Altı fazlı enerji iletim sistemlerinde şönt reaktör lokalizasyonunun etkilerinin incelenmesi

Abstract

Uzun enerji iletim hatlarının iletim kapasitelerinin, gerilime bağımlı olarak arttırılabilmesi için iletim de daha yüksek gerilim kademelerine çıkılması gerekir. Üst gerilim kademelerinde iletim yapılması izolatör, yalıtım mesafeleri, korona gibi etkenlerden dolayı sınırlandığın dan, çok fazlı enerji iletimi iletim kapasitesini artırmak için bir çözüm olmaktadır. Ayrıca çift devre üç fazlı bir enerji iletim hattının iletim kapasitesi, iletim hattı altı fazlı hatta dönüştürülerek artırılabilir. Enerji iletim hatlarının iletim kapasitesini -etkileyen bir başka faktör olan hattın seri empedansı ve şönt süseptansmın etkisini azaltmak amacı ile hattın muhtelif noktalarında seri ve şönt kompanzasyon yapılır. Seri kom- panzasyon hatta seri olarak yerleştirilen kapasite bankları, şönt kompanzasyon ise faz ile nötr arasına yerleştirilen şönt reaktörler ile yapılır. Bu çalışmada üç fazlı çift devre Keban-Kayseri-Göl- başı enerji iletim hattı temel alınarak bu hat altı fazlı bir enerji iletim hattına dönüştürülmüştür. GÖzönüne alınan altı fazlı enerji iletim hattında seri ve şönt kompan- zasyonun muhtelif yerlerde yapıldığı altı değişik iletim Mod' u oluşturulmuştur. İncelemelerde Gölbaşı barası sonsuz güçlü bara olarak alınmış ve altı fazlı enerji iletim hat tının dokuz ayrı çalışma noktasında güç ilettiği varsayılmıştır. Bilgisayarda yazılan program kullanılarak herbir Mod için dokuz ayrı çalışma noktasında enerji iletim sis temlerinin işletilmesi ve planlanması açısından çok önemli olan arıza analizleri yapılmıştır. İncelenen arıza çeşidi onbir adettir. Elde edilen sonuçlar Mod' lar ve çalışma noktaları gözönüne alınarak karşılaştırılmış, etkiler değer lendirilmiştir.

In recent years, because of increasing generation and consumption, there has been an increased interest in high phase order (HPO) power transmission. High phase or der transmission (HPO), the use of more than the conven tional three phases, is a unique approach to encreasing the power transmission capability of overhead electric po wer transmission rights-of-way. At present, six phase transmission appears to be the most promising among multi phase systems for possible realization in near future. Be cause of the growing interest in this area, quite a num ber of papers have reported on different aspects of this new power transmission technology. Power transmission lines for many types of analy ses, can be represented by a single-line equivalent with lumped resistance (R), inductive reactance (Xl) and shunt susseptance (Bc) parameters per phase. For more exact cal culations, it is important to model all parameters uni formly distributed along the line. The six phase lines have been modelled by their phase impedance matrices, ABCD-parameters and ir-representations. The performance of transmission lines, especially those of medium length and longer, can be improved by reactive compensation of a series or parallel type. Seri es compensation consists of a capasitor bank plased in series with each phase conductor of the line. Shunt com pensation refers to the placement of inductors from each line to neutral to reduce. Partially or completely the shunt susceptance of a high-voltage line, which is parti cularly important at light loads when the voltage at the receiving end may otherwise become very high. Series com- persation reduces the series impedance of the line, which is the principal cause of voltage drop and the most impor tant factor in determining the maximum power which the line can transmit. Six phase transmission systems, if ever realized, will always be integrated in an otherwise three phase systems. Three phase/six phase transformers will be requ ired to connect six phase systems to the existing network at all levels viz. stepping up generation voltages to six phases, primary distribution, distribution to multi phase loads etc. Suitable representations of six phase lines and the associated transformers are, therefore, required Vlll - for analysing the impact of additions of six phase sys tems in the existing three phase networks for effective planning and realization of such systems. Network matrices are used in the analysis of an electrical network by using computer. In matrix notation/ the performance equation in impedance form is VBUS = ZBUS#IBUS (1) or in admittance form is I = Y v (2) BUS BUS* BUS K ' where V, bus voltage vector IB g/ bus current vector Z, bus impedance matrix YmiD, bus admittance matrix Fault studies form an important step in the design of adequate protective schemes. A detailed fault analysis employs symmetrical components or phase coordinate trans formations. According to Fortescue's Theorem, six unbalanced (voltage or current) phasors of a six-phase system can be resolved into six balanced systems of phasors. The balan ced sets of components are (1) First- (or positive) sequence components (2) Second-sequence components (3) Third-sequence components (4) Fourth- sequence components (5) Fifth- (or negative) sequence components (6) Sixth- (or zero) sequence components Each of the i sequence components ( i=0,1,2,3,4,5) consists of six phasors equal in magnitude and displaced from each other by i (60) in phase. The six-phase operator b, b = ej1T/3 = 0,5fj0,866 (3) This operator b is related to the three-phase operator a by b = -a2 (4) The unbalanced voltage phasors matrix V, P where Vt> = [TsJ-Vs (5) - IX - V ; symmetrical components of the unbalanced voltage pha- s sors. [t ] ; six-phase symmetrical component transformation mat- s rix DU - 111111 1 b5 b4 b3 b2 b 1 b4 b2 1 b4 b2 1 b3 1 b3 1 b3 1 b2 b4 1 b2 b4 2 3 4 5 1 b b^ bJ b* bD (6) The fault analysis of a six-phase system is much more complex than that of a three phase system. The vari ous types of faults that can occur in a six-phase system, which is considered in studies, are: (1 (2 (3 (4 (5 (6 (7 (8 (9 (10 (11 single-phase-to-ground fault (LG) two-phase-to-ground fault (LLG) two-phase fault (LL) three-phase-to-ground fault (LLLG) three-phase fault (LLL) four-phase-to-ground fault (LLLLG) four-phase fault (LLLL) five-phase-to-ground fault (LLLLLG) five-phase fault (LLLLL) six-phase-to-ground fault (LLLLLLG) six-phase fault (LLLLLL) The symmetrical component trransformation method for three-phase systems employing the bus impedance des cription of the network is generalised to six-phase sys tems or the systems represented on, an equivalent six- phase basis The expression for fault currents at a six-phase bus p involving a fault impedance/admittance matrix z£/Y° is given by 4(f) - <4- ^"^(o) (7) i* - y£. (u6+z6 ?,y1)'.E6,, p(F) F pp F p(o) (8) The fault voltages are given by -1,. Ep(F, -4-»6F + *n>.E P(o) (9) - x - and for other buses; Ei(F) = Ei(o) " Zip -'W) (11) 1=1,2,,N; i ^ p The following steps are required to carry out the foult analysis: i) Perform the equivalent single-phase load flow analysis to determine the pre fault voltages ii) Form the sequence component bus impedance matri ces. iii) Calculate the sequence component fault impedan ce/admittance matrices. iv) Determine the fault current v) Calculate the post-fault voltages, currents and power flows in the network For understanding localization effects of shunt reactors in a six-phase power transmission systems, 380 kV three phase double circuit Keban-Gölbaşı transmission line is converted to the six-phase line. For this six- phase energy transmission system, short-circuit calcula tions are realized at the state of different six circuit types. In these types of circuit which are shown in the figure 1, the total magnitude of the shunt reactor admit tance is distributed to the different places of the line. The bus of Golbasx is taken as a infinite power bus. Before the fault analysis, the prefault voltages of the power transmission system are calculated for nine operating points. These operating points which are power- values transmitted to the infinite power bus are shown in figure 2. - xi - 711 J I wîfy Scheme 1 Scheme 4 77777 7T77J ""TH Wi 7mr mm ^ M Scheme 2 Scheme 5 mrr i - iy 1T^^^ Scheme 3 Scheme 6 Fig.l. Different schemes of the given power system. - xii - I 1 1 t ® j -210 700 350 P(MW) © i<3> :© 210 Q(MVAr) Fig. 2. Operating points of the six-phase system. The calculated fault currents and voltages obtai ned by using a computer program are compared each other and tables are given for this purpose. As a result, for scheme 5 given in Figure 1 the fault current values are greater than the other transmis sion circuit types.