Protection parameters

Based on the risk factors of Dayangquan Coal Mine, the permanent refuge chamber of No. 12 coal seam has the functions such as high temperature resistance, shock resistance and air-tightness. The protection parameters are shown in Table 1 (Sui 2007). 

Table 1. The protection parameters of the permanent refuge chamber of Dayangquan Coal Mine. 

The protective parameters are / = h and Ex = 4>x = 4>o when x = 0 [3]. According to Ohm s law, the leakage resistance is equals to the potential drop from the leakage point divided by the polarization current difference at the coating-metal interface. Thus,... 

Concepts of CP kinetic criteria were postulated from the beginning of the 1970s, but at that time no appropriate measurement method was available to put them into practice. Reliable corrosion rate measurements of metals in CP conditions were ensured by only two physical methods gravimetric and resistometric measurements. Both methods allow the determination of increasing corrosion losses over longer time intervals (due to relatively low sensitivity) however, they do not allow the determination of the instantaneous corrosion rate. Such information would be required by users of CP installations, allowing the regulation of protective parameters in a feedback system. 

Very often there is a need to determine the cathodic protection parameters of ob-... 

An important reaction parameter is the choice of the base and NajCO or NaOAc have been shown to be preferable to EtjN in some systems[2]. The inclusion of NH4CI has also been found to speed reaction[2]. An optimization of the cyclization of A -allyl-2-benzyloxy-6-bromo-4-nitroaniline which achieved a 96% yield found EtjN to be the preferred base[3]. The use of acetyl or inethanesulfonyl as N-protecting groups is sometimes advantageous (see Entries 4 and 5, Table 4.1). 

Eluoride added to a compatible dentifrice base at a level of 1000 ppm has been clinically proven to reduce the incidence of dental caries by about 25% on average, even in areas where the water supply is fluoridated (4). Elevation to 1500 ppm increases the protection. Sources of fluoride approved for use in dentifrices are sodium fluoride [7681-49-4] (0.22%), sodium monofluorophosphate (0.76%), and stannous fluoride [7783-47-3] (0.41%). The Eood and Dmg Administration regulates fluoridated dentifrices as dmgs and has estabUshed parameters for safe and effective products. CompatibiUty of the fluoride with the abrasive is an important requirement. 

Because there are many other properties that also are important, coatings cannot be selected only on this basis. The mechanical and chemical properties of the coating, change of properties with temperature, dielectric and adhesion properties, and particulady the cost of fabrication are all important parameters. Coatings can also be used to transport heat created away from a component and keep the component functioning as designed, or to protect a component from temperature variations in the environment. 

If the upset can be detected and dealt with in short order, the system can be protected. Some of the probes that measure parameters... 

M (marginal) indicates that the stability of the protected functionality is marginal, and depends on the exact parameters of the reaction. The protective group may be stable, may be cleaved slowly, or may be unstable to the conditions. Relative rates are always important, as illustrated in the following example (in which a monothioacetal is cleaved in the presence of a dithiane), and may have to be determined experimentally. 

The role of SCRs is to vary the supply parameters, which require frequent changes in V, i.e. du/df and in /, i.e. di/di in an energized condition. Becau.se of momentary phase-to-phase short-circuit, dv/di occurs during switching OFF and d 7df during switching ON sequences. Both are transient conditions and may damage the semiconductor devices used in the circuit. To protect the devices, the transient conditions can be dealt with as follows ... 

Having discussed the effect of the above parameters on the motor s performance, we will now illustrate by way of an example a general case to broadly suggest a procedure that can be followed to select the protective scheme for a motor. For more detailed selection of the motor protection relay, reference may be made to the relay manufacturer. 

These are protection CTs lor special applications such as biased differential protection, restricted ground fault protection and distance protection schemes, where it is not possible to easily identify the elass of accuracy, the accuracy limit factor and the rated burden of the CTs and where a full primary fault current is required to be transformed to the secondary without saturation, to accurately monitor the level of fault and/or unbalance. The type of application tind the relay being used determine the knee point voltage. The knee point voltage and the excitation current of the CTs now form the basic design parameters for such CTs. They are classified as class PS CTs and can be identified by the following characteristics ... 

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. 

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