NR Electric’s PCS-9578 Controllable Shunt Reactor (CSR) is a shunt-type reactive power compensation system for supplying step-changing reactive power with fast response time and low-cost maintenance. It is designed based on high leakage reactance transformer and high-power thyristor semiconductor technology.
CSR is used to solve the contradiction between reactive power compensation and restraining over-voltage especially in an extra-high voltage and long distance power transmission system. It can adjust the reactive power to stabilize the line voltage and achieve a reasonable power flow distribution.
Furthermore, CSR can also restrain the secondary arc current to improve reclosing success rate. So far, it has been used successfully in electric power system.
Suppress the overvoltage and compensate the system reactive power
Adjust and stabilize the system voltage.
Restrain the secondary arc current and improve reclosing success rate
Increase the transmission capacity of lines.
Improve the power flow distribution
High leakage impedance transformer
The main part of CSR system is a step-down transformer with high leakage impedance rate over 90%. The primary winding is connected to grid in parallel. The transformer changes high voltage to low voltage in order to protect the devices in controllable part.
The supplementary reactor usually adopts air-core reactors which are stable and have good linear performance. The air-core reactor is used to absorb the reactive power. Usually several air-core reactors are linked in series and connected with secondary winding of high leakage impedance transformer.
Bypass breakers are a controllable part in CSR system. It operates when CSR starts to change level. All breakers act in sequence according to a certain control and protection strategy.
Thyristor valves are the other controllable part in the CSR system. The valve is connected in parallel with bypass breaker and cooperates with bypass breaker. It turns on once
In order to energize the Thyristor Control Unit (TCU) installed in thyristor valves, each bypass breaker is connected with an energy-gaining reactor in series. Thus the voltage on thyristor valves will be sufficient even when the bypass breaker in parallel is closed.
When the CSR is applied to transmission line, a grounding reactor is installed at the neutral point of the primary side of high leakage impedance transformer. The reactor with appropriate reactance value, cooperating with correct action of controllable shunt reactor, can offset capacitive secondary arc current generated in line faults. This helps increase the success rate of reclosing.
Control and protection system
The CSR control system is composed of operator workstation, LAN and printers. It realizes CSR remote control, monitoring and event alarm functions from the control room.
The PCS-9578 CSR system consists of a controllable shunt reactor and a control and protection system, which is used to control and protect transformer and reactors in the valves. The controllable shunt reactor is composed of main part and controllable part. Main part is a high leakage impedance transformer. Controllable part consists of supplementary reactors and composite switches. Under normal operating conditions, the absorbed power is graded to several levels and changes step-by-step according to the whole impedance of controllable part.
The output power level of the CSR is adjusted by switching the supplementary reactor. Each level power is determined by a settled status of switches. High level indicates that the CSR system absorbs more inductive reactive power from grid. Normally the output power gap between two adjacent levels is identical. Controllable shunt reactor changes one or more than one levels at one time according to control and protection system.