Grounding stations

Maximum touch and step voltages of a grounding station 22/712... 

Figure 22.3 A typical arrangement of a pipe electrode grounding station...

Refer to Figures 22.1 tint 22.3. illustrating a normal arrangement of grounding stations with provision for ehemiciil or salt treatment. The salts used need not be in direct contact vvith the electrode. 

This is a vast subject, on which extensive research has been done by many authors over the years. The grounding stations in such areas are normally spread over the entire station, and sometimes may even extend beyond its boundary to achieve the desired results. Here we discuss briefly, the basic criteria behind the requirement of a grounding system in a power station and its design considerations. 

This is Ihe maximum totich voltage of a grounding station that may occur under the worst sittiation (position 3. Figure 22.9). The design of the grounding station must ensure thtit in actual service this voltage does not exceed the permissible tolerable limits noted in Section 22.9.6. 

There are a few important parameters that must be determined before beginning the detailed engineering of a grounding station. 

The flow of circulating currents in the grounding conductors or ground of region two caused between two or more interconnected grounding stations, for a fault occurring in region one is termed the telluric effect. 

The ground resistance is a function of the area occupied by the grounding station and the stratification of the soil. The stratification of the soil is usually of a non-uniform nature and may vary the resistivity of soil vertically as well as horizontally, thus varying the resistance of soil. The minimum value of ground resistance (resistance of the grounding station) at a certain depth h from the ground surface may be expressed by... 

This may be substituted with the estimated maximum ground grid current, /q (Section 22.9.6), that may occur during the life of the grounding station thermal capacity factor from Table 22.5, in J/cmV°C. This is derived from formula (4,184) p), Ps in Ws/cm V °C (for details refer to lEEE-80)... 

L = total length of tbe buried conductors of the grounding station (equation (22.1.3)). 

Since there are too many variables and parameters related to a grounding station, the following practical example illustrates a step-by-step procedure to design a grounding station. 

After the final designs are complete it is recommended that the actual touch (actual) and step voltage (actual) are rechecked for both power plant and switchyard areas separately, to ensure that they are within the tolerable limits as determined above. After the ground stations have been finally installed the actual step and touch voltages must be measured to verify the designs. 

For small power houses, which may be captive and small switchyards or sub-stations, receiving and distributing currents to industrial or domestic loads, such an elaborate design is not required and simple grounding stations as discussed in Section 22.1 will be sufficient. 

For those produets that have many diverse modules that ean be reeonfigured over the life of the produet, sueh as PCB eard eage systems and eellular telephone ground stations, ete., then the distributed power system is more appropriate. This type of system typieally has one main bulk power supply that provides power to a bus whieh is distributed throughout the entire produet. The power needs of any one module within the system are provided by smaller, board-level regulators. Flere, voltage drops experieneed aeross eonneetors and wiring within the system do not bother the eireuits. 

Field surv have confirmed oxidant injury to ponderosa pine and associated species at numerous locations in the Sierra Nevada foothills east and southeast of Fresno. Oxidant measurements at ground stations and by instrumented aircraft show late-aftemoon peaks of transported oxidant on the western slopes of the Sierras. Limited measurements by instrumented aircraft suggest the development of a layer of oxidant approaching the forested mountain slopes between 610 and 1,829 m during the late afternoon. A very weak inversion or isothermal layer may serve as a reservoir of oxidant, which is advected to the mountain slope in the southern coastal air basin, as suggested by Edinger. Considerable concern has been registered about air quality in the Lake Tahoe basin, where local development may cause adverse oxidant concentrations. ... 

If instead of transmitting a continuous wave, the Doppler system transmits a sawtooth frequency-modulated (FM) wave, both the velocity and the instantaneous distance betw the missile and the ground station can be detd simultaneously. This ptinciple is explained in Ref 2, p 166 and illustrated in the graph. The FM radar system is capable of measuring accurately only short distances (Ref 2, p 166)... 

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