News
Down to Earth Conference 2022 – Highlights and Safearth Technical Talks
DTEC has wrapped up for another year. Despite the delays and postponements caused by COVID, the conference evolved into a very informative and worthwhile event for all attendees, speakers, and sponsors. Over two days the conference allowed engineers and technical professionals across Australia and New Zealand to discuss, engage, share experiences, communicate research developments, and promote best practices in power system earthing, grounding, and lightning protection.
Running for the sixth time, DTEC was hosted by the Australian Earthing Institute and featured 30 technical presentations from fifteen different industry leading businesses. The topics focused on eight important areas related to earthing; distribution, design, testing, rail, pipeline interference, safety criteria, lightning and transients.
The novelty of finally being able to meet face to face with their industry peers was not lost on the crowd of 125 attendees. Networking was a large focus at DTEC, with every corner of the venue filled with huddles of engineers deep in technical discussion. It was great to welcome back so many familiar faces and meet some new ones as well. Many attendees commented on the collaborative atmosphere of the event and saw it as an excellent platform for knowledge-sharing among the different power engineering sectors.
Safearth felt very privileged to be part of this critical industry event again in 2022. Our representatives offered a plethora of engaging presentations which produced much conversation and debate. From electric shock, injection testing, safety criteria and electricity spills to energisation of 11kV timber poles and Ohmic targets, our experienced consultants covered it all at the Down to Earth Conference.
Safearth topics presented at DTEC 2022:
DISTRIBUTION
- Energisation of 11kV timber pole: Investigation of electrical effects and safety risks by test – Matthew Bale, Director of Engineering, Safearth
DESIGN
- The necessary transition from Ohmic targets – Stephen Palmer, Managing Director
- Improvements to earthing design and testing for Utility Scale Renewables (staging & commissioning) – Josh Bowman, Electrical Engineer
- On the Impedances of earth return circuits – Brent Pawlik, Senior Engineer – SME Electromagnetics & EMC
PIPELINE INTERFERENCE
- On the problems with AS/NZS 4853 – Brent Pawlik, Senior Engineer – SME Electromagnetics & EMC
TESTING
- Current Injection Testing Equipment – Hazards, Risks and Controls – Paul Griffiths, Development & Production Manager
- Are we really testing R, Z or something else? – Matthew Lee, Development Engineer
- Testing Wind Farms – Rowan McMurray, Senior Engineer
- Earth Resistivity and Grounding Design – A brief history and the missing link – Bill Tocher, Engineering Director Business Development Manager
SAFETY CRITERIA
- DC Safety Criteria – Bill Tocher, Engineering Director Business Development Manager
- Looking at Safety Criteria for Transients – Dr Darren Woodhouse, Technical Director Business Services Manager
- Three Electric Shock Case Studies – Investigation and Mitigation – Benton Grieve, Senior Engineer
RAIL
- Learnings from 2 big rail projects (earthing & bonding) – Lachlan McKerrow, Principal Engineer IL, SME Rail
- Stray current interference testing criteria associated with DC traction systems – Jim Hickey, Ausgrid and Ben Staddon, Safearth
The next DTEC is scheduled for 2024. Please email enquiries@dtec2022.com for further information.
For more detail on the technical topics presented by Safearth consultants at DTEC 2022, please find all the abstracts below:
COVID 19 – A Case Study in Societal Risk Perception
Dr Darren Woodhouse
With the worldwide use of ‘social distancing’ becoming a social norm, will that make the idea of coincidence in quantified risk calculation more palatable to the public, politicians, the courts, the power industry, or the earthing industry?
The past year has been a public demonstration of how risk can be used to public benefit and detriment. Different states around the world have responded by varying degrees of effectiveness in protesting their population from the consequences of the virus, ranging from infection to financial hardship and physiological strain. It has also been a clear demonstration of how differently risk is interpreted and acted upon.
To take this further in some circumstances society reacts to risks when it is clearly being presented as a rate of occurrence. For instance, the reaction in the uptake of the Astra Zeneca vaccine because to blood clotting. This occurred not because the risk was greater than acceptable, but because of the rate at which people were presenting symptoms. It was clear that the rate at which differing incidents were being reported created a public reaction, to which both governments and health authorities reacted, as well as recipients.
Similarly, the public understanding of what the vaccine will do is outstanding, and not in a good way. Vaccination is not a 100% cure, but it will change the tide. What do the effectiveness rates of vaccination mean, particularly in light of what the statistics tell us about the impacts of COVID-19 on various segments of society.
To cast some light on what it all means this paper goes back to basics, defines the various forms of risk and perceived risk. From that basis hopefully we can define a reasonable reaction to these and future circumstances and what is just an unjustified emotional response.
DISTRIBUTION
Energisation of 11kV timber pole: Investigation of electrical effects and safety risks by test
Matthew Bale
Latent energisation of timber poles carrying high voltage overhead lines is a troublesome and potentially hazardous fault scenario for network service providers. Such conditions can occur through electrical or mechanical failure of insulators or incorrect line construction. The resulting high impedance fault invariably fails to be detected by protection systems, but can result in electric shock risk to the public and utility operatives, as well as secondary damage to other services strung on the pole. This paper/presentation presents the findings of a testing investigation into the effects of timber pole energisation including circuit impedances, measurements of leakage current and voltage, and an assessment of electrical safety risks under dry and wet conditions.
DESIGN
The necessary transition from Ohmic targets
Stephen Palmer
For more than 20 years leading practitioners have wrestled to find the right balance between efficiency and responsibility with respect to earthing safety criteria. How could one reconcile the contradictions in published targets internationally and within Australia? Quantified Risk Analysis (QRA) based improvements to this pursuit have led to better coordinated and understood criteria and is influencing how earthing is being analysed globally. In contrast some parts of Australian standards, codes and regulations continue to support simple ohmic targets. Does there remain a place for ohmic targets? Or are they a shortcut no longer justifiable? This presentation will summarize the key elements and present a proposed framework for answering this question.
Improvements to earthing design and testing for Utility Scale Renewables (staging & commissioning)
Josh Bowman
Earthing design in utility scale solar has progressed significantly in Australia since it initially arrived and began being constructed in mass. Now the earthing design of these large-scale projects is well understood. However, there are still several challenges for an earthing designer that come along with each project. This presentation focuses on the challenges of design and testing of the earthing systems for utility scale solar projects associated with staging of construction and commissioning. This presentation presents challenges and ideas that should be considered to provide a compliant low risk earthing design throughout the construction and staged commissioning phases of the project without the requirements for over specified earthing or the entire earthing system to be completed before anything can be energised. The goal is that the earthing design and testing can be completed in such a way as to assist in maintaining the projects energisation dates and construction timeline.
On the Impedances of earth return circuits
Brent Pawlik
During a power system earth fault an earth return circuit is created between the source and point of fault. Consequently, the correct calculation of the circuit elements associated with the earth return circuit is essential to the safety assessment of any power system. While the physical realisation of the circuit itself is simple, the theory associated with the resulting circuit elements is quite complex. Misinterpretations or lack of understanding of the full picture easily results in inappropriate application of the theory and worse still the development of theoretical solutions to particular parts of the circuit parameters that are incompatible with others.
This paper first establishes the circuit elements of a simple earth return circuit together with the underlying theory associated with each. The limitations of the theory associated with each circuit element are clarified and the reason certain applications of the theory for particular circuit elements are incompatible with others is explained. These realisations are expected to prevent future misapplication of earth return circuit theory within the industry which is essential to the safe operation of the electrical network.
PIPELINE INTERFERENCE
On the problems with AS/NZS 4853
Brent Pawlik
AS/NZS 4853 is the Australian and New Zealand standard governing the requirements for electrical hazards induced into metallic pipelines from exposure to high voltage power system infrastructure. The present 2012 version of the standard has been in usage now for almost a decade. While from a theoretical perspective the standard may appear to be sound, extensive experiencing in applying the standard within Australia over this time period has revealed numerous deficiencies with an intent lacking clarity.
This paper explores these deficiencies and where viable offers practical solutions. Points of contention associated with the intent of the standard are identified and discussed. It is hoped that these learnings provide direction for future versions of the standard so that these inherent deficiencies and points of uncertainty may be realised and rectified.
TESTING
Current Injection Testing Equipment – Hazards, Risks and Controls
Paul Griffiths
Current Injection Testing (CIT) is now commonly used in the commissioning and ongoing testing of the earthing systems of major substations, as is required under AS 2067. Whilst CIT is generally considered safe, there are hazards and risks that must be managed. Utilising overhead lines or cables as part of the injection circuit presents further hazard sources and mechanisms and can make assessment more difficult. The risks include damage to equipment or instruments being used, and in recent years ther are reports of failures and potential harm to staff. This presentation reviews the electrical risks associated with CIT and offers a checklist of risks requiring management. This involves identifying the events that instruments must survive, or at least fail safely.
Are we really testing R, Z or something else?
Matthew Lee
In the cursory, earthing system testing is very simple; apply a voltage between the systems under test and a remote reference earth, measure the current, measure the voltage ‘across’ the system under test, and divide it by the current. In practice it gets a little more complicated; how do you establish remote earth, what type of voltage do you apply, how much current flow do you need, where and how specifically do you measure the voltage, how do you measure both reliably, how do you detect and reject (for correct for) electrical noise, both AC and DC, are all important questions. Whilst many of these questions have reasonable answers, a question remains in dispute: if you test with an applied voltage that has DC and AC characteristics, do you measure a resistance or an impedance? The IEEE committee revising Std 81, amongst others, have wrestled with this question, and yet, there isn’t consensus. To answer this question the authors have investigated and tested a range of scenarios and instrument and sought to be definitive. This presentation presents their methods, results and conclusions.
Testing Wind Farms
Rowan McMurray
Earthing systems are seldom seen, and, on many projects, they are seldom needed. For this reason, they are often ignored, but the consequences of a malfunctioning earthing system can be disastrous. Increased downtime, reduced asset life and even injury or death of staff or public can be direct outcomes of an earthing system not performing to design specifications.
Because of this there are growing requirements to ensure that earthing systems are appropriately maintained, but appropriate maintenance of an earthing system is sometimes unclear.
For high capital investment projects such as wind farms, the development of an appropriate Earthing System Management Plan (ESMP) is important for project planning and financing, as well as ensuring ongoing regulatory compliance. This presentation will look at the drivers for ESMPs as well as how they can be developed to maximise project returns and minimise downtime and operational costs, with particular attention paid to routine condition assessment techniques that can be carried out with minimal operational impact.
The presentation will be relevant to designers, testers, and owners of electrical assets, particularly those responsible for maintenance budgets and asset lifecycle management.
Earth Resistivity and Grounding Design – A brief history and the missing link
Bill Tocher
In 1915 Wenner (Frank Wenner 1873-1954) of the National Bureau of Standards’ electrical resistance measurement section published a landmark bulletin describing a method of measuring earth resistivity. That method we now obviously call the Wenner Method. Wenner devised his method as a way of injecting a current into the ground via two electrodes insulated to a known depth and then measuring the voltage response at two other similar electrodes either within the first two, or outside, aligned, and equidistant. The purpose for conducting such a test was for Electrical Prospecting, ideally used to identify oil and ore deposits potentially worth extracting. Another well-known and alternative earth resistivity measurement method is the Schlumberger method (Conrad Schlumberger 1878-1939) and was also developed in the early 1900’s as a means of improving the outcomes of geological surveying and prospecting, particularly for petroleum exploration, with outstanding success!
It is quite likely that neither gentleman ever thought that their testing methods would be used to measure earth resistivity for earthing/grounding design. The purpose of which is to develop one of the cornerstone building blocks of a safe electrical system, that is the electrical resistivity of the earth in which we design and build substation grids. When did these geo-physicist’s names enter the common vernacular of electrical power system earthing and grounding?
This paper presents a practitioner’s re-proof of the basic electrical theory that led to the development of these test methods. It also discusses the correct application of soil electrical resistivity models for earthing/grounding design and helps to refine the method by which surface resistivity is assessed, which is an important and often ill-considered factor in the development of safety criteria for electrical safety.
SAFETY CRITERIA
DC Safety Criteria
Bill Tocher
Electrical safety criteria is a field of study unto itself within the realm f earthing system analysis. Safety criteria is based on the study of how the body responds to the external stimulus of electricity and aims to establish tolerable limits of current flow through the hear and ultimately establish how and when ventricular fibrillation (VF) might be expected.
Substantially more work has been done in the area of ac electrical system analysis and safety criteria development compared to dc electrical systems. Key researchers such as the American Dalziel and Englishman Lee contributed to the venerable IEEE Standard 80 ‘accidental ground circuit touch voltage criteria’, which until only recently saw widespread usage for ac electrical system safety design.
Electrical safety criteria for dc applications is, however, far more uncommon with one of the better resources being the Euro standard EN50122-1 for Railway applications and protective provisions against electric shock. This standard calculates tolerable voltages for both ac and dc systems and sues for the human body’s electrical characteristics form the 60479 series of internationally accepted standards.
This presentation looks at the continuing development of dc safety criteria and provides practical and probably usage cases for its application. Fibrillation probabilities are recalculated using the data from AS60479 and compared to its ac equivalents. Contact probably is then considered, and a true quantitative risk assessment process is also proposed à la the Energy Networks Australia earthing system management guide, ENA EG0.
Looking at Safety Criteria for Transients
Dr Darren Woodhouse
We take it for granted that when an earth fault occurs on the power system that the hazards created will be assessed against a set of criteria in some appropriate or required manner. What is usually not appreciated, particularly by our oblivious public, is that there is no such assessment of hazards generated by other sources or with alternative characteristics. There is no safety criteria for lightning, static discharges or other transients sources causing hazards within the power system or to the built environment to which it connects.
Shorter events, less than a few cycles of the power system, are more complex than their longer counterparts. The transient nature of the power system itself becomes a consideration, which is treated by some standards. But then as the durations become even shorter the nature of the hazard should no longer be even considered to be sinusoidal, and the frequency of the excitation increases. How it increases and how the response on the human body changes has not been explored.
For these reasons most of the published safety criteria only consider fault durations down to a tenth of a second and not much further. This paper is an attempt to open the conversation in this space with the goal of one day defining safety criteria for transients and lightning related events. It may be all we do is look at events down to a fraction of a cycle, but it is a beginning!
Three Electric Shock Case Studies – Investigation and Mitigation
Benton Grieve
At three different sites in NSW, people reported experiencing electric shocks:
- Underground Mine: A hard rock mine worker in western NSW reported a mild electric shock which in contact with metallic roof mesh and the chassis of a cable fed electric drill rig. Investigation by site staff identified a persist and reproduceable voltage hazard between the ground and the drill rig chassis, but no protection operation or insulation failure was evident. The problem was also identified at a range of other Jumbo’s of various makes and ages, and parts of the supply circuit including starters and junction boxes.
- Construction Site: A construction site in Sydney reported electric shocks to a worker when commissioning a crane and in contact with its flexible steel wire rope (FSWR). Sparks were also noted when the FSWR made contact with well-earthed items, such as concrete re-bar installed in piles. No protection operation or insulation failure was evident. Site electricians disconnected the 415V electrical supply (including the neutral), however, the reported voltages were still present. Prior to this shock, the worker had been in contact with all parts of the crane structure and had not received shocks in any other location.
- Open-Cut Mine: A worker at a long-established mine site reported receiving multiple electric shocks while taking a shower at the end of their shift. Investigations found several contributing factors including supply reconfigurations, documentation issues and inadvertent energisation of out-of-service equipment.
For each case study Safearth conducted a review of the situation, analysis, and an investigation to identify causes. This involved a combination of site testing, modelling, and liaising with stie personnel. This presentation summarises each of the shock incidents, the engineering problems, results from the testing and analysis, and the practical cost-effective measures used to mitigate the electric shock risk.
RAIL
Learnings from 2 big rail projects (earthing & bonding)
Lachlan McKerrow
Managing earthing related risk in the rail environment requires approaches that can be significantly different to typical HV power systems.
Hazardous voltages may be present not only under fault conditions but also due to the flow of traction currents under normal operations. Current draw of moving trains combined with currents injected by regenerative breaking, results in a power system load flow analysis were the connection points of multiple sources and multiple loads move based on timetables.
Typical earthing approaches applicable to above ground meshed power system are often difficult to implement in constrained tunnel environments where parallel exposure lengths are significant and available real estate is minimal. This combined with significantly higher likely hood of the presence of people add considerable complexity to earthing designs.
This presentation outlines learnings from recent rail projects where aspects of these complexities were encountered.
Stray current interference testing criteria associated with DC traction systems
Jim Hickey, Ausgrid
Ben Staddon, Safearth
The unprecedented levels of investment in dc powered rail developments in the Sydney area has and will have significant impacts on the surrounding infrastructure. This has made dc traction power a particularly significant area of investigation and concern for third party asset owners.
It is well-known that when current strays from the traction negative conductive return network during normal operation, that current can cause corrosion in metallic systems such as pipelines, power cables and nearby steel reinforced structures. As a result, it is crucial that we accurately identify concerning or non-complaint stray current interference during ongoing testing throughout the life cycle of the traction network and what standards and acceptable criteria are relevant.
In this paper, initially existing standards and relevant documentation are reviewed to identify current acceptable stray current interference anodic and cathodic potential shift criterion associated with differing conductive structure materials. These differing criterions will incorporate comparisons between structures with and without cathodic protection systems along with comparisons between the currently broadly accepted standards and relevant documentation utilised within industry. Following this initial comparison and review, further analysis and discussion will be presented to aim to formulate a consolidated stray current interference potential shift criterion and examine what could be embedded into industry practices and future standards. This component of the paper will also look to bridge currently existing gaps within some existing standards and work towards ensuring appropriate levels of stray current interference criteria are recognised.