Touch voltage-based earth-fault protection ensures compliance with safety codes and enhances availability of electrical power

Touch voltage-based earth-fault protection ensures compliance with safety codes and enhances availability of electrical power

Climate change is one of the major threats we are facing today on a global scale. Its impacts are already visible across various aspects of our daily lives. In the electricity distribution sector, tasks such as the need for building weatherproof networks, managing distributed electricity production, and preparing for the forecasted increase in electricity consumption are just a few examples.

Written by Olli Rintamäki
Written by Olli Rintamäki
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The growing demand for weatherproof networks is fueled by our current lifestyle, where a constant and high-quality electricity supply is the prerequisite for running our professional and social lives. To address this demand Distribution System Operators (DSOs) have a few options available, and one is replacing existing overhead lines with underground cables. 

Increasing the amount of underground cabling comes at a price, where the actual cable investment cost is only one side of the story. Expanding the cable network will lead to an increase in earth-fault current levels and hazard voltages which must be dealt with. The solution is to compensate the earth fault currents by installing or scaling up the existing Petersen coils. The earth fault protection scheme will need some attention too, as the new network set-up will pose challenges to the conventional earth fault protection schemes.

ABB’s solution for these challenges is the award-winning multi-frequency admittance protection function, which can manage even the most difficult fault cases to provide reliable protection with excellent dependability.

To rise to the challenge ABB has, together with partners, invested heavily in studying the phenomena related to earth faults in isolated and compensated networks and specifically the new challenges faced with increasing cabling. Our objective was to offer the best protection features that safeguard human lives and installed assets with the minimum impact on the quality of electricity supply in the form of unnecessary supply breaks.

The extensive research effort has paid off – and with significant results. We have proudly introduced our latest development in the field of earth fault protection, namely touch voltage-based earth-fault current protection, also known as IFPTOC. As the name implies, the function can calculate the fault current and estimate the resulting hazardous touch voltage in the actual fault location.

Now, for the first time, network operators can install earth-fault protection that offers an optimal balance between safety and supply quality. Conventional earth-fault protection functions measure the fault current present at the substation without any knowledge about the fault current level in the fault location. Depending on the feeder in question and the current topology of the network, the difference can be considerable. Set parameter values for conventional earth-fault protection functions are typically a poor compromise between safety and supply continuity, which may result in hazardous fault conditions or unwanted power outages for the customers.

The new protection function introduces a dynamic operation delay dependent on the calculated fault current and touch voltage level at the fault location. In this way, the function can satisfy the electrical safety codes, such as EN 50522 or IEEE 80, requirements concerning maximum allowed touch voltages while still avoiding unnecessary supply breaks. In other words, responsible network operations managers can be reassured that their network is protected according to the prevailing safety code continuously, even under changing network topology, or fault conditions.

You can learn more about ABB’s new protection method in the “Enhancing electrical safety and reliability of protection with novel touch voltage-based earth-fault current protection” technical paper, available for download here.

About the author

Olli Rintamäki works as a product line manager at ABB Distribution Solutions in Vaasa, Finland. He has authored or co-authored a number of conference papers on the topic of protection and control of electrical grids.

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