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Discussion on rural distribution reactive power decentralized compensation scheme

Abstract: Discussion on rural distribution reactive power decentralized compensation scheme 1. Effect of reactive power compensation of distribution line; 2. Reactive power compensation method and distribution scheme of distribution line; 3 examples of the effect of installing capacitors on distribution lines

key words: reactive power compensation of distribution line 1. Effect of reactive power compensation of distribution line (1) reduce the active power loss of the line:

when the current passes through the line, its active power loss is: △ p=3i2r × Or △ p=3 × (P/Ucos Φ) two × R × Where △ P -- active power loss of the line kwi -- current passing through the line ar -- Resistance of each phase of the line Ω P -- active power transmitted by the line kwq -- reactive power transmitted by the line kvarcos Φ-- Power factor of line load; According to the above formula, the active power loss is inversely proportional to the square of the power factor. Increasing the power factor can greatly reduce the line loss. When the power factor increases from 0.6 to 0.8, the copper loss decreases by nearly half. (2) Improve the voltage quality of users: the formula of line voltage loss is: △ u= (pr+qx)/u × Where △ U -- line voltage loss kvu-- line voltage kvp-- line active load kwq-- line reactive load kvarx-- line inductive reactance Ω r-- line resistance Ω. It can be seen from the above formula that if the system power factor is increased and the reactive load transmitted by the line is reduced, the voltage loss will decrease. (3) Reduce the capacity of system components and improve the transmission capacity of electricity: apparent power s=p/cos Φ， It can be seen from this that when the power factor is increased and the same active power is transmitted, the installed capacity of the equipment can be reduced and the investment can be saved. If the installed capacity of the equipment remains unchanged, the transmission of active power can be increased. The benefit of installing capacitors to improve the transmission of active power can be determined by the following formula: △ p/q= (COS Φ 2-cos Φ 1)/cos Φ 2(tg Φ 1-tg Φ 2) Where △ P -- the increase of active power Q -- the reactive power cos required to reach △ P Φ 1、cos Φ 2 -- power factor before and after compensation, if cos Φ From 0.8 to 0.95, each kvar capacitor saves about 0.38kva of the installed capacity of transformers and other equipment on the distribution line. The cost of each KVA installed capacity on the network is more than dozens of times the price of each kvar capacitor. 2. Reactive power compensation method and distribution scheme of distribution line (1) reactive power compensation method: install low-voltage self-healing capacitor at the low-voltage outlet of distribution transformer, switch with the transformer at the same time, and directly crack to compensate the reactive power consumed by the transformer itself and the reactive power required to compensate some inductive loads. (2) Distribution scheme: ① the influence of the loading method of the compensation capacity spring testing machine on the experimental results can not be ignored: the compensation capacity is determined by the power load and the power factor before and after compensation. The calculation formula is as follows: qbch=ppj (TG Φ 1-tg Φ 2) Or qbch=ppj (1-tg Φ 2/tg Φ 1) Where qbch -- the required compensation capacity kvarppj -- the average active load of the maximum load month kwqpj -- the average reactive load of the maximum load month kvartg Φ 1 -- power before compensation, otherwise it will accelerate the wear factor cos of all parts of the hydraulic system Φ Tangent value Tg of 1 Φ 2 -- power factor cos required after compensation Φ In addition, we must pay attention to Cos Φ 2 the value must be determined appropriately. When the power factor is increased from 0.95 to 1, the compensation capacity required increases a lot, and the gain is not worth the loss. Therefore, it is unreasonable to increase the power factor to 1. ② Reasonable distribution of capacitors of each branch line of the distribution line: in the radial distribution network, Q1, Q2, Q3... QN are set as the average reactive load of each branch line before compensation; Qbc1, qbc2... Qbcn refers to the reactive power of capacitors to be installed on each branch line; R1, R2, R3... RN is the calculation group of each branch line (its value is the resistance value of each branch line multiplied by the coefficient α And get, general α Take 0.55). The equivalent resistance RD of all lines equipped with capacitors is: rd=1/(1/r1+1/r2+1/r3+... +1/rn). The calculation results show that when the conditions of the following formula are met, the reactive power compensation effect of capacitors is the best, that is: (q1-qbc1) r1= (q2-qbc2) r2=... = (q-qbc) Rd. therefore, The most reasonable distribution of the reactive power of the capacitor installed on each branch line is: qbc1=q1- (q-qbc) rd/r1................. Qbcn=qn- (q-qbc) rd/rn, where q- the reactive load before the compensation of the whole line qbc- the reactive load after the compensation of the whole line. In addition, the reasonable distribution of the capacitor in the distribution can also be obtained by the graphical method. Take qnrn of each line as the ordinate and QN as the abscissa to draw a right triangle in the same proportion, as shown in Figure 1 (a), (b) and (c); Then draw a comprehensive broken line, whose abscissa should be equal to the sum of abscissa of each component under the given ordinate, as shown in Figure 1 (d). If the QBC value is drawn on this abscissa, and a straight line intersects the polyline at point D, through point D, a straight line parallel to the abscissa is made, and the hypotenuse of each right triangle intersects points a, B, and C, the abscissa of points a, B, and C are the reasonable distribution values of qbc1, qbc2, and qbc3 respectively. Figure 1 rational distribution of capacitors in power distribution (a) figure is a right triangle with q1r1 as the ordinate and Q1 as the abscissa; (b) The figure shows a right triangle with q2r2 as the ordinate and Q2 as the abscissa; (c) The figure shows a right triangle with q3r3 as the ordinate and Q3 as the abscissa; (d) The figure is a comprehensive broken line with the sum of the abscissa in figure (a), (b) and (c) as the abscissa under the given ordinate. 3. An example of the effect of installing capacitors on the distribution line is the Huangkan farmland line of Huairou power supply bureau. The total length of the line is 76.264km (the line number is lgj-70 TPU and rubber, which constitute a cost-effective composite line of 17.30km, lgj-50 conductor of 3.538km, lgj-25 conductor of 22.432km). There are 105 distribution transformers, totaling 7100kva (the special transformers for factories and mines are not counted). There are two rural electricity. In April 1996, the active power of the line was 454100 kW · h, and the reactive power was 744400 kvar · H. Power factor: cos Φ= 45.41/45.412+74.442=0.61 calculated value of reactive power consumption of distribution transformer: qtr=7100 × zero point zero eight × 720=40896 kvar · h, from which we can see that the reactive power loss of distribution transformer accounts for the total of the line

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