Synchronous Condenser (Rotating Reactive Power Compensation)

A synchronous machine (IEC 60034-3) that, unlike a generator, supplies no mechanical drive power but instead spins unloaded — or only with the power needed to cover its own friction and windage losses — as a motor, with its sole function being to absorb or supply reactive power to the grid, controllable via its excitation. By increasing the excitation current ('over-excited') the machine supplies capacitive reactive power and supports the grid voltage; by reducing the excitation ('under-excited') it instead absorbs inductive reactive power. The main advantage over a STATCOM or capacitor bank is the physical rotating mass (moment of inertia) of the rotor, which — as with a conventional generator — contributes to the system's inertia and to the grid's short-circuit power contribution, something that is becoming increasingly important for frequency stability in grids with a growing share of inverter-connected, inertia-less generation.