WG C4.50 Evaluation of Transient Performance of Grounding Systems in Substations and Its Impact on Primary and Secondary Systems


Direct lightning strikes, lightning electromagnetic waves or switching operations can all introduce high levels of transient current flow in the grounding system of substations. The probability that the substation’s grounding system is subjected to such transient currents is much higher than that due to a power frequency fault. For example, with the widespread use of power electronic equipment, switching operations are frequent. Under such transient excitations, the potential distribution of the grounding grid is very uneven, especially for the EHV and UHV substations due to the very large area. At present, more attention is paid to the power frequency characteristics of grounding system, and less to the transient characteristics.

Besides the primary system, secondary systems are most likely to be affected by the transient ground potential because the secondary cables are laid over a large area, the paths taken are long, and the ability of secondary equipment to withstand the transient impact is weak. With the extensive application of electronic devices in substation, the impact of transient potentials on the secondary system is more and more serious.

By optimizing the arrangement of the grounding grid and the grounding method of the secondary system, the impact may be reduced. However, studies of the transient characteristics of grounding devices are mainly for transmission towers, not for substation. Although EMC in substation has been widely discussed over the past few decades, the effects of transient ground potential differences on secondary systems have not been adequately studied. At present, there is a lack of a systematic guide for the design of grounding grid considering its transient performance, and the impact on the primary and secondary systems. There is also no effective method to measure the transient performance of grounding systems in substations and its impact on the systems.

The objective of this working group is therefore to fill the gap in this area by formulating a clear set of guidance notes.


  1. Define and classify various transient current characteristics injected into grounding grid in substations.
  2. Review and propose best available simulation methods of transient characteristics of grounding grid in substation.
  3. Investigate the impact of transient ground potential difference on primary and secondary systems.
  4. Review and summarize the ability of primary and secondary systems to withstand transient impact.
  5. Identify and explain all available measures to protect primary and secondary systems from the impact of transient ground potential difference.
  6. Review and propose measurement methods to evaluate the transient characteristic of a grounding grid and its influence on mitigation required for primary and secondary systems.

Deliverables: Technical Brochure, Executive summary in Electra, Electra report and Tutorial

Time Schedule: start: July 2018 Final Report: June 2021

ConvenerBo Zhang (China)