Abstract: The causes of fire and explosion of power capacitors were analyzed and corresponding measures were proposed to effectively prevent the occurrence of capacitor fire and explosion accidents. Keywords: partial discharge, overvoltage, real-time monitoring, resonance, breakdown 1 Introduction The oil pumping stations under the long-distance pipeline all use 6kV high-voltage motors for oil transportation. The rated power of the high-voltage motors is generally above 1000kW. The motors are inductive loads, so the operation of the high-voltage motors deteriorates the power supply quality of the power grid and increases reactive power loss. In order to improve the power supply quality and reduce reactive power loss, capacitor compensation must be adopted. Power capacitors are oil-filled devices. The crude oil transported by the pumping station is easy to volatilize. If the capacitor is improperly installed, operated or operated, it may cause fire or even explosion accidents. Therefore, ensuring the safe operation of the capacitor is of great significance. 2 Analysis of the causes of fire and explosion 2.1 Backward management concept and lack of advanced capacitor real-time monitoring technology (1) The on-duty personnel failed to detect the fault hazards in time. For example, they failed to detect and deal with the leakage of oil from the capacitor porcelain bushing and shell in time, which led to the internal dampness of the bushing and the reduction of insulation resistance, resulting in breakdown discharge; the lack of advanced monitoring technology made it impossible to detect the internal partial discharge, etc. (2) Inadequate maintenance, such as excessively high capacitor temperature, without cooling measures, causing the insulating oil to produce a large amount of gas, resulting in deformation and bulging of the tank wall; failure to clean the equipment regularly, resulting in serious dirt on the surface of the porcelain insulator, which leads to insulation breakdown and surface discharge under the condition of internal and external overvoltage and system resonance in the power grid, causing flashover damage to the porcelain bushing. (3) Untimely capacitor calibration and non-standard operation have buried potential safety hazards. 2.2 The hazards of overvoltage caused by frequent switching of capacitors In order to control the power factor at a high level, some oil pumping stations have installed automatic reactive power compensation devices. The frequent fluctuation of reactive power of the high-voltage oil pumping motor has caused frequent switching of capacitors. When the capacitor is connected to the power grid, it forms an oscillating circuit, generating overvoltage and overcurrent. Under the action of frequent overvoltage, the partial discharge of the capacitor is continuously excited and aggravated, which will inevitably promote the aging of the insulating medium and the decay of the capacitance. It is generally believed that a 10% increase in voltage reduces the life by half. The national standard GB/T12747.1-2004 stipulates that capacitor operations should not exceed 5000 times per year. This is because although the overvoltage generated by connecting capacitors is instantaneous, its impact on the insulating medium can accumulate. After installing automatic compensation devices, capacitor banks are frequently operated, with each capacitor operating more than three times the national standard requirement per year. This accelerates the aging of the insulating medium, gradually leading to electrical breakdown, and ultimately, capacitor explosion and fire. 2.3 Hazards of High-Order Harmonics: Harmonics can cause distortion of the sinusoidal waveforms of system operating current and voltage, accelerate the aging of the insulating medium, reduce equipment lifespan, or cause damage due to prolonged overheating. Especially when high-order harmonics resonate, capacitors are most prone to overload, overheating, vibration, and even damage. 2.4 Flammable and Explosive Environments: Crude oil transported by pump stations is volatile, and the mixture formed after mixing with air may reach the explosive limit. Once exposed to a source of ignition, it may ignite and explode. 2.5 Unreasonable capacitor structure, poor manufacturing quality and improper installation (1) Improper selection Improper insulation treatment of capacitor electrodes to the oil tank, poor quality of product components, etc. are the causes of partial discharge. The electric field strength and current density are high at the electrode edge, corner and lead contact, which can easily cause partial discharge and overheating burn insulation, leading to capacitor element breakdown. (2) Improper installation If the capacitor bank adopts local compensation, the oil and gas density in the pump room is high, and it is easy to ignite and explode when it encounters a spark; the capacitor bank does not have a fan cooling device, etc. (3) Improper protection Please log on to: Power Transmission and Distribution Equipment Network to browse more information When selecting fuses specifically used to protect capacitors and prevent capacitor tank explosions, the rated current of the fuse wire is too large; the setting value of unbalanced or differential relay protection and time-delayed overcurrent protection used in the capacitor bank is too large, and the setting time is too long, etc. Once the capacitor fails, it cannot play a protective role, causing fire and explosion accidents. 3 Fire and explosion prevention measures 3.1 Improve the real-time monitoring technology of capacitors Traditional capacitor detection methods are carried out offline and without power, which affects the power supply quality of the power grid and the measurement results are static, while capacitor faults are random. The current real-time monitoring system determines whether the capacitor is faulty by detecting the current flowing through the capacitor, the capacitance and the dielectric loss tangent. However, the change in capacitance and dielectric loss angle is the result of discharge accumulation to a certain extent, which lags behind the fault. We know that partial discharge is a precursor to common capacitor accidents. Therefore, we can use advanced technology to monitor capacitor partial discharge in real time to detect capacitor faults in a timely manner and effectively prevent accidents. Please log in to: Power Transmission and Distribution Equipment Network to browse more information 3.2 Introduce the HSE (Health, Safety and Environmental Protection) management concept (1) Correctly put the protection on, regularly check the reliability of the protection, and standardize the verification work of capacitor banks. For example, the capacitance and fuse of the capacitor should be checked at least once a month, and the loss tangent of the capacitor should be measured two or three times a year. The purpose is to check the reliability of the capacitor. (2) Strengthen the inspection of capacitor banks and implement a system of one inspection per hour and one parameter record per two hours. If the capacitor shell is found to be leaking oil, bulging, current exceeding 1.3 times the rated current of the capacitor, grid voltage exceeding 1.1 times the rated voltage, or ambient temperature exceeding the rated value, the capacitor should be taken out of operation for maintenance. (3) Strengthen the maintenance of capacitors. Keep the surface of the capacitor bushing, capacitor shell, iron frame for placing the capacitor, contactor and reactor clean; take cooling measures for the capacitor in summer. (4) Operate according to the operating procedures. It is forbidden to close the capacitor while it is energized or to frequently switch it on and off. It is not allowed to force power back on after the switch trips. It is not allowed to replace the fuse if the cause of the fuse blows is unclear. 3.3 The hidden danger of centralized compensation capacitors being distributed and compensated locally is that the pump room is a flammable and explosive place. Discharge of the capacitor shell and flashover discharge caused by dirt or defects in the bushing may cause fire and explosion accidents in the pump room. Our solution involves centralized capacitor compensation. When selecting and constructing the capacitor bank, considerations should be given to maintaining a safe distance from the pump room, ensuring good ventilation, dust and rain protection, and ease of inspection. 3.4 To reduce the number of switching operations, cyclic switching of capacitor banks should be implemented, while simultaneously extending the delay interval of the automatic compensation device controller, thereby reducing the number of switching operations to no more than 5000 times per capacitor bank per year. 3.5 To strengthen the management of high-order harmonic components in the power grid, harmonics should be suppressed by installing series reactors or filtering devices to improve the power supply quality.