In daily work, the quality of equipment power supply has always been a concern for managers. Here we will introduce the role of capacitors and related usage methods.

Why use capacitors?

Capacitors are mainly used to compensate for inductive reactive power in power frequency power systems to increase power factor, improve power supply quality, and reduce line losses.

At what voltage does the capacitor operate normally?

The capacitor is allowed to operate for a long time at no more than 1.1 times the rated voltage, and can operate at 1.5 times the rated voltage (except transient over voltage) for no more than 30 minutes every day and night. In order to extend the service life of the capacitor, the capacitor should always operate at a voltage not exceeding the rated voltage.

Environmental requirements of capacitors

Capacitors are generally used in places where the ambient air temperature is -40°C to +40°C. The altitude of the installation area does not exceed 1,000 meters. Low-voltage parallel capacitors can be used at altitudes below 2,000 meters.

Precautions for installing capacitors

In addition to meeting the ambient temperature requirements, the capacitor should be installed in a place free from corrosive vapors and gases, free from dust and other erosion, and well ventilated. (Indoor products should be protected from rain, snow, etc.)
Capacitors can be installed on the iron frame in one or two rows. Each row should not be placed in more than three layers. There should be sufficient insulation distance between layers. The distance between capacitors in each layer should be no less than 100 mm. When installing, the capacitors should be Upright (specially designed can also be placed horizontally). In order to maintain good ventilation and facilitate staff's inspection and maintenance, the capacitor device should be equipped with a maintenance channel whose width should not be less than 1.2 meters.

Horizontal partitions that hinder air circulation must not be installed. The cooling air outlet should be installed above each group of capacitors.
Before the capacitor is installed on the shelf, the capacitance must be matched to make it have the same capacitance balance (accuracy is 5%).The voltage waveform and characteristics of the line should be determined before and after installing the capacitor, and corresponding measures should be taken, especially for lines with harmonic sources (rectifiers, etc.).

The capacitor is directly connected to the outlet end of the induction motor. When the motor is disconnected from the line, self-excitation may occur, so the voltage on the capacitor may rise above the rated value. In order to avoid this, when selecting the capacitor, the capacitor must be The rated current is less than the no-load current of the motor.

How to connect and disconnect the capacitor?

Use a megger to check the discharge circuit of the capacitor bank before connecting it.
When the voltage on the bus exceeds the specified maximum allowable value, it is prohibited to connect the capacitor bank to the network.
The capacitor bank must not be reconnected immediately after it is disconnected from the network. If it is connected immediately, the voltage on its terminals should not be higher than 10% of the rated voltage.

When connecting and disconnecting capacitors, a switch that cannot generate dangerous over voltage should be selected, and equipment that can suppress dangerous over voltage should be installed. The rated current of the switch should not be less than 1.5 times the rated current of the capacitor bank.

What are the precautions when using capacitors?
Frequently conduct visual inspection of the running capacitor bank. If the box shell is found to be significantly expanded (the expansion amount of each side below 100Kvar should not be more than 10mm; the expansion amount of each side of 100Kvar and above should not be more than 20mm), stop using it to avoid malfunctions.

Pay attention to the temperature of the capacitor bank during operation. If it exceeds the maximum design temperature, artificial cooling (installing fans, etc.) or disconnecting the capacitors from the network should be used. The temperature of the installation site and the hottest spot on the capacitor shell can be checked with a mercury thermometer, etc., and temperature records must be kept (especially in summer).

The working voltage and current of the capacitor shall not exceed the maximum voltage and current during use.
The surface of the capacitor sleeve, the capacitor shell, and the iron frame of the discharge vessel should not be filled with dust and other dirt.
Careful attention must be paid to the contact reliability of all connections on the electrical circuit connected to the capacitor bank, because a failure at one connection on the line or even a loose nut may cause early damage to the capacitor and cause an accident to the entire equipment.

 After the capacitor has been running for a period of time, a withstand voltage test is required.

 Common troubleshooting in the use of capacitors

 If oil leakage is found in the capacitor case during transportation or operation, it can be repaired by soldering with tin-lead solder.
 If oil leaks from the casing weld, it can be repaired with tin-lead solder, but care should be taken that the soldering iron cannot be overheated to avoid desolating of the silver layer.