Fire protection measures can be subdivided into life-safety and investment categories.
Life-safety measures are considered to be mandatory by ﬁre codes, building codes, or safety codes. As such, the codes mandate speciﬁc types of substation ﬁre protection, with very little ﬂexibility in their selection.
Investment-related ﬁre protection is provided to protect assets, conserve revenue, and help maintain service to customers. This type of ﬁre protection is not commonly mandated by legislation but is driven by economic reasons such as asset losses, revenue losses, and the possible loss of customers.
The selection of investment-related ﬁre protection can be done based on company policies and standards, insurance engineering recommendations, industry practices, speciﬁc codes and standards (IEEE 977 and NFPA 850), or by risk-based economic analysis.
TABLE 1 – Probability of Fire for Various Transformer Voltages
|Transformer Voltage||Annual Fire Frequency|
|69 kV||0.00034 ﬁres/year|
|115–180 kV||0.00025 ﬁres/year|
|230–350 kV||0.0006 ﬁres/year|
|500 kV||0.0009 ﬁres/year|
Source: IEEE 979, Guide for Substation Fire Protection.
The risk-based economic analysis is the evaluation of the investment measures in relation to the probability of ﬁre, the potential losses due to ﬁre, and the cost of the ﬁre protection measures.
This analysis requires a reasonable database of the probability of ﬁres for the different hazard areas or types, an assessment of the effectiveness of the proposed ﬁre protection measures, an estimate of the ﬁre loss costs, and a fair degree of engineering judgment. The potential losses usually include the equipment loss as well as an assessment of the lost revenue due to the outage resulting from the loss of equipment.
One of the most common risk-based economic analysis types is a beneﬁt/cost analysis. This analysis is calculated using the following equation:
Normally, this ratio should be greater than one and preferably greater than two. A beneﬁt/cost ratio of two means that the beneﬁt (avoided ﬁre loss costs) is twice the cost of the ﬁre protection. Therefore it is a good investment.
One of the greatest difﬁculties is to estimate the frequency of ﬁre for the speciﬁc hazards. Some companies have extensive ﬁre loss histories and loss databases. These databases can be used to estimate speciﬁc ﬁre frequencies, but the results may be poor due to the small statistical sample size based on the company’s records. There are a number of other databases and reports that are in the public domain that provide useful data (i.e., NFPA data shop, EPRI Fire Induced Vulnerability Evaluation Methodology, and IEEE 979 Transformer Fire Survey). Table 1 shows the estimated probability of ﬁre from the IEEE 979 Transformer Fire Survey.
Once the potential ﬁnancial loss due to a ﬁre has been calculated, the designer should input costs and effectiveness of any proposed ﬁre protection measure into the beneﬁt/cost equation and determine the B/C ratio. If the B/C ratio is less than one, provision of the ﬁre protection measure is not an acceptable investment.
Example of a Risk-Based Economic Analysis
The following is a simpliﬁed example of an analysis:
- A substation has four 138-kV single-phase oil-insulated transformers. One of these transformers is a spare and is located remote from the others. The load supplied by these transformers is 25 MW. A water-spray deluge system is being considered to suppress or control a ﬁre in the trans-formers. The deluge system is expected to protect the adjacent transformers, but not save the transformer that catches ﬁre.
The estimated cost of a deluge system for all three transformers is $60,000. The individual transformers have a replacement value of $300,000.
- The utility’s chief ﬁnancial ofﬁcer questions whether this is a good investment.
- The company uses a discount rate of 10% and requires that all investments have a beneﬁt/cost ratio greater than two. The assigned value of energy is $25/MW. The standard amortization period is 25 years.
- The annual frequency of ﬁre for a single 138-kV transformer is estimated as 0.00025 ﬁres/year. Therefore, the combined frequency for the three transformers is 0.00075 ﬁres/year.
- The estimated effectiveness of the deluge system protecting the adjacent transformers is 0.9. The deluge system will not save the transformer in which the ﬁre originates; it is assumed to be a total loss.
- The ﬁre is assumed to originate in the center transformer in the bank of three single-phase transformers. It is assumed that in the absence of suppression, the ﬁre will spread to destroy the two adjacent transformers. The spare transformer is not affected because it is remote from the other transformers.
- The estimated station outage period for this scenario is the difference between the outage time to replace all three transformers (a ﬁre in the center transformer could destroy all three transformers) and the outage time to replace the center transformer (assuming the deluge system will protect the adjacent transformers).
The outage time to replace a single unit is ﬁve days and to replace three units is 40 days. Therefore, the expected outage loss period is 35 days.
The expected lost revenue is 35 days × 24 h/day × 25 MW/h × $25/MW = $525,000.
The estimated annual revenue and equipment loss costs = (composite annual ﬁre frequency) ×
(revenue loss for the station outage period + replacement value of the adjacent transformers) =
(0.00075 ﬁres/year) × [$525,000 + (2 × $300,000)] = $843.75/year.
The net present value of the annual revenue and equipment losses for the 25-year amortization period at a discount rate of 10% = $7659.
The beneﬁt/cost ratio = $7659/[$60,000 × (1.0/0.9)] = 0.115.
Example conclusion //
The calculated beneﬁt/cost ratio of 0.115 is considerably less than the min-imum required ratio of two. The proposal to install deluge protection should be rejected, since it is not economical. Other ﬁre protection measures could be considered, or the risk could be transferred by purchasing insurance to cover the possible loss of the assets (transformers) and the revenue. These other measures can also be analyzed using this methodology for economic risk analysis.
It should be noted that the above example does not include societal costs, loss of reputation, and possible litigation.
SOURCE // Substation Fire Protection – Don Delcourt, BC Hydro
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