Orta gerilim dağıtım şebekelerinde reaktif güç kompanzasyonu uygulaması

Abstract

Bu tezde Orta Gerilim Reaktif Güç Kompanzasyonu üzerinde çalışmalar yapılmıştır. Reaktif güç kompanzasyonunun önemi, sakıncaları ve sağladığı faydalar anlatılmıştır. Kompanzasyon çerçevesinde, Türkiye enerji tüketiminin 1/9 'una yakın bir kısmına sahip olan İstanbul İli Avrupa Yakası orta gerilim sistemi incelenmiştir. Dağıtım şebekelerinde çok az uygulaması olan orta gerilim reaktif güç kompanzasyonu İstanbul için tasarlanmış ve 1998 yılı için pratiğe geçirilmesi planlanmıştır. Orta gerilimde yapılacak olan reaktif güç kompanzasyonunun, Boğaziçi E.D.A.Ş 'a ve dolayısı ile sisteme getireceği faydalar anlatılmıştır. Kompanzasyon tesislerinin yapılması kadar önemli ve dikkat edilmesi gereken harmonikler ve bunların sebep olduğu rezonans olayları incelenmiştir. Harmonik rezonanslarına karşı alınması gereken önlemler anlatılmıştır. Tez içinde pratikte rezonans olayı durumu gösterilmiştir. Avrupa yakasında bulunan 67 adet 34.5/10-15 kV transformatör merkezindeki toplam 147 adet transformatör için tesis edilecek olan kondansatör bankları sonrası şebekenin durumu araştırılmıştır. Güç faktörü tancp=0.3 ( cosç =0.95 ) civarında salınım yapacak şekilde tasarlanan kondansatör bankları tesis edildiğinde sistemin 5. harmonik açısından tehlike oluşturmadığı, 7. harmonik açısından bazı merkezlerde rezonans ihtimali olduğu fakat bunun da önlem alınarak tehlikenin giderilebileceği sonucuna varılmıştır. Tezin son bölümünde 1998 yılında uygulamaya konulması planlanan İstanbul Avrupa Yakası kompanzasyon sistemi tablo halinde sunulmuştur. Kompanzasyon tesislerinin yapımından önce 34.5/10-15 kV transformatör merkezlerindeki aktif-reaktif güç değişimi ile aylara göre güç faktörü değişimi gösterilmiştir. Mevcut sistemin özellikle yaz aylarında reaktif sının aştığı ve kompanzasyon sonrasında, tesis edilecek kondansatör bankları sayesinde de sistemin reaktif sıkıntıdan kurtulacağı sonucuna varılmıştır. Sonuçta reaktif güç kompanzasyonun yapılmasının vazgeçilmez bir unsur olduğu, İstanbul Avrupa Yakası orta gerilim dağıtımım yürüten Boğaziçi E.D.A.Ş için çok karlı bir yatırım olduğu, kompanzasyon sayesinde enerji kalitesinin artacağı, müşterilerin şikayetlerinin (gerilim düşüklüğü, kaliteli enerji dağıtımı...vb) giderileceği, dağıtım şirketinin TEAŞ 'a reaktif ceza ödemeyeceği... gibi faydaları da beraberinde getireceği tesbit edilmiştir.

Current consumed by the consumers that use alternative current, consist of two main components which are called active and reactive currents. Active power, formed by the active current, is transformed into mechanical power in motors, light power in lighting. Reactive power is only depended on reactive current and it only causes generators, transformers, electrical network and coils to be louded unnecessarily but also heat losses and voltage drops. Inspide of its not being transformed into useful power, it can not be abondened. The magnetic field that is needed in the equipments which works according to the electro dynamic rules such as generators, transformers, coils and motors is created by the reactive current. Re Figure5. 1.Active, Reactive and Visiable power in the complex plane Reactive powers causes an increase in the system losses, decreases the conducting capasity of lines. It is a necessary of the electrical energy, which becomes more expensive and which is being in lack of, to be cheap in conducting and in consuming as an active energy. If the extra losses that is caused by the low powerfactors is annihilated ; the cost of investments and management will be cheaper. Controlling and obtaining the reactive power, causes the harmful effects that are stated above, from another source, is called Reactive Power Compensation. There are 3 main aims of compensation. These are as fallows ; a-) To have a better power factor b-) Voltage regulation c-) Load stability Reactive power compensation can be performed in 3 ways. These are ; i-)Direct compensation In this method, each load has its own capacitors groups ii-) Group compensation In this method, the loads that are in or out of the system are compensated altogether. iii-) Central compensation The active power of the consumers that are fed from only one node is replied. There are lots of benefits in the aspect of consumers and producers. In the aspect of producers, the benefits are ; i-) an increase in the system capacity ii-) a decrease in heat losses iii-) a decrease in voltage drop. In the aspect of consumers, the benefits are ; i-) No need to unnecessary investment. ii-) Decrease in losses. iii-) Decrease in quality iv-) No need to pay for reactive power. Electrical energy consumption increases every year and this is proportional to the population growth. The plans that are made to reply the demand are, generally inadequate. That is because the population growth is more than the predictions. So in order to reply the demand, different ways have been used such as higher price for electricity in demand times. The other ways is the regulation of the power factor. The best method to compensate the reactive power that limits the active power as it is mentioned above is to establish the compensation systems at the last point such as motors, air condition and lihting. For great distribution systems, there are a big number of consumers, dispersed into a great diffuculty to make compensation at this point namely 400 V. Especially in the big cities such as Istanbul, it is not convenient to compensate this power at the low- voltage level. Boğaziçi Electricity Distribution Company ; which is responsible for the distribution of electricity in european part of Istanbul has more than 2.400.000 consumers. Some of these are fed from the primer part of the system, the others are fed from the seconder part. According to the council of minister communication, the consumer whose demand power is 250 kVA or more, have to compensate their reactive power by them selves. The other consumers, that is the biggest part in number, demand inductive power and this demand not only increases day by day but also, it becomes more difficult to control. According to the statistical datas ; the power factor in European part of Istanbul, is below of 0.9 in summer ( in May, June, July, August) To compensate the reactive power at the 10 - 15 kV bars of the 34.5 / 10-15 kV transformer stations, will cause an ease in the distribution system. There are 3 main reasons to compansate the rective power at medium voltage level. i-) The ability of production in bloks at Medium Voltage and increase in possibility to control and repair. İİ-) increase in cost for the big powers in Low Voltage iii-) There are lots of consumers at 400 V In the compensation system of Istanbul, mentioned in section 3 and 4, the power factor is taken as 0.958. In this planning, the most important points are as fallows. i-) Reactive power demand will increase as result of technology and population growth because both of them means equipments that consume reactive power, ii-) This planning mustn 't be for a short period, iii-) Increase in the active power must be maximum after compensation During the compensation period, the most important problem is the harmonics and the rezonance events. In section 5, the effects of harmonics, how the harmonics are created, calculation of harmonics, rezonance and the precautions against them are examined in details. In electrical network, generators, transformers, lines, condensators, dynamic compensators, motors, inverters, direct frequency converters, power fiters, static VAr systems, power supply, are used. If the characteristics of V-I are not linear at the gates ; these are called a non linear circuits. These circuits cause harmonics by the deforming sinusoidal wave - from of current and voltage of the network In the stationary condition at symmetrical loaded 3 phase alternative current networks, there may be harmonics that are in odd numbers, which are also sinusoidal. Some of these ( 3rd and its powers ) may be neglected because of symmetry. In figure 5.1, it can be seen the 1st. 3rd and 5th harmonics of a voltage wave - form. v(wt) -1 Q wt. 2 ÎT Figure 5.11.1.3 and 5 harmonics of a voltage wave - form Some precautions must be taken to the results of harmonics first of all, harmonics must be detected by the help of an oscilograph and their values must be calculated by means of an analyser. The condansator must be observed if it causes resonance or not. Critical value for this can be calculated as follows ; In a parallel circuit; Qcr 1.1 Sk In a serial circuit ; Qcr = Str (n2uksinq>k) XI The frequency of compensation system must be less than the frequency of the network, which causes rezonance for this; a-) Compensation system must be linked by means of cables ( not only one cable ). This will caues an increase in the resistance b-) Compensation systems must be in off condition. When the network is not so loaded. This can be achieved by otomatically c-) In order to reduce the frequency of the compensation group, serial coils must be used d-) Filters that consist of coils and condansators must be used. It is very important for the security of the network to take this precautions mentioned above in planning and to prevent rezonance. Choosing at medium voltage compensation system equipment, it must be take into consideration not only worker safety but also practicalness, it is important for reliable; using of lasting vacum conductor, equiping of on-off units and energized others part with metal-clad or metal enclosed. During project, compensation system must be investigated well.Instead of observation of power factor variation at network, immedite variation of reactive power should be observed. Moreover while the system building up, condansator group should be establish as need of reactive power at network.