Energy Efficiency of Amorphous Metal Based Transformers R. Hasegawa Metglas, Inc 440 Allied Drive, SC 29526 USA October 2004
OVERVIEW Basics Introduction Amorphous versus crystalline magnetic material Properties of amorphous magnet - why amorphous? Exchange Interaction and Magnetization Magnetic Anisotropy, Magnetostriction, Magnetic Domain and Structure B-H Characteristics and Magnetization Processes Magnetic Losses Applications Electric Power Transformers High Frequency Power Electronics Telecommunication Pulse Transformers and Pulse Power Devices Magnetic Sensors and Electronic Article Surveillance Automotive Magnetics Medical Applications Magnetic Shielding
FUNDAMENTALS CASTING To achieve an amorphous structure in a metallic solid, one has to solidify the molten metal before constituent atoms take their positions in a crystalline atomic structure. The required rate for molten-metal cooling is about one million degrees Celsius per second for most of the amorphous metal we are interested in. The schematic drawing shown below is a method we use to mass-produce amorphous metal in our company.
FUNDAMENTALS ATOMIC STRUCTURE & MAGNETIC PROPERTIES Crystalline Amorphous Ordered structure magnetocrystalline anisotropy Polycrystalline structure higher coercivity These features do not help for easier magnetization and demagnetization. Random network of atoms lack of crystalline anisotropy Absence of phase boundaries lower coercivity These features lead to faster flux reversal.
ATOMIC STRUCTURE - AMORPHOUS
FUNDAMENTALS OF AMORPHOUS METAL Electrical Properties The electrical resistivity of many amorphous metals ranges from about 100 to 150 µω-cm. This is two-to-three times higher than that of silicon steel or Fe50-Ni50 alloy, which is partially responsible for low core losses in these metals. The temperature coefficient of the resistivity is relatively low and can reach nearly zero in some of the Fe-based alloys. Mechanical Properties Amorphous metals are hard with Vickers hardness ranging from about 700 to 1000, but mechanically ductile in the as-cast state. Elastic modulus is about 60x10 9 N/m 2. Thermal expansion coefficient is about 6-13 ppm/ o C.
MAGNETIZATION PROCESS AND CORE LOSS Magnetization processes are via uniform rotation ( high frequency limit) and domain wall motion (low frequency limit). Macroscopic magnetic loss (e.g. core loss) arises from eddy current (caused by magnetization rotation) and hysteresis behavior (caused by domain wall motion). Empirically we find: Core Loss = a B 1.5-2 f + b B 1.5-2.5 f 1.5-2 1000 100 10 Supermendur 100 µm Deltamax 50 µm METGLAS SA-1 25 µm Core Loss /f = a B 1.5-2 + B 1.5-2 f 0.5-1.0 (loss separation) Core Loss (W/kg) 1 0.1 Supermalloy 25 µm METGLAS 2714A 25 µm 0.01 0.001 B max =0.2T H7C4 (ferrite) (estimated) 0.1 1 10 100 1000 Frequency (khz)
FUNDAMENTALS SOFT MAGNETIC PROPERTIES 10 10 10 10 10 7 6 5 4 3 2 Co-base AM Supermalloy Fe-Ni base AM Sendust Fe-base AM Relative Permeability 78 Permalloy Hipernik Ni-Zn Ferrite Fe-3Si Fe 10 10 10 10 10 10 10-3 -2-1 0 1 2 Coercivity (A/cm) Mg-Zn Ferrite 3.0 2.5 2.0 1.5 1.0 0.5 Fe-base AM Co-base AM Saturation Induction (T) Fe-3Si Fe-6.5Si Fe-50Co Fe-- Fe-(40-50)Ni Fe-(70-80)Ni Fe-Ni base AM Soft Ferrites Carbon Steel Fe & Fe Alloy Powder Permalloy Powder 0.0-3 -2-1 0 1 2 10 10 10 10 10 10 Coercivity (A/cm)
FUNDAMENTALS OF AMORPHOUS METAL Why amorphous versus crystalline soft magnets? Examples: Effects of Field Annealing B H LONGITUDINAL TRANSVERSE
FUNDAMENTALS OF MAGNETICS Why amorphous versus crystalline soft magnets? Amorphous Metals exhibit: - easier magnetization (low coercivity and high permeability); - lower magnetic loss (low coercivity, high permeability and high resistivity); - faster flux reversal (as a result of low magnetic loss) - versatile magnetic properties resulting from post-fabrication heat-treatments and a wide range of adjustable chemical compositions.
ELECTRICAL POWER APPLICATIONS Three basic families of amorphous soft ferromagnets Fe-Base (e.g. METGLAS 2605SA1) Main Application: Distribution Transformer
ELECTRICAL POWER APPLICATIONS High saturation induction and low core losses at 50/60 Hz are required for electrical transformer applications. Amorphous metal-based transformers have 75-80% lower core losses than crystalline Fe-Si base units under linear loads. When higher harmonics are present, the difference in core losses becomes even greater. Load losses are still less than Fe-Si based transformers. Significant savings can be achieved when existing Fe-Si based transformers are replaced by amorphous metal-based units. The energy efficiency translates to reduced emission of hazardous gasses such as CO 2, SO 2, etc.
NO LOAD LOSSES Amorphous vs SiFe Steel Transformers Transformer Rating Core Loss (W) Silicon Steel In Service Best Amorphous Metal Loss Reduction % 50 kva, 1-Phase 300 kva, 3-Phase 210 1000 105 500 35 165 75 to 80%
TRANSFORMER LOSS Amorphous vs SiFe Steel Transformers
TRANSFORMER EFFICIENCY 100.0% % Efficiency 99.5% 99.0% 98.5% 98.0% 97.5% 97.0% 96.5% Amorphous Metal Conventional 2000 kva Transformer Efficiency 96.0% 0% 25% 50% 75% 100% 125% 150% Load
IMPACT ON Co 2 GAS GENERATION 20 000 2000 kva Comparison Watt Rating 18 000 16 000 14 000 Average Loading Range - Commercial and Industrial Watts 12 000 10 000 8 000 6 000 4 000 Other Cast Coil UltraGlas 2 000 UltraGlas Other Cast Coil 0 0% 25% 50% 75% 100% Load
AMORPHOUS METAL TRANSFORMERS & TOTAL HARMONIC DISTORTION Build-In Superior Performance for Harmonic Conditions
What Are Harmonics And Where Are They Found? 200 150 100 Pure Power Adjustable Speed Motor Drives Distorted Power 50 0 0-50 -100-150 -200 UPS HID Lighting PCs 0 Step Up Step Down Substation Distribution 24 kv 765-236 kv 230-34.5 kv 34.5-1.2 kv < 1.2 kv Utility Generation Transmission Subtransmission Primary Distribution Secondary Distribution Commercial &Industrial
Harmonics Basics fundamental =100 Amp RMS 200 150 100 50 0 0-50 0.004 0.008 0.012 0.016-100 -150-200 Any periodic waveform can be considered as a summation of sinusoidal waveform of different discrete frequencies 400 300 200 ASD Line Current =143.8 Amp RMS 150 100 5th Harm(300 Hz) =79.5 Amp RMS 100 0-100 -200 0 0.004 0.008 0.012 0.016 50-300 0 0 0.004 0.008 0.012 0.016-50 -400-100 -150 7th Harm(420 Hz) =66 Amp RMS 150 100 50 0 0 0.004 0.008 0.012 0.016-50 -100-150
500 KVA Transformer Loss Study Total Loss Increase: ~100 % (Amorphous) ; ~300 % (SiFe) 24 22 20 18 Actual hourly and weekday/weekend data SiFe Total Losses (kw) 16 14 12 10 8 6 4 2 0 AM Expected losses based on laboratory NL and LL tests 0 0.2 0.4 0.6 0.8 1 1.2 Load Ratio SiFe AM
Laboratory Test Data on Harmonics Effects on No Load Losses (30 kva Units with Identical Coils) 100 No Load Loss (W) 900 800 700 600 500 400 300 200 100 0 AMT SiFe 50 230 "Pure" Power 80 770 w/ 75% THD % of Fundamental 80 60 40 20 0 67 Harmonic # 40 75 % THD 2 7 7 4 2 3 5 7 9 11 13 15 No-Load Loss Increase: 60% (Amorphous) ; 235% (Silicon Steel)
AMT Performance under Harmonics 250 KVA Transformer Losses @ ~56% Loading ERDA Industrial Site Field Tests 3000 2500 AM Increase - 41 W SiFe Increase - 387 W 698 2000 Losses (W) 1500 74 99 311 155 Core Eddy Current Core Hysterisis Coil 33 155 1000 99 1553 1671 500 966 1084 0 Expected AMT Actual AMT Expected CRGO Actual CRGO Eddy Current Losses Increase in Both the Core and Coil, but Much Less for the Amorphous Core
Harmonic Impact on Transformer Losses Total Harmonic Distortion = (Σ i n2 ) 1/2 / i 1 i n : n-th harmonic current Magnetic Loss = A f + B d l f m B n /ρ (A, B : constant) Property/Exponent ρ(resistivity) d (thickness) l m n Amorphous Metal ~ 130 µω-cm ~ 20 µm 1-2 ~ 1.5 ~ 2 Silicon Steel ~ 50 µω-cm 200 µm 2 ~ 2 ~ 2 Smaller thickness and higher resistivity coupled with smaller exponent m lead to lower magnetic loss at higher frequencies in amorphous transformer cores.
Harmonic Impact on Transformer Losses -250 kva A. Harmonic Content (THD~25%) Harmonics 1 3 5 7 9 11 13 15 17 Content (%) 100 1 20 10 1 9 6 1 5 B. Transformer Losses without Harmonic Distortion Loss (W) Hyteresis Eddy Current Total Core Loss Coil Loss Loading Level (%) Total Transformer Loss Amorphous Metal 99 33 132 966 55 1,098 Silicon Steel 155 311 466 1,084 58 1,550 C. Transformer Losses with Harmonic Distortion of Table A Loss (W) Amorphous Metal Silicon Steel Hyteresis Eddy Current Total Core Loss Coil Loss Loading Level (%) Total Transformer Loss 99 74 173 1,553 55 1,726 155 698 853 1,671 58 2,524
Harmonic Impact on Transformer Losses Twofold Effect CURRENT DISTORTION VOLTAGE DISTORTION INCREASES WINDNG LOSS INDUCES VOLTAGE DISTORTION, INCREASING NO-LOAD LOSS INCREASES NO-LOAD LOSS DECREASES POWER FACTOR Direct Consequences: Very High Total Transformer Losses much higher than spec values Transformer Failure / Electrical Fire Associated Problems: Deterioration of Electrical Power Quality Extra Energy Cost Decreased Distribution Capacity
Solution to THD Problems using Amorphous Metal-based Transformers No Need for Added Devices such as Isolation Transformers, Harmonic Filters Impact of THD on Transformer Losses (examples) Transformer Loss Increase (THD=75%): 60-100 % (Amorphous); 200-300 % (Silicon Steel) Transformer Loss Increase (THD=25%): 57 % (Amorphous); 63% (Silicon Steel) Increased Energy-Savings (Example: 500 kva, unit price at $7,500) Condition Energy Consumption Annual Savings (@$.125/kWh) Without Harmonics 20,000 kwh/y $2,500 (Payback: 3 years) With Harmonics 130,000 kwh/y $16,250 (Payback: 0.5 year) Worldwide Annual Electrical Energy Savings (current estimate) Without Harmonics ~125 TWh ($16 billion) ~100 million tons of CO 2 gas reduction With Harmonics ~220 TWh ($28 billion) ~170 million tons of CO 2 gas reduction Electrical power pollution is costing US businesses $26 B/y in damage and prevention. By the year 2000, 60 % of all electricity will be passing through nonlinear loads. - Business Week
CONCLUSIONS Under pure sinusoidal excitation, amorphous metal-based transformers exhibit about ¼ of the no-load loss of a high-grade silicon-steel. This corresponds to an annual worldwide potential savings of about 125 TWh and annual reduction of CO 2 emission of about 100 million tons. Under harmonic conditions which are the actual conditions we are in, potential energy savings are considerably higher than the above. The energy savings is estimated at ~220 TWh. Worldwide use of amorphous metal-based transformers, therefore, will help us reduce fossil-fuel dependency and create cleaner environment with higher air quality.