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Transcript
Transformer Short Circuit Performance Tutorial of Cigre Working Group A2.19 Convener: Jim Fyvie, Scotland, 2002 Updated by: Jos Veens, Netherlands, 2009 Develop the WG Philosophy How do we deal with different cultures. – Small, Medium, Large (Power Transformers) How do we allow for manufacturing differentials. – Coreform: Disc, Spiral, Layer; Shellform: Pancake. How do we deal with different safety margins. – Green-Orange-Red – Add a percentage Short-Circuit Performance of Power Transformers – Cigre Tutorial of WG A2.19 2 Structure of WG12.19 Task Force #1 • Service Conditions – Field Survey Task Force #2 • Design Calculation Task Force #3 • Design Review Task Force #4 • Diagnostic & Monitoring Short-Circuit Performance of Power Transformers – Cigre Tutorial of WG A2.19 3 Results – TF#1 Service Conditions – Field Survey S/C Tests = 23 % failures in 3934 Tests • 905 failures on new units Field Failures = 0.0123 % failures in 121460 Transformer years • 1 failure every 8000 transformer years Short-Circuit Performance of Power Transformers – Cigre Tutorial of WG A2.19 4 Data from Test Stations - TF#1 Transformers, > 25 MVA 1996: 8 tested 1997: 6 tested 1998: 12 tested 1999: 15 tested Short-Circuit Performance of Power Transformers – Cigre Tutorial of WG A2.19 5 Results of Round Robin – TF#2 Design Calculation Made the design data of a large transformer (400 MVA, 220 kV) available for comparision. Good agreement on Radial forces – The axial fields were very similar Poor agreement on Axial forces. – The radial fields were different due to different assumptions made on the outer boundaries. Short-Circuit Performance of Power Transformers – Cigre Tutorial of WG A2.19 6 Short-Circuit Calculations: steps Fault Currents Field Distribution Force Distribution Mechanical Stresses Mechanical Strength LV 2Drotational symmetric HV (magneti c circuit on left side) Short-Circuit Performance of Power Transformers – Cigre Tutorial of WG A2.19 7 Fault Currents I_fault_rms = V1 / Z ; (Z = Z_grid + Z_transformer) I_fault _rms = 100 / Z% x In I_fault_peak = I_fault_rms x peak factor (2.55/2.69/2.77) Forces :: (I fault peak)^2 Short-Circuit Performance of Power Transformers – Cigre Tutorial of WG A2.19 8 Typical Magnetic Field Plots Short-Circuit Performance of Power Transformers – Cigre Tutorial of WG A2.19 9 Components of Force (axial and radial) Radial Forces LV (inward) Radial Forces HV Axial Forces (outward) Short-Circuit Performance of Power Transformers – Cigre Tutorial of WG A2.19 10 Radial forces (due to the axial field) LV HV Short-Circuit Performance of Power Transformers – Cigre Tutorial of WG A2.19 11 Radial Forces Frad D 2a F Frad D (pressure, forces on winding lead-out) Frad l 2 2bt2 (Forces translated Into pressure on copper) crit crit E h2 4 R2 E ( ) (t r N ) 2 12 D 2 Short-Circuit Performance of Power Transformers – Cigre Tutorial of WG A2.19 12 Examples of deformation - LV- Radial Buckling Short-Circuit Performance of Power Transformers – Cigre Tutorial of WG A2.19 13 Axial Forces (due to the radial field) LV HV Short-Circuit Performance of Power Transformers – Cigre Tutorial of WG A2.19 14 Axial forces; deformation effects Continuously Transposed Conductor Rectangular Copper Conductor Wcrit c t 2 starea 2 E b CSA 30 LMT b Short-Circuit Performance of Power Transformers – Cigre Tutorial of WG A2.19 15 Clamping Arrangement (A-leg) (B-leg) (C-leg) Short-Circuit Performance of Power Transformers – Cigre Tutorial of WG A2.19 16 If the winding clamping fails….. (Winding support structure had collapsed ) Short-Circuit Performance of Power Transformers – Cigre Tutorial of WG A2.19 17 Strength ? Short-Circuit Performance of Power Transformers – Cigre Tutorial of WG A2.19 18 Results of TF#3 Design Review Relational equations were agreed – This allows for different ‘manufacturer’s constants’ to be used. Equations for Critical Stress were agreed – With the basic material strength and shape factors dependant on construction and conductor type. Design Review to be Interrogative rather than Comparative. – Allows manufacturers to explain their philosophy. Short-Circuit Performance of Power Transformers – Cigre Tutorial of WG A2.19 19 Copper Proof Stress Short-Circuit Performance of Power Transformers – Cigre Tutorial of WG A2.19 20 Conductor Profiles Short-Circuit Performance of Power Transformers – Cigre Tutorial of WG A2.19 21 Effect of bonding CTC Short-Circuit Performance of Power Transformers – Cigre Tutorial of WG A2.19 22 Compilation of Maximum Stresses Windings LV Stress Strength HV + Tap Stress Strength Tap Stress Strength Compressive Stress on Stampings(MPa) Axial Bending Stress(MPa) Compressive Stress on Sticks(Mpa) Radial Buckling Stress(Mpa) Radial Bending Stress(MPa) Hoop Stress(MPa) Tilting Force(Tonnes) Winding End Axial Force Top/Bottom (Tonnes) Force on Lead Exits (Tonnes) Force on Lead Runs Short-Circuit Performance of Power Transformers – Cigre Tutorial of WG A2.19 23 Manufacturing Ability Winding Techniques Processing Dimensioning Support Structures • • Internal to winding External to winding Short-Circuit Performance of Power Transformers – Cigre Tutorial of WG A2.19 24 Winding Techniques Vertical winding – Normally used for HV windings with all round access for winders. Interleaved windings and shielded windings. Continuous disc windings may be wound out and spun back to keep tight. Horizontal winding – Used for large LV windings with parallel CTC’s winding supplied from a hanging catenary to keep tension and prevent caging, or under tension if strip. Windings must be free from gaps. Short-Circuit Performance of Power Transformers – Cigre Tutorial of WG A2.19 25 Processing Insulation must be consolidated, ie fully dried and shrunk. No gaps within the windings and all major insulation fully oil impregnated with hot de-gassed oil. No locked oil pockets and Cooling ducts the correct size. Short-Circuit Performance of Power Transformers – Cigre Tutorial of WG A2.19 26 Dimensioning The leakage field plots are carried out by using the design dimensions with some building tolerance. The units must be manufactured within this tolerance or the calculations are meaningless. ‘A’, ‘d’ and Diameters must be correct and the windings must be balanced axially. Short-Circuit Performance of Power Transformers – Cigre Tutorial of WG A2.19 27 Supporting Structures The inner winding must have round radial support, else we cannot claim the higher buckling mode criteria. Core The Copper must have the correct hardness. The lead ends must be supported or the windings will twist and move all the supporting blocks. The Clamps must tolerate the end forces and any pre-load on the windings, and allow for any lifting required. LV Short-Circuit Performance of Power Transformers – Cigre Tutorial of WG A2.19 HV 28 Check List of TF #3 (by no means complete) Are the fault currents correct Is the field model suitable Is the force program suitable Is the construction suitable Are the materials suitable Are the strength values traceable Is the failure risk acceptable Short-Circuit Performance of Power Transformers – Cigre Tutorial of WG A2.19 29 Results from TF#4 Diagnostic & Monitoring Techniques Reviewed – – – – – Winding Capacitances Magnetising currents Leakage reactance Low Voltage Impulse Frequency Response Analysis Most Popular Development is FRA Short-Circuit Performance of Power Transformers – Cigre Tutorial of WG A2.19 30 Need for Detection Means • Visual inspection (in the field) is impractical (access to inner windings). • Significant winding shrinkage can occur with age. • Winding displacement may take place leading to reduction of mechanical strength against future short circuits. • Detection of those displacements provides early warning of impeding failures Short-Circuit Performance of Power Transformers – Cigre Tutorial of WG A2.19 31 Winding Capacitance(s) • Requires standard test equipment . • Sensitivity depends on the type of fault • More effective when it is possible to make separate measurements for each phase HV LV C between LV and HV Core C between LV and core Short-Circuit Performance of Power Transformers – Cigre Tutorial of WG A2.19 32 Magnetising current • Require only very simple equipment • Easiest way of detecting any shorted turns • Limited sensitivity for other types of faults Short-Circuit Performance of Power Transformers – Cigre Tutorial of WG A2.19 33 Impedance • Probably the most widely accepted method of detecting winding movement • technique is simple and requires relatively standard equipment • Impedance often differ significantly between phases • most winding mechanical failures can be diagnosed by impedance measurements • Provides a numerical criterion for test conclusion Short-Circuit Performance of Power Transformers – Cigre Tutorial of WG A2.19 34 Impedance change example (from actual tests in short circuit testing station) IEC : < 1 % change (coreform transformer) Short-Circuit Performance of Power Transformers – Cigre Tutorial of WG A2.19 35 Frequency response analysis (FRA) Detection of change in a global quantity: • May be Winding capacitance. • or Magnetising current • or Impedance. Shows in local change in signal propagation in: • Low Voltage Impulse (LVI, not so repeatable) • Frequency Response Analysis (FRA) range: 10 kHz-2 MHz; interpretation always together with results of the previous measurement types Short-Circuit Performance of Power Transformers – Cigre Tutorial of WG A2.19 36 WG 12.19 members: Convenor; Jim Fyvie – U.K. Task Force Leaders; TF #1 Anders Lindroth – Sweden TF #2 Kees Spoorenberg – Netherlands TF #3 Jim Fyvie – U.K. TF #4 John Lapworth – U.K. Members; Serge Therry – Switzerland Anatoly Panibratetz – Russia Endre Matthe – Hungary Rafael Gonzalez – Spain Masami Ikeda – Japan Wolfgang Knorr – Germany Wladislaw Pewca – Poland Horoshi Murakami – Japan Eric Chemin – France Hasse Nordman – Finland Volodimir Zaitsev – Ukraine Victor Lazarev – Ukraine Joe Foldi – Canada Willi Felber – Austria Benedikt Damm – Austria Bob Del Vecchio – USA Gerard Robert – France Luis Cheim – Brasil Chen Kui – China V Pitsuriya – Thailand Tim Noonan – Ireland Walter Wasinger – Australia Short-Circuit Performance of Power Transformers – Cigre Tutorial of WG A2.19 37 Cigré Technical Brochure N° 209 – 2002 (for core-type and shell-type transformers) http://www.e-cigre.org Short-Circuit Performance of Power Transformers – Cigre Tutorial of WG A2.19 38 IEC Standard: 60076-5 Ed. 3.0 (2006-02) Title: Ability to withstand short circuit Annex A (informative) Theoretical evaluation of the ability to withstand the dynamic effects of short circuit Thank you ; Questions ? Short-Circuit Performance of Power Transformers – Cigre Tutorial of WG A2.19 39
