Meeting Touch and Step Standards

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.

LED Lighting Enhancing Safety

Underground coal mining requires safe, effective and durable lighting solutions. By improving visibility, reducing glare and decreasing maintenance requirements LED lighting is enhancing safety in these environments.

Improved visibility is critical in maintaining a safe working environment underground, with poor lighting cited as a contributing factor in many underground accidents.

Glare is a significant issue in determining the design of lighting systems for underground coal mining. Traditional fluorescent lighting creates a wide and broad dispersion of light which generates spill light that can contribute to reflection or glare off PPE cap shields.

In comparison, LED light sources are directional, where 100 per cent of the light emission from the LEDs is directed onto the task area, maximising lighting efficiency, minimising light spill and reducing the instances of glare. The white light emissions from LED sources also allows for more precise colour recognition when compared to fluorescent lighting. This provides a strong contrast to black backgrounds and a high perception of illuminance.

Reducing maintenance requirements

By design LED lights reduce maintenance requirements and increase safety through reduced downtime, instances of failure and maintenance. Also, LEDs last significantly longer than fluorescent lighting, reducing maintenance costs and the instances of individuals conducting lighting maintenance in hazardous areas.

LED light manufacturers state a useful working life in excess of 50,000 hours, equating to over five years of 24 hour use.  In comparison, the working life of a fluorescent light is significantly less than five years and therefore requires more frequent changeout of the light source, more maintenance activity and potential operational impact. LEDs do not typically catastrophically fail, as is usually the case with fluorescent lighting, but rather the light output generally decreases over time. This allows for a regular maintenance schedule to be implemented ensuring replacement prior to failure thus maintaining consistency of lighting and improving safety underground.

Underground lighting is required to withstand high levels of vibration and mechanical movement as well as high pressure washes and cleaning to remove surface dust, making durability paramount. Ampcontrol’s LED lighting fixtures for underground mining are designed to be robust and compact with clear solid resin casings and IP66 ratings.

Decreasing power requirements

The industry is trending towards intrinsically safe low voltage lighting. This trend is due in part to LED lights that operate at lower voltages in comparison to traditional lighting options. Specialised low voltage power supplies provide regulated 12VDC power that has multiple levels of over voltage and over current protection circuits to ensure that should an overload or short circuit occur, there is not enough current to create sparks to ignite any presence of volatile gasses.

Longwall lighting solutions

Burn Brite, a Member of the Ampcontrol group, has developed an innovative IS LED Lighting System that mounts high intensity, long-life LEDs into a low profile static dissipative light enclosure. Designed with safety and ease of maintenance in mind the lighting system has been installed in the majority of Australian longwall mines.