Güç transformatörlerinde aşırı gerilim dağılım sorunu ve alınan önlemler
The Problem of overvoltage distribution along power transformers and measures to be taken
- Tez No: 39130
- Danışmanlar: PROF.DR. NURDAN GÜZELBEYOĞLU
- Tez Türü: Yüksek Lisans
- Konular: Elektrik ve Elektronik Mühendisliği, Electrical and Electronics Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1993
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 86
Özet
ÖZET Çalışmada enerji iletim hatlarında her türlü elektriksel iç ve dış etkilere açık olan güç transformatörlerin sargılarında oluşan aşın gerilim dağılışı bulunmuştur. Gerilim dağılışını belirleyen transformatör sargı kapasitelerinin matematiksel ifadeleri çıkarılmıştır. Daha sonra başlangıç gerilim dağılışım düzelten yöntemler incelenmiştir. Önce seri kapasitenin artırılması yöntemi ve buna bağlı olarak sargıda oluşabilecek düzgünsüzlüğün etkileri örneklerle incelenmiştir. Ardından bu yöntemlerden biri olan ve pratikte de uygulama bulan toprağa karşı paralel kapasitelerin etkilerini yok eden yöntemin matematiksel bağıntıları çıkarılmış ve ekranın sargıyla yapması gereken açı hesaplanmıştır. Çıkan sonucu bir örnek transformatör üzerinde uygulayarak gerçekte yapılanla bir uyum gösterip göstermediği kontrol edilmiştir. -v-
Özet (Çeviri)
SUMMARY :“THE PROBLEM OF OVERVOLTAGE DISTRIBUTION ALONG POWER TRANSFORMERS AND MEASURES TO BE TAKEN”First of all, the main purpose of this study is to investigate the problem of the overvoltage distribution along a power transformer. Since a transformer is subjected to various external and internal harmful effects, optimum solution for this problem, that is to construct a transformer which withstands overvoltages and also works in normal conditions without increasing cost of transformer, should be found. So far various methods of the transformer protection, for example, different kinds of dischargers, special spark gaps called co-ordinators, proper choice of the transmission line route, the reactive coils and capacitors, were employed. These ones are not used today, since experience has shown and subsequent analysis has confirmed that the efficiency of such protection is insufficient. Nowadays, concepts of reinforcement of the input and output coil insulation, interleaving coil windings and capacitive protection are argued. In the first chapter, this study investigates overvoltage waves along a transformer windings on the basis of standing and travelling waves and according to Wagner theory, starting from the sets of differential equations describing the transient process and using the simplified mathematical model of a winding, the equations giving the voltage distribution within the transformer winding are given. In this chapter depending on if the winding end is open or earthed, the initial and the final voltage distribution are studied on and found as follows: "C-* For at one end earthed winding; the initial voltage u(-j,0) sinhaCl- j) U sinha the final voltage U 1 -vi-For an open end winding; the initial voltage u{^,0) coshccCL-^) U cosha the final voltage u Here:...... U : Terminal voltage, [kV] I : the full winding length, [m] x : the coordinate of a given point of the winding, [m] a=J £ Cr = C.l the resultant parallel capacitance, [F] Kr = K/l the resultant series capacitance, [F] And then voltage oscilations taking place between these two processes are found out. The primary importance of the Wagner model and of the calculation based on it, is the very informative qualitative picture provided by the phenomena taking place in transformer windings under the effect of steep-front overvoltage waves. Also from a practical point of view, the factor calculated from the resultant shunt and series capacitances is of great significance, since conclusions can be drawn from it also as to the uniformity of initial voltage distribution within the winding and to the liability of the latter oscillations. This method, however, is unsuitable for the purpose of voltage distribution calculations required for the insulation design. The infinitesmall homogenous winding model proposed by Wagner, where the series and parallel capacitances and the self-inductances are alone taken into account, idealizes the real conditions very much. Therefore Wagner's classic model is also criticized. As a matter of fact, a real transformer winding is composed of a finite number of elements (e.g. discs, pairs of discs), therefore it is more obvious to present it by a model consisting of a finite number of elements than by an infinitesmall model. Thus in the case of disc type transformer windings, it is convenient to consider each disc, each pair of discs or each group of discs as a separate element. Further, real transformer windings are not homogeneous in every case but generally at the beginning and end of the winding, and sometimes inside it, often contain winding elements (discs) in which the number of turns, geometrical arrangement or shape deviates from the majority of elements constituting the winding. The Wagner model also simplifies real condition by neglecting the mutual inductance within the winding and the damping effect of eddy current losses on voltage oscillations. Finally, in the majority of cases, it is not a single winding that is to be investigated, but a transformer or a winding system consisting of two or more windings. Then according to these opinions overvoltage distribution along a transformer winding is -vii-investigated. As it is known that there are capacitances present between transformer windings, series capacitances, and earthed parts (core, tank, etc.), grounded or parallel capacitances, within each winding between discs, turns and layers, and between individual coils. These series and parallel capacitances determine the voltage distribution. Therefore expression of the series and the parallel capacitances are found out in details. The series capacitance of normal disc windings is, N 2nbt 3 26 1 ^ 6a- and the parallel capacitance between two concentric cylindrical windings of heights H, and H? is 21, BD x 2 C= -?. 1(T12F Here. D : the mean winding diameter, [m] N : the number of layers n : the number of turns in a layer h : the size of copper conductor used for calculating the turn capacitance, [m] (\ : the thickness of inter turn insulation, [m] £, : its permittivity. [F/m] r : radial size of winding, [m] S,, : the thickness of spacers between discs, [in] £,, : the resultant permittivity of (oil and solid) insulation of thickness 5,,, [F/m]
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