Design of 25 KA Current Injection Transformer Core with Finite Element Method

Transcription

1 1 Design of 5 KA Current Injection Transforer Core ith Finite Eleent Method HOSSEIN HEYDARI, MOHSEN ARIANNEJAD, FARAMARZ FAGHIHI Iran University of Science and Technology, Tehran, Iran Abstract.Since Current Injection Transforers (CIT) are ithin the ajor group of the standard type test equipents in electrical industry, their perforances are very crucial. CIT is idely used for standard tests in electrical industry for a variety of purposes, such as relay protection systes consisting of insolated HV conductor, fuses, SF sitches, lo voltage sitches (ACB, and MCCB), sectionalizing sitches, and so on With the help of Finite Eleent Method (FEM), soe of the proinent probles can be solved. This paper attepts to fill this void by aking direct coparison of the localized flux in 5KA CIT ith three-lib single phase transforer cores. Flux distribution is solved by Ansys5.4 softare.then e copare results of the three-lib single phase transforer cores together and e obtain effect of overlap size of the core lainations on its hot-spot teperature. Key-Words: Current Injection Transforer (CIT), Finite Eleent Method (FEM), Local Flux density. 1-INTRODUCTION As an electrical utility you have the right to deand that every piece of poer equipent installed on your syste eets your exact specifications. The reliability and safety of your syste depends on all of the coponents perforing as intended. As a anufacturer, the perforance and conforance to industry standards of your product are of prie iportance. Testing can assure that your product eets or exceeds perforance standards. Current Injection Transforers (CIT) is ithin the ajor group of the standard type test equipents in electrical industry and its perforance is very critical.. Secondary voltage of this transforer are very lo, is less than 10 volts, and its output current varied fro 1 to 100KA. The final objective of this paper is to establish a FEM ethod hich leads to localized fluxes of the CIT [1, ]. Case study in this paper is drytype transforer that its output current, is 5KA, its secondary voltage is 5 volts and short-circuit tie duration is about 3 seconds for 5KA test. -CURRENT INJECTION TRANSFORMER EQUATIONS.1- The Voltage Equation Faraday s La relates the ipressed voltage on a inding to the rate of change of flux density db v = NA () 1 dt Where N is the nuber of turns and A is the effective cross sectional area of the agnetic core. In the case of lainated and tape-ound cores, this is less than the physical area A c due to interlaination space and insulation. The layout of the transforer is shon in Fig (1) and the physical paraeters are illustrated. Fig.1, Typical layout of Current Injection Transforer The to areas are related by the core stacking factor K f ( A = k f Ac ).Typically, K f is 0.9 for lainated cores.

2 1 T 1 V = vdt = NB A ( ) T o T Where V is the average value of the ipressed voltage in the tie period. The for factor K is defined as the ratio of the rs value of the applied voltage avefor to V Vrs k = () 3 V Cobining () and (3) yields V rs = KfNB A ( 4) Where f is the frequency of v and T is the period of v. Equation (4) is the classic equation for voltage in a transforer. Winding ith K, the avefor factor, defined by k, and T. Evidently, for a sinusoidal avefor K=4.44, and for a square avefor K=4.0. The core anufacturer norally supplies the core data: cross section A, indo area W a, the ean length of a turn MLT ( V ω = MLT W a ), and the core ass ( = ρ c V c ) [, 3]. 3-Design of the CIT and results of -D finite eleent analysis With the help of above equations e design this transforer as belo: Secondary voltage of the CIT, V 5[ v] output current is, I = 5 KA Q = VI = 15 KVA If the voltage per turns be as: [ ] [ ] [ v turns] E t = 5 / Maxiu flux density obtains as: E t 5 φ = = =. 5[ T ] 4.44 f B = 1. T e have For flux density [ ].5 10 A = = A c = = / 9 A c = c ax [ ] [ c ] [ ], K = 0. 9 f = and Fig., Geoetrical diensions of the Current Injection Transforer Because agnetic fluxes becoe half for left and right legs, cross section of each one is half of central leg. b=a a =. 5[ c] If the current density δ = 10 A indos area, A obtained as [, 3]: Q =. f B K δ A A 15 = / 7 10 A D = 930 = 1 H = H W = D [ c ] H = 45[ c] [ c] + H y + b = 7 = = 57.5 [ c] i [ ] I1 313 A1 = = = 15.5 δ 10 I 5000 A = = = 0 / 015 δ 10 [ ] 0 / 015 A [ c] The transforer odeling in this ork has been carried out using electroagnetic FEM analysis softares, Ansys 5.4 [4]. The calculation of flux distribution and resulting core losses perfored using a -D finite eleent ethod (FEM). The solution is accounts for the agnetic anisotropy and nonlinearity of the aterial, all coponents of the aterial iron loss, and localized losses in the joint region due to distorted flux distribution. This calculation ethod is accurate for all core aterials, at all operating inductions, for all core geoetries and for both 50 and 0 Hz [5]. W

3 In all transforers, only half of the core idth is odeled and boundary conditions are placed on all nodes on the outer edge of the core half, i.e. the centerline of the core. This is based on the assuption that the centre of the core is placed at zero agnetic potential. In all transforers, full load conditions are established in all the indings in the odel, by proper external excitation [1]. This transforer is odeled ith 4 areas as the core, the air gaps, and the priary and secondary indings. Fig (3) shon B-H curve of the core lainations, used in finite eleent odel. Fig.5, Core joints in left and right of T shape single phase transforer core ith 5 overlap Fig., Single phase transforer core ith 45 core joints Fig.3, B-H curve of 30M5 core lainations used for Finite Eleent Model Boundary conditions are, flux is parallel ith external node and e use 5 overlap in the core arrangeents Results of -D analysis are as belo: Fig.7, Core flux density distribution of the current injection transforer ith T-45 joins ith 5 overlap b Fig.4, Core joints in T shape single phase transforer core ith 5 overlap Fig.8, Single phase transforer core ith 90 core joints

4 Fig.9, Core flux density distribution of the current injection transforer ith 90 joints ith 5 overlap b Fig.13, Core flux density distribution of the current injection transforer ith 45 joints ith overlap b Last results shon that increasing of overlap size; decrease the flux density in internal edge of the transforer core and it leads to decrease of hot spot teperature of those point. For loss calculation e use loss curve of 30M5 core laination that shon in fig (1) Fig.10, Single phase transforer core ith 45 and 90 core joints Fig.11, Core flux density distribution of the current injection transforer ith 45 and 90 joints ith 5 overlap b Fig.1, Core flux density distribution of the current injection transforer ith 45 and 90 joints ith overlap b Fig.14, 30M5 /kg curve of core lainations used for calculation of iron losses Mass of the transforer core is about 190 [ ] losses for this transforer is about 175 [ ] kg and.obtained loss factor fro above results are as table(1) kg Table.1, Core losses obtained fro core flux distribution Degree of joints 90 Y-45 and Y-90 Y-45 losses kg

5 4-CONCLUSIONS Finite eleent ethod for solving of ain proble of transforers is an effective ethod. Sizes of overlap in this transforer are a deterinant factor for hot spot teperature of core in this particular case. If overlap size be less than 3 localized flux increases than 1.95 spot, out of the safe range. b and it create hot REFERENCES [1] Günter F. Meckler and Ra sis S. Girgis, Fello, IEEE "Magnetic Flux Distributions in Transforer Core Joints" IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 15, NO. 1, JANUARY 000 []Willia Gerard Hurley, Werner Hugo Wolfle,"Optiized Transforer Design Include of High-Frequency Effects,"IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL.13, NO.4, JULY 1998 [3] R. Petkov, Optiu design of a high-poer high-frequency transforer, IEEE Trans. Poer Electron. vol. 11, no. 1, pp. 33 4, 199. [4]"ANSYS Siulation Softare", ver5.4, 1997 [5]H.Heydari,"Selection criteria in Respect of 3- phase Transforer Core Building Techniques "International Journal of engineering Science, vol.9, no.4, 1998, pp.35-40, Iran University of Science & Technology