SCR and its variations provide a convenient way to calculate this impedance under normal or contingency conditions (these estimates are not intended for the actual short-circuit state).
When connecting HVDC/FACTs devices based on current source converters to weak AC systems, particular technologies must be employed to overcome SCR of less than three.
Failing to use these technologies will require special studies to determine the impact and take measures to prevent or minimize the adverse effects, as low levels of SCR can cause problems such as high over-voltages, low-frequency resonances, and instability in control systems.
Problems with voltage stability that arise from incorporating large-scale wind power into vulnerable systems are crucial issues that require attention.
GE indicates that the standard parameters of their wind turbine model are appropriate for systems with a Short Circuit Ratio (SCR) of five or higher.
Specifically designed control methods for wind turbines or dynamic reactive compensation devices, such as STATCOM, are required to ensure optimal performance.
[9] An experience at ERCOT in early 21st century provides a prime example of how the wind turbine's performance is affected by a weak system strength.
The wind power plant, linked to the ERCOT grid through two 69kV transmission lines, worked efficiently when the SCR was around 4 during normal operations.
However, when one of the 69kV lines was disconnected, the SCR dropped to 2 or less, leading to unfavorable, poorly damped, or un-damped voltage oscillations that were documented by PMUs at the Point of Interconnection (POI) of the wind plant.