Working Group B1.44, “Guidelines for safe work on cable systems under Induced voltages or currents

When working on or in the vicinity of power cable systems, it is critical to understand the level of risk from induced voltages or currents and how to ensure these risks are properly managed.  Technical Brochure 801 examines current global practice regarding how to calculate induced voltages on the cable to be worked on, how to plan the works in case of induced voltages and how to proceed with the work in situations where there is a risk of hazardous voltages or currents due to induction. With safety as a top priority for all Australian utilities, the understanding of these hazardous conditions is vital for the wellbeing of all personnel dealing with high voltage power cables.  The Australian member for the WG was George Bucea and the Convenor of Australian Panel B1 is Russell Wheatland, who produced this article. 

There are several types of induced voltages that can affect the potential of the cable core, screen and metal sheath. The different types can be divided into three categories depending on how they are transferred from an electrical source to the object of induction.

• inductive coupling
• capacitive coupling
• conductive coupling (Earth Potential Rise)

All three issues must be evaluated when dealing with induced voltages. The influence from each coupling depends on the presence of other electrical systems in the surroundings of the cable, and how the cable system is bonded to earth. 

During several stages of a cable system life (installation/maintenance/testing/upgrading/removal), it may be required to work under induced voltages or induced currents to perform some of the following operations:

• cable pulling or laying in the vicinity of an energised system such as underground cables or overhead lines
• jointing operations of cable circuit installation, during repair after cable system failure and/or throughout an upgrading process
• maintenance and testing of cable earthing and bonding systems including link boxes and ancillary equipment
• removal for disposal of the cable system at the end of its life 

Even when the cable circuits are switched off, hazardous conditions may occur on the cable systems and, as a consequence, it is important that the Target Groups (utilities, manufacturers, contractors, operation and maintenance entities or others) be provided with guidelines for safe working conditions on cable systems. 

One of the important findings that has been identified, is that there is no clear guidance or an appropriate standard for the evaluation of maximum permissible touch voltage for cable systems outside of substations. As a result, in this TB are cited several standards and guidelines which are related and used in different countries. Furthermore, a recommendation is included to IEC to update the existing standard IEC 61936, where the limits of touch voltages as a function of clearance time, for cable systems within substations are given. 

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