Influence of Renewables on Switchgear Equipment

Over the last two decades, the integration of renewable energy sources and inverter-based technologies has increased significantly across the world. While this has been a positive impact on the environment, compared to the conventional fossil fuel-based energy generation, there are also trade-offs associated with it, including the complexity of control issues as the system inertia decreased significantly due to the absence of conventional synchronous generators, diminishing power quality, increased over voltages as the level of fault current are in flux.

While there has been extensive research in a few key areas, particularly the challenge of diminished inertia, the impact of inverter – based technologies on the electrical equipment is less understood and further research is needed.

For example, its influence on T&D switchgear.  IEEE-1547 Standard IEEE Standard for Interconnection and Interoperability of Distributed Energy Resources with Associated Electric Power Systems Interfaces allows DERs to operate continuously at 110% of rated voltage. ANSI-C84.1 is considering increasing stead-state voltage limits, as well, until recently. Currently some switchgear standards allow for up to +10% tolerance in test voltages, but not all. Capacitive and inductive switching especially might be affected, with increased re-strike probabilities, and higher transient and recovery voltages.

In addition, if the DER operator is allowed to form an intentional island, the switchgear may see >200% of rated voltage due to phase angle differences. This is well beyond what such devices are tested to in accordance with current standards.

Moreover, Inverter-based DERs are known to add higher harmonic currents to the grid. Alternative gas designs may be even more sensitive to these stresses, except for vacuum. Short circuit currents may be reduced, but high harmonic content may be problematic for interruption, even for lower short circuit duties. High harmonics could expedite thermal and dielectric failure of switchgear and other equipment.

For these reasons, Switchgear IEEE Switchgear Technology and Innovation subcommittee formed a task force to investigate the influence of inverter – based technologies on MV and HV switchgear. The first goal of the task force is to review requirement from IEEE 1547 standard on 200% open gap and develop recommendation for standardization of testing practices.