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Abstract This article compares the advantages and disadvantages of different grounding methods for the neutral point of distribution networks. The impact of resistor grounding of the distribution network on power supply reliability, communications, personal safety, and switch maintenance was analyzed. It is pointed out that for distribution networks dominated by cables, grounding the neutral point through a resistor is the preferred method. The article also explains the principles for selecting the neutral point resistor value and the domestic practice of grounding the neutral point through a resistor. 1 The neutral point grounding method was stipulated in our country in the early days: The neutral point grounding method of the power system is divided into two categories: large ground short-circuit current system and small ground short-circuit current system. Because the magnitude of the current is difficult to clearly define by classifying the neutral point grounding method of the power system, it is changed into a neutral point effective grounding system and a neutral point non-effective grounding system. The neutral point of the power system is effectively grounded, including direct grounding or grounding through a low-value resistor or low-value reactor. The ratio of the zero-sequence reactance (X 0 ) to the positive-sequence reactance (X 1 ) of the entire system (X 0 /X 1 ) is required to be positive and lower than 3, and the ratio of the zero-sequence resistance (R 0 ) to the positive-sequence reactance (X 1 ) is required to be positive and lower than 1. On the contrary, it is a neutral point non-effectively grounded system. The neutral point of the power system is not effectively grounded, including resonant (arc suppression coil) grounding and ungrounding. 2 Advantages and Disadvantages of Different Grounding Methods for the Neutral Point of the Distribution Network. The electrical connection method between the neutral point of the distribution network and the reference ground. According to the operation needs, the neutral point can be ungrounded, grounded through an arc suppression coil, grounded through (high, medium, and low value) resistors, grounded through a low value reactor, and directly grounded. Each of these neutral point grounding methods has unique advantages and disadvantages. 2.1 Advantages and Disadvantages of Ungrounded Neutral Point of Distribution Network Ungrounded neutral point of distribution network means that the neutral point is not artificially connected to the earth. In fact, such a distribution network is grounded through the grid-to-ground capacitance. Main advantages of ungrounded neutral point system: When a single-phase ground fault occurs in the power grid, the steady-state power frequency current is small. In this way, instantaneous faults such as lightning strike and insulation flashover can be automatically cleared without tripping. · If there is a metallic ground fault, it can operate with single-phase grounding, which improves the uninterrupted power supply of the power grid and improves the reliability of power supply. · The ground current is small, which reduces the ground potential rise. Reduced step voltage and contact voltage. Reduces interference to information systems. Reduce the counterattack to the low-voltage network, etc. Economic aspect: It saves grounding equipment and requires less investment in the grounding system. Disadvantages of systems with ungrounded neutral point: a Compared with the neutral point resistor grounding system, the overvoltage generated is high (arc overvoltage, ferromagnetic resonance overvoltage, etc.), and the probability of breakdown of weak insulation is high. b The high-frequency oscillation current generated during intermittent arc ground faults is large, reaching hundreds of amperes, and may cause phase-to-phase short circuits. c So far, fault location has been difficult, and the ground fault line cannot be removed correctly and quickly. 2.2 Advantages and Disadvantages of Distribution Network Neutral Point Resonant Grounding (Arc Suppression Coil) Neutral point harmonic grounding of distribution network means that one or more neutral points of the distribution network are connected to the earth through arc suppression coils. The steady-state power frequency inductive current of the arc suppression coil tunes the steady-state power frequency capacitive current of the power grid, so it is called resonant grounding. The purpose is to make the ground fault residual current small, and the ground fault may self-clear. Therefore, the neutral point ungrounded system has all the advantages of the neutral point arc suppression coil grounded system and is better. Similarly, the disadvantages of the neutral point ungrounded system and the neutral point arc suppression coil grounded system are all the same, but the probability of maximum amplitude arc overvoltage is smaller. This is because the arc suppression coil reduces the arc building rate when single-phase grounding occurs. The success of the arc suppression coil grounding method also depends to a large extent on the reliability of the arc suppression coil, tracking system, and line selection device itself. 2.3 Advantages and Disadvantages of Direct Grounding of Distribution Network Neutral Points Direct grounding of distribution network neutral points means that all or part of the transformer neutral points in the distribution network are directly and fully connected to the earth (ground grid) without the addition of artificial impedance. Let R 0 ≤ X 1 and X 0 / X 1 ≤ 3 be achieved at the power grid. The advantages of a directly grounded neutral point system are:: a The internal overvoltage is low, and a lower insulation level can be used to save infrastructure investment. b Large ground current, easy fault location, and can correctly and quickly remove the ground fault line. The disadvantages of a directly grounded neutral point system are:: a The ground fault line is quickly removed and the power supply is interrupted. b The ground current is large and the ground potential rises high. so: l Increased damage to electrical equipment. l Increase contact voltage and step voltage. l Increase the interference to information systems. l Increase the counterattack against low-voltage networks. 2.4 Advantages and Disadvantages of Grounding Neutral Point Resistors in Distribution Networks At least one neutral point in a distribution network is connected to a resistor in order to limit the ground fault current. The neutral point is grounded through a resistor (zero resistance per phase R 0 ≤ Since the grounding current of this system is smaller than that of a directly grounded system, the rise in ground potential and the interference to the information system and the counterattack to the low-voltage power grid are weakened. Therefore, the neutral point resistor grounding system has some advantages of the ungrounded neutral point and arc suppression coil grounding system or direct grounding system, but also has some disadvantages of these two grounding methods. According to the different requirements for limiting the size of the ground fault current, there are high, medium and low value resistor grounding systems, and the specific advantages and disadvantages are also different. 2.4.1 Advantages and Disadvantages of Neutral Point High Value Resistor Grounding System The neutral point high value resistor grounding system limits the ground fault current level to below 10A. The design of the high resistance grounding system should comply with the criterion of zero sequence resistance per phase R 0 ≤ advantage: a Can prevent and dampen resonant overvoltage and intermittent arc grounding overvoltage, at 2.5P·U and below. b The ground current level is below 10A, which reduces the rise in position. c The ground fault does not need to be cleared immediately, so it can operate with a single-phase ground fault phase. shortcoming: The scope of use is limited, and it is suitable for some small 6 ~ 10KV distribution networks and power plant power systems. 2.4.2 Advantages and Disadvantages of Neutral Point Low Value Resistor Grounding Systems In order to obtain correct and rapid removal of ground fault lines, the resistance value of the resistor must be reduced. advantage: a The level of internal overvoltage (including arc overvoltage, resonance overvoltage, etc.) is low, improving the reliability of the network and equipment. b Large ground current (100 ~ 1000A), easy fault location, and can correctly and quickly remove the ground fault line. shortcoming: a Due to ground fault, the ground current I f =100 ~ 1000A, the ground potential rise is higher than that of ungrounded neutral point, grounded arc suppression coil, high value resistor grounding system, etc. b The ground fault line is quickly removed and the power supply is interrupted. 2.4.3 Advantages and Disadvantages of Neutral Point Median Value Resistor Grounding Systems To overcome the disadvantages of high and low value earthing systems while retaining their advantages, median value resistors are used. The ground fault current is controlled between 50 and 100A, which still retains the advantages of low internal overvoltage level, small increase in ground potential, and accurate and rapid removal of ground fault lines. It also has the disadvantages of cutting off ground fault lines and intermittent power supply. 3. Problems in the neutral point grounding mode of the urban distribution network in my country. In recent years, with the rapid development of my country's power industry, the structure of the urban distribution network has changed greatly. Cables account for an increasing proportion of the feeder lines. Some problems in the neutral point grounding mode of the arc suppression coil have become increasingly exposed. With the rapid increase of the distribution network capacitor current, it is difficult to ensure that the arc suppression coil operates with overcompensation under a certain degree of detuning. The main reason is: (1) The adjustment range of the arc suppression coil is limited, generally 1 : 2. Not suitable for the needs of the initial and final stages of the project. (2) The error between the nominal current and the actual current of each tap of the arc suppression coil is large, and some can even reach 15%. During operation, resonance has occurred due to the difference between the actual current value and the nameplate data. (3) There is a large error between the calculated capacitance current and the actual capacitance current. Most substations are power supply networks with a mixture of cables and overhead lines. It is difficult to accurately and timely grasp the length of distribution lines. Moreover, there are many types of cables, and the capacitance current per unit length is also different. (4) Some distribution networks contain a certain amount of 5th harmonic current in the entire grounding capacitor current, with a proportion as high as 5% to 15%. Even if the power frequency grounding current is calculated very accurately, the harmonic current value in the 5% to 15% grounding capacitor current cannot be compensated. To sum up, when a single-phase ground fault occurs in a distribution network dominated by cables, the ground residual current is large, and the conditions for operating in over-compensation are often not met. Single-phase grounding faults in the main distribution network of cables are mostly caused by system equipment breakdown due to insulation defects under certain conditions, and the grounding residual current is large. Especially when the grounding point is on the cable, the grounding arc is a closed arc, and the arc is more difficult to extinguish on its own (the value of the arc light generated by the single-phase grounding capacitor current that can self-extinguish itself is far less than the value stipulated in the regulations. For cross-linked polyethylene cables, it is only 5A ), so single-phase ground faults in cable distribution networks are mostly permanent faults. Since the system in which the neutral point is grounded through an arc suppression coil is a small current grounding system, after a single-phase permanent grounding fault occurs, it is difficult to detect the ground fault point and the line where the fault point is located cannot be quickly detected. In this way, on the one hand, the system equipment will be subjected to overvoltage for a long time, posing a threat to the equipment insulation. On the other hand, the advantage of not causing users to lose power will no longer exist. In a system where the neutral point is grounded through an arc suppression coil, the overvoltage value is relatively high, posing a threat to the insulation of the equipment. (1) To detect the line where the single-phase ground fault point is located, test pulling is generally used. During the test of the circuit breaker on the line, an operating overvoltage with a relatively high amplitude will sometimes be generated. (2) Compared with a system with an ungrounded neutral point, a system with a neutral point grounded through an arc suppression coil can only reduce the probability of arc grounding overvoltage, but cannot reduce the amplitude of the arc grounding overvoltage. (3) Under certain conditions, a resonance overvoltage will occur in a system with a neutral point grounded through an arc suppression coil. Due to the above reasons, and because the cable is a weakly insulated device, for example, the 1-minute power frequency withstand voltage of a 10kV cross-linked polyethylene cable is 28kV, which is more than 20% lower than that of ordinary equipment. Therefore, during the fault point detection process of a single-phase ground fault, the cable often develops into a phase-to-phase fault due to the long-term effect of power frequency or transient overvoltage, causing one or more lines to trip. When a single phase is grounded, the non-faulty phase voltage rises to the line voltage or even higher. If the fault point line cannot be detected in time, the gapless metal oxide arrester (MOA) operates at the line voltage for a long time and is easily damaged or even exploded. Such accidents were not uncommon in previous years. After increasing the rated voltage of the MOA, although the occurrence of such accidents can be greatly reduced, without significant improvement in the characteristics of the MOA valve plate, the residual voltage of the MOA under lightning impulse current will inevitably increase, reducing the protection performance. In addition, when arc ground overvoltage or resonance overvoltage occurs in the neutral point grounded system through the arc suppression coil, the overvoltage action time may be longer. MOA is generally not required to limit such overvoltage due to the operating load problem. This reduces the voltage limiting effect of MOA and weakens its advantages, which is not conducive to the promotion and use of MOA in distribution networks. 4 Several issues that people are concerned about when the neutral point of the distribution network is grounded through a low-value resistor 4.1 About reliability 4.1.1 Requirements for power supply reliability and factors affecting power supply reliability: According to the relevant regulations on power supply reliability management in my country, there are three main indicators to judge the reliability of power supply.: Frequency of power outages, duration of power outages and low power supply. These indicators are related to many factors, including planned power outages and faulty power outages. The main factors affecting the power supply reliability indicators of the 10kV distribution network are basically concentrated in four aspects: user influence, climate factors, municipal construction, and equipment aging. It should be said that the different grounding methods of the neutral point of the 10kV distribution network have a comprehensive impact on the power supply reliability of the 10kV distribution network. After the neutral point grounding method of the distribution network is changed, the probability of failure may increase for a certain cause of failure, while the probability of failure may be reduced or not affected for another cause of failure. In order to improve power supply reliability, some measures should be taken based on the impact of grounding methods on faults. 4.1.2 Impact of neutral point grounding method on power supply reliability: As we all know, the biggest advantage of the distribution network neutral point being ungrounded or grounded through an arc suppression coil compared to the neutral point grounding through a small resistance method is that when a single-phase ground fault occurs, if it is an instantaneous fault, when the system capacitance current or the residual current after compensation by the arc suppression coil is small enough to extinguish itself, the fault can be eliminated by itself. If it is a permanent fault, the system can run with a single-phase ground fault for 2 hours, allowing enough time to troubleshoot the fault to ensure uninterrupted power supply to users. However, this advantage is not prominent in urban distribution networks dominated by cables. According to statistics, the causes of cable faults are mainly insulation aging, cable quality, external force damage, etc. They are generally permanent faults and should not be operated with faults when a ground fault occurs. Judging from the actual operation situation, in a distribution network dominated by cables, when the neutral point is not grounded or is grounded through arc suppression lines, there are more phase-to-phase short circuit faults caused by single-phase ground faults. Some actual accidents have shown that a single-phase grounding fault develops into a phase-to-phase fault, which in turn expands the scope of the power outage. Especially when it develops into a bus short-circuit fault, it is equivalent to a short-circuit at the transformer outlet. Since some current transformers are weak in resisting short-circuit impacts, they may cause damage to the transformer. Based on the actual situation of the urban distribution network power supply mode, the dual power supply mode, the use of overhead insulated wires, ring network layout, open-loop operation mode, the proportion of cable lines and other factors have resulted in the advantages of using the neutral point ungrounded or arc suppression coil grounded method. Analysis from the actual operation conditions of substations that have changed to small resistance grounding methods ； Proper protection configuration will not reduce power supply reliability. Based on the above analysis, the substation that mainly supplies cable power uses the neutral point to be grounded through a small resistance, which will not have much impact on the reliability of the power supply. In some aspects, it will be beneficial to the improvement of the reliability of the power supply. 4.2 Regarding the impact on communication, the ground fault current entering the ground and the zero-sequence current during operation generate longitudinal electromotive force through inductive coupling of adjacent communication lines. The asymmetric voltage generated by the three phases produces electrostatically induced voltage on the capacitive coupling of adjacent communication lines. The ground potential generated by the ground fault in the distribution network increases and generates voltage on the grounded telecommunications lines through the resistive coupling between the ground electrodes, which is called resistive coupling or direct transmission. The above-mentioned voltage and current generated in the communication system can harm the communication system and are called dangerous effects. The effects of reduced communication quality, noise generated by telephone calls, distortion of telegraph signals and data transmission, etc., are called interference effects. Because the neutral point of the power grid is directly grounded and the neutral point resistor (or reactor) is grounded, the ground fault current flowing into the ground is larger than that of an ungrounded (insulated) neutral point and a grounded arc suppression coil. The former has a greater impact on the communication system than the latter. This is the result of the following concept: a single power supply feeds a single-phase ground fault at the end of the line (point F). The fault current induces a larger voltage on the communication line parallel to the power line (if one end of the communication line is grounded, it can be measured with a voltmeter at the other end), which increases with the increase of the fault current. The judgment of the electromagnetic induction of communication lines based on this simple basic concept is obviously too large. In actual urban distribution networks, only one end of the neutral point is grounded, and the other end is rarely open circuit. Actual distribution networks are much more complex than this. When a single-phase ground fault occurs somewhere on the line F, the ground fault current flows from both ends into the fault point F in the opposite direction of the line current. The induced voltage along the entire length of the communication line is equal to ( i 1 l 1 -i 2 l 2 ) is proportional to the absolute value. Therefore, the neutral point directly grounded system and the neutral point low-value resistor (or low-value reactor) grounded system may not necessarily have a greater induced voltage on the communication line than the neutral point arc suppression coil grounded system and the neutral point ungrounded (insulated) system. Specific calculations and actual measurements are required, such as Considering the most serious extreme situation, when the neutral point arc suppression coil is grounded and the neutral point is not grounded (insulated), the two-phase conductor ground fault occurs (fog flash on the overhead lines of this system often causes two-phase different ground faults), the induced voltage on the communication line will be more serious. In fact, the distribution network and communication network in large cities are all cables, and the ground fault current is diverted from the cable outer sheath, which generally has no impact. In short, the specific situation requires detailed calculation and analysis. It must also be pointed out that there are many protective measures that can be taken when the induced voltage exceeds the specified value. 4. 3 Regarding personal safety, from the analysis of actual examples provided by the power supply bureau, whether it is in an ungrounded or arc-extinguishing coil grounded system, or in a small-resistance grounded system, there are examples of electric shock casualties and escape from electric shock accidents. Therefore, for such direct contact with high voltage accidents, the key to whether personal casualties will be caused is not which neutral point grounding method, but the way in which the person who gets an electric shock comes into contact with the electrified body and the time it takes to escape after the electric shock. Therefore, from the perspective of protecting personal safety, a system with an ungrounded neutral point or a grounded arc suppression coil will not trip immediately when a single-phase grounding occurs, so it will cause greater harm to people who accidentally touch a live line and cannot easily disconnect from the power supply immediately. However, for a system with a neutral point grounded by a small resistance, when a metallic single-phase grounding occurs, the time is short and the protection function is correct. Accurate and timely action will immediately remove the electric shock person from the power supply. Therefore, although the short-circuit current is large, the personal injury caused will be relatively small. However, if the neutral point is grounded through a small resistance and a single phase is grounded through a transition resistor (such as the Zhuhai Airport Substation example), because the protection cannot act accurately and timely, personal injury will still be caused at this time. Therefore, the method of electric shock, the action of protection after electric shock, etc. should be comprehensively considered. In many cities, overhead lines have been replaced by insulated wires, so the accidents of single-phase grounding of overhead lines caused by external forces will be greatly reduced. When a single-phase grounding occurs on a cable, due to the shunting effect of the outer skin, only a small part of the ground current flows, so the potential increase is also small. So from this aspect, 10kV The use of a low-resistance grounding system in the power distribution system is superior to an ungrounded or arc suppression coil grounding system in terms of personal safety. 4.4 About the circuit breaker Theoretically, the original neutral point is not grounded (insulated) and the arc suppression coil is grounded, so the line circuit breaker will not trip when a single-phase ground fault occurs. If the neutral point is changed to a low-value resistor (or low-value reactor) grounding system, the line circuit breaker will trip when a single-phase ground fault occurs, resulting in the worries of "frequent tripping, equipment burnout" and "increased maintenance workload." According to the long-term operation experience in Shanghai and other places, it is proved that it will not happen. The workload of repairing the circuit breakers of the 23KV neutral point low-value resistor grounding system in the western suburbs of Shanghai is no greater than that of the circuit breakers of the 35KV neutral point arc suppression coil grounding system of the same substation. The reason is that the fault current is not large. The ground current of a single-phase ground fault is limited to 1 to 2KA, which is slightly larger than the load current and less than one-eighth of the circuit breaker's breaking current. It will not cause serious burning of the circuit breaker.: The conditions for a circuit breaker to break a single-phase short circuit are much better than breaking a phase-to-phase short circuit. In systems where the neutral point is not grounded (insulated) and the arc suppression coil is grounded, the probability of a phase-to-phase short circuit fault caused by a single-phase arc ground fault is very high. 5 Considerations for relay protection when the resistance is grounded. After the neutral point is grounded by a small resistance, for a single-phase fault, the fault current increases and zero-sequence current is generated. Therefore, the protection configuration should add zero-sequence protection. According to experience, the protection configuration should adopt zero-sequence current protection with different time limits or zero-sequence direction protection. Protection configurations should also consider: (1) Distribution lines use zero-sequence current transformers and zero-sequence current ground protection that reflects the power frequency current value as the main single-phase ground protection to act on tripping. (2) The protection setting value avoids the capacitor current in this section, and the reliability coefficient can be 2.0. (3) Sensitivity is calibrated based on the capacitive current flowing through the faulty line. Sensitive Systems Engineering>1.25. (4) The open triangle 3 U 0 of the bus voltage transformer in this section is used as a signal. (5) It is best to use a single CT on a three-phase cable for zero sequence CT to avoid unbalanced current caused by the error and saturation difference of the three CTs. (6) The protection configuration can be coordinated through time to minimize the fault scope. 6 Reasonable selection of resistance value When using a neutral point resistor for grounding, the selection of the resistance value must be based on the specific conditions of the power grid, and factors such as limiting overvoltage multiples, sensitivity of relay protection, impact on communications, personal safety, etc. should be comprehensively considered. (1) For high-resistance grounding, when a single-phase grounding occurs in the system, it is allowed to operate with fault, and the current at the fault point should be limited to less than 10A. Therefore, the grounding resistance R 0 is selected as Xc ≧ R 0 , and R 0 ≧ U φ /10A. Xc is the ground capacitance of each phase of the system, and U φ is the system phase voltage. (2) For low-resistance grounding a, from the perspective of reducing internal overvoltage, according to TNA simulation and computer calculation, when I 0 ≥Ic (I 0 is the current flowing through the neutral point resistor, Ic is the system capacitance current), the sound phase overvoltage multiple can be limited to less than 2.8 times. When I 0 ≥1.5Ic, the sound phase overvoltage multiple can be limited to less than 2 times. After I 0 ≥1.5Ic, the effect of limiting overvoltage has not changed much. Therefore, the resistance value can be selected according to 1.5Ic≥I 0 ≥Ic. R 0 = U φ / I 0 . b From the perspective of ensuring the sensitivity of relay protection, the smaller the resistance value, the better. Current microcomputer protection generally has a zero-sequence protection function, and the starting current value is quite small. The single-phase ground fault current is much larger than the ground capacitance current of each line, and generally can meet the sensitivity requirements of zero-sequence protection. The problem is that when the ground transition resistance is high, the sensitivity of the relay protection will be affected. According to the resistance value selected in a), when the transition resistance is not greater than 100Ω, the protection sensitivity is generally no problem. For cable-based distribution lines, the transition resistance is generally less than 100Ω. c From the perspective of reducing interference to communication, the resistor should not be selected too small. my country's four-part agreement stipulates that if no arrester is installed between the communication cable and the earth, the dangerous impact voltage shall not be greater than 430V, and for high-reliability lines, it shall not be greater than 630V. At present, the neutral point resistance of Shenzhen Power Grid is 15Ω, Beijing Power Grid is 10Ω, and Shanghai Power Grid is 5.7Ω. The corresponding currents are 400A, 600A, and 1000A respectively. There was no impact on communication lines. d From the perspective of personal safety, the larger the neutral point grounding resistance, the better. Because the neutral point has low resistance when a single-phase ground fault occurs, the ground short-circuit current passing through the fault point is relatively large, causing the ground potential at the fault point to rise, which may cause step voltage and contact potential to exceed the allowable value. Therefore, when selecting the resistance value, it is necessary to calculate whether the step voltage and contact potential exceed the regulations based on the ground resistance of the ground network, protection action time, and ground short-circuit current. According to the practical experience of Shenzhen, Guangzhou, Shanghai, and Beijing, no personal accidents have occurred due to excessive step voltage and contact potential caused by the use of resistor grounding. 7 Conclusion The selection of neutral point grounding method in distribution network is a comprehensive technical issue. Ungrounded neutral point, resonant grounding, and resistance grounding each have their own advantages and disadvantages, which should be determined through technical and economic comparison based on the specific conditions of the power grid. In other words, each neutral point grounding system has its own advantages and has been developed. In the same city, systems with the same nominal voltage and multiple neutral point grounding methods coexist. It is wrong to determine the neutral point grounding method "one size fits all" according to the voltage level. Each system with a neutral point grounding method has its own shortcomings (disadvantages). Therefore, when choosing, you must proceed from specific realities, weigh the pros and cons, and choose the pros outweigh the cons. For example: For small power grids with overhead lines, that is, where the network capacitance current is small, a neutral point high-value resistor grounding system can be used. For large power grids with overhead lines, where the network capacitance current is large, a neutral point resonant grounding system can be used. For urban cable distribution networks, the network structure is good and neutral point mid-value or low-value resistor grounding systems can be used. If the compensation network capacitor current is required to limit the ground fault current into the ground, a grounding method in which the neutral point is connected in parallel with the arc suppression coil through a median resistor can be used. The neutral point mid-value or low-value resistor grounding method and the mid-value resistor and arc suppression coil parallel grounding method can overcome the two major disadvantages of ungrounding and resonant grounding methods.: (1) Limit the transient overvoltage and transient current generated when a single-phase intermittent arc is grounded. (2) Solve the difficulty of line selection and achieve correct and rapid line selection to disconnect single-phase ground fault lines. Neutral point grounding through resistor has been used abroad since the 1940s. In 1995, Hualite Electric Company took the lead in introducing neutral point grounding resistors from the American PGR Company, and has successively used them in power supply bureaus in Shenzhen, Shanghai, Beijing, Tianjin, Jiangsu, Fujian and other regions as well as petrochemical, steel, subway, and power plant industries. The use of more than 2,000 resistance cabinets per year shows that its performance is advanced and reliable. References 1 Wan Shanshan Technical analysis of the neutral point grounding method of Shanghai urban distribution network Shanghai Electric Power 1993 Issue 6 2 Dong Zhenya Development and improvement of the neutral point grounding method of urban distribution network China Electric Power 1998 Issue 8 3 Xu Ying 3 ~ 66kV power grid neutral point grounding method 4 Feng Baoyi Cable distribution network neutral point grounding method's impact on power supply reliability