The role of power capacitors

(1) The role of series capacitors

1) Increase the line end voltage. The capacitor connected in series in the line uses its capacitive reactance xc to compensate the inductive reactance xl of the line, so that the voltage drop of the line is reduced, thus increasing the voltage at the end of the line (the receiving end), and generally the line end voltage can be changed. It can increase by 10% ~ 20%.

2) Reduce voltage fluctuations at the receiving end. When the line is subjected to a highly variable shock load (such as electric arc furnaces, welding machines, electrical rails, etc.), series capacitors can eliminate sharp fluctuations in voltage. This is because the compensation effect of series capacitors on voltage drop in the line is changed with the load passing through the capacitor, and has the performance of instantaneous adjustment with the change of load, and can automatically maintain the voltage value of the load end (the receiving end).

3) Improve the transmission capacity of the line. Because the line is connected with the compensating reactance xc of the capacitor, the voltage drop and power loss of the line are reduced, and the transmission capacity of the line is correspondingly increased.

4) Improved power flow distribution in the system. Some capacitors are connected in series on some lines in the closed network, which partially changes the line reactance, so that the current flows according to the specified line, so as to achieve the purpose of power economic distribution.

5) Improve the stability of the system. After the line is strung into the capacitor, the transmission capacity of the line is improved, which itself improves the static stability of the system. When the line fault is partially excised (for example, the double circuit is excised once, but the circuit single-phase grounding excises one phase), the equivalent reactance of the system increases sharply. At this time, the series capacitors are forcibly compensated, that is, the number of capacitor series and parallel is forcibly changed for a short time, and the capacitive reactance xc is temporarily increased, so that the total equivalent reactance of the system is reduced. The transmission limit power (Pmax=U1U2/xl-xc) is increased, thus improving the dynamic stability of the system.

(2) The role of parallel capacitors

The shunt capacitor is connected to the bus of the system in parallel, similar to a capacitive load on the bus of the system, which absorbs the capacitive reactive power of the system, which is equivalent to the shunt capacitor emitting inductive reactive power to the system. Therefore, the shunt capacitor can provide the inductive reactive power to the system, the power factor of the system operation, and improve the voltage level of the bus at the receiving end. At the same time, it reduces the inductive reactive power transmission on the line, reduces the voltage and power loss, and thus improves the transmission capacity of the line.

Shaanxi power capacitor

Installation of power capacitors

The environmental requirements for installing compensation capacitors are as follows:

1) Capacitors should be installed in non-corrosive gas, no steam, no violent vibration, impact, explosion, flammable and other dangerous places. The fire rating of the capacitor is not less than two.

2) Capacitors installed outdoors should be protected from direct sunlight.

3) The ambient temperature of the capacitor room should meet the requirements specified by the manufacturer, which is generally specified as 40 ° C.

4) When the capacitor room is equipped with a fan, the outlet should be installed at the upper end of the capacitor bank. Air inlet and exhaust machines should be installed in diagonal positions.

5) The capacitor room can use natural lighting or artificial lighting, and there is no need to install heating devices.

6) The door of the high-voltage capacitor room should be opened outwards.

The technical requirements for installing capacitors are as follows:

1) In order to save the installation area, the high-voltage capacitor can be installed on the iron frame in layers, but the number of vertical layers should not be more than three layers, and the horizontal layer partition shall not be installed between the layers to dissipate heat. The installation position of the upper, middle and lower three layers of capacitors should be consistent... Out.

2) The iron frame for the installation of high voltage capacitors is arranged in one or two rows, and there should be a walkway for inspection between the rows, and the width of the walkway should not be less than 1.5m.

3) The iron frame of the high voltage capacitor bank must be blocked by barbed wire, and the mesh of 3 ~ 4cm2 should be blocked.

4) The distance between the shell of the high-voltage capacitor, generally should not be less than 10cm; The distance between low-voltage capacitor housings should not be less than 50mm.

5) In the high-voltage capacitor room, the net distance between the upper and lower layers should not be less than 0.2m; The distance between the bottom of the lower capacitor and the ground should not be less than 0.3m.

6) The wiring between each capacitor and the bus should be connected by a separate flexible wire, not by a hard bus connection, so as to avoid oil leakage or damage caused by stress on the porcelain bushing during installation or operation.

7) When installing, the contact surface of the electrical circuit and the grounding part should be good. Because any bad contact in the capacitor circuit may produce a high-frequency oscillating arc, resulting in an increase in the working electric field strength of the capacitor and heat damage.

8) When capacitors of lower voltage levels are run in series in a network of higher voltage levels, the shells of each of them should be reliably insulated between the ground by installing insulators equivalent to the operating voltage level.

9) After the capacitor is connected by a star, it is used for a higher rated voltage and the system neutral point is not grounded, the capacitor shell should be insulated to the ground.

10) Before the capacitor is installed, it is necessary to allocate the primary capacitance so that it is balanced between phases, and the deviation does not exceed 5% of the total capacity. When the relay protection device is installed, it should also meet the requirements that the balance current error during operation does not exceed the relay protection action current.

11) The wiring of individual compensation capacitors should be done: for induction motors started directly or by rheostat, the capacitor to improve the power factor can be directly connected with the electrical outlet terminal of the motor, and do not install switchgear or fuse between the two; For the induction motor started by the star-triangle starter, it is best to use three single-phase capacitors, each capacitor is directly connected to the two terminals of each phase winding, so that the capacitor wiring is always consistent with the connection of the winding.

12) For the packet compensation low-voltage capacitor, it should be connected to the outside of the low-voltage packet bus power switch to prevent the self-excitation phenomenon when the packet bus switch is disconnected.

13) The low-voltage capacitor bank with centralized compensation should be specially switched and installed on the outside of the main switch of the line, rather than installed on the low-voltage bus.