For all electricians, capacitors are quite common, and they are used quite frequently. So we will often see some exposed problems, and then how should we solve them for these.
1. Oil seepage (leakage)
Question: For capacitors, oil leakage is just like commonplace, and the causes are many and varied, mainly as follows:
1. Due to improper handling methods, or lifting of the porcelain sleeve, cracks are formed in the welding of the flange;
2. When wiring, the welding part of the porcelain sleeve is damaged due to excessive tightening of the screws;
3. Some defects in the product manufacturing process may cause leakage and oil leakage of the capacitor;
4. After the capacitor is put into operation, due to the drastic temperature change and the increase of internal pressure, the oil leakage and oil leakage will be more serious;
5. Due to improper operation and maintenance, long-term operation of the capacitor www.okcis.cn/shebeizb-dianrongqi/ lack of maintenance leads to peeling of the paint layer of the shell and corrosion of the iron sheet, which is also a cause of leakage and oil leakage of the capacitor during operation.
Although it is relatively common, it cannot be ignored. Sometimes a small problem can easily cause a big problem. The consequence of capacitor leakage and oil leakage is to reduce the impregnating agent, and the upper part of the component is easy to get damp and break down and damage the capacitor. Therefore, timely treatment must be carried out.
Solve:
1. When installing capacitors, the wiring of each capacitor should be connected to the bus with a separate flexible wire. Do not use hard bus connections to prevent assembly stress from damaging the capacitor casing and breaking the seal and causing oil leakage.
2. When handling the capacitor, it should be placed upright, and it is strictly forbidden to carry the bushing; when wiring, do not tighten the screws with excessive force and pay attention to protect the bushing.
3. Oil seepage at the welding seam of the capacitor case and casing, the seepage and leakage can be removed, and then repaired with tin brazing material. When repairing the welding seam of the casing, the soldering iron should not be overheated to prevent the silver layer from falling off. Paint afterwards. If oil seepage or oil leakage is serious, replace the capacitor.
2. Deformation of the capacitor shell
Question:
Due to the release of the medium inside the capacitor under the action of a high-voltage electric field, the medium is decomposed and gas is released, or due to the breakdown of some components, the capacitor electrode discharges to the shell and other reasons, etc., will cause the medium to release gas. These gases in the sealed shell will cause an increase in internal pressure, which will cause the shell to expand and deform. Therefore, the deformation of the capacitor shell is a symptom before the failure or failure of the capacitor.
Solve:
Perform visual inspection of the operating capacitor bank frequently. If the capacitor shell is found to be swollen and deformed, take immediate measures. If the expansion is serious (the expansion of each side of 100Kvar should not be greater than 10mm; the expansion of 100Kvar and above should not be greater than 20mm). Stop using, find out the cause, and replace the capacitor. If the shell expansion is not serious, ventilation measures should be taken to strengthen the operation inspection work.
Three, protection device action
Question:
1. Because the three-phase capacitance of the capacitor bank is unbalanced, the three-phase current is unbalanced, which causes the capacitor bank protection device to trip the capacitor bank circuit breaker;
2. For capacitors equipped with fuse protection devices, the fuse of the fuse is blown due to abnormalities in the capacitor, changes in capacitance, grounding of the pole to the shell, excessive inrush current and overvoltage;
3. Improper operation operation causes the operating voltage of the capacitor to exceed the specified value and causes the protection device to trip the circuit breaker.
Solve:
1. Periodically measure the capacitance value of the capacitor. The deviation of the capacitance value shall not exceed the range of -5%～+10% of the rated value, and the capacitance value shall not be less than 95% of the factory value.
2. Before the capacitor bank is installed, the capacitance should be allocated once to balance the three-phase capacity, and the error should not exceed 5% of the total capacity of one phase; when a relay protection device is installed, it should also meet the balance current error during operation. Exceeds the requirement of relay protection action current; after the protection device is activated, the insulation resistance of the capacitor pole to the shell should be measured not less than 2000MΩ.
3. In order to limit the inflow of inrush current and higher harmonics, the capacitor bank should be equipped with a series reactor;
4. The capacitor should be used under the rated voltage. If the voltage on the power grid is too low, the capacitor will not reach the rated output. Long-term over-voltage operation will cause the capacitor to heat up, accelerate the insulation aging, and easily damage the capacitor. According to regulations, when the grid voltage exceeds 10% of the capacitor's rated voltage for a long time, the capacitor should be taken out of operation;
5. When a fuse is used for capacitor protection, the selection of the fuse should be appropriate. Generally, the rated current of the melt should not be greater than 1.3 times the rated current of the capacitor;
6. Measure the insulation resistance between the pole and the shell of the capacitor should not be less than 2000MΩ.
4. Flashover discharge on the surface of the capacitor porcelain sleeve
Question:
During the operation of the capacitor, due to lack of cleaning and maintenance, the porcelain insulation surface is dirty. After the dirt adsorbs moisture, the insulation of the porcelain sleeve is reduced, the surface leakage current increases, and the surface of the porcelain sleeve is flashed and discharged. In addition, the surface of the ceramic sleeve of the capacitor is dirty, which causes flashover discharge on the surface of the ceramic sleeve under the action of a certain overvoltage of the system. As a result of the flashover discharge, the porcelain on the surface of the porcelain sleeve is damaged, which may cause the insulation breakdown of the porcelain sleeve and the circuit breaker tripping accident.
Solve:
The capacitor bank in operation should be checked and cleaned regularly; corresponding anti-pollution measures should be taken according to the anti-pollution level. In severely polluted areas, capacitors should not be installed outdoors.
Five, the capacitor exploded
Question:
The explosion of a capacitor during operation is a vicious accident. Generally, when the internal components are inter-electrode or when the insulation breakdown of the casing, other capacitors connected in parallel with it will release a large amount of energy to the capacitor, which may cause the capacitor to explode and cause a fire. The reasons are:
1. Breakdown of the internal components of the capacitor: mainly caused by poor manufacturing process.
2. The insulation of the capacitor shell is damaged: the high-voltage side lead wire of the capacitor is made of thin copper sheet. If the manufacturing process is poor, the edge is uneven with burrs or severely bent, its tip capacity will produce a corona, which will cause the oil to decompose and the case. Breakdown caused by swelling and lowering of oil level. In addition, the welding time at the corners is too long when the cover is sealed, which will burn the internal insulation and generate oil and gas, which will greatly reduce the breakdown voltage and damage.
3. Poor sealing and oil leakage: due to poor sealing of the assembly casing, moisture enters the interior, which reduces the insulation resistance; or the oil level drops due to oil leakage, resulting in pole-to-shell discharge or component breakdown.
4. Bulging and internal dissociation: mainly due to internal corona, breakdown discharge and severe dissociation. Under the action of overvoltage, the capacitor will reduce the initial dissociation voltage of the component below the working electric field strength, which causes A series of physical, chemical and electrical effects accelerate the aging and decomposition of insulation and produce gas. A vicious circle is formed, causing the pressure of the tank shell to increase, causing the outer wall of the tank to bulge and cause an explosion.
5. Capacitor explosion caused by live switching: any capacitor bank with rated voltage is forbidden to be switched on. Each time the capacitor bank is reclosed, the capacitor must be discharged for 3 minutes when the switch is off. Otherwise, the voltage polarity at the moment of closing may be opposite to the polarity of the residual charge on the capacitor and cause an explosion. For this reason, it is generally stipulated that capacitor banks with a capacity of more than 160Kvar should be equipped with automatic tripping devices when there is no voltage, and it is stipulated that the switches of the capacitor banks are not allowed to be equipped with automatic reclosing.
In addition, it may also cause an explosion due to excessive temperature, poor ventilation, excessive operating voltage, excessive voltage harmonic components, or operating overvoltage.
Solve:
In order to prevent the capacitor from bursting accidents, the most important thing is to install the protective device of the capacitor in addition to the requirement to strengthen the patrol and inspection during the operation, and to cut off the capacitor in time before the burst accident occurs. During operation, if the capacitor is found to make a "cooing" sound, it is a precursor to the collapse of the capacitor's internal insulation. Therefore, the operation should be stopped and the faulty capacitor should be found. After the capacitor bursts, the capacitor should be replaced.
Sixth, the terminal is not installed firmly
Question:
If the capacitor terminal is not installed firmly, the contact resistance will increase when the current flows through the wire, and sometimes it will emit a "squeak" discharge sound, which will cause the terminal to heat up and deform, and emit a discharge sound. In severe cases, the terminal will burn and melt.
Solve:
Use an infrared camera to measure the temperature of the terminals and the body. If the surface of the terminal is overheated and oxidized, the contact surface of the terminal should be polished, coated with conductive grease and then tighten the screw. If the terminal heats up severely or melts, the terminal should be replaced.
Seven, the capacitor temperature rises
Question:
The main reasons are the long-term overvoltage operation of the capacitor, the inflow of high-order harmonics generated by the nearby rectifier device, the overcurrent of the capacitor, the improper selection of the capacitor, the insufficient oil volume and the poor ventilation conditions. In addition, due to the aging of the capacitor's dielectric after long-term operation, the continuous increase of dielectric loss (tanδ) may lead to excessive temperature rise of the capacitor. The increase in the temperature of the capacitor will affect the life of the capacitor and cause the insulation breakdown and damage of the capacitor.
Solve:
The ambient temperature of the capacitor room should be strictly monitored and controlled during operation. In order to facilitate the monitoring of the ambient temperature during operation, the worst heat dissipation condition (two-thirds of the height of the capacitor) should be selected to install the thermometer, and the location of the thermometer should be installed. Easy to observe. In order to monitor the temperature of the capacitor case, a temperature-indicating wax sheet can be pasted on the capacitor case (near the nameplate). If the room temperature is too high, necessary ventilation and cooling measures should be taken. If the requirements for room temperature control below 40°C are still not met after the measures are taken, the operation should be stopped immediately. If it is a capacitor problem, replace the capacitor.