對MNS低壓抽屜柜在額定負荷運行條件下出現(xiàn)起火燃燒故障進行了描述，分析故障發(fā)生的相關(guān)原因，提出了隱患的應(yīng)對措施。關(guān)鍵詞：MNS低壓抽屜柜；單相接地短路；弧光放電；透明軟管MNS低壓抽屜柜以檢修方便、出線回路多、占地面積小等優(yōu)勢受到廣大電力用戶的青睞。行業(yè)內(nèi)雖然生產(chǎn)廠家眾多，但是技術(shù)及生產(chǎn)能力參差不齊，很多小型開關(guān)廠由于技術(shù)力量薄弱，對低壓配電設(shè)備相關(guān)的標準和規(guī)范沒有的了解，在抽屜開關(guān)柜設(shè)計和裝配方面存在隱患，再加上用戶運維情況差等因素，隨著運行時間增加柜內(nèi)零部件逐漸老化，將導(dǎo)致開關(guān)柜事故頻發(fā)以致發(fā)生燒損等嚴重事故。

　　This article describes the occurrence of fire and combustion faults in MNS low-voltage drawer cabinets under rated load operating conditions, analyzes the relevant causes of the faults, and proposes countermeasures to eliminate hidden dangers. Keywords: MNS low-voltage drawer cabinet; Single phase grounding short circuit; Arc discharge; The transparent hose MNS low-voltage drawer cabinet is favored by a large number of power users due to its advantages of easy maintenance, multiple outgoing circuits, and small footprint. Although there are many manufacturers in the industry, their technology and production capabilities vary greatly. Many small switch factories, due to weak technical strength, do not have a comprehensive understanding of the standards and specifications related to low-voltage distribution equipment. There are safety hazards in the design and assembly of drawer switch cabinets. In addition, factors such as poor user operation and maintenance will gradually age the components inside the cabinet as the operating time increases, leading to frequent switch cabinet accidents and serious accidents such as burning.

　　1 故障經(jīng)過2024年7月28日凌晨，某配電室正常運行的一臺MNS低壓抽屜柜突然發(fā)生燃燒起火故障，為防止故障擴大，現(xiàn)場運維人員將上一級10kV開關(guān)分閘后進行滅火，因救火及時未造成大面積起火，經(jīng)確認起火源為低壓側(cè)D28饋線柜，整柜燒損嚴重，已完全喪失運行功能。相鄰柜未受影響，滅火后將重要負荷投入備用線路，繼續(xù)投入運行。經(jīng)與現(xiàn)場工作人員確認，此配電室于2015年整體投入運行，期間運行正常，無維護保養(yǎng)記錄?；馂?zāi)報警發(fā)生前，各出線開關(guān)、負載未出現(xiàn)開關(guān)故障、跳閘、停電及大規(guī)模啟、停設(shè)備（設(shè)施）現(xiàn)象，同時經(jīng)檢查運行記錄確認，各單元進線開關(guān)電流顯示正常，無過負載情況。

　　On the early morning of July 28, 2024, a MNS low-voltage drawer cabinet that was operating normally in a certain distribution room suddenly caught fire. In order to prevent the fault from expanding, on-site operation and maintenance personnel opened the 10kV switch of the previous level and extinguished the fire. Due to timely firefighting, no large-scale fire was caused. It was confirmed that the ignition source was the D28 feeder cabinet on the low-voltage side, which was severely burned and had completely lost its operating function. The adjacent cabinets were not affected, and after extinguishing the fire, the important load was put into the backup line and continued to operate. After confirmation with on-site staff, this distribution room was put into operation as a whole in 2015 and operated normally during this period, with no maintenance records. Before the fire alarm occurred, there were no switch faults, trips, power outages, or large-scale start/stop of equipment (facilities) in each outgoing switch and load. At the same time, after checking the operation records, it was confirmed that the current display of each unit's incoming switch was normal and there was no overload situation.

　　2故障分析

　　2 Fault analysis

　　2.1現(xiàn)場故障狀況如圖1所示，D28柜完全燒毀，柜內(nèi)元器件呈焦炭狀，金屬殼架已完全變形，所有元件、標識嚴重燒毀無法辨認。經(jīng)對現(xiàn)場局部燒損痕跡的比對分析，如圖2所示，第8回路出線單元（下數(shù)一）金屬殼架燒損情況為嚴重，燒損程度由下往上逐級降低。圖1D28柜體燒損情況

　　2.1 The on-site fault condition is shown in Figure 1. The D28 cabinet is completely burned out, and the components inside the cabinet are in the shape of coke. The metal shell frame has been completely deformed, and all components and markings are severely burned out and cannot be identified. After comparing and analyzing the local burn marks on site, as shown in Figure 2, the metal shell frame of the 8th circuit outgoing unit (bottom one) suffered the most severe burn, with the degree of burn decreasing step by step from bottom to top. Figure 1D28 Cabinet burning situation

　　2.2故障原因分析通過對D28柜現(xiàn)場情況的詳細勘測、取樣，并對樣件進行檢測及綜合分析，運用仿真技術(shù)模擬還原運行狀態(tài)，并得出結(jié)論：開關(guān)柜起火的主要原因是第8回路開關(guān)進線端導(dǎo)體單相接地短路，引發(fā)弧光放電，起火燃燒。具體分析如下：經(jīng)對D28柜第8回路進、出兩端插接件檢查，插接件無明顯燒損痕跡，同時檢查內(nèi)部斷路器情況，內(nèi)部導(dǎo)體未發(fā)現(xiàn)異常，可排除插接件和斷路器內(nèi)部短路情況。經(jīng)對D28柜第8回路燒損樣件檢查發(fā)現(xiàn)，第8回路開關(guān)進線端B相銅導(dǎo)線為雙股70mm且已完全熔斷，AC相也存在不同程度的大面積燒熔情況。第8回路開關(guān)進線端B相銅導(dǎo)線為銅編織線，熔點溫度為1083℃，柜內(nèi)其它主要可燃物主要為PVC塑料，其燃燒溫度為350℃，參考ISO834國際標準中火災(zāi)溫度-時間特性曲線，燃燒1h后的溫度約為950℃，小于導(dǎo)體的熔點溫度，并且開關(guān)出線側(cè)電流互感器測量線為僅4mm卻未熔斷。經(jīng)上述分析推斷，引起導(dǎo)體熔斷的原因，并非起火后持續(xù)燃燒導(dǎo)致，通常此類情況的發(fā)生是由于接地故障或者相間短路造成。經(jīng)對燒損件觀察，D28柜第8回路開關(guān)進線端導(dǎo)體及出線端導(dǎo)體均為銅編織線，查看其它柜體發(fā)現(xiàn)，導(dǎo)體外部均套有透明軟管（圖3）。經(jīng)現(xiàn)場查驗臨柜情況，此透明軟管由于長時處于高溫環(huán)境運行，相關(guān)標識已腐蝕模糊，無從查證其功能特性及合格性，經(jīng)現(xiàn)場取樣進行了絕緣測試，發(fā)現(xiàn)其并不具備相應(yīng)的絕緣性能。

　　2.2 Fault Cause Analysis: Through detailed investigation and sampling of the D28 cabinet site, as well as testing and comprehensive analysis of the samples, simulation technology was used to simulate and restore the operating status. The conclusion was drawn that the main cause of the switchgear fire was a single-phase ground short circuit in the conductor of the 8th circuit switch inlet, which caused arc discharge and ignition. The specific analysis is as follows: After inspecting the connectors at both ends of the 8th circuit of D28 cabinet, there were no obvious burn marks on the connectors. At the same time, the internal circuit breaker was checked and no abnormalities were found in the internal conductor. Therefore, it can be ruled out that there is a short circuit between the connectors and the circuit breaker. After inspecting the burnt sample of the 8th circuit of D28 cabinet, it was found that the B-phase copper wire at the inlet of the 8th circuit switch was a double stranded 70mm wire and had completely melted, and the AC phase also had varying degrees of large-area melting. The B-phase copper wire at the input end of the 8th circuit switch is a copper braided wire with a melting point temperature of 1083 ℃. The other main combustible materials in the cabinet are mainly PVC plastic, with a combustion temperature of 350 ℃. Referring to the fire temperature time characteristic curve in the ISO834 international standard, the highest temperature after 1 hour of combustion is about 950 ℃, which is lower than the melting point temperature of the conductor. In addition, the measuring wire of the current transformer on the output side of the switch is only 4mm but not melted. Based on the above analysis, it can be inferred that the cause of conductor melting is not due to continuous combustion after ignition. Usually, such situations occur due to grounding faults or phase to phase short circuits. After observing the burnt parts, it was found that the incoming and outgoing conductors of the 8th circuit switch in D28 cabinet were both copper braided wires. Upon inspection of other cabinets, it was found that the conductors were covered with transparent hoses on the outside (Figure 3). After on-site inspection of the cabinet situation, it was found that the transparent hose had corroded and blurred its relevant markings due to long-term operation in a high-temperature environment, making it impossible to verify its functional characteristics and qualification. After on-site sampling and insulation testing, it was found that it did not have the corresponding insulation performance.

　　現(xiàn)場隨機取樣后，對其進行化驗分析，發(fā)現(xiàn)透明軟管主要成分為聚氯乙烯，是一種不穩(wěn)定的聚合物，在光、熱、機械力、氧及某些活性金屬離子存在時會發(fā)生分解，放出氯化氫，隨著氯化氫分解的數(shù)量增加，軟管會老化，由原來透明逐漸發(fā)黃，逐漸變薄、變脆，容易斷裂；同時，其介電性能與受熱情況有關(guān)：當加熱使PVC分解釋放出氯化氫，氯離子的存在會導(dǎo)致其電絕緣性能明顯下降，因此此透明軟管通常不作為主回路導(dǎo)體絕緣通流使用。與此同時，對相應(yīng)臨柜進行檢查，這種透明軟管均已發(fā)黃老化，且這種導(dǎo)體安裝在柜體中易緊貼金屬外殼，承受殼體內(nèi)凸出的金屬固定件的擠壓，呈明顯受力狀態(tài)，這些情況都極易造成老化的軟管破裂。這種安裝方式不符合GB/T7251.1-2013《低壓成套開關(guān)設(shè)備和控制設(shè)備》第1部分總則中8.6.3條裸導(dǎo)體和絕緣導(dǎo)線的規(guī)定。經(jīng)現(xiàn)場調(diào)查，D28柜第8回路抽屜柜所帶負載為大容量空調(diào)，時值夏季高溫，且長期處于較高負載運行，配電室風扇、空調(diào)等環(huán)控降溫設(shè)施配備不足，導(dǎo)體承受內(nèi)外雙重高溫，致使處于擠壓、受力狀態(tài)的導(dǎo)體外部包覆的透明軟管在高溫下加速老化、開裂，造成單相導(dǎo)體對地短路，弧光放電，產(chǎn)生高溫起火燃燒，由下向上蔓延，逐級引燃各出線回路，所有的導(dǎo)體包覆的透明軟管成為大火燃燒的助推器，導(dǎo)致D28整柜完全燒損。從圖4可以看出，熔斷點在導(dǎo)體與母線連接端、非導(dǎo)體與斷路器連接端，從多個臨柜驗證，此位置緊貼金屬外殼，且受力、擠壓嚴重，已出現(xiàn)不同程度的劃傷、破裂，短路風險極大。

　　After random sampling on site and laboratory analysis, it was found that the main component of the transparent hose is polyvinyl chloride, which is an unstable polymer that decomposes in the presence of light, heat, mechanical force, oxygen, and certain active metal ions, releasing hydrogen chloride. As the amount of hydrogen chloride decomposition increases, the hose will age, gradually turning yellow from its original transparency, becoming thinner, brittle, and prone to breakage; Meanwhile, its dielectric properties are related to the heating conditions: when heating causes PVC to decompose and release hydrogen chloride, the presence of chloride ions will significantly reduce its electrical insulation performance. Therefore, this transparent hose is usually not used as a main circuit conductor for insulation and current flow. At the same time, inspections were conducted on the corresponding adjacent cabinets, and it was found that these transparent hoses have yellowed and aged. Moreover, these conductors are easily attached to the metal shell when installed in the cabinet, and can withstand the pressure of protruding metal fasteners inside the shell, resulting in obvious stress. These situations can easily cause the aging hoses to rupture. This installation method does not comply with the provisions of Article 8.6.3 for bare conductors and insulated conductors in Part 1 of GB/T7251.1-2013 "Low voltage switchgear and control equipment". After on-site investigation, it was found that the load carried by the drawer cabinet of the eighth circuit of D28 cabinet is a large capacity air conditioner, which operates at high temperatures in summer and has been running at high loads for a long time. The environmental control cooling facilities such as fans and air conditioners in the distribution room are insufficient, and the conductor is subjected to dual high temperatures inside and outside. This causes the transparent hose wrapped around the conductor, which is in a compressed and stressed state, to accelerate aging and cracking at high temperatures, resulting in a single-phase conductor short circuit to ground, arc discharge, and high-temperature ignition. It spreads from bottom to top, igniting each outgoing circuit step by step. All the transparent hoses wrapped around the conductor become boosters for the large fire, causing the entire D28 cabinet to be completely burned. From Figure 4, it can be seen that the melting point is located at the connection end between the conductor and the busbar, and the connection end between the non conductor and the circuit breaker. Through multiple cabinet verifications, this position is tightly attached to the metal shell and is subjected to severe force and compression, resulting in varying degrees of scratches and ruptures, posing a great risk of short circuit.

　　2.3故障其它原因分析柜內(nèi)溫度過高。高負荷運行，導(dǎo)體長時通流，而且柜體缺乏維護，導(dǎo)致柜體積灰嚴重，整體散熱不良，配電室無、無空調(diào)降溫設(shè)施，開關(guān)本體及導(dǎo)線高溫運行，整體性能下降，壽命降低。設(shè)備及線路老化。該配電室于2005年正式投運，截止目前連續(xù)運行時間近14年，因運行工況不具備停電運檢條件，連續(xù)長時間運行，核心部件未得到及時的保養(yǎng)、檢測、更換，加速設(shè)備及線路老化，使用壽命降低。

　　2.3 Analysis of Other Causes of Malfunctions: The temperature inside the cabinet is too high. High load operation, prolonged current flow of conductors, and lack of maintenance of the cabinet body result in severe dust accumulation and poor overall heat dissipation. The distribution room lacks dehumidification and air conditioning cooling facilities, and the switch body and wires operate at high temperatures, leading to a decrease in overall performance and lifespan. Equipment and circuit aging. The distribution room was officially put into operation in 2005 and has been in continuous operation for nearly 14 years. Due to the operating conditions not meeting the conditions for power outage operation and inspection, the core components have not been maintained, tested, and replaced in a timely manner, accelerating the aging of equipment and lines and reducing their service life.

　　3應(yīng)對措施抽屜柜中進出線導(dǎo)體應(yīng)選用正規(guī)低壓電纜或者帶有絕緣熱縮管包覆的銅排，并按照相關(guān)標準進行安裝；配電室應(yīng)確保開啟設(shè)備監(jiān)控系統(tǒng)，以便于調(diào)取、查閱設(shè)備運行狀態(tài)。針對歷史數(shù)據(jù)做好統(tǒng)計分析，并對標實際運行數(shù)據(jù)，及時發(fā)現(xiàn)異常并隱患。同時配電室應(yīng)加強送排風系統(tǒng)的管理，送排風功率及效能應(yīng)滿足正常運行需求；配電室內(nèi)的運行低壓柜應(yīng)定期進行質(zhì)量排查，尤其針對內(nèi)部開關(guān)、銅導(dǎo)線、插接件等核心部件，必要時進行更換。配電室所帶負載應(yīng)進行分級分類并逐一進行標識，對非常重要及重要負荷應(yīng)增加必要的保護裝置，制定針對性運檢計劃并落地實施；定期組織運維人員及配電室管理人員進行有效的技能培訓(xùn)，比如配電室運維知識、突發(fā)異常緊急處理、防護等課題培訓(xùn)，并定期開展應(yīng)急演練及實操考核，提升人員技能水平和應(yīng)對突發(fā)事件的應(yīng)變能力[6]。

　　The incoming and outgoing conductors in the drawer cabinet should be selected from regular low-voltage cables or copper bars with insulation heat shrink tubing, and installed in accordance with relevant national standards; The distribution room should ensure that the equipment monitoring system is activated for easy retrieval and viewing of equipment operating status. Conduct statistical analysis on historical data and benchmark it against actual operational data to promptly identify anomalies and eliminate potential hazards. At the same time, the management of the air supply and exhaust system in the distribution room should be strengthened, and the power and efficiency of the air supply and exhaust should meet the requirements of normal operation; The low-voltage cabinet in the distribution room should undergo regular quality checks, especially for core components such as internal switches, copper wires, and connectors, which should be replaced if necessary. The loads carried by the distribution room should be classified and labeled one by one. Necessary protective devices should be added for very important and critical loads, and targeted operation and inspection plans should be developed and implemented; Regularly organize effective skill training for operation and maintenance personnel and distribution room management personnel, such as training on distribution room operation and maintenance knowledge, emergency handling of sudden abnormalities, safety protection, and other topics. Regularly conduct emergency drills and practical assessments to comprehensively improve personnel skill levels and their ability to respond to emergencies.

　　4 結(jié)語MNS低壓抽屜柜是配電室低壓系統(tǒng)的重要配電裝置，通過此次事故希望能引起開關(guān)柜生產(chǎn)廠家的重視，應(yīng)嚴格按照標準進行設(shè)計、生產(chǎn)和安裝，作為電力用戶也應(yīng)該對設(shè)備進行定期檢查、維護和保養(yǎng)，才能共同保證設(shè)備正常運行。

　　Conclusion: The MNS low-voltage drawer cabinet is an important distribution device in the low-voltage system of the distribution room. Through this accident, we hope to draw the attention of the switchgear manufacturer, who should strictly follow national standards for design, production, and installation. As a power user, we should also conduct regular inspections, maintenance, and upkeep of the equipment to ensure its normal and safe operation.

　　附：MNS 單元抽屜開關(guān)分勵脫扣后的復(fù)位操作1、出線單元內(nèi)的主開關(guān)（塑殼斷路器）因故障電流分勵脫扣后，操作機構(gòu)的把手仍然處于“∣”（合閘）位置。1單元以上（抽屜）應(yīng)將合閘機構(gòu)把手（逆時針方向）旋轉(zhuǎn)左下方45°RESET位置，然后再將把手（順時針方向）旋轉(zhuǎn)“○”（分閘）位置。此時斷路器回到正常分閘位置（熱備用狀態(tài)），完成復(fù)位操作。2. 復(fù)位操作完成后，才可再次進行合閘操作。

　　Attachment: Reset operation after the MNS unit drawer switch is tripped due to fault current. 1. After the main switch (molded case circuit breaker) in the outgoing unit is tripped due to fault current, the handle of the operating mechanism is still in the "∣" (closed) position. For units above 1 (drawer), the closing mechanism handle (counterclockwise) should be rotated to the 45 ° RESET position at the bottom left, and then the handle (clockwise) should be rotated to the "○" (opening) position. At this point, the circuit breaker returns to its normal opening position (hot standby state), completing the reset operation. After the reset operation is completed, the closing operation can be performed again.

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