Mechanics, Materials Science & Engineering, September 2016 – ISSN 2412-5954
proposed to make decision not only on the basis of the equivalent reliability indices assessment, but also taking into account the expected damage from unreliability. To assess the effects of the most serious outages the VaR-method (Value at Risk) is used [7], the value of the membership function (confidence level) μ = 0.02. Damage is represented as a unilateral fuzzy number with a boundary in the form of the Cauchy curve. The value of the technological damage DTECH for μ – level:
DTECH DB ( D AV DB )
1
1 ,
(2)
where DAV – average damage; DB – boundary damage. This approach is similar to the popular delta-normal method, which is based on the use of normal distribution fractile and volatility of risk factors, which is acts as its coefficient of variation [8]. The value of μ could also be determined by the experts method. In case of sufficient statistical information about outages in power supply system for particular enterprise the average damage DAV could be determined on the basis of calculated values of recovery time:
DAV D0 PTR ,
(3)
where D0 – damage, depending on the type of production, RUB/kW∙h (for the enterprises of Iron and steel industry D0=18.3 RUB/kW∙h); TR – recovery time, h; ΔP – consumer`s load limitiation, kW. The boundary damage in this case can be calculated approximately on the basis of the coefficient of variation CV of outage time resulting from processing information about emergency events in the power supply system: DB DAV (1 u0,95CV ) ,
(4)
where u0,95 – the quantile of the normal distribution relevant to the confidence probability of 0,95 ( u0,95 = 1,67). The characteristic feature of the large industrial enterprises is the installation of power plants on their territory. In this regard in case of stopping the power plant equipment, additionally to the technological damage there will occur the damage caused by underproduction of electric power DSt by the enterprise power plants, due to the need to purchase electricity at a higher price: DSt (C g C p )PSt TR ,
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