### Paper Menu >>

### Journal Menu >>

Energy and Power Engineering, 2013, 5, 1303-1307 doi:10.4236/epe.2013.54B247 Published Online July 2013 (http://www.scirp.org/journal/epe) Economic Benefit Analysis of 220 kV Energy-saving Power Tr ansformer* Weili Chen1, Xian Ma1, Jingtian Bi1, Zhisen Li2, Tong Jiang1 1State Key Laboratory of Alternate Electrical Power, System with Renewable Energy Sources, North China Electric Power University, Beijing, China 2Tai’an Power Supply Company, Shandong Electric Power Corporation Email: 303696602@qq.com Received January, 2013 ABSTRACT Power transformer serves as one of the most widely used electrical equipments in power grid. During the operation, terrible losses are produced. With the development of loss reduction technology of power transformers, in order to save energy saving and reduce emissions, the old power transformer should be replaced. The paper summarizes the main method to reduce the losses of power transformers and brings up the improved Total Owning Cost (TOC) algorithm, which applies to 220 kV power transformers’ comprehensive benefit analysis. Using the improved Total Owning Cost (TOC) algorithm, based on today 220 kV energy-saving power transformer manufacturing level, the economic benefits of new energy-saving power transformer and the return period of investment are analyzed. Finally, combined with energy-saving effect, the appropriate replacement proposal of 220 kV power transformers has been given. Keywords: 220 kV Power Transformer; Loss Reduction Technology of Transformer; TOC Algorithm; Economic Analysis 1. Introduction As the transmission and distribution infrastructure, power transformer is widely used and always run a long time. Power transformer on the one hand is high efficiency transmission electrical products, on the other hand is consumption power electrical equipment. Although the efficiency of the transformer can be as high as 99%, but the consumption of electric energy is still very amazing [1]. According to the statistics, the losses of power transformer itself account for more than 3% of genera- tion [2], therefore carrying out power transformer com- prehensive benefit calculation and putting forward rea- sonable replacement proposal is the important link to reduce the power loss and to achieve the results of en- ergy saving and emission reduction. 2. Today 220 kV Transformer Manufactur- ing Leve According to GB/T 6451-2008, specification and techni- cal requirements for oil-immersed power transformers, the highest rated no-load active loss of 180000 kVA/ 220 kV three winding on-load changer transformer is Po = 156 kW, and the highest rated load reactive loss is Pk = 630 kW[3]. Now, through inputting new materials and manufacturing technology improvement, the load and no-load losses of 220 kV power transformers have been greatly reduced. The main reduction means mainly con- sists of the following: 2.1. Reduce the No-load Loss of Power Transformers Now the mainstream of technologies to reducing the no-load loss of transformers are using new type of core material; using best quality core manufacturing process; using high quality insulation structure; reducing the technology coefficient; improving core structure; reduce- ing the core window size; designing no resonance core; using wound core transformer, etc. [4]The most effective method is using new type of core material and using wound core transformer. Due to the cost, low saturated flux density, easy to produce debris and other reasons, amorphous alloy is not suitable for large power trans- former. Similarly, because the today’s technology is still unable to meet the requirements of the large size core be winded continuously, wound core currently only suitable for small and medium distribution transformer. For 220 kV power transformers, high-quality silicon steel sheet is suitable to reduce the unit loss of the core, such as 23ZH90. The relationship between silicon steel sheet and *Supported by the National High Technology Research and Develop- ment of China 863 Pro g ram ( 2012AA050208 ) . Copyright © 2013 SciRes. EPE W. L. CHEN ET AL. 1304 power transformer no-load loss is calculated. The results are shown in Table 1 . With the reduction of no-load loss, the cost is increasing. 2.2. Reduce Load Loss of Power Transformers The common methods to reduce load losses are using improved core structure to reduce the coil turns; calcu- lating ampere-turns balance of coil to control the radial leakage; using low loss low resistance wire; using ad- vanced insulation structure; choosing appreciate conduc- tor transposition way, etc.[3]Among them, the most fun- damental method to reduce load losses is reducing the resistance of conductor, which can be achieved by in- creasing the cross-sectional area of the wire, namely se- lect the wire in accordance with the requirement of larger capacity transformer. 2.3. Reduce the Additional Loss of Power Transformers The measures to reduce additional loss are using transpo- sition wire and composite wire reasonably to reduce ed- dy-current loss, stray loss and additional loss; opti- miz- ing parallel wires’ transposition to reduce circulation loss caused by magnetic flux leakage; taking effective shiel- ding measures in the structure. Table 1. Different silicon steel sheet and no-load active losses Comparison. Specifications of silicon steel sheet The no-load active losses(kW) Drop rate(%) 0.3mm Common silicon steel sheet 30Q150 204.5 0 0.3mmHI-B High permeability silicon steel sheet 30QG130 177.3 13 0.3mmHI-B Laser processing high permeability silicon steel sheet 30RGH120 163.6 20 0.27mm Common silicon steel sheet 27Q140 190.9 6.67 0.27mmHI-B High permeability silicon steel sheet 27QG110 150.0 26.7 0.23mmHI-B Laser processing high permeability silicon steel sheet 23ZH90 122.7 40 Table 2. Transformers’ parameters and prices. Transformers’ parameters and prices Id Pk（kW）P0（kW）I0% Uk% Sn(kVA) price(yuan) 1 520 84 0.20 14 180000 6660000 2 500 86 0.20 14 180000 6780000 3 480 87 0.20 14 180000 6720000 4 460 88 0.20 14 180000 6960000 5 430 94 0.20 14 180000 7500000 6 400 102 0.20 14 180000 8190000 Shandong Electric Power Equipment Company have made some research achievements in the loss reduction technology of power transformers, typical SSZ-180000/ 220 products’ rated load active loss dropped gradually from 600 kW to 390 kW, rated no-load reactive loss from 130 kW to 90 kW, there are some actual products in this interval. The price of transformers is estimated, setting the typ- ical transformers’ rated load active loss to constant value, using the most advanced no-load loss reduction tech- nique, which guarantees the lowest no-load loss. Trans- formers’ parameters and prices are estimated such as Table 2 shows: 3. Select 220 kV Power Transformer Using Total Owning Cost (TOC) Algorithm 3.1. Total Owning Cost (TOC) Algorithm and Its Improving The Total Owning Cost (TOC) algorithm is the tradi- tional method to make economic analysis and evaluation of distribution transformer. TOC value = initial invest- ment of distribution transformer + the power losses’ cost during the life of distribution transformer. According to the TOC value of different transformers, choose the low- est as the optimal solution [5]. When using The Total Owning Cost (TOC) algorithm to choose 220 kV power transformers, there are some defects, which mainly embodied in the calculation for reactive economic equivalent. Reactive economic equiv- alent is determined by the position of transformer in power grid. For the distribution transformer, Reactive economic equivalent is generally assigned k = 0.1 kW/kVAR. Because 220 kV power transformers mainly used for transmission line, reactance value far outweigh the resistance value, so the value should be less than 0.1. Improved TOC algorithm calculate reactive economic equivalent of transmission transformer. 1) Calculation formula of TOC TOC=C+A×NL+B×LL where, NL is rated no-load losses, kW; LL is rated load losses, kW; A is the capital cost per kilowatt of no-load losses during life of transformer, yuan/kW; B is the capital cost per kilowatt of load losses during life of transformer, yuan/kW; C is the price of transformer; 2) Parameters 0 000 % N L( 100 % LL( ) 100 n kn kkk ) I S PkQ Pk US PkQPk where, P0 is no-load rated active loss, kW; Q0 is rated no-load exciting power, kVAR; Pk is load rated active Copyright © 2013 SciRes. EPE W. L. CHEN ET AL. 1305 loss, kW; Qk is rated load exciting power, k”VAR; I0% is no-load current,%; Uk% is impedance voltage,%; Sn is transformer rated capacity, kVA. k is reactive economic equivalent. Reactive economic equivalent means transformers’ reactive power consump- tion increase or decrease per 1 kVAR formed the heat losses increase or decrease kW value in higher level electricity grid. The Heat losses increase or decrease in value only by Reactive power consumed power itself Current Square caused. Reactive economic equivalent is calculated as follow: The active losses of higher level electricity grid with no transformer accessed in: 22 23 3 0 PQ PQ P3IR10R10 R10 UU PP 3 where, 0 is the active losses of higher level electricity grid with no transformer accessed, kW; I is system cur- rent, A; U is system voltage, kV; R is line resistance, Ω; P is system active power, kW; Q is system reactive pow- er, kVAR; P is the active power losses caused by De- livery active power, kW; Q is the reactive power losses caused by Delivery reactive power, kVAR.. P P P The active losses of higher level electricity grid when transformer accessed in: 2 3 11 PP QQ PR10 R UU 2 3 10 where, ΔP is the active losses of higher level electricity grid when transformer accessed, kW; ΔQ1 is reactive losses of transformer, kVAR; ΔP1 is active losses of transformer, kW. The active loss changes of higher level electricity grid when transformer accessed in: 22 11 1 b0 2 3 PQ2PP2QQ PPP U R10 1 where, b P are the active losses changes of higher level electricity grid when transformer accessed in. So, the reactive economic equivalent is: b 1 P kQ Assume that the system power factor cos0.9 , load rate is 70%. Using per-unit value, estimate the value of reactive economic equivalent. Because 220 kV trans- mission line resistance value is about 20% of reactance value, and the reactance value generally take for 0.1Ω, so resistance value is 0.02. The reactive economic equiva- lent of 220 kV new energy-saving transformers listed equal 0.04. 3) Coeffici above can be calculated. The values are approximately ent A and B a 2 12 ) B(12) 1 1/1/1 PW PY PW PW ELh kEJLEL P kain A(kEJL where, kpW is present value; EJL is the basic tariff in dual 3.2. The Example of Improved Toc Algorithm rithm, the economic bene- fit hat the average loss parameters of 220 kV po , Pk =520 kW tariff system, yuan/kW·month; EL is the Power tariff, yuan/ kWh; hpY is Annual operating hours, generally is 8760h; τ is annual maximum load loss hours; P is Trans- former maximum load factor; i is Annual interest rate; a is inflation rate; n is useful life. 1) The Total Owning Cost Using improved TOC algo s of 220 kV power transformers listed above can be analyzed. Assume t wer transformers using in power grid approximated as the loss parameters specified in GB/T 6451-2008. P0 = 156 kW, Pk = 630 kW, I0% = 0.49, Uk% = 14.3. the price is estimated ￥6000000. Other new energy-saving transformers’ parameters is shown in Table 2. Taking the transformer whose P0 = 84 kW as an example, assume the load rate of transformer is 70%, n=20, i = 7%, a = 5%, P W k = 15.72, EJL = 20, EL = 0.52, hpY = 8760. 0 000 % NL()98.4kW 100 % LL 1528kW 100 n kn kkk I S PkQ Pk US PkQPk Assume the maximum load rate is 100%, the annual m TOC=C+A×NL+B×LL=73456434yuan Similaformers un turn period of investment placed, but se- le f the capital, the return pe aximum load loss hours τ can be calculated, τ = 4292.4 h. From the Table 2, can see the price of transformer is C = 6660000yuan. Thus, coefficient A and B and the total owning cost (TOC) can be calculated. A( 12)kEJL ELh 2 75380.54 B(12)38860.59 PW PY PW kE JLEL P rly, the TOC value of different trans der different load rates can be calculated. As shown in Figure 1. 2) The re The old power transformer should be re cting different transformer to replace, the return period of investment is also different. Regardless of the time value o riod of investment = the price of transformer/the loss cost price between old and new transformer. Copyright © 2013 SciRes. EPE W. L. CHEN ET AL. Copyright © 2013 SciRes. EPE 1306 .59×(1659.6 Considering plug 8.6 into th Similarly, the retustment of different transformers under different load rates can be calculated. As shown in Figures 2 and 3, here just list the situation of load rate is 70% and 50%. =6660000÷{[75380.54×(192－98.4)＋38860 －1528) ]÷15.72}=8.6years the time value of the capital,Figure 1 shows that The Total Owning Cost of typical energy-saving transformers has greatly reduced com- pared with old transformers. Although the differences is small between new energy-saving transformers, but the return period of investment and the total energy-saving benefit can vary a lot. e formula of kpW, Can get the return period of invest- ment in consideration of the time value of the capital: n=ln[1-(0.07-0.05)×8.6] ÷ ln[(1+0.05) ÷(1＋ 0.07)]=10yerars rn period of inve Figure 1. The TOC of different transformers under different load rates. Figure 2. The return period of investment of differe nt transformers under 70%load rates. W. L. CHEN ET AL. 1307 Figure 3. The return period of investment of differe nt transformers under 50%load rates. If the average load rate of local 220 kV transformers is ab r assume that the average loss parameters of 22 4. Conclusions ent of the energy-saving technology illustrated by an example in which the load rate is 70%. REFERENCES [1] B. C. Ying, “ys to Transformer Industry Standard Expansion of s,” h of Economy Capacity of Me- out 70%, choose the transformer which the return pe- riod of investment is shortest. According the calculation, new energy-saving transformer 3 and 4 is the most opti- mal selection. The price of transformer 3 is lower, but the total energy-saving effect of transformer 4 is more obvi- ous. Choose transformer according to need. If choose transformer 4, The Total Owning Cost lowers 13.24 mil- lion yuan. This pape 0 kV power transformers using in power grid approxi- mated as the loss parameters specified in GB/T 6451- 2008. But the actual situation may be different. Therefore the replacement proposal in the paper only applies for the transformers whose loss parameters is equal to or higher than the loss parameters specified in GB/T 6451-2008. With the developm tio of power transformers, the losses of 220 kV transformers reduce obviously. In order to save energy and reduce emission, it is advised to replace the transformers whose loss parameters is equal to or higher than the loss pa- rameters specified in GB/T 6451-2008 by new energy- saving ones. The replacement should base on the Total Owning Cost, the return period of investment, energy- saving effect, and the local load rate of transformers. It is The calculation of several typical power transformers is made and the conclusion is drawn. The energy-saving effect is best if the substitution is energy-saving power transformers whose Pk = 460 kW and P0 = 88 kW. The initial investment is least if the substitution is energy- saving power transformers whose Pk = 460 kW and P0 = 87 kW. The Energy-saving Wa and the Analysis of Its Potential,” Energy Conservation, Vol. 4, 1992, pp. 4-7. [2] K. He, “Transformer Energy-saving [N/OL], China Quality News, 2012-11-08 (2) http://www.cqn.com.cn/news/zgzlb/dier/642204.html. [3] General Administration of Quality Supervision, “Inspec- n and Quarantine of the People's Republic of China,” Specification and Technical Requirements for Oil-immersed Power Transformers GB/T 6451-2008. China ISBN, Beijing: Standards Press of China, 2008. [4] J. L. Xu, “Method to Reduce Power Transformer Los Vol. 3, 2012, pp. 26-35. [5] Y. B. Gao, “The Researc dium Voltage Distribution Transformer,” Shanghai: Shanghai Jiao Tong University, 2010. Copyright © 2013 SciRes. EPE |