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Power Capacitor Bank To Ensure The Safe And Reliable Operation Of The Key
- Jul 07, 2017 -

The Power Capacitor Bank is a static reactive power compensation device. Its main role is to provide reactive power to the power system, improve the power factor. The use of local reactive power compensation, can reduce the transmission line transmission current, play a line to reduce energy loss and pressure drop, improve power quality and improve the utilization of equipment an important role.

Now the Power Capacitor Bank maintenance and operation of some of the problems, for a brief introduction, for reference.

First, the protection of Power Capacitor Banks

(1) The capacitor group shall be suitably protected, such as the use of balanced or differential relay protection or the use of transient overcurrent relay protection. For capacitors of 3.15 kV and above, separate fuses may be provided on each capacitor, The rated current of the fuse should be selected according to the characteristics of the fuse and the inrush current, usually 1.5 times the rated current of the capacitor is appropriate to prevent the capacitor tank explosion.

(2) In addition to the forms of protection indicated above, the following protection may be made, if necessary:

 ① If the voltage rise is frequent and long time, take measures to make the voltage rise of not more than 1.1 times the rated voltage.

 ② with the appropriate current automatic switch protection, so that the current rise of not more than 1.3 times the rated current.

 ③ If the capacitor with the overhead line connection, the appropriate lightning arrester can be used for atmospheric over-voltage protection.

 ④ In the high-voltage network, short-circuit current exceeds 20A, and short-circuit current protection device or fuse can not reliably protect the ground short circuit, you should use single-phase short circuit protection device.

(3) the correct choice of the capacitor group protection, is to ensure the safe and reliable operation of the capacitor key, but no matter what kind of protection, should meet the following requirements:

 ① protection device should have sufficient sensitivity, regardless of the capacitor group within a single capacitor failure, or part of the components damaged, the protection device can be reliable action.

 ② It is possible to selectively remove the faulty capacitor or to check the damaged capacitor after all the power of the capacitor bank has been disconnected.

 ③ protection device can not malfunction when the capacitor is stopped and the power system is grounded or other fault.

 ④ protection device should be easy to install, adjust, test and operation and maintenance.

 ⑤ consumption of electricity to be less, operating costs to be low.

(4) capacitor does not allow the installation of automatic reclosing device, the opposite should be installed without pressure release automatic trip device. Mainly because of the capacitor discharge takes some time, when the capacitor group switch trip, if immediately reclosing, the capacitor is too late to discharge, in the capacitor may be remnant with the reclosing voltage polarity of the opposite charge, which will close Instantly produce a large impact current, resulting in expansion of the capacitor shell, fuel injection or even explosion.

Second, the Power Capacitor Bank on and off

(1) The Power Capacitor Bank bank shall use the megger to check the discharge network before turning on.

(2) When turning on and off the capacitor bank, the following points must be considered:

 ① When the voltage on the busbar (bus) exceeds 1.1 times the maximum permissible value of the rated voltage, it is forbidden to connect the capacitor bank to the grid.

 ② In the capacitor group 1min after the disconnection from the grid shall not be re-access, but the automatic repeat access except.

 ③ When the capacitor bank is turned on and off, use a circuit breaker that can not generate dangerous overvoltages, and the rated current of the circuit breaker should not be less than 1.3 times the rated current of the capacitor bank.

Third, the discharge of Power Capacitor Banks

(1) Each time the capacitor is disconnected from the grid, it should be automatically discharged. The terminal voltage is rapidly reduced, regardless of the capacitor rated voltage is how much, in the capacitor from the grid after 30s off, the terminal voltage should not exceed 65V.

(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 connected directly to the capacitor (the circuit breaker, disconnector and fuse are not allowed in the middle). A capacitor group having a non-dedicated discharge device, for example, a voltage transformer for a high-voltage capacitor, an incandescent bulb for a low-voltage capacitor, and a capacitor group directly connected to the motor may not be equipped with a discharge device. When using the lamp, in order to extend the lamp life, should be appropriate to increase the number of light bulb series.

(3) Before discharging the conductive part of the capacitor which has been disconnected from the grid, even if the capacitor has been discharged automatically, it must be discharged with an insulated grounded metal rod and shorted to the outlet of the capacitor.

Fourth, the operation of the capacitor maintenance and maintenance

(1) capacitors should be on duty, should do a good job of equipment operation records.

(2) the appearance of the operation of the capacitor group inspection inspection should be carried out according to the regulations every day, such as the discovery of the expansion of the shell should be stopped to avoid failure.

(3) Check the capacitor group per phase load can be carried out with ammeter.

(4) When the capacitor group is put into the ambient temperature can not be lower than -40 ℃, the operating ambient temperature is 1 hour, the average does not exceed +40 ℃, 2 hours average shall not exceed +30 ℃, and the average shall not exceed +20 ℃. If it is over, use manual cooling (install fan) or disconnect the capacitor bank from the grid.

(5) The temperature check of the installation site and the inspection of the hottest temperature on the capacitor housing can be carried out by means of a mercury thermometer and the temperature record (especially in summer).

(6) The operating 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) connected to the capacitor, will cause the grid voltage increases, especially when the load is light, in this case, should be part of the capacitor or all the capacitors from the power grid disconnected.

(8) Capacitor bushing and support Insulator surface should be clean, no damage, no discharge traces, capacitor shell should be clean, no deformation, no oil, capacitors and iron shelves above should not be filled with dust and other dirty things.

(9) Care must be taken to ensure the reliability of all contact points (electrified busbars, ground lines, circuit breakers, fuses, switches, etc.) on the electrical circuit connected to the capacitor bank. Because a contact on the line at the fault, even the screw is not tight, may cause early damage to the capacitor and the entire equipment accident.

(10) If the capacitor is subjected to a withstand voltage test after a period of operation, the test shall be carried out at the specified value.

(11) the capacitor capacitor and fuse inspection, not less than once a month. In a year to test the capacitor tg 2 ~ 3 times, the purpose is to check the reliability of the capacitor, each measurement should be rated voltage or near the rated conditions.

(12) The circuit breaker of the capacitor bank is turned off due to the relay action, and the reason for the jump is not set before the fault is set.

(13) in the operation or transport process, if found in the capacitor shell oil leakage, tin solder paste can be used to repair the way.