Earthing Studies for Power Systems
What is earthing and why is it important?
Earthing of electrical systems has been around almost as long as the electrical system itself. While there are still some specialised electrical systems out there that don’t need to be earthed as part of their design and operation, the vast majority of the ones we deal with do!
Quite simply, Earthing Systems exist to safeguard us against electrical shock. Electrical shock incidents can result in harm to a person with various degrees of consequence ranging from burns to death.
There are different codes of practice regarding earthing that depends on where you are in the world. Consequently, they all approach this subject in different ways through national regulations and standards. However, they all share the aim to achieve specific common objectives: the most important of which being safety to personnel.
When an electrical fault occurs, the short circuit energy must be dissipated as safely and as quickly as possible for the protection system to interrupt the current flow. Typically, the short-circuit current flows to earth rods and disappears into the Earth, causing a potential rise in hazardous conditions in and around the area of the earth rods.
What is Step and Touch Potential?
The difference in the surface potential experienced by a person bridging a distance with their feet apart without contacting any other grounded object is often referred to as Step Voltage Potential. You could be at risk of injury during a fault simply by standing near the grounding point.
The potential difference between the ground potential rise and the device surface potential at the point where a person is standing while in contact with the faulted structure is often referred to as Touch Voltage Potential.
How do we avoid Step and Touch potential?
There are a variety of causes that lead to high Step and Touch potentials. An excellent earthing design and its continued upkeep is essential to avoid electric shock events. A well designed earthing system considers all possible causes to provide an effective means of dissipating the fault current into the earth without exceeding the safety boundaries or adversely affecting continuity of service. It provides a safe environment to protect personnel in the vicinity of those grounded facilities from dangers of electric shock under the fault condition.
What does this mean to me?
You should understand what earthing arrangements are in place, which should be documented, reviewed and tested and above all, you need to be clear that any mitigation you have in place is sufficient. If you don’t, then seeking the advice and support from a professional electrical engineering company would be a great place to start.
Above all, always remember that the earthing of electrical systems serves an invaluable purpose to keep both people and equipment safe.
3 key techniques to mitigate Step and Touch potential hazards:
- Carry out a detailed review of ground surface materials
- Conduct an analysis for soil resistivity
- Consider a review of additional ground conductors
What Earthing Studies services can Covol provide?
At Covol, we undertake studies to determine the overall effectiveness of the various earthing systems in order to satisfy the requirements of the HSE.
These cover the following areas:
- Assess whether touch and step potential calculations are necessary and if so, ensure they are within tolerable limits as defined in BS EN 50522.
- Schematic drawings showing the earth connection arrangement for transformers. As each installation may be slightly different, a separate drawing is allowed for each transformer.
- Consideration of HV earthing for transformers.
- Ensuring the reliable operation of protective relays and to ensure that no excessive touch and step potentials occur.
Static Earthing and Equipotential Bonding
- It is important to ensure that steel work is effectively bonded together to avoid the generation of a sparking hazard, which could ignite a flammable gas or vapour.
- Ensuring that all metalwork and noncurrent-carrying metalwork is securely bonded together so that in the event of a fault, it would prevent exposed items of metalwork that are not designed to carry an electric current from being made live.
- Ensuring that a lightning discharge will be diverted safely to earth without causing danger to personnel or any structural damage.