protection also includes failures due to low-voltage blocking, differential protection, and distance protection, as well as the presence of cascading fire incidents, etc. Knowing the proportion of each is crucial for analyzing the true cause. In high-voltage power grid protection, high-voltage circuit breakers and relay protection devices are manufactured, selected, and installed separately, ultimately combined and set by the power department to form a complete protection system. Both components can potentially cause failures to trip. Current statistics do not show the proportion of failures to trip caused by relay protection failures and cascading fire incidents, thus failing to identify the true culprit behind the rise in cascading fire incidents in high-voltage power grids. Perhaps there are other internal statistics; careful analysis should reveal the problem. The failure of circuit breakers to trip and close, which perform the interruption task, is a problem of the switch manufacturer and can be determined by whether the relay protection signal relays issue operating signals. If an action signal is issued, it means the circuit breaker has failed to trip; if no action signal is issued, it means the relay protection device has malfunctioned and failed to trip, preventing the circuit breaker from performing its tripping function. These two are fundamentally different and should not be confused. Relay protection device malfunction can be either the main protection device or the backup protection device, which is a problem with the relay protection device and the power station's settings, and is unrelated to the circuit breaker manufacturer. Main/backup protection malfunctions and excessively long protection times often lead to cascading fires. However, the probability of a cascading fire caused by a circuit breaker malfunction is very small because the circuit breaker's breaking time is <0.1s, typically 0.06s, making it unlikely that both upstream and downstream circuit breakers will simultaneously fail to trip. The operating time of the third-level circuit breaker's remote backup protection should be 0.5–0.7s to avoid cascading fires. Therefore, cascading fires are generally caused by relay protection device malfunctions and excessively long protection operating times, and are usually due to problems with the power station's device settings and the plant's responsibility. This is something that even power plants and departments that fail to report faults might not have thought of, and the problem actually lies in their own relay protection system. The breaking performance of circuit breakers should be guaranteed by the manufacturer's type test and factory test, and a test report should be issued; the time, current, ampere-second action characteristics of relay protection devices and various main/backup protections should be verified by energizing the secondary circuit during installation, setting and commissioning, and a verification data report should be issued. Strictly speaking, it must be ensured that the main protection can operate within 0.1s when the end is the minimum single-phase short-circuit current, and the backup protection should operate within 0.3 to 0.5s when the same current is present. The recommended arc time of switchgear in the International Electrotechnical Commission IEC62271-200:2003 internal fault arc test standard is 1s/0.1s[4], that is, the operation time of remote backup protection should not exceed 1s, and it is best to control it within 0.7s. Otherwise, it is very easy to burn out switchgear and cause fires to spread to other areas! In fact, many power plants in my country and the world, including some developed countries, do not meet this requirement. This is the result of the misconception in the relay protection setting principle [5]. Foreign data shows that for every 0.1s increase in the arcing time of the switchgear from 0.1s, the cost of the switchgear will increase by 10%. When it is increased to 1s, the cost of the switchgear will increase by 100%. If the short circuit protection time of the power grid is required to be 4s as it is now, the cost of the switchgear will be unbearable and users will not accept it. If the protection time is extended further, the cost will be astronomical! It is impossible to achieve. Therefore, using long delay as the main short circuit protection in the relay protection principle is a subjective misleading and naive conjecture! The principle of short circuit protection should minimize the action time, so that the arcing damage of the fault is small and the power supply restoration time is short, which is beneficial to the country, the people and the industry. The past short circuit protection principle lacked a systematic economic concept combined with actual manufacturing. Because the low-voltage circuit breaker is manufactured and set as a whole with the relay protection device, the manufacturer has found a solution in a pragmatic way: setting a simple and practical three-stage protection to avoid the low-voltage system fire chain accident. The separate manufacturing of high-voltage circuit breakers and relay protection devices has led power sectors to overly rely on the misconception of relay protection setting principles. This results in cumbersome, complex, and impractical protection methods with broad but imprecise setting values, contributing to the persistently high rate of cascading fires. Developed countries have not yet escaped this vicious cycle, as evidenced by the fact that long-delay rotary table simulation characteristics, as defined in international electrotechnical standards IEC60255-3, British standard BS142, American standard ANSI C37.112, and Chinese national standard GB/T14598.7-3, are still being used in microcomputer-controlled short-circuit protection. Such microcomputer protection can only be called "crisis" protection. Don't assume that microcomputer protection guarantees safety; microcomputer control is not a panacea. Its principles are designed by humans, and it's best to have human settings to ensure it provides the necessary protection. The objective reality is the cruel reality of cascading fires and widespread, prolonged power outages, which must be resolutely and seriously prevented. Whatever the problem is, we should solve it. The most fundamental change is the change in mindset. We should analyze, digest, and discard foreign technologies. 2. Implicit factors of high-voltage circuit breaker failure to trip The reason why the relay protection device and setting cannot meet the requirements of the action characteristics of main protection <0.1s/backup protection 0.3～0.5s/remote backup protection 0.5～0.7s when the minimum single-phase short circuit current is at the end is: the relay protection setting principle has always used long delay as the main protection and backup protection for short circuit, which makes the time too long; and the instantaneous protection and short delay protection are set according to the maximum short circuit current, which makes the protection dead zone equal to no instantaneous/short delay protection and backup protection. This loses the function of short circuit protection in terms of both time and current parameters [5]. Unfortunately, the relevant universities are still teaching these contents, which misleads students. Domestic and foreign microcomputer protection devices also do not have this clear protection function. It is not surprising that a short circuit causes a fire and a large-scale long-term power outage. For example [6]: On March 21, 2008, a power outage occurred at the 220kV Caoqiao substation of the Beijing power grid, resulting in the complete shutdown of the substation and its three subordinate 110kV substations. In addition, two 220kV substations and four 110kV substations switched power supplies. This involved 16 switching stations and two important users, resulting in a large-scale power outage and a loss of 78MW of load. The accident was caused by a grounding flashover of the circuit breaker on the right power supply side, which was operating in parallel. The fault was cleared by the distance protection and zero-sequence protection of the upper-level A and N stations, which are both protected by a fully microcomputer system. The action time was 0.546s + 0.061s of acceleration protection after reclosing, and the reclosing interval was 1.117s. That is, the switch burnout time was 0.607s, which caused the switch to burn out so badly that it had to be replaced. Why is the first action time of the distance protection and zero-sequence protection 0.546s (longer than the 0.3s of the short-delay backup protection)? The subsequent acceleration protection only reached 0.061s? With the main protection taking so long, what's the point of the subsequent acceleration? Does this mean "both protection systems operated correctly"? Logically, both actions should have a momentary duration of 0.06s, meaning the switch burnout time should be 0.12s. Compared to 0.607s, this reduces burnout by 4/5! Perhaps with minor repairs, it can still be used without replacement. This would also benefit users in minimizing losses and restoring power. Although the accident was attributed to improper manufacturing and installation, the degree of burnout is likely related to the power station protection system's setting principle. Consider this: which manufacturer's switch design can withstand a 0.607s internal fault arc without burning out? Is the setting principle of modern microprocessor-based protection necessarily without problems? This deserves serious consideration. The relay protection setting principle lacks clarity regarding the functions of long-delay/short-delay/instantaneous protection, specifically which is responsible for short-circuit protection and overload protection, and which should be the main and backup protection. The basis for determining protection sensitivity is also unclear, and there is no solution to the selectivity problem of protection between circuit breakers at the beginning and end of the same line. All of these factors contribute to the distortion of the protection setting principle. Long-delay protection has a very long duration, generally >1 second, making it unsuitable for short-circuit protection. It can only be used for overload protection to avoid the motor starting time. The current setting is 1 times the rated current In, with an operating multiple of 1.2 to 6 times. It has backup protection functionality, but its instantaneous tripping capability for short-circuit protection is lost. Short-delay protection with a delay of 0.2/0.4/0.6 seconds is intended to ensure selectivity by coordinating upper and lower levels, but it can only be used for short-circuit backup protection, not as the main protection. It should be set according to the rated current; setting it according to the short-circuit current will create a protection dead zone. Line current settings are generally set to 3-4 times In to avoid inrush current spikes (generally 2-3 times In). The current settings of upstream and downstream protection should be offset by at least 1.1 times to ensure selectivity, with a short delay added for backup selectivity. The instantaneous protection's overcurrent time <0.1s determines that it should be the main short-circuit protection; it should also be set to rated current to eliminate protection dead zones. Line current settings are generally set to 5 times In to avoid inrush current spikes. The current settings of upstream and downstream protection should be offset by at least 1.25 times to ensure selectivity between upstream and downstream protection and between the beginning and end of the same line. The selectivity of the protection is related to the relay return coefficient (generally 0.85) and the accuracy error of the relay protection device components (generally ≤5%). A comprehensive offset of at least 1.25 times is necessary to ensure that the upstream protection can return after the downstream protection operates. The sensitivity Sp of the protection is related to the accuracy error of the relay protection device. Ideally, the backup protection should achieve a sensitivity of 1.1 at the minimum single-phase short-circuit current at the end, meaning the total accuracy error should be less than 10% to ensure reliable operation. Naturally, the higher the sensitivity of the main protection, the better. Currently, protection principles set based on the maximum short-circuit current cannot achieve a sensitivity greater than 1.1; they are all less than 1, meaning there is a dead zone and failure to trip. Other protections, such as differential protection and undervoltage blocking protection, are redundant, added after the instantaneous protection has a dead zone due to flaws in the protection principle. If the instantaneous protection had no dead zone, they would be meaningless. This can be seen from the setting values: differential protection set in the range of 0.4 to 4.5 times In for internal short circuits is equivalent to operating when an external short circuit of 1 times In is added, resulting in 1.4 to 5.5 times In. Wouldn't it be simpler to directly use instantaneous instantaneous overcurrent protection set to 5 times In for operation? When the setting value of differential protection is lower than the rated current and inrush current, its identification device becomes very complex, leading to a risk of maloperation. There are frequent reports of differential protection maloperation. In the past, instantaneous protection was set to about 30 times the rated current In (short-circuit current is generally several tens of times the rated current), resulting in a large protection dead zone that even extended into the transformer. Differential protection was invented because it was considered advantageous. However, after the protection principle was corrected, instantaneous protection is now set to within 5 times In to avoid inrush current, eliminating the protection dead zone. Therefore, differential protection has lost its superiority and its value. Instantaneous protection will operate as long as the current is greater than the normal allowable value, with avoiding inrush current as the bottom line. The smaller the setting value, the better; this is the original intention of protection. Equipment and circuits are designed according to rated current. A very large short-circuit current can burn out the equipment and circuits, requiring protection to disconnect them. If the short-circuit current or internal short-circuit current is smaller than the rated current, then protection operation is unnecessary. If the current is within the peak surge current range (generally ≤ 4 times In), short-delay protection can be used, and the setting value should be different, such as: instantaneous 5 times / short-delay 3 to 4 times / or a second set of short-delay 1.5 to 3 times In (0.5 to 0.7s). Wouldn't it be better to solve the short circuit problem with the simplest instantaneous protection? There is no need to go to the trouble of using differential protection, which is already an unnecessary addition, or even to use differential protection originally used for transformer internal short circuits for bus protection. The impedance of the bus is much smaller than that of the transformer. With such a small impedance range, how can the setting value be determined reasonably? It is equivalent to using the most cumbersome and complex differential protection to protect a single point. Is it necessary and practical? Moreover, the range of differential protection is limited to a certain range. 3. Key points of the updated relay protection setting principle: 1) Overturning the century-old misconception of using long-delay for short circuit protection and setting instantaneous protection according to the maximum short circuit current. Instantaneous and short-delay should be used as the main/backup protection for short circuits, and the protection should be set according to the rated current to eliminate dead zones. 1) This method can prevent chain-reaction fires and is simple, economical, and practical. 2) It proposes that after setting the short-circuit protection based on the rated current, low-voltage blocking protection and differential protection become redundant, and the range of line distance protection will increase several times or even the entire range. 3) It points out another advantage of setting based on the rated current: it is less affected by changes in system operating mode, especially in the minimum operating mode, where the protection reliability is high. 4) It indicates that based on the typical range of the difference between the rated currents of upper and lower levels, short-delay backup protection can only be coordinated in pairs. The setting value should be converted from the setting current of the lower level to a multiple of the In of the upper level, generally 3 to 4 times. It is recommended to set a second set of short-delay protection, with a setting value of 1.5 to 3 times/0.5 to 0.7s, as the third level of remote backup protection. 5) It proposes that the protection sensitivity Sp, originally set according to the short-circuit current of 1.25 to 2 (which still does not protect the end), can be reduced to 1.1 for remote backup protection, with the total accuracy error reduced to 10%. This also leads to the conclusion that current transformers cannot use a protection accuracy class of 10P, and should be ≤5P. 6) It is proposed that the effective value of the short-circuit impulse current Ish is beneficial to the reliability of protection sensitivity, and the average value within the instantaneous tripping time of 0.08s is calculated to be 1.22Ik. 7) It is pointed out that there is confusion in the setting calculation formula of the return coefficient Kre. It should be considered when setting the upper-level backup protection, but not when setting the end protection. This can improve the sensitivity of the backup protection. 8) The derivation of the commonly used minimum single-phase short-circuit current in low-voltage TN-S systems is: IK(1min)≈0.7IK(3min). 9) The current requirement for protection selectivity is supplemented by the fact that the setting values ​​of the upper and lower level circuit breakers and the first and last circuit breakers of the same line should be staggered by at least 1.25 times. For short-delay protection, it can be 1.1 times, which can expand the protection range to the lower level. 10) The time of 0.01s for the effective value of the short-circuit impulse current Ish to reach the maximum value of 1.5Ik affects the return time of selectivity. And based on this, the return time interval Δt of the upper level is calculated as the basis for judgment. If the return time is insufficient, it should be combined with the reclosing function. [5] The above are just the beginning, and I hope that my country's high-voltage power grid short-circuit instantaneous main protection can be at the forefront of the world. References: [1] Operation analysis of high-voltage switchgear in power system from 1998 to 2002. "High Voltage Switchgear" [J] 2004-1, p16. [2] Operation analysis of high-voltage switchgear of State Grid Corporation in 2004. "High Voltage Switchgear" [J] 2005-3, p13. [3] Operation analysis and reliability of high-voltage circuit breaker. "High Voltage Switchgear" [J] 2008-5, p7, p34. [4] IEC62271-200:2003 standard and internal fault arc test. Li Jianji. "High Voltage Switchgear" [J]. 2008-5, p28. [5] On the problem of power grid relay protection principle from the perspective of the generation of fire chain accident. Wang Qiang. "Relay" [J]. 2008, (8). [6] 3.21 Investigation and analysis of the power outage accident at the 220kV Caoqiao Substation of Beijing Power Grid. "High Voltage Switch" [J] 2008-6, p1.