Electricity + Control April 2016

TRANSFORMERS + SUBSTATIONS

• Most facilities have grounded electrical systems – in the event of a lightning strike, current will find a safe path to earth. • A ground electrode provides the contact between the electrical system and the earth. • Electrical codes and standards specify a minimum impedance for the ground electrode.

take note

John Wilson specialises in Metrology and Accreditation consultation and training. He is a Senior member of the SA Institute of Electrical Engineers, a Fellow of the Society for Automation, Instrumentation, Measurement and Control. John has over thirty years’ experience with Fluke products (including having worked directly for Fluke) and has practical experience in different fields of metrology and electronic design. John has recently presented ECSA CPD Point Approved Seminars on this subject at Comtest’s Linbro Park Offices. Enquiries: John Wilson. Email jgpwilson@xsinet.co.za

Figure 5: Stake positions for the 62 % rule.

References [1] IEEE 142. 2007. Recommended practice for grounding of industrial and commercial power systems (‘Green Book’). [2] IEEE-81. IEEE 81. 2012. Guide formeasuring earth resistivity, ground Impedance, and earth surface potentials of a ground system.

Electricity+Control April ‘16

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