Reactor / Shunt Reactor

A shunt reactor is an inductive device connected to the network to absorb reactive power. Its main role is to control voltage in systems where capacitive effects, especially from long transmission lines or cables, tend to push voltage upward under light-load conditions.

Shunt reactors are an important counterpart to capacitor banks because they provide inductive compensation rather than capacitive support. They are especially relevant in high-voltage networks where line charging can become a dominant operating issue during low-demand periods.

Key Aspects of Shunt Reactors:

• Reactive-Power Absorption: A shunt reactor consumes reactive power from the system, which helps restrain voltage rise and reduce Ferranti-effect problems on long lightly loaded lines. This makes it a standard tool for managing overvoltage risk.
• Typical Applications: Reactors are often installed on EHV transmission lines, cable systems, and substation buses where charging current is high. They are particularly useful at night or during low-load operating conditions.
• Fixed and Variable Designs: Some reactors are permanently connected, while others are switched or adjustable. Variable shunt reactors offer more flexibility when system conditions change widely over time.
• Complement to Other Voltage Controls: Reactor operation must be coordinated with tap changers, generator reactive control, capacitor banks, SVCs, and STATCOMs. Good coordination avoids unnecessary switching and improves overall voltage management.
• System-Planning Relevance: The need for shunt reactors often increases as grids add long HVAC export lines, underground cables, or lightly loaded reinforcement corridors. Their presence can materially affect planning economics and switching strategy.