IEEE 81.2-1991

New IEEE Standard - Inactive-Withdrawn.

Practical instrumentation methods are presented for measuring the ac characteristics of large, extended or interconnected grounding systems.

Measurements of impedance to remote earth, step and touch potentials, and current distributions are covered for grounding systems ranging in complexity from small grids (less than 900m²), with only a few connected overhead or direct burial bare concentric (2) neutrals, to large grids (greater than 20,000m²), with many connected neutrals, overhead ground wires (sky wires), counterpoises, grid tie conductors, cable shields, and metallic pipes.

This standard addresses:

• Measurement safety;
• Earth-return mutual errors;
• Low-current measurements;
• Power-system staged faults;
• Communication and control cable transfer impedance;
• Current distribution (current splits) in the grounding system;
• Step, touch, mesh, and profile measurements;
• The foot-equivalent electrode earth resistance; and
• Instrumentation characteristics and limitations.

Test methods and instrumentation techniques used to measure the ac characteristics of large grounding systems include the following topics:

• Measurement safety
• Earth-return mutual errors
• Low-current measurements
• Power-system staged faults
• Communication and control cable transfer impedance
• Current distribution (current splits) in the grounding system
• Step, touch, mesh, and profile measurements
• The foot-equivalent electrode earth resistance
• Instrumentation characteristics and limitations

Grounding electrodes consisting of a single ground rod, arrays of ground rods, tower footings, and many grids (if no external grounding is connected) can be measured, interference voltages permitting, with methods outlined in IEEE Std 81-1983 [2].

Even if a large grid has an impedance phase angle of 18°, the resistance component will be only 5% lower than its impedance.

However, for large grounding grids in low-resistive earth (<75 Ω-m) and for grounding systems that have numerous extended grounding conductors, the impedance could be significantly greater than the resistive component measured with the conventional test sets of IEEE Std 81-1983.

The purpose of this guide is to present practical instrumentation methods that may be used for the measurement of impedance to remote earth, step and touch potentials, and current distributions of large extended or interconnected grounding systems ranging in complexity from small grids (less than 900 m²), with only a few connected overhead or direct burial bare concentric neutrals, to large grids (greater than 20,000 m²), with many connected neutrals, overhead ground wires (sky wires), counterpoises, grid tie conductors, cable shields, and metallic pipes.