Protection level

The main objectives of RCRA ate to protect pubHc health and the environment and to conserve natural resources. The act requires EPA to develop and adininistet the following programs soHd waste disposal practices providing acceptable protection levels for pubHc health and the environment transportation, storage, treatment, and disposal of hazardous wastes practices that eliminate or minimize hazards to human health and the environment the use of resource conservation and recovery whenever technically and economically feasible and federal, state, and local programs to achieve these objectives. 

Select the nearest voltage rating of a station class surge arrester (see also Section 18.8) from the manufacturer s catalogue, (Table 18.8) as 6 kV which has the following protective levels ... 

The current limiting gaps, as noted above, in series with the non-linear resi.stors make it possible to adjust the protection level of the surge arrester for different values of discharge currents. They also help to maintain... 

BIL of the equipment Impulse protection level of the arrester (Vres)... 

The protection level of the arrester diminishes with the steepness of the wave. As / falls, of the arrester rises, leaving a smaller protection margin across the protected equipment. Refer to the characteristics of an arrester as shown in Figure 18.7, for a 10 kA, 8/20 /is impulse wave. For a front time of, say, 0.5, tis, it will have a of approximately 118% of its rated at 8 /is, and hence will reduce the protection margin as in equation (18.2). 

Table 18.3 Establishing the protection level of a surge arrester...

Transient condition as in Table 18.1 Protection level of a gapped surge arrester Protection level of a gapless surge arrester ... 

The protective levels of the surge arresters, al different system voltages are furnished by the manufacturers in their product catalogues. Tables 18.9 and 18.11 furnish typical data for a few established manufacturers. 

TOV is considered only to select the MCOV and the rated voltage, V, of the surge arrester. This is a reference parameter to define the operating characteristics of an arrester. It plays no part in deciding the protective level of the arrester, which is solely dependent on the transient conditions of the system, as discussed later. V, is used to make the right choice of an arrester and its energy absorption capability to ensure that it does not fail under the system s prospective traiisieut conditions. 

Whether its protective level can protect the BIL of the system and/or the equipment it is protecting, and... 

Increasing the TOV level, i.e. choosing a higher protective level (V,es) of the arrester, may increase the life of the arrester but will reduce the margin of protection for the protected equipment. Selection therefore should be done judiciously bearing all these aspects in mind. 

By a manufacturer it is determined for each particular arrester to establish its protective level. It is established... 

The criteria to determine the safe protective level of an arrester are the BIL of the equipment, as shown in Table 11.6 for motors. Tables 13.2 or 14.1 for switchgears, Table 32.1(A) for bus systems, and Tables 13.2 and 13.3 for all other systems. Motors have a comparatively lower BIL, but they are not connected directly on an outdoor... 

The protective level as determined above is true only when the surge arrester is mounted directly on the protected equipment (Figure 18.21), But this is seldom possible, us there is usually a gup between the surge arrester and the equipment, due to arrester height, connecting leads... 

Figure 18.20 Variation in protective level of an arrester with front time...

A lightning surge protective level is found to be more stringent than the switching surge or FOW protective levels. Hence, it is sufficient to check the protective distance requirement for the lightning surge alone. 

Example 18.5 in. Section 18.10 ilhistrates the procedure to determine the energy capability requirement of an arrester for a particular system. The tiltiinate selection of an arrester is a compromise between its protective level, F,., , TOV capability and energy absorption captibility. 

As regards the primary selection of the arrester, it is complete at this stage. But this selection must be checked for its adequate protective level and the energy absorption capability... 

We should keep in mind that the main difference between level D and C equipment is the amount of respiratory protection. Level C protection requires use of a respiratory device (APR). Requiring workers to work in level C for more than a small percentage of the time can prove to be a challenging situation for both workers and managers. Respirators, especially full-face respirators, can provide excellent protection for workers, but are also found to be a source for worker complaints. 

FIGURE 9-22. Components of airline-type respiratory protection, level B. Photo Courtesy 3M... 

Working in more protective levels of protection than conditions trnly warrant, as noted in the above andit finding, is commonplace and still happens today. There is an old saying, Better safe than sorry however, when all items are considered, too mnch protection in the form of PPE can create a dangerons sitnation. 

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