Analysis on fire and explosion prevention of power

2022-08-09
  • Detail

Brief analysis on the fire and explosion prevention of power capacitors

1 introduction

each oil transmission pump station under the long-distance transmission pipeline adopts 6kV high-voltage motor for oil transportation. The rated power of the high-voltage motor is generally above 1000kW, and the motor is an inductive load, so the operation of the high-voltage motor worsens the power supply quality of electricity, and increases the reactive power loss at the same time. In order to improve the quality of power supply and reduce reactive power loss, capacitance compensation must be adopted. Power capacitor is an oil filling equipment, and the crude oil transported by the pump station is easy to volatilize. If the capacitor is installed, operated or operated improperly, it may cause fire or even explosion accidents. Therefore, it is of great significance to ensure the safe operation of the capacitor

2 cause analysis of ignition and explosion

2 1. The management concept is backward and there is no advanced capacitor real-time monitoring technology

(1) the personnel on duty fail to find the hidden trouble in time

if they fail to find and deal with the leakage of oil from the capacitor porcelain bushing and shell in time, resulting in moisture inside the bushing, reduced insulation resistance and breakdown discharge; Without advanced monitoring technology, partial discharge cannot be found inside

(2) the maintenance is not in place

if the temperature of the capacitor is too high and no cooling measures are taken, a large amount of gas is produced by the insulating oil, causing the tank wall to deform and bulge; The equipment is not cleaned regularly, and the surface of the porcelain insulator is seriously polluted, which leads to insulation breakdown and surface discharge in the case of internal and external overvoltage and system resonance, resulting in the flashover damage of the porcelain insulator bushing matching with the different materials tested

(3) the capacitor calibration is not timely and the operation is not standardized, which embeds the hidden danger of accidents

2. 2. The harm of overvoltage caused by frequent switching of capacitors

in order to control the power factor at a high level, some oil delivery pump stations are equipped with automatic reactive power compensation devices, and the frequent fluctuation of reactive power of high-voltage oil delivery motors causes frequent switching of capacitors. When the capacitor is powered on, an oscillation circuit is formed, resulting in overvoltage and overcurrent. Under the action of frequent overvoltage, the partial discharge of the capacitor is continuously excited and intensified, which will inevitably promote the aging of the insulating medium and the attenuation of capacitance. It is generally believed that the voltage increases by 10% and the service life decreases by half. National standard GB/t12747 1 - 2004 stipulates that the capacitor operation shall not exceed 5000 times per year, because although the overvoltage generated by putting the capacitor into operation is instantaneous, the impact of Overvoltage on the insulating medium can be accumulated. After installing the automatic compensation device, the frequent operation of the capacitor bank finally saved the expenses for the kindergarten. The number of operations of each capacitor every year was more than three times that required by the national standard, which accelerated the aging of the insulation medium, gradually developed to electric breakdown, and finally the capacitor burst, causing fire

2. 3 harm of high-order harmonics

harmonics can cause sinusoidal waveform distortion of system operating current and voltage, accelerate aging of insulation medium, reduce service life of equipment or damage due to long-term overheating, especially when high-order harmonics resonate, capacitors are most likely to be overloaded, overheated, vibrated and even damaged

2. 4. There is a flammable and explosive environment

the crude oil transported by the pump station is volatile, and the mixture formed after mixing with air may reach the explosion limit. Once encountering the fire source, it may catch fire and explode

2. 5. The unreasonable structure of the capacitor itself, poor manufacturing quality and improper installation

(1) improper type selection

the improper insulation treatment process of the capacitor electrode to the oil tank and the poor quality of the product components are the reasons for partial discharge. The electric field intensity and current density at the edge, corner and lead contact of the electrode are high, which is prone to partial discharge and overheating burn insulation, resulting in the breakdown of the capacitor components

(2) improper installation

if the capacitor bank adopts local compensation, the oil and gas density in the pump room is high, and it is very easy to catch fire and explode in case of sparks; The capacitor bank is not equipped with fan cooling device, etc

(3) improper protection

when the fuse specially used to protect the capacitor from the explosion of the capacitor oil tank is selected, the rated current of the fuse is too long, and the regulation of the three-dimensional network structure is large in the process of fiber-reinforced polymer injection molding; The setting values of unbalanced or differential relay protection and time-delay overcurrent protection adopted by capacitor banks are too large, and the setting time is too long. Once the capacitor fails, it cannot play a protective role, resulting in fire and explosion accidents

3 fire and explosion prevention measures

3 1 improve the real-time monitoring technology of capacitors

the traditional capacitor detection method is to cut off power and off-line, which affects the power supply quality of electricity, and the measurement result is static, while the capacitor fault is random. The current real-time monitoring system judges whether the capacitor is faulty by detecting the current, capacity and dielectric loss tangent value flowing through the capacitor, but the change of capacitance and dielectric loss angle is the result of discharge accumulation to a certain extent, lagging behind the fault. We know that partial discharge is the precursor of common capacitor accidents. Therefore, we can find capacitor faults in time and effectively prevent accidents by adopting the advanced technology of real-time monitoring capacitor partial discharge

on the other hand, it completely solves the pollutants. 3 2. Introduce HSE (health, safety and environmental protection) management concept

(1) correctly apply protection, regularly verify the reliability of protection, and standardize the verification work of capacitor banks, such as checking the capacitance of capacitors and fuses at least once a month, and measure the loss tangent of capacitors twice or three times in a year, in order to check the reliability of capacitors

(2) strengthen the patrol inspection of capacitor banks, and implement the parameter system of one hour patrol inspection and two hours recording. It is found that the capacitor shell leaks oil, expands and bulges, and the current exceeds the rated current of the capacitor by 1 3 times. The electric voltage exceeds the rated voltage by 1 If the ambient temperature exceeds the rated value, the capacitor shall be removed from operation for maintenance

(3) strengthen the maintenance of capacitors. Keep the surface of capacitor bushing, capacitor shell, iron frame for placing capacitor, contactor and reactor clean; Take cooling measures for capacitors in summer

(4) operate according to the operating procedures. It is forbidden to switch on the capacitor with power and switch frequently. It is not allowed to forcibly send power after the switch trips, and it is not allowed to replace the fuse after the fuse is fused for unclear reasons

3. 3 centralized compensation

the hidden danger of decentralized local compensation of capacitors is that the pump room is a flammable and explosive place, and the discharge of the capacitor housing and the flashover discharge caused by the dirty or defective bushing may cause the fire and explosion accident of the pump room. Our solution is to adopt capacitor centralized compensation. When selecting and constructing the capacitor room, we should consider maintaining a safe distance from the pump room, good ventilation, dust and rain prevention, and easy inspection

3. 4. Reduce the number of switching

adopt the cyclic switching of capacitor banks, and extend the delay time interval of the automatic compensation device controller, so as to reduce the number of switching, so that each group of capacitors can be operated no more than 5000 times a year

3. 5 strengthen the management of high-order harmonic components

adopt the method of adding series reactor or filter device to suppress harmonics and improve the quality of power supply

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