Technical guide
Detailed information about SELVaz Earthing Measurements
SELVaz grounding measurement — this guide covers the scope, application method, quality criteria and reporting process for your needs.
Grounding safety in energy facilities
The grounding system aims to limit the step and touch voltages that personnel can be exposed to by distributing the fault current safely. In a substation, power plant, or industrial facility, the performance of the grounding grid cannot be reduced to a single low resistance value. The network fault current, tripping time, soil structure, grid geometry, and surface layer must be evaluated together. SELVaz grounding measurement is one of the field methods used to examine the real system behavior on large sites.
Before the measurement, Plan-Test reviews the single-line diagram, grounding design, site layout, connected metallic systems, and operating conditions. The measurement objective is clarified as grounding impedance, potential distribution, step-touch voltage, or soil resistivity. The current to be applied, the probe routes, the safe work area, and interference control are planned. The results are interpreted within the framework of IEEE 80, EN 50522, IEC 61936-1, and the relevant operational criteria.
How is SELVaz measurement applied?
The SELVaz method is based on injecting a controlled test current into the grounding grid with a current source suited to the site conditions and measuring the resulting voltages at selected points. The frequency and magnitude of the test current are chosen so that it can be distinguished from network-borne interference and applied safely. The positions of the remote current electrode and the voltage probes are planned taking the site geometry, access, and buried metallic connections into account.
In large grounding grids, the current spread can be affected by transmission line protection conductors, cable screens, pipelines, and neighboring facilities. For this reason, the assumptions of a classical small-facility measurement are not applied directly. Plan-Test checks the stability and interference level by taking data from different probe points. The raw current, voltage, phase information, and site coordinates are recorded; the calculated grounding impedance is reported together with the measurement uncertainty.
Step and touch voltage measurements
Touch voltage expresses the potential difference between the hand and the foot of a person touching a grounded metallic part during a fault, while step voltage expresses the difference between two feet standing a certain distance apart on the ground. The safe limits are assessed according to the fault duration, the body current approach, and the surface material. The measurement points are selected according to the risks at the control building, fence, gate, equipment enclosures, transformer surroundings, and routes where personnel may be present.
In the field measurement, the contact arrangement and loading resistance defined in the standard are used. The voltage measured with the test current is scaled appropriately to the real fault current conditions; the distribution of the current into the grounding grid and the parallel return paths are taken into account. Points that come out high are examined in terms of connection continuity, grid geometry, surface gravel, or equipotential arrangement. The result is presented not merely as a compliance statement but with the location of the hazardous area and an applicable improvement recommendation.
Soil resistivity and site modeling
Soil resistivity is one of the fundamental inputs of grounding design and varies according to the soil's moisture, temperature, chemical composition, and layering. With arrangements such as the Wenner four-electrode method, measurements are made at different electrode spacings to obtain data about different depths. Because a value at a single point may not represent the entire site, an appropriate number of routes is planned across the power plant or substation area.
The measurement data can be used to build a layered soil model. At the design stage, the grid impedance, potential distribution, and step-touch voltages are calculated with this model. In an existing facility, the field measurement is compared with the design assumptions. Seasonal variation and the effect of dry periods are taken into account. Plan-Test ensures that the resistivity results are used not merely as a table but in connection with grounding grid sizing and the safety assessment.
RES, GES, and substation grounding measurement
RES GES grounding testing must take into account the common behavior of turbines, inverters, transformers, cable screens, and metallic structures spread over a wide area. Wind turbine foundations and ring conductors can be interconnected along the collector system; in GES sites, many tables and inverter stations join the equipotential system. Because these connections affect the distribution of the test current, the measurement plan is prepared specifically for the site layout.
In substation grounding measurement, the switchyard, control building, fence, transmission line, and cable systems are examined together. When the facility is in operation, the safe injection level, the work area, and existing leakage currents are taken into account. No connection is made without the required permits and coordination. On large sites, Plan-Test aims to collect reliable data with the SELVaz current source and a suitable measurement arrangement and to compare the results with the project and safety limits.
Grounding report and improvement options
The grounding report includes the measurement objective, the site plan, the devices, the connection arrangement, the current electrode and voltage probe positions, the weather-ground conditions, and the raw measurements. The calculation steps, the fault current used, the clearing time, and the acceptance limits are shown clearly. Factors affecting the result such as interference, parallel conductors, and measurement uncertainty are assessed. The risky step-touch points are marked on the plan.
If a nonconformity is seen, options such as additional conductors or electrodes, connection repair, an equipotential ring, improvement of the surface layer, fence arrangement, or reduction of the protection clearing time are considered in terms of technique and applicability. A verification measurement after the intervention is recommended. A well-prepared SELVaz grounding measurement report does not merely complete the compliance file; it provides a concrete improvement roadmap for personnel safety and the facility's behavior at the moment of a fault.
Plan-Test’s quality, safety and reporting approach
Plan-Test does not treat the service scope merely as a list of operations to be performed on site. The facility's operating objective, outage availability, existing documentation, equipment history, and risk level are evaluated together. Before the work begins, responsibilities, access conditions, de-energization and re-energization steps, and reporting expectations are clarified. This is intended to keep teams working from the same plan, prevent critical checks from being skipped, and make efficient use of site time. Because each project is planned according to its own technical conditions, the method, devices, team size, and delivery documents to be used are clearly defined at the proposal stage.
Our quality approach is based on explaining what the result means rather than presenting the measurement result on its own. The calibration status of the test devices used, the ambient and load conditions, the connection arrangement, the applied standard, manufacturer criteria, and any previous measurements are linked together in the report. Nonconformities are classified by severity; findings requiring immediate intervention, issues that can be addressed in planned maintenance, and trends that should be monitored are separated from one another. This method helps the investor, the operations manager, and the site team turn the same technical data into a decision-ready output.
Occupational health and safety is an inseparable part of all services. The site-specific risk assessment, personal protective equipment, lockout-tagout steps, absence-of-voltage verification, and grounding and bonding rules are reviewed before the field work begins. Inspections carried out in an energized facility are based on safe approach distances and operating instructions. Plan-Test's goal is to combine technical verification with a safe working discipline in the same process and deliver sustainable, traceable, and auditable engineering services in 1–380 kV energy facilities.
At the proposal and mobilization stage, clearly defining the scope matters for both the employer and the site team. Plan-Test determines the required activities by reviewing the existing drawings, the equipment list, the facility's operating regime, previous reports, and the employer's expectations. Out-of-scope items, necessary preparatory work, the need for de-energization, operational accompaniment, and third-party responsibilities are put in writing. When a new condition arises on site, no uncontrolled scope change is made before its impact is evaluated in terms of technical, schedule, and resource aspects. In this way, all parties understand throughout the project which activity is being performed and why, which data is expected, and against which criterion acceptance will be made. This clarity reduces repeat visits and misplaced expectations while making the delivered engineering service comparable.
The quality of field work depends on the team's experience and cross-disciplinary communication as much as on the equipment used. Plan-Test assigns tasks according to the test or maintenance steps and opens points requiring primary, secondary, project, and operational knowledge to joint evaluation. Measurement devices are used with accessories suited to the application, their calibration validity is checked, and raw data is stored securely. When a critical result is observed, the connection, device settings, environmental conditions, and the equipment's operating history are reviewed again instead of jumping to a hasty interpretation. Verification with a different method is proposed when necessary. This culture of technical scrutiny helps prevent incidental or erroneous measurements from steering the decision process and helps define the real risk on site more accurately.
Completion of the service does not end with the delivery of the report; the actions in the report must be implementable and traceable. Plan-Test links its recommendations to priority, the responsible discipline, the recommended due date, and the verification method. If the employer wishes, a scope for a technical meeting, post-correction check, or repeat measurement can be established for critical items. When new results are compared with historical data under the same equipment code, the facility's condition trend becomes visible. These records support the preparation of the future maintenance budget, spare parts plan, modernization decisions, and outage calendar. The goal is not to document a single project moment, but to build a corporate technical memory that contributes to safe operation and high availability targets throughout the energy facility's entire life cycle.
In every engagement, the relevant national legislation, the grid operator's requirements, IEC and IEEE standards, and the equipment manufacturer's instructions are considered together. While the general provisions of the standards are adapted to the facility's actual conditions, the contract and approved project requirements are also preserved. Where several criteria give different limits, the acceptance approach used is explained in the report; uncertain points are recorded with the employer as a technical decision. Using unique site codes instead of equipment names in documents strengthens traceability among drawings, test results, photographs, and actions. With this documentation discipline, Plan-Test aims to ensure that the technical evidence needed during an audit, provisional acceptance, warranty discussion, or a future failure investigation can be found quickly and reliably.
For the site program you need, it is sufficient to share the facility type, voltage level, equipment count, location, and target date. After the preliminary review, the technical team clarifies the appropriate scope, preparations, and delivery plan.