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The Benefits of Baseline Testing for Informing Future Earthing System Assessment Requirements

Earthing System Baseline Testing (ESBT) provides the datum point from which all future evaluations of that earthing system can be referenced. Without reference points, nuances in results could be mis-interpreted and overlooked and it’s ideal for the asset owner/operator to have a reference to check against when works within the system are undertaken.

What is Baseline Testing?

Earthing System Baseline Testing (ESBT) is the beginning. From the time the earthing system is installed, the system commences to degrade. Degradation occurs for various reasons and at different rates, but, without knowing how things were at the start, how can we measure its rate of change and allow integrity and performance of the earthing system to be managed over its design life?

It is important to understand that designs represent predictions of performance, but testing is actual performance measurement.  This is where baseline testing plays a critical role. The data acquired from ESBT can provide the asset owner with reliable insight into the existing condition of the earthing system. In addition to this, the information acquired from this test are important when performing future routine testing of the assets, as asset owners will be able to ascertain the key characteristics of their earthing system and understand how these are changing over time. This information can assist in the decision-making for earthing system maintenance and upgrades.

The typical framework for an ESBT is illustrated in Figure 1.

Figure 1: ESBT Framework
Figure 1: ESBT Framework

Tests Involved in Baseline Testing

The typical scope for baseline testing consists of performance testing, achieved via current injection testing (CIT), and condition testing. A CIT simulates a power system earth fault at the test location, which is referred to as a Low Current Off Power Frequency Injection Test. This allows scaled measurements of real hazards to be taken safely and allow comparison to safety criteria. These measurements are used to either verify the installed earthing design achieves compliance, or trigger and guide remediation where compliance is not achieved. The components of the simulation consist of the earthing grid under test, an injection current power source such as AX-1 (refer to Figure 3), a connecting circuit (such as overland cable lead) and connection to a remote grid. A typical setup of the test can be seen in Figure 2.

Figure 2: Current Injection Test
Figure 2: Current Injection Test

As part of baseline testing, it is also imperative to understand the soil resistivity for the area that the earthing grid is buried. This characteristic has an impact on key parameters such as the local earth grid resistance, soil voltage contour spread away from the grid, and is also required in the derivation of safety criteria. Due to this, soil resistivity testing is also conducted as part of baseline testing, as acquiring this information provides insight into the in-situ resistivity, and allows monitoring of soil changes over time due to seasonal or rainfall fluctuations. This is informative for an ESBT as resistivity can be a variable when assessing changes in the earthing system performance.

The final test activity involved in ESBT is condition testing, which establishes a baseline for the physical condition and connectivity of assets. This test will confirm that the integrity of critical earthing connections or isolations throughout the site are working to achieve safety compliance as per standards. Overall, this set of test data acquired from baseline testing forms the foundation for developing an informed plan maintenance of the earthing system.

Figure 3: AX-1 Injection Source
Figure 3: AX-1 Injection Source

Benefits of Baseline Testing #1: Establishing the key characteristics

To gain an understanding of the baseline testing results, we should ask ourselves: what exactly do all these acquired key characteristics mean? The first crucial parameters that are acquired from baseline testing are the earth grid resistance and earthing system impedance. The earth grid resistance represents the impedance at the local earth grid at the test location only, while the earthing system impedance comprises of the local earth grid and all other connected auxiliary earth impedances. Each parameter informs us of its respective impedance and thus capability to carry fault currents returning to the source. Another characteristic attained from baseline testing is compliance of EPR related voltage hazards such as touch voltages & step voltages to AS 2067. It informs us of the earthing system’s safety compliance under fault and thus suitability for service. The final key characteristic attained is the compliance of hazards at nearby third-party infrastructure (particularly telecommunication and metallic pipeline assets) resulting from interaction with voltage contours extending from the earthing system. An earthing system will need to be compliant to standards such as AS/NZS 3835 and AS/ZNS 4853, and this information can be valuable particularly when developments in the area occur, and decisions need to be made about encroachments or exclusion zones for third-party assets.

Benefits of Baseline Testing #2: Identifying trends and outliers

With the key characteristics outlined from baseline testing results, subsequent repeat test results in the future can be compared and contrasted to identify trends, deviations and remediation areas to address. An example of a trend could be made for the earthing system impedance. In the case where the impedance has increased over time, this could be an indication to asset owners that the earthing system performance has degraded due to effects such as corrosion in the earthing grid or at critical connections. On the other hand, if the earthing system impedance has changed drastically compared to the baseline results, this would be a trigger for asset owners to further investigate the cause and re-establish the asset’s compliance to standards. Furthermore, in the case that the baseline testing highlighted non-compliance in the earthing system, these items can be identified and remediation works can be initiated early to ensure asset compliance and operator safety. Such examples would be non-compliant touch voltages or inadequate earthing connections to equipment.

Benefits of Baseline Testing #3: Streamlined routine testing

HV earthing systems are generally expected to perform adequately and remain in sound condition for 40-100 years. ESBT establishes the datum point from which all future assessments of the earthing system can be compared. Following ESBT, periodic routine testing is recommended by standards such as AS 2067 and AS 1768, to confirm the state of an earthing system. With the critical elements and remediation works identified during baseline testing, ongoing routine testing can be simplified to help asset owners to focus attention and spending on key elements highlighted in baseline testing as either critical to performance, monitoring identified trends or outliers, and remediated items. This approach can provide a more systematic method to confirm ongoing compliance, identify emerging or critical failures in the earthing system and plan for earthing maintenance.

Conclusion

Earthing system baseline testing is the crucial first step that serves at the reference point for all future earthing system tests. It allows us to reliably understand how the earthing system has changed or will change over time, from which asset owners will be able to streamline future maintenance and make informed planning decisions. In a landscape where reliability and safety are paramount, baseline testing is not just a technical formality – it’s an essential investment in the long-term management of earthing systems.

By Paolo Jaldon – Electrical Engineer, Safearth

For more information on Safearth’s products and services, visit their website at au.safearth.com