Maintenance and operation of the hottest power cap

Maintenance and operation of power capacitor

power capacitor is a static reactive power compensation equipment. Its main function is to provide reactive power to the power system and improve the power factor. Local reactive power compensation can reduce the transmission current of transmission lines, reduce the energy loss and voltage drop of lines, improve power quality and improve the utilization rate of equipment. Some problems in the maintenance and operation management of power capacitors are briefly introduced for reference

1 protection of power capacitors

(1) capacitor banks should adopt appropriate protection measures, such as balance or differential relay protection or instantaneous overcurrent relay protection. For capacitors of 3.15kv and above, separate fuses must be installed on each capacitor. The rated current of the fuses should be selected according to the characteristics of the fuse and the inrush current when connecting, and it is generally appropriate to be 1.5 times the rated current of the capacitor, To prevent the capacitor oil tank from exploding

(2) in addition to the above-mentioned protection forms, the following types of protection can be made when necessary:

① if the voltage rise is frequent and long-term, measures should be taken to make the voltage rise not more than 1.1 times the rated voltage

② protect with appropriate automatic current switch, so that the current increase does not exceed 1.3 times the rated current

③ if the capacitor is connected with the overhead line, a suitable lightning arrester can be used for atmospheric overvoltage protection

④ in high stroke voltage network, when the short-circuit current exceeds 20a, and the short-circuit current protection device or fuse cannot reliably protect the short-circuit to ground, the single-phase short-circuit protection device should be used

(3) the correct selection of the protection mode of the capacitor bank is the key to ensure the safe and reliable operation of the capacitor, but no matter which protection mode is adopted, the following requirements should be met:

① the protection device should have sufficient sensitivity, and the protection device can operate reliably regardless of the internal failure of a single capacitor in the capacitor bank or the damage of some components

② the faulty capacitor can be selectively cut off, or it is convenient to check the damaged capacitor after all the power supplies of the capacitor bank are disconnected

③ in the process of capacitor power off and transmission, and in case of grounding or other faults in the power system, the protection device shall not operate incorrectly

④ the protection device shall be convenient for installation, adjustment, test, operation and maintenance

⑤ the power consumption should be less and the operation cost should be low

(4) the capacitor is not allowed to be equipped with automatic reclosing device, and the phase reaction is equipped with no voltage release automatic tripping device. It is mainly because it takes a certain time for the capacitor to discharge. If the switch of the capacitor bank trips and is reclosed immediately, it is too late for the capacitor to discharge, and there may be a charge in the capacitor with the opposite polarity of the reclosing voltage, which will produce a large impulse current at the moment of closing, resulting in the expansion of the capacitor shell, oil injection and even explosion

2 connection and disconnection of power capacitor

(1) before connection of power capacitor bank, use a megger to check the discharge circuit

(2) when connecting and disconnecting the capacitor bank, the following points must be considered:

① when the voltage on the busbar (bus) exceeds 1.1 times the maximum allowable value of the rated voltage, it is forbidden to connect the capacitor bank to electricity

② it is not allowed to re connect the capacitor bank within 1min after the capacitor bank is disconnected automatically, except for automatic re connection

③ when connecting and disconnecting the capacitor bank, the circuit breaker that cannot produce dangerous overvoltage shall be selected, and the rated current of the circuit breaker shall not be less than 1.3 times the rated current of the capacitor bank

3 discharge of power capacitor

(1) the capacitor should be discharged automatically every time it is disconnected from power. The terminal voltage decreases rapidly. No matter what the rated voltage of the capacitor is, the terminal voltage should not exceed 65V after the capacitor is disconnected from the electricity for 30s

(2) in order to protect the capacitor bank, the automatic discharge device should be installed on the load side of the capacitor circuit breaker and often directly connected in parallel with the capacitor (circuit breakers, disconnectors, fuses, etc. are not allowed to be installed in the middle). Capacitor banks with non dedicated discharge devices, such as voltage transformers for high-voltage capacitors, incandescent bulbs for low-voltage capacitors, and capacitor banks directly connected to motors, may not be equipped with additional discharge devices. When using bulbs, in order to prolong the service life of bulbs, the number of bulbs in series should be appropriately increased

(3) before contacting the conductive part of the capacitor that is electrically disconnected, even if the capacitor has been automatically discharged, the material with high toughness can be fully designed into a snap in cover. The insulated grounding metal rod must be used to short-circuit the outlet end of the capacitor for separate discharge

4 maintenance of capacitors in operation

(1) the capacitors should have personnel on duty and make records of equipment operation

(2) the appearance patrol inspection of the operating capacitor bank should be carried out every day according to the regulations. In case of expansion of the tank shell, it should be stopped to avoid failure

(3) check the load of each phase of the capacitor bank with an ammeter

(4) when the capacitor bank is put into operation, the ambient temperature shall not be lower than -40 ℃, and the ambient temperature during operation shall not exceed +40 ℃ on average for 1 hour, and +30 ℃ on average for 2 hours, and +20 ℃ on average for a year. If it exceeds, manual cooling (installing fans) or disconnecting the capacitor bank from the electricity should be adopted

(5) the temperature inspection of the installation site and the hottest spot temperature on the capacitor shell can be carried out through mercury thermometer, etc., and the temperature records shall be made (especially in summer)

(6) the working voltage and current of the capacitor shall not exceed 1.1 times the rated voltage and 1.3 times the rated current when used

(7) after connecting the capacitor, the electric voltage will rise, especially when the load is light. In this case, the cost and energy consumption of the tensile testing machine should be reduced and the capacitor or all capacitors should be disconnected from the electricity

(8) the surface of capacitor bushing and supporting insulator should be clean, without damage and discharge trace, the capacitor shell should be clean, without deformation and oil leakage, and the capacitor and iron shelf should not be full of dust and other dirty things

(9) carefully pay attention to the reliability of all contacts on the electrical circuit connected with the capacitor bank (current collection bank, grounding wire, circuit breaker, fuse, switch, etc.). Because a contact on the road fails, or even the nut is not screwed tightly, it may cause early damage to the capacitor and accidents to the whole equipment

(10) if the capacitor needs voltage withstand test after running for a period of time, it should be tested according to the specified value

(11) check the capacitor capacitance and fuse at least once a month. The Tg of the capacitor should be measured 2 ~ 3 times in a year to check the reliability of the capacitor. Each measurement should be carried out under the rated voltage or near the rated value

(12) if the circuit breaker of the capacitor bank trips due to the action of the relay, it shall not be closed again until the cause of the trip is found out

(13) if oil leakage is found in the capacitor shell during operation or transportation, it can be repaired by brazing with tin lead solder

5 precautions during switching operation of power capacitor bank

(1) under normal circumstances, when the whole substation is powered off, the circuit breaker of capacitor bank shall be disconnected first, and then each outgoing circuit breaker shall be opened. The sequence shall be reversed when power transmission is restored

(2) in case of an accident, the circuit breaker of the capacitor bank must be disconnected after the whole substation has no power

(3) the capacitor bank circuit breaker industry and information technology department will focus on the research and development, production and utilization of aviation aluminum materials. After tripping, forced power transmission is not allowed. After the protective fuse is blown, it is not allowed to replace the fuse for power transmission without finding out the cause

(4) it is forbidden to switch on the capacitor bank with charge. When the capacitor bank is switched on again, it must be carried out 3 minutes after the circuit breaker is disconnected

6 troubleshooting of capacitors in operation

(1) when the capacitor is on fire due to oil injection, explosion, immediately disconnect the power supply and extinguish the fire with sand or dry fire extinguisher. Such accidents are mostly caused by overvoltage inside and outside the system and serious internal faults of capacitors. In order to prevent such accidents, it is required that the fuse specifications of a single fuse must match, and the cause must be carefully found after the fuse is blown. Reclosing is not allowed for capacitor banks, and forced power transmission is not allowed after tripping, so as to avoid greater damage accidents

(2) the circuit breaker of the capacitor trips, while the fuse of the shunt fuse is not fused. After discharging the capacitor for 3min, check the circuit breaker, current transformer, power cable and the outside of the capacitor. If no abnormality is found, it may be caused by external fault or bus voltage fluctuation. After checking that it is normal, it can be put into trial operation. Otherwise, a comprehensive power on test should be carried out for the protection. Through the above inspection and test, if the cause is still not found, the capacitor bank should be disassembled and inspected and tested one by one. However, trial operation is not allowed until the cause is found out

(3) when the fuse of the capacitor is blown, report to the dispatcher on duty, and disconnect the circuit breaker of the capacitor after obtaining consent. After cutting off the power supply and discharging the capacitor, first conduct external inspection, such as whether there is flashover trace on the outside of the bushing, whether the shell is deformed, whether there is oil leakage and whether the grounding device is short circuited, and then use an insulation megger to measure the insulation resistance between poles and between poles to ground. If there is no sign of failure, replace the fuse and continue to operate. If the fuse of the fuse is still blown after power transmission, the faulty capacitor shall be exited and the power transmission operation of the rest shall be resumed

7 safety precautions for handling fault capacitors

handling fault capacitors should be carried out after disconnecting the circuit breaker of the capacitor, opening the isolating switches of the two circuit breakers, and discharging the capacitor bank through the discharge resistance. After the capacitor bank is discharged by the discharge resistance (discharge transformer or discharge voltage transformer), a manual discharge should still be carried out because some of the remaining charges cannot be discharged for a time. When discharging, first connect the grounding terminal of the grounding wire, and then discharge the capacitor with the grounding rod for many times until there is no discharge spark and discharge sound, and then fix the grounding terminal. As the faulty capacitor may have poor lead contact, internal disconnection or fuse fusing, part of the charge may not be discharged. Therefore, before contacting the faulty capacitor, the maintenance personnel should also wear insulating gloves, short circuit the two poles of the faulty capacitor with a short line, and then disassemble and replace it

for the neutral line of the capacitor bank with double star connection and the series connection of multiple capacitors, separate discharge shall be carried out

among all kinds of equipment in the substation, the capacitor is an electrical appliance with relatively weak reliability. Its insulation is weaker than that of other equipment of the same voltage. The internal components heat more, and the heat dissipation is poor. There are many opportunities for internal faults. The combustible components of the internal materials used to manufacture power capacitors are large, so it is very easy to catch fire during operation. Therefore, good low temperature and ventilation conditions should be created for the operation of power capacitors as far as possible

8 repair of power capacitor

(1) the following faults can be repaired at the installation place:

① the oil leakage on the box shell can be repaired with tin lead solder

② oil leakage at the casing weld can be repaired with tin lead solder, but it should be noted that the soldering iron should not be overheated to prevent the silver layer from desoldering

(2) capacitor insulation breakdown to ground, capacitor