TRANSFORMERS. Pascal Tixador. Grenoble INP - Institut Néel / G2Elab. Introduction

Transcription

1 TRANSFORMERS Pascal Tixador Grenoble INP - Institut Néel / GElab Introduction! Discovered in 188 «!secondary generator!»! The transformers: an essential link in the a.c. electric systems Adjust with very high efficiency the voltage levels for an economical and technical electricity transportation! Electricity passes through 4 to 5 transformers between production and use! Transformers very usefull for voltage regulation (load tap changer) Institut Néel, GElab 011 ESAS

2 Introduction Gaulard & Gibbs (1884) Typical large scale transformer Courtesy from H. Fujimoto Superconducting transformer 3 Institut Néel, GElab 011 ESAS Introduction! Evolutions Materials Magnetic materials iron losses reduction Dielectric materials Design and calculation Numerical modelling Better understanding P (ton/mva) 1,5 1, ,5 0, Year P iron (W/kg) 1.5 T, 50 Hz! Next breakthrough: superconducting transformers 4 Institut Néel, GElab 011 ESAS

3 Outline - Transformer! Basis! Transformer general design! SC transformer history! SC transformer design! Cooling! Economic considerations! Conclusions! Examples 5 Institut Néel, GElab 011 ESAS Superconducting transformers Basis

4 Basis Energy transfer by electromagnetic way I 1 I V 1 V Primary winding N 1 series turns Receives energy Magnetic circuit Secondary winding N series turns Provides energy 7 Institut Néel, GElab 011 ESAS Basis 1/ primary 1/ secondary 1/ primary 1/ secondary HIGH MAGNETIC COUPLING GOOD MAGNETIC CIRCUIT USE 8 Institut Néel, GElab 011 ESAS

5 Basic equations I 1 I Primary winding N 1 series turns Receives energy V 1 V Secondary winding N series turns Provides energy Magnetic circuit Loop C Electrical equations (Lenz s law) v 1 = N 1 d! 1 /dt + R 1 i 1 v = - N d! /dt - R i Magnetic equation (Ampere s law) 9 Institut Néel, GElab N 1 i 1 - N i = 011 ESAS C H dl Equivalent circuit v 1 i 1 i # v " m v 1 m : transformer ratio? v % $ i " 1 m i 1 % % Perfect & transformer m = N N 1

6 Model referred to secondary Real transformer i 1 R t X t i (= (i 1 -i o )/m) v 1 L m i o m v 1 v R f Magnetic circuit Very high impedances 11 Institut Néel, GElab m Core (iron) losses P iron = P o = V 1 R f i o : no-load current (excitation current) 011 ESAS i o : very low I o /I a < some % (L m " & R f very high) Real transformer Joule losses i 1 R t X t i (= (i 1 -i o )/m) v 1 L m i o m v 1 v R f m Model referred to secondary " R t = R + N % $ ' # & N 1 R 1 = R + m R 1 1 Institut Néel, GElab 011 ESAS

7 Model referred to secondary Real transformer i 1 R t X t i (= (i 1 -i o )/m) v 1 L m i o m v 1 v R f m Flux leakage coupling 13 Institut Néel, GElab 011 ESAS X t = m (1-k ) L m " X t value! Low leakage impedance Good voltage regulation High short-circuit current! High leakage impedance Large voltage drop Short-circuit current limitation 4 % < z sc < 17 % (5 %) Required by electronic converters (on board transf.) An interesting solution: fault current limiter SC transformers " Low weight, SC quantity (large A.T.): z sc increase 14 Institut Néel, GElab 011 ESAS

8 Transformer general design Apparent (design) power S a = V 1 I 1 + V I V 1 = N 1 B iron S iron " (Lenz law : v 1 = N 1 d# iron dt ) S a = B iron S iron " # $ % N 1 I 1 + N I & ' ( N 1 I 1 = J 1 N 1 S 1 N I = J N S 16 Institut Néel, GElab 011 ESAS

9 Apparent (design) power J 1 = J = J S a = B iron S iron " # $ % N 1 I 1 + N I & ' ( S a = B iron S iron " J # $ % N 1 S 1 + N S & ' ( S a = B iron S iron " J # $ % S cond & ' ( = ) B iron S iron f J S cond 17 Institut Néel, GElab 011 ESAS Apparent (design) power S a = " B iron S iron f J S cond SC transformer interest clearly appears Especially for low frequency transformer 18 Institut Néel, GElab 011 ESAS

10 SC transformers! Reduction of weight (1/)! Reduction of volume (1/)! Improved insulation, no thermal aging! Better efficiency Savings over the transformer life (30 years)! Environmental benefits No oil Attractive for mobile systems Substantial technical & economical benefits 19 Institut Néel, GElab 011 ESAS Conclusions Conventional 75 tons 3,000 l of oil Cryocooled 4 tons Open-cycle LN 16 tons 30 MVA Transformer 0 Institut Néel, GElab 011 ESAS Waukesha-IGC-RGE-ORNL picture

11 Superconducting transformers History SC transformer history! Riemersma (1981)! Low T c (NbTi): AC losses & cryogenic cost! 80 : AC ultra fine NbTi composites SC transformers possible with technical benefits 4 K cryogenics prevents further developments! 90 : HTS discovery High temperature operation enables industrial product Numerous developments throughout the world Conductors First generation (Bi-PIT) : cost and AC losses Second generation (Y-Coated Conductors) : large hopes Institut Néel, GElab 011 ESAS

12 AC NbTi composites 3 T strand (Ø = 0.5 mm) "m filaments Institut Néel, GElab 011 ESAS NbTi 0 kva transf. (AAR, 1986) Transformer " Conductors " Magnetic circuit " Dielectrics

13 Conductors - properties Superconductors - J c (T, B, #) Bi-3 PIT 1000 J e (MA/m ) // c axis! = 0 // ab plans! = "/ // c axis! = 0 // ab plans! = "/ 0 K 77 K # B 0 0, 0,4 0,6 0,8 1 5 B (T) Institut Néel, GElab 011 ESAS Conductors - properties Superconductors - AC losses P l # $ I c f d %B B a ( B a > B p ) d B Transverse field d B Longitudinal field J c & AC losses: avoid transverse field High interest of Coated Conductors in long. fields 6 Institut Néel, GElab 011 ESAS

14 Transverse field Transverse field area 8 9 layer PIT solenoid (Ø a = 154 mm; h = 163 mm) Longitudinal field area P (mw) Outer layer (ratio : 5) Central layer (rato 55) Institut Néel, GElab ESAS Tape number Transverse field Transverse field reduction " flux diverter 8 Institut Néel, GElab 011 ESAS

15 Magnetic materials Three parameters Saturation magnetic flux density => operating magnetic flux density Core losses => efficiency, heat removal, cryogenic power Ease of establishing magnetic flux density => no load current (magnetization comp.) 9 Institut Néel, GElab 011 ESAS Core losses 30 # Temperature effect Iron specfic losses (W/kg) 1,6 1, 0,8 0,4 Scr FeSi 77 K (3/100) FeSi 77 K (30/100) FeSi 300 K (30/100) 0 0 0,5 1 1,5 Institut Néel, GElab B (T) Specific iron losses (W/Kg) 0,8 0,6 0,4 0, 011 ESAS 1 FeNi Imphy 77 K 300 K 0 0,9 1 1,1 1, 1,3 1,4 1,5 1,6 Core losses to be multiplied by coefficient of performance 30 K, 70 K) Interest for amorphous materials B (T)

16 Isolation! Solid (epoxy, frp, ) Good performances if no voids (impregnation) Sometimes little breakdown strength decrease with T! Coolant (N, He, ) Gas BAD dielectrics especially He at 300 K! Vacuum Function of surface (cleanness and materials) Vacuum degradation: Paschen minimum => Make insulation using solid <= 31 Institut Néel, GElab 011 ESAS Cooling " Bath cooling - fluid to handle (cooling down & quench) " Conduction cooling - easier for users

17 Bath cooling Warm iron Cold iron Low iron losses Low cryogenic load Complex shape composite cryostat Complex fluid connections Three cryostats (3 phases) Single & very simple metallic cryostat Interfaces with cooling system easy Iron losses brought back to 300 K High cryogenic load (cooling down,...) 33 Institut Néel, GElab 011 ESAS Conduction cooling Magnetic core Single & very simple metallic cryostat Interfaces with cooling system easy Iron at 300 K Temperature gradients (heat pipes) Exchanges little efficient (hot spots) Recovery after a quench 34 Institut Néel, GElab 011 ESAS

18 Cooling Do not forget the current leads! May be a large contribution especially for low voltage winding. Optimized conduction cooling current leads (minimum losses): * Q cl I T c = $ "(# ) % (# ) d# T o Brass: good compromise (I*, I=0) Brass: 74 K 4 K 35 Institut Néel, GElab 011 ESAS Coolings - conclusion Cooling design depends on application! Stationary / on board! Design objectives (weight, efficiency)! Mean load! Rating! Special requirements! 36 Institut Néel, GElab 011 ESAS

19 Superconducting transformers Economic considerations Some data! Resistive transformer cost: $/kw! Energy cost: $/kwh! Number of hours per year: 8760! No load losses: 8760 h/year! Cryogenic losses: 8760 h/year! Load losses: function of the mean load 38 Institut Néel, GElab 011 ESAS

20 Example 40 MVA - 60 Hz on board transformer! Conductor cost (coated conductor, 15 $/ka/m) $! Magnetic circuit $! Cryocooler (5 $/W) $ $ Conventional transformer: $ + savings: factor in weight & volume Little higher efficiency 39 Institut Néel, GElab 011 ESAS Comparison MgB 40 Similar weight: 6 tons (YBCO) / 8 tons (MgB ) Institut Néel, GElab 011 ESAS

21 Some transformer projects Courtesy M. Noe 41 Institut Néel, GElab 011 ESAS Examples Siemens & RTRI on board transformer Many thanks to Dr. Neumüller, Leghissa, Fujitomo and Noe for their informations and documents

22 Siemens transformer Transformer for railway application (strong weight requirements) 43 Siemens picture Institut Néel, GElab 011 ESAS! 1 MVA - 50 Hz! 5 kv / 1.4 kv! 1 A / 360 A! u cc = 5 %! Forced flow 67 K! Closed-cycle Stirling! Cold FeSi core (538 W) Siemens transformer Weight Total 1010 kg " Core 655 kg " Leakage Fe 140 kg " HTS 54 kg " LN tank 7 kg 44 Institut Néel, GElab 011 ESAS Siemens picture

23 RTRI transformer Japan, JR Rating Voltages (P/S/T) Frequency SC P AC Coolant Size Weight 3.5 MVA 5 kv/4x100v/440v 60 Hz Bi-3 tape MVA Liquid nitrogen 1.9 x 1. x 0.7 m t (ref. & comp. Exc.) Courtesy from H. Fujimoto 45 Institut Néel, GElab 011 ESAS Recovery under load Courtesy M. Noe 46 Institut Néel, GElab 011 ESAS

24 US SFCL transfo. project Waukesha Electric Systems SuperPower Inc. University of Houston Oak Ridge National Southern California Edison (utility) SFCL Transformer Specifications: 8 MVA 3-phase 69 kv/1.47 kv class ~ 40% overload capability fault current limiting capability G HTS wire 47 Institut Néel, GElab 011 ESAS Superconducting transformers Conclusions

25 Conclusions! HTS transformer very attractive Weight, footprint & loss high reductions limitation unique function! Two main issues HTS conductor: cost and AC losses Cryogenics: cost and performances! Y Coated conductors: right HTS? Higher temperature operation Lower AC losses (B lg ) and cost (10 $/ka/m) 49 Institut Néel, GElab 011 ESAS