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FLEXIBLE AC TRANSMISSION SYSTEMS | integrated solutions, system stability, and superior performance





Thyristor Valves
Thyristor valves are used to control the level of inductance and capacitance applied to the system. The thyristor valves use solid-state silicon controlled rectifiers (thyristors) connected in anti-parallel pairs to control AC current. These anti-parallel pairs are then connected in a series to operate at distribution voltages. The thyristors control the reactors and capacitors in the circuit, and can operate on a per-cycle basis, allowing fast, precise voltage control.
Capacitor Banks
Capacitor banks are switched on and off by the thyristor valves. If the system’s load is inductive, these banks switch on to provide VARs to the system in order to raise the system voltage. The capacitor switching operation is completed within one cycle of the fundamental frequency and does not generate any harmonic currents.
The amplitude of the current through the reactors can be changed by varying the firing angle of the thyristor valves. This angle can be varied from zero to 90 degrees and can be fully changed within one cycle of the fundamental frequency. This provides smooth and fast control of reactive power to the system. Reactors can be installed as single phase structures or stacked vertically to optimize the station footprint.
Fixed Capacitor (FC) Harmonic Filter
Harmonic filter banks are primarily used to mitigate the harmonics
generated by the TCR branch(es).
Coupling Transformer
To maximize the performance of the thyristor valves, coupling transformers are used to step the current down from the transmission system operating voltage to levels between 10kV and 34.5kV.
Valve Cooling System
Forced air systems are traditionally applied for cooling small capacity valve stations. However, Mitsubishi Electric Power Products has also developed a high-efficiency liquid cooling system for large capacity stations. Using a combination of water and glycol, these cooling systems come complete with filters and deionizers to remove excess heat generated in the thyristor valves. Designs are fully redundant for reliability, compact, use a minimum amount of piping and ensure that the thyristors operate at their maximum capability.
Station Control System
A digital controller is supplied with every power electronics system. Using a LINUX-based operating system, the controller incorporates data from high-precision digital signal processors (DSP) through multiple processing units to control the thyristor valves and all ancillary equipment throughout the station. The digital technology offers high flexibility, reliability and easy maintenance. The digital controller is also suitable for LAN and SCADA communication.

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