Australian operators of power systems are required to meet Australian Standards concerning touch, step and transfer potentials.
Earthing systems form an integral part of any power system and provide personnel safety, equipment protection and system operating requirements for protection schemes.
The Standards
These standards include ENA EG1 and AS2067 which outline design and testing requirements. The 2010 version of AS2067 introduced the requirement to design and prove touch and step potentials to meet specific design criteria rather than simply ensuring that the grid impedance was below 1 ohm. Mining sites also need to meet the requirements of AS3007.2 for touch potentials and clearance times.
Why is it required?
New installations require injection testing to prove the Earth Grid design criteria has been meet. This injection testing results in touch potential measurements being taken and compared to the design criteria.
Periodic testing of Earthing Systems is also required as Earth Grid impedance can change due to corrosion of earth cables, changes in surrounding infrastructure, soil movement, excavation works and theft or vandalism. Periodic testing ensures the Earth System impedance has not changed from the commissioning stage thus ensuring the touch and step potentials are still within the design criteria.
How is it done?
Periodic testing on substation earthing systems is carried out to ensure compliance with the original design criteria or against the relevant standards when the design criteria is not available. This will ensure touch and step potentials remain at safe levels.
Our experience
We offer comprehensive field testing and analysis using state of the art off frequency current injection methods and analysis technology. Our services include measurement of soil resistivity, electrode and earth grid resistance, calculation of touch and step potentials, all completed without interruption as tests can be performed whilst the substation is still energised.
Our technology provides accurate knowledge of the voltage gradients around the earthing system allowing highly accurate analysis of the step and touch voltages that require monitoring. This is achieved using off frequency current injection in the area surrounding the substation. Our engineers can assess the stability of the measured voltages at increasing distances to provide an accurate earth grid impedance measurement.
Ampcontrol conducts periodic Earth Grid testing which includes the provision of manuals and documentation to support analysis and findings. These reports can be also supplied to relevant government authorities to support auditing processes.
We provide Earth System testing services for mining and industrial applications during commissioning of new substations along with routine Earth System testing for pre-existing systems. High Voltage safety compliance audits against AS2067 and AS3007 can also be conducted at the same time as the Earth System testing to confirm compliance to standards as well as the touch and step tolerances.