The increasing penetration levels of renewable power affects one of the critical parameters of the power grid, namely reactive power, causing stability issues.
Most developed countries have set renewable energy targets backed by policy directives to achieve these targets. In the early stages of renewable energy, these assets had little impact on grid stability as they could be either connected or disconnected because of their low penetration level.
However, as the amount has increased over the years, that tactic is no longer viable as to do so would adversely affect the power system stability and reliability. As a result, some regions are already experiencing bottlenecks in the supply of reactive power. Managing this reactive power is how operators ensure voltage levels on the system remain within a given range, above or below nominal voltage levels.
This is achieved by asset owners being instructed to either absorb or generate reactive power. Managing voltage levels comes from maintaining a balance between elements on the system, which absorb reactive power (decreasing voltage) or generate reactive power (increasing voltage).
Devices that store energy through a magnetic field produced by a flow of current are said to absorb reactive power; those that store energy through electric fields are supposed to generate reactive power.
The reactive power in a network will influence the voltage levels. While the frequency is stable across the network, voltages across the system are determined by the prevailing real and reactive power supply and demand.
If the network does not have suitable reactive power injections at the right locations, the voltage profile of the transmission system will exceed statutory planning and operational limits.
If there are no appropriate reactive power sources available locally and reactive power compensation devices cannot be used, the bottlenecks are corrected by voltage-related redispatch.
Ensuring a stable and reliable grid This increased renewable generation also causes local and regional pipeline congestion, such as transmission lines that must absorb electricity from offshore wind farms and move the electricity to remote load centres. To maintain the system stability, the n-1 criterion must be observed; that is, the failure of a line must not lead to system failure, with the current always able to travel by at least one alternative way. In these cases, the affected network elements are relieved by current-related redispatch.