- AG C4.1: Strategic Directions
- AG C4.2: Institutional Liaison
- AG C4.3: Tutorials and Conferences
- JWG A1/C4.52 Wind generators and frequency-active power control of power systems
- JWG A2/C4.309 Electrical Transient Interaction between Transformers and the Power System
- JWG A2/C4.52 High-frequency transformer and reactor models for network studies
- JWG A3/B5/C4.37 System conditions for and probability of Out-of-Phase
- JWG B4/B1/C4.73 Surge and extended overvoltage testing of HVDC Cable Systems
- JWG C1/C4.36 Review of Large City & Metropolitan Area power system development trends taking into account new generation, grid and information technologies
- JWG C2/C4.37 Recommendations for Systematic Framework Design of Power System Stability Control
- JWG C4.24/CIRED Power Quality and EMC Issues Associated with Future Electricity Networks
- JWG C4.31/CIRED EMC between Communication Circuits and Power Systems
- JWG C4.40/CIRED Revisions to IEC Technical Reports 61000-3-6, 61000-3-7, 61000-3-13, and 61000-3-14
- JWG C4.42/CIRED Continuous assessment of low-order harmonic emissions from customer installations
- JWG C4/B4.38 Network Modelling for Harmonic Studies
- JWG C4/B4/C1.604 Influence of Embedded HVDC Transmission on System Security and AC Network Performance
- JWG C4/B5.41 Challenges with series compensation application in power systems when overcompensating lines
- JWG C4/C6.29 Power Quality Aspects of Solar Power
- JWG C4/C6.35/CIRED Modelling and dynamic performance of inverter based generation in power system transmission and distribution studies
- WG C4.111 Review of LV and MV Compatibility Levels for Voltage Fluctuation
- WG C4.112 Power Quality Monitoring in Flexible Power Networks
- WG C4.206 Protection of the High Voltage Power Network Control Electronics Against Intentional Electromagnetic Interference (IEMI)
- WG C4.207 EMC with communication circuits, low voltage systems and metallic structures
- WG C4.208 EMC in HV Substations and Generating Stations
- WG C4.23 Guide to Procedures for Estimating the Lightning Performance of Transmission Lines
- WG C4.25 Issues related to ELF Electromagnetic Field exposure and transient contact currents
- WG C4.26 Evaluation of Lightning Shielding Analysis Methods for EHV and UHV DC and AC Transmission-lines
- WG C4.27 Benchmarking of Power Quality Performance in Transmission Systems
- WG C4.28 Extrapolation of measured values of power frequency magnetic fields in the vicinity of power links
- WG C4.30 EMC in Wind Generation Systems
- WG C4.303 Pollution and Environmental Influence on Electrical Performance
- WG C4.305 Practices in Insulation Coordination of Modern Electric Power Systems Aimed at the Reduction of the Insulation Level
- WG C4.306 Insulation Coordination of UHV AC systems
- WG C4.307 Resonance and Ferroresonance in Power Networks and Transformer Energization Studies
- WG C4.32 Understanding of the Geomagnetic Storm Environment for High Voltage Power Grids
- WG C4.33 Impact of Soil-Parameter Frequency Dependence on the Response of Grounding Electrodes and on the Lightning Performance of Electrical Systems
- WG C4.34 Application of Phasor Measurement Units for monitoring power system
- WG C4.36 Winter Lightning – Parameters and Engineering Consequences for Wind Turbines
- WG C4.37 Electromagnetic Computation Methods for Lightning Surge Studies with Emphasis on the FDTD Method
- WG C4.39 Effectiveness of line surge arresters for lightning protection of overhead transmission lines
- WG C4.407 Lightning Parameters for Engineering Applications
- WG C4.408 Lightning Protection of Low-Voltage Networks
- WG C4.409 Lightning Protection of Wind Turbine Blades
- WG C4.410 Lightning Striking Characteristics to Very High Structures
- WG C4.43 Lightning problems and lightning risk management for nuclear power plants
- WG C4.44 EMC for Large Photovoltaic Systems
- WG C4.45 Measuring techniques and characteristics of fast and very fast transient overvoltages in substations and converter stations
- WG C4.501 Numerical Electromagnetic Analysis and Its Application to Surge Phenomena
- WG C4.502 Power system technical performance issues related to the application of long HVAC cables
- WG C4.503 Numerical techniques for the computation of power systems, from steady-state to switching transients
- WG C4.603 Analytical Techniques and Tools for Power Balancing Assessments
- WG C4.605 Modelling and aggregation of loads in flexible power networks
WG C4.33 Impact of Soil-Parameter Frequency Dependence on the Response of Grounding Electrodes and on the Lightning Performance of Electrical Systems
The transient response of grounding electrodes is a complex phenomenon that can significantly influence the lightning performance of the electrical power system. Though accurate computational models based on different approaches are currently available to simulate the behavior of electrodes subject to lightning currents, some basic aspects of this behavior still require further clarification, notably those related to the frequency dependence of soil parameters.
Experimental results, such as those by Smith-Rose, Scott, Longmire and Smith, and Visacro, show a significant frequency dependence of soil resistivity and permittivity. However, due to the lack of accurate general formulation to express this effect, it has been neglected and, in a conservative approach, soil resistivity is assumed as that measured at the low frequency range and relative permittivity of soil is assumed to vary from 4 to 81, according to the soil humidity.
In the last years new methodologies have been developed to determine this frequency dependence based on measurement under field conditions. The results provided by their application have demonstrated significant variation of both parameters in the representative frequency range of lightning currents. It has also be shown that the conservative assumption of constant values for soil resistivity and permittivity lead to large errors in the simulated response of electrodes subjected to currents with lightning-patterned waveforms (from 30% to 150%, in terms of measured impulse impedance). Furthermore, the results have suggested that it is feasible to develop general formulations for expressing this frequency dependence for accurate estimates of the lightning response of grounding electrodes.
In addition to the relevance of this effect on the impulse response of electrodes, another important issue to address is how this change in the electrode response impacts the lightning performance of the electrical power system, notably of transmission lines. This is a significant issue with respect to power system technical performance, since the lightning performance of the EHV lines can significantly impact overall system reliability. Therefore, it is very important to provide guidelines to take this frequency dependence of soil into account in calculations of the impulse response of grounding electrodes and of the lightning performance of the electrical power system.
- Demonstrate in a concise manner the frequency dependence of soil parameters within the frequency range of 0 to 4 MHz (where most of the lightning energy typically resides) by providing the fundamental scientific basis for this dependence and by referring to the relevant literature addressing its significance based on experimental results.
- Develop critical analysis of the existing experimental methodologies for determining this frequency dependence and corresponding published results. In this respect, it is fundamental to assess whether experimental measurements provide consistent verifiable results and how easily these measurable results can be obtained. Eventually, new feasible methodologies could be proposed.
- Summarize reliable published results and propose complementing them by means of short term cooperation among participants of different countries.
- Suggest plausible general expressions for prediction of the frequency dependence of soil parameters.
- Evaluate the impacts of this dependence on grounding-electrode behavior and on the lightning performance of the electrical power system. In particular, it is of interest to develop equivalent circuits for selected arrangements of electrodes buried in different soils to represent their response to the impression of lightning currents, taking this effect into account. This includes an analysis of substation ground grids.
A Cigre technical brochure with summary in Electra.
Convener: S. Visacro (Brazil)