Analysis of Faults and Solutions for 17.5kV Ring Main Units in Distribution Networks

With the improvement of social productivity and people's quality of life, the demand for electricity is continuously increasing. To ensure the effectiveness of power grid system configuration, it is necessary to reasonably construct distribution networks based on actual conditions. However, during the operation of distribution network systems, 17.5kV ring main units play a very important role, so the impact caused by failures is extremely significant. At this point, it is essential to adopt reasonable and effective solutions based on common failures of 17.5kV ring main units. Only then can we ensure the effectiveness and stability of 17.5kV ring main unit operation, reduce the occurrence of common failures, and improve the operational performance of distribution networks.

1.Advantages of 17.5kV Ring Main Units 

Advantages of 17.5kV Ring Main Units: 17.5kV ring main units (as shown in the figure below) have advantages such as node connection distribution and convenient operation and maintenance. The following will provide a brief analysis and explanation of these two aspects.

1.1 Convenient Operation and Maintenance 

Since the internal components of 17.5kV ring main units are relatively numerous and compactly concentrated, the cabinet body is miniaturized, relatively lightweight, and doesn't occupy much space. At the same time, the switch structure of 17.5kV ring main units is in a sealed state. During equipment operation, it generally isn't affected by the environment. The internal structure layout is also reasonably designed, installation is relatively simple, and subsequent operations are quite convenient, bringing great convenience to maintenance and repair work. Additionally, it has an anti-interlock function that can immediately issue an alarm in case of operational errors, thereby ensuring the personal safety of maintenance personnel.

1.2 Node Connection and Distribution 

17.5kV ring main units also serve the function of node connection and distribution, primarily because the switch devices have enclosed metal housings with busbars installed inside, along with circuit breakers and load switches. At the same time, fuses, circuit breakers, and load switches serve as core components of 17.5kV ring main units. High-voltage switch equipment is typically used to install aluminum-zinc coated steel plates or stainless steel metal materials within them. This provides a certain separation function while also effectively connecting various distribution nodes of the power system, thereby realizing the ring main unit's own functions and meeting the power supply needs of the electrical system.

2. Common Factors Causing Typical

Failures in 17.5kV Ring Main Units Operational failures in 17.5kV ring main units can easily trigger tripping and power outages (see table below), consequently bringing significant negative impacts.

2.1 Lightning Strikes and Natural Disasters 

Lightning strikes and natural disasters are significant factors causing failures in 17.5kV ring main units. This is primarily because lightning strikes can easily cause wire breaks, lightning arrester explosions, transformer burnouts, and other problems, thereby affecting the normal operation of 17.5kV ring main units. Meanwhile, the environment where 17.5kV ring main units are located is relatively complex. If tall poles and natural lines form lightning-attracting equipment, lightning strikes can easily occur. 

Additionally, if the lightning protection facilities on the lines are poorly maintained or outdated, this will increase the possibility of lightning-induced tripping on the lines, affecting the normal power supply of the distribution system. Furthermore, after being struck by lightning, 17.5kV ring main units experience lightning overvoltage that generates large currents. These currents can puncture insulators, cause conductor breaks, damage lightning rods, and burn out distribution transformers, severely affecting the normal performance of 17.5kV ring main units. As for natural disasters, heavy rain, floods, and other factors can erode pole foundations, causing landslides at pole foundations or line tripping, which leads to failures in 17.5kV ring main units.

2.2 Distribution Network Equipment

 Distribution network equipment is also a major factor affecting the normal operation of 17.5kV ring main units. Due to inadequate regular maintenance of some distribution equipment during long-term use, potential faults cannot be discovered in time, thereby increasing the possibility of failures in 17.5kV ring main units. At the same time, during normal operation of 17.5kV ring main units, failure to replace outdated equipment in a timely manner means these old devices have relatively poor internal insulation, which reduces the safety and stability of 17.5kV ring main units.

2.3 User Equipment

User equipment failures mainly occur because users fail to perform proper maintenance and inspection of electrical equipment during use, combined with quality issues in the equipment itself, leading to failures in user equipment. At the same time, although equipment failures in dedicated line users causing tripping won't significantly affect other users, users on supporting lines lack targeted switches to isolate faulty equipment. In this case, tripping and power outages in 17.5kV ring main units will affect the normal electricity use of other users.

2.4 External Damage

During normal operation of 17.5kV ring main units, they are easily affected by external factors, leading to operational failures. For example, birds and flying animals often build nests or perch on 17.5kV ring main units in forested or mountainous areas, which can easily cause failures. Meanwhile, some roads with high traffic volume can cause damage to poles supporting 17.5kV ring main unit lines, leading to power outage failures. Additionally, illegal theft of connection materials from 17.5kV ring main units significantly increases the occurrence of failures, causing widespread power outages that bring considerable negative impacts to social production and people's daily electricity use.

3 Solutions for 17.5kV Ring Main Unit Failures 

To ensure 17.5kV ring main units operate in a normal, safe, and stable state, corresponding solutions must be adopted based on the main factors causing common failures. Only then can common failure risks be reduced, meeting the needs of social production and people's daily electricity use. During the resolution of 17.5kV ring main unit failures, the following points should be noted:

3.1 Enhancing Insulation Performance

Enhancing insulation performance is an important measure to ensure the safety and stability of 17.5kV ring main units. This mainly involves regular inspection of 17.5kV ring main units to analyze whether the insulation performance of switch cabinets meets qualified standards. If not, immediate action must be taken to avoid significant negative impacts. 

At the same time, areas most prone to insulation problems should be treated as priorities and can be handled using epoxy resin materials with good flame retardancy to achieve excellent insulation performance. The contact status of cabinet busbar plugs and insulation protective sleeves should also be regularly inspected to avoid problems going undetected and affecting normal use. Additionally, before the official use of 17.5kV ring main units, electrical safety distances should be measured to ensure compliance with relevant standards and prevent phase-to-phase short circuit problems.

3.2 Optimizing Moisture Resistance in Switch Cabinets

During the resolution of 17.5kV ring main unit failures, optimizing moisture conditions inside switch cabinets can not only meet the need for installing heaters in electrical space gaps but also allow for the installation of air inlets at the top and air outlets at the bottom of switch cabinets. After heating, the switch cabinet can expel moisture through these outlets, avoiding impacts on the normal operational state of 17.5kV ring main units. 

Additionally, regular inspections of moisture conditions inside 17.5kV ring main units are necessary. If moisture levels are severe, heating and dehumidification treatment is required. To ensure effective dehumidification, intelligent temperature measurement and dehumidification equipment can be installed inside, which not only allows for effective monitoring of 17.5kV ring main units but also ensures the effectiveness of dehumidification and heating, preventing operational failures.

3.3 Equipment Maintenance

During normal operation of 17.5kV ring main units, regular maintenance and inspection based on equipment operating conditions are necessary to avoid operational failures. This allows for timely discovery of potential faults and immediate handling to prevent significant impacts. At the same time, during equipment inspections, special attention should be paid to checking for foreign objects in the upper front cabinet, lower front cabinet, rear cabinet, etc. 

If any are found, they should be immediately removed to avoid affecting the operation of 17.5kV ring main units. For maintenance of 17.5kV ring main units, isolated cleaning work should be performed to ensure no foreign objects or dust remain. Special attention should also be paid to checking and maintaining equipment connections inside switch cabinets, primarily checking for loosening or falling off. If found, immediate action is required. During maintenance, equipment that is severely damaged or aged should be immediately replaced to ensure 17.5kV ring main units operate in a safe and stable state.

3.4 Creating a Good Operating Environment

A good operating environment is also key to ensuring the safe and stable operation of 17.5kV ring main units. First, openings should be sealed to prevent moisture from entering the interior of ring main units. Second, ventilation windows should be installed in high-voltage rooms, and screens or filters should be installed on exhaust devices to reduce impurities entering the room, providing good ventilation and purification. Finally, the operating environment should be regularly cleaned to create a good operating environment.

3.5 Preventive Testing

During the resolution of 17.5kV ring main unit failures, attention should be paid to preventive testing of internal equipment. Through preventive testing, the operational status of internal equipment can be effectively judged, and appropriate adjustments can be made based on operational conditions to prevent failure problems. However, during preventive testing, operations must be conducted according to relevant standards and specifications. If data from preventive testing shows abnormal conditions, detailed analysis is required, combining past information for further verification to obtain reliable data conclusions.

Additionally, conclusions cannot rely solely on one set of data or information; multiple sets of information and data must be comprehensively analyzed to determine whether 17.5kV ring main units have safety hazards, ensuring the effectiveness of safety hazard handling. After preventive testing is completed, proper restoration work must be done, and during this process, special attention must be paid to the connectivity of contact points and contact surfaces to avoid abnormal heating problems caused by poor connections, which could affect the normal operation of 17.5kV ring main units.

4 Conclusion

In conclusion, 17.5kV ring main units in distribution networks occupy a very important position during power system operation, and their operational stability and safety directly affect power supply quality. Therefore, to ensure the stability and safety of distribution network 17.5kV ring main unit operation, research and analysis of factors causing common failures must be conducted, such as external damage, user equipment, distribution network equipment, lightning, and natural disasters. Only then can targeted solutions address failures, preventing or eliminating the occurrence of 17.5kV ring main unit failures, ensuring their operational safety, and providing fundamental assurance for stable power supply in the power system.