IEEE 81.2-1991 pdf free.IEEE Guide for Measurement of Impedance and Safety Characteristics ofLarge, Extended or Interconnected Grounding Systems.
The purpose of this guide is to present practical instrumentation methods that may be used for the measurement ofimpedance to remote earth, step and touch potentials, and current distributions of large extended or interconnectedgrounding systems ranging in complexity from small grids (less than 900 m2), with only a few connected overhead ordirect burial bare concentric neutrals, to large grids(greater than 20 000 m*), with many connected neutrals, overheadground wires (sky wires), counterpoises, grid tie conductors, cable shields, and metallic pipes.
Grounding electrodes consisting of a single ground rod, arrays of ground rods, tower footings, and many grids (if noexternal grounding is connected) can be measured, interference voltages permitting, with methods outlined in IEEEStd 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 92-m) and for grounding systems that have numerous extended grounding conductors, the impedance could be significantly greater than theresistive component measured with the conventional test sets of IEEE Std 81-1983[2].
Measurement of low-impedance grounding-system characteristics, with injection currents between 0.1-100 A, usingtechniques described in Section 8. is generally preferred.Or, grounding-system parameters may be measured orverified under power-system conditions with the staged-fault methods of Section 9. Due to the diversity in stationgrounding configurations and the variety of possible test connections,this guide cannot narrowly define the testmethod for each application. The user must take responsibility for the adequacy of the method selected (see Section13. for a review of instrumentation components).
Test methods described in this guide require test connections between the grid and locations on the earth remote fromthe grid. Extended test leads,out-of-service transmission lines used in the current circuit, and the power systemconnected to the substation under test present a high degree of exposure to atmospheric disturbances or power systemline-to-ground faults and ground potential rise(GPR).The following precautionary measures are recommended:
Do not schedule field measurements of either the power system grounding,during periods of forecast lightning activity，in areas (determined by conditions at each utility) that encompass the station beingmeasured or of the power network connected to the station being measured.
Do not lay out test leads or connect test leads to out-of-service transmission lines during a period whenlightning is prevalent.
When test procedures are not in progress, externally routed test leads should be disconnected and isolated from the grid and treated as being energized.In the event lightning appears in the zone defined above when test procedures are underway, stop all testing, open the test connection to the out-of-service transmission line, and isolate from the grid any temporarilyinstalled test conductors routed externally to the grid.IEEE 81.2 pdf download.IEEE 81.2 pdf download.