Abstract: Current medium-voltage busbar protection schemes cannot meet the requirements for rapid clearing of busbar faults, necessitating the installation of dedicated medium-voltage busbar protection. This article recommends a novel dedicated medium-voltage busbar protection solution based on arc flash detection – the arc flash medium- and low-voltage busbar protection system. Keywords: Low-voltage busbar protection system, busbar protection, fault. 6-35kV medium-voltage switchgear in power and industrial systems is widely used and prone to accidents. According to the "High Voltage Switchgear Technology Communication," over 200 switchgear cabinets burned out in the national power system in a single year. Arc flash short-circuit faults in switchgear often develop into medium-voltage busbar faults due to delayed clearance, posing serious risks such as power plant auxiliary power outages, power cuts to important users, and even cascading fires involving multiple switchgear cabinets burning out simultaneously. In recent years, damage to main transformers due to the massive short-circuit current surges caused by busbar faults has also been common. These accidents result in significant economic losses, and some even cause personal injury or death. Many factors contribute to medium-voltage switchgear failures, such as unreasonable structural design, poor manufacturing quality, insulation aging and mechanical wear, harsh operating conditions (high temperature, humidity, dirt, chemical corrosion), improper user maintenance and operation, external forces (entry of small animals, leaving objects inside the switchgear), and changes in the power grid structure (increased system capacity, increased cable usage). Therefore, the probability of medium-voltage busbar failures caused by arcing short circuits in switchgear is relatively high. Because busbar failures are not promptly cleared, they develop and expand, ultimately causing significant economic losses. After nearly a decade of rectification and improvement of medium-voltage switchgear, the accident rate has decreased. However, why do so many switchgear units still suffer severe economic losses due to arcing short circuits, even leading to medium-voltage busbar failures? The fundamental reason is that the switchgear itself has limited tolerance for arcing short circuit faults. Measures such as strengthening insulation, sealing and isolating unit compartments, and installing release plates and pressure relief channels are only passive protections, lacking proactive protection measures for rapid fault clearing, allowing the fault to develop and expand. The current medium-voltage busbar protection scheme cannot meet the requirements for rapid clearing of busbar faults, and there is an urgent need to install dedicated medium-voltage busbar protection. In addition, we recommend a new type of dedicated medium-voltage busbar protection solution that detects arc flash – the Arc Flash Medium and Low Voltage Busbar Protection System. Question 1: What is the internal arcing time that existing switchgear can withstand? When discussing internal arc flash short-circuit faults in switchgear, the internal arcing time must be mentioned. In IEC298, the specified internal arcing time is 100ms. Most switchgear on the market is manufactured according to the IEC298 standard, and its internal arcing withstand time is 100ms. That is to say, the arc burning time that the switchgear can withstand, i.e., the sum of the protection action and the circuit breaker clearing the fault, should be less than 100ms to achieve the purpose of protecting the switchgear, because the fault short-circuit arc continues to burn before the circuit breaker operates. The following are descriptions of the damage caused to equipment under various arcing times from foreign sources: -35ms: No significant damage; generally, it can be put into use after testing the insulation resistance. -100ms: Minor damage, cleaning or some minor repairs are required before the switchgear can be put back into operation. -500ms: Severe equipment damage, serious injury to personnel on site, and replacement of some equipment is required before it can be put back into operation. Of course, strengthening the structure of the switchgear can increase the internal arc withstand time. In foreign countries, if a switchgear with a higher internal arc withstand time is required, it needs to be negotiated between the user and the manufacturer, which will inevitably increase the production cost of the switchgear. According to the application experience of a foreign power distribution network, if the internal arc withstand time is increased to 200ms, the production cost will increase by 10%; if 1 second is required, the production cost will increase by 100%. Question 2: Can the existing medium-voltage bus protection scheme meet the requirements for quickly clearing the internal arc short circuit fault of the switchgear? At present, the available medium-voltage bus protection schemes are as follows: (1) Transformer backup overcurrent protection scheme. This is the most widely used medium-voltage bus protection scheme in China. The protection trip time is generally set to 1.2–1.4 seconds, and some are even longer, reaching more than 2.0 seconds. It is obvious that it is far from meeting the requirements for rapid clearing of medium-voltage bus faults. (2) Feeder overcurrent protection blocking transformer overcurrent protection scheme. This is a so-called overcurrent blocking medium-voltage bus protection scheme proposed by foreign countries that uses feeder overcurrent elements to block transformer overcurrent protection in recent years. The operating time of this protection scheme is generally 300-400ms. It also cannot meet the requirement of clearing medium-voltage bus faults in 100ms. (3) High impedance bus protection scheme using the circulating current principle. This is a special current differential bus protection scheme, which is sometimes used in some important projects abroad. Its operating time is generally 35-60ms, which is faster than the above two schemes. In addition, the circuit breaker tripping time of 35-60ms can barely meet the requirements for operating speed in some situations, but the margin left is definitely not enough. This protection scheme has complex wiring, high requirements for CT, and many difficulties in installing it on 6-35KV bus, and it is also very uneconomical. Furthermore, since most faults in switchgear occur in the cable compartment, the protection range of this scheme cannot cover faults within the cable compartment due to the limitation of the CT installation location. Therefore, it is also unsuitable for medium-voltage busbar protection applications. From the discussion of the above two issues, we can conclude that despite structural reinforcement measures for switchgear, many switchgear still suffer severe damage due to arc short-circuit faults. This is due to the limited arc tolerance of the switchgear itself and the lack of dedicated high-speed medium-voltage busbar protection. In recent years, with the rapid development of the domestic power industry, the number of medium-voltage switchgear applications has increased significantly, leading to a rise in medium-voltage busbar faults caused by arc short-circuit faults in switchgear. On the other hand, users have increasingly higher requirements for power supply reliability. Some domestic experts have consistently emphasized the importance of installing dedicated medium- and low-voltage busbar protection, and users also hope for a low-cost, simple-principle busbar protection system suitable for 6–35KV to minimize damage to equipment from busbar faults and improve power supply reliability. Question 3: Is there currently a simple-principle dedicated protection system suitable for medium- and low-voltage busbars? In the early 1990s, foreign countries began to study the phenomenon, mechanism, and hazards of arc flash faults, and studied various protective measures and schemes. The dedicated medium and low voltage bus protection we recommend - arc flash bus protection - is a comprehensive embodiment of these research results and is currently the ideal and mature medium and low voltage bus protection solution. It is a system introduced from abroad. At present, nearly 2,000 sets of this arc flash protection system are in operation in power plants, substations and industrial and mining enterprises, with nearly 10 years of mature operation experience and no record of incorrect operation. The system has the following main features: (1) Reliable operation - adopts the dual criterion principle of arc flash detection and overcurrent. (2) High-speed operation - the protection operation time is less than 1ms, and the total fault clearing time, including circuit breaker tripping, can be guaranteed to be within 100ms. (3) Flexible configuration - the protection zone is covered by the arc flash sensor. (4) Fault location - can display the location of the detected arc flash short circuit point. (5) Adaptable to various medium and low voltage bus wiring methods to provide selective protection applications.