(IEC 287-3-2 / 1995), which is based on the economic optimization of the power cable core section, based on the initial investment of the cable and the cost of the operation during the cable. The lowest cost for the construction of economic objectives, and thus has been widely used [2]. [8] on the low-voltage cable in the economic current density of a more in-depth study, given the 2000 economic selection related Data, for the convenience of discussion, hereinafter referred to as the original economic selection data.

In recent years, copper prices continue to rise, resulting in doubling the cost of copper cable, so that the original economic selection data is no longer applicable. In order to ensure the accuracy of the current cable cross-section economic selection, the economic selection data of the various types of cables need to be updated. However, it is difficult to collect relatively complete cable materials and installation costs, and the cable reference price given by the relevant national regulatory agencies lags behind the actual demand. For example, the study report in [8] is based on the 1998 " Raw material budget price "as the basis for the.

This paper presents a simplified method to estimate the new material cost of cable by using the recent copper price and the simplified method to update the economic current density on the basis of the traditional method. Large fluctuations in the case of rapid access to more accurate economic selection data, to a large extent simplify the use of traditional methods of data update process.

1 Approximate method of updating the economic current density with a new cable material fee

The economic current density of the cable is derived from the IEC 287-3-2 / 1995 standard economic selection principle. The pseudo - economic current density, A / ram2, is the maximum load current. For the economic section, mm2; A is the variable part of the cost, yuan / m); to help the equivalent loss cost factor, yuan / l [w; P ∞ ℃ when the cable DC resistivity, Q · m; Cable proximity effect coefficient. And the skin effect coefficient y8, B = I + Y, + y. ; ^ 0 strider temperature of the cable when the resistance temperature coefficient Or20 and the average operating temperature as a function of K = I + ot20 (0m_20), m in units of ℃.

It is known that the change in the initial investment of the cable causes a change in the cost variable part A, which in turn affects the value of the economic current density.

According to IEC 287-3-2 / 1995 standard economic selection principle, the initial investment of the cable can be used as the linear function of the cross section, S is the cable section, mm2; C is the fixed part of the cable cost, yuan / m; L is the cable length, m The

The initial investment ci can be expressed as the sum of the material fee and the installation fee. As the same type of cable cross-section of the A value and the value are equal, so according to formula (2), the use of two adjacent standard cross-section cable can be the difference between the initial investment A, taking into account the cable installation costs in the cable initial The proportion of investment in the smaller assumption that the original cable material costs cic, due to fluctuations in copper prices caused by the new material charges c'k, so that the material cost growth factor K = C ', jc. , The new value A 'of the cable cost variable part A, and then the new economic current density can be obtained. The error analysis of this simplified process is shown in Table 1. The original value in the table is taken from the literature. The exact update value of A is the data of 2006, and the cable material fee is referred to in the process of updating (the price information of construction cost in Shenzhen, Guangdong Province, 2006). And the estimated cost of the Electricity-Install Project Proposal - Electrical Equipment Installation Project, 2001. Verification: When the A value fluctuates by no more than 20%, the error is not more than 10% and does not affect the economy The accuracy of the selection is shown in Table 1. The results of this analysis show that the error caused by this approximation method is within the allowable range to meet the accuracy requirements of the economic selection of the cable section.

An Approximate Method for Estimating the Material Cost of Copper Cable by Copper Price

It is difficult to collect the complete material cost of all types of cables, and considering the fact that the cost of copper in the cable cost is large, try to estimate the cable price with copper price.

The material cost G of the cable is divided into parts directly related to the copper price. And part of the civic unrelated to the price of copper, showing the proportion of the relevant part of the copper price.

It can be approximated that G fluctuates linearly with copper, while civ remains the same. Assuming that the research base is based on the cable material cost of the initial year, the relevant part of the copper price is ‰, the proportion of the relevant part of the copper price is ao, the material cost for the nth year is Cia.i The relevant part of the copper price is C female, The ratio of the copper price in the first year is K, and if the material cost of the initial year is higher than that of the initial year, the material cost of the first year is related to the proportion of the copper price. Type cable tXo, you can estimate the new cable material fee based on the copper price of the study year. The research work of this paper takes the year 2000 as the starting year, and the relevant data is used as the original data, and the coefficient is determined by the use formula. The average value of the five% values ​​of each model cable is used as the starting price Part of the specific gravity coefficient, different types of cable 0c0 value simplified update method for the rapid growth of copper prices, based on the beginning of the year) economic selection of the relevant parameters and data, the use of the current copper and Table 2 in the value of the le can quickly get Applicable to the current situation of the economic current density data. Specific steps are as follows:

(10) estimate the current material cost of the cable by using the material cost of the corresponding cable (2000), the current copper price and the initial year's copper price, and the corresponding cable parameters.

Calculate the growth factor K of the material cost using the estimated cable material cost and the corresponding cable material cost for the starting year.

The new economic current density Jn is calculated according to equation (6) using the material cost growth factor K and the economic current density data of the starting year.

4 Simplify the accuracy of the update method

Using the relevant data in 2006 to verify the simplified method of economic selection data update, that is, the simplified update method and the exact update method to compare the results obtained. When the economic current density is updated by the precise method, the cable material fee reference ((2006 Guangdong Shenzhen Construction Project price information), the installation fee reference ((2006 Guangdong municipal engineering comprehensive quota) and "power construction project budget fixed - electrical Equipment installation project "in 2001 revised price estimates, and other related parameters and literature [8] the same process, the price of electricity to take the national high price of electricity prices.

According to the conclusion of the sensitivity analysis of economic current density in [8], the error of economic current density obtained by simplified updating method is less than 10%, which can meet the accuracy and economy of economic selection of wire cross section.

5 Conclusion

In view of the international copper price fluctuation caused by the copper core cable economic selection data update needs and the traditional method of the existence of the update process is more cumbersome, data collection work more difficult and other issues, put forward a copper price replacement copper core cable economic election Type data, and its accuracy is verified. The results show that the method is simple and the update data can meet the accuracy of the economic selection of the wire cross section, and the purpose of speeding up the process of cable economic selection is realized.

In this paper, the relevant data in [8] are the original data, so only the six types of cables involved are analyzed, and the purpose is to prove the superiority and practicability of the proposed simplified method.

Other types of cable economic selection data update, can refer to the simplified method proposed in this article, this article does not give a case analysis.