The improvement of power quality is mainly through power quality equipment and current signal and other parameters in the current transformer detection system, so as to correctly control the power quality problem in real time and improve the environment of the distribution system. 

For capacitor bank, we usually only use a CT mounted on the power side for sampling. 

For SVG / APF, a set (3) CT is required for the three phases of the system, which is usually recommended to be installed on the load side.

Current transformer is an electrical device used for measurement and protection. Its main function is to convert large current into small current to facilitate measurement, control and protection. In practical applications, the secondary side of the current transformer cannot be open-circuited for the following reasons:

1. Principle of electromagnetic induction: The working principle of current transformer is based on the principle of electromagnetic induction, that is, when there is current passing through the primary side, a corresponding electromotive force will be generated on the secondary side. If the secondary side is open-circuited, the electromotive force cannot form a loop, causing the output signal of the transformer to be unable to be transmitted.

2. Magnetic saturation phenomenon: When the primary side current of the current transformer is too large, the magnetic flux on the secondary side will also increase, which may lead to magnetic saturation. Magnetic saturation will cause the measurement error of the transformer to increase and may even damage the transformer. Therefore, in order to ensure the accuracy of measurement and the safe operation of the transformer, the secondary side cannot be open circuit.

3. Thermal stability problem: The iron core of the current transformer will generate heat during operation. If the secondary side is open, the heat cannot be dissipated, which may cause the temperature of the transformer to rise. Excessive temperature will affect the performance and life of the transformer, and may even cause safety accidents such as fires. Therefore, in order to ensure the safe operation of the transformer, the secondary side cannot be open circuit.

4. Protection function failure: The current transformer has a protective function in the power system. When short circuit, overload and other abnormal conditions occur on the primary side, the secondary side will induce corresponding current, thereby protecting the primary side equipment. If the secondary side is open-circuited, this protection function will fail, which may cause damage to the primary side equipment or a safety accident.

5. Measurement error: The measurement error of the current transformer is related to the load on the secondary side. When the secondary side is open circuit, the measurement error will increase because there is no load. In order to ensure the accuracy of measurement, the secondary side cannot be open circuit.

6. Affects the normal operation of the relay protection device: In the power system, the secondary side of the current transformer is usually connected to the relay protection device to protect the primary side equipment. If the secondary side is open-circuited, the relay protection device may not work properly, causing the protection function to fail.

To sum up, in order to ensure the measurement accuracy, safe operation and effectiveness of the protection function of the current transformer, the secondary side cannot be open circuit. In practical applications, it should be ensured that the secondary side of the current transformer is always closed to avoid open circuit. At the same time, attention should also be paid to the selection, installation and maintenance of current transformers to ensure their normal operation in the power system.