Abstract: in recent years, the rising price of copper leads to a substantial increase in the cost of copper core cable, and the original economic selection data is no longer applicable, so it is necessary to update the economic selection data of various types of cable with the latest cost data. However, there is a lot of work to do, because it is quite difficult to collect relatively complete cable material costs and installation costs in different regions. Under this background, an approximate method to estimate the cost of new cable materials based on copper price and a simplified method to update the economic current density are proposed, and the traditional updating process of economic selection data is simplified by combining the two methods. This method can alleviate the difficulty of collecting complete new cable price data to a certain extent, and speed up the update speed of economic current density.
Key words: power cable; economic current; economic section; economic type selection
introduction
Based on the economic optimization standard of the cross section of power cable core, taking into account the initial investment and the loss cost during the operation period of the cable, the economic selection method of the cable cross section is adopted, and the lowest total electricity cost is taken as the economic goal of the engineering construction, which has been widely used. In reference [8], the economic current density of medium and low voltage cables is deeply studied, and the relevant data of economic type selection in 2000 are given. For the convenience of discussion, it is hereinafter referred to as the original economic type selection data.
In recent years, the rising price of copper leads to the doubling of the cost of copper core cable, which makes the original economic selection data no longer applicable. In order to ensure the accuracy of the current economic selection of cable section, it is necessary to update the economic selection data by using the current cost of various types of cables. However, it is very difficult to collect a relatively complete cable material cost and installation cost, and the cable reference price given by the relevant national regulatory agencies lags behind the actual demand. For example, the research report in reference [8] is based on the 1998 "estimated price of raw materials for power construction equipment".
Due to the heavy workload and time-consuming of updating the data of cable economic selection by using the traditional method, this paper puts forward an approximate method to estimate the cost of new cable materials by using the recent copper price and a simplified method to update the economic current density on this basis, which can quickly obtain more accurate data of cable economic selection under the condition of large fluctuation of copper price and simplify the use of the traditional method to a great extent Method is a complex process of data updating.
Approximate method of updating economic current density with new cable material cost
According to the economic selection principle of iec287-3-2 / 1995 standard, the expression of economic current density of cable is obtained. The pseudo economic current density, a / ram2, is the maximum load current: s. Is the economic section, mm2; a is the variable part of the cost, yuan / · m); auxiliary equivalent loss cost coefficient, yuan / L [w; P ∞ is the DC resistivity of the cable at ℃, Q · m; B is the proximity effect coefficient of the cable, y. And skin effect coefficient Y8, B = I + y, + y. The resistance temperature coefficient or20 and the average operating temperature of the cable at ^ 0 ℃ is a function of k = I + OT20 (0m)_ 20) The unit of M is ℃.
It can be seen that the change of cable initial investment will cause the change of variable cost part a, and then affect the value of economic current density.
According to the economic selection principle of iec287-3-2 / 1995 standard, the initial investment of cable can use the linear function of cross section, s is the cross section of cable, mm2; C is the fixed part of cable cost, yuan / M; L is the length of cable, M.
The initial investment CI can be expressed as the sum of material cost and installation cost. Because the value and value of a of each grade section of the same type of cable are equal, according to equation (2), a can be obtained by using the difference between the initial investment of two adjacent cables with nominal section. Considering that the proportion of cable installation cost in the initial investment of cable is small, assume that the original material cost of cable is CIC, and the new material cost caused by copper price fluctuation is c'k, which makes the material cost increase multiple k = C ', JC. The error analysis of this simplified process is shown in Table 1. The original value in the table is from the literature, and the accurate updated value of a is the data in 2006. During the updating process, the cable material cost is estimated by referring to the unit price of (2006 Guangdong Shenzhen construction project price information), the installation cost is estimated by referring to (2006 Guangdong municipal engineering comprehensive quota) and "electric power construction engineering budgetary estimate quota - electrical equipment installation engineering" revised in 2001. It has been verified that when the fluctuation of a value is less than 20%, the error of a value is less than 10%, which does not affect the accuracy of economic model selection. It can be seen from the analysis results in Table 1 that the errors caused by this approximate method are within the allowable range, which meets the accuracy requirements of economic selection of cable section.
2 approximate method of estimating material cost of copper core cable by using copper price
Because it is very difficult to collect the complete material cost of all types of cables, considering that the copper cost accounts for a large proportion in the cable cost, this paper attempts to use the copper price to approximately estimate the cable price.
Divide the material cost g of cable into the part directly related to copper price. And the part civ that has nothing to do with the copper price shows the specific gravity coefficient of the part that has nothing to do with the copper price.
It can be approximately considered that G fluctuates linearly with copper price, while civ remains unchanged. Assuming that the cable material cost in the starting year is ‰, the copper price related part is ‰, the proportion coefficient of the copper price related part is Ao, the material cost in the nth year is CIA. I, the copper price related part is C, and the ratio of the nth year to the starting year is k, if the material cost in the starting year C, the proportion coefficient of the copper price related part in the starting year le and the copper price growth multiple are known, the material cost in the nth year can be calculated As long as the TXO of various types of cables can be determined, the cost of new cable materials can be estimated according to the copper price of the studied year. In this paper, the year 2000 is taken as the starting year, and the relevant data of each year is taken as the original data. The coefficient% is determined by using the formula. The average value of the five% values of each type of cable is taken as the proportion coefficient of the relevant part of the copper price in the starting year. The 0c0 value of different types of cables is simplified and updated. For the situation of rapid growth of copper price, based on the comparison of economic type selection in the starting year According to the parameters and data, the economic current density data suitable for the current situation can be quickly obtained by using the current copper price and the values in Table 2. The specific steps are as follows:
Using the material cost of corresponding cable in the initial year (2000), the ratio of current copper price to the copper price in the initial year and the parameters of corresponding cable, the current material cost of cable is estimated according to equation (10).
Using the estimated cable material cost and the corresponding cable material cost in the initial year, the growth multiple K of the material cost is calculated.
The new economic current density jn is calculated according to equation (6) by using the growth multiple K of material cost and the economic current density data of the starting year.
4. Accuracy analysis of simplified updating method
Using the relevant data of 2006 to verify the simplified updating method of economic model selection data, that is to compare the results of the simplified updating method with the accurate updating method. When the accurate method is used to update the economic current density, the cable material cost is estimated by referring to the unit price of (2006 Guangdong Shenzhen construction project price information), the installation cost is estimated by referring to (2006 Guangdong municipal engineering comprehensive quota) and "power construction engineering budgetary estimate quota - electrical equipment installation Engineering" revised in 2001, and other relevant parameters are the same as those in reference [8]. In the process of calculation, the annual electricity price of the national high electricity price area is selected.
According to the sensitivity analysis conclusion of economic current density in reference [8], the error of economic current density obtained by the simplified updating method is less than 10%, which can meet the accuracy and economy of economic selection of conductor section.
5 Conclusion
In view of the need to update the data of economic type selection of copper core cable caused by the fluctuation of international copper price and the problems existing in the traditional methods, such as cumbersome update process and difficult data collection, a simplified method to update the data of economic type selection of copper core cable by using copper price is proposed, and its accuracy is verified. The results show that the updating process of this method is simple, and the updating data can meet the accuracy of economic type selection of conductor section, and realize the purpose of accelerating the data updating process of economic type selection of cable.