ECONOMIC BENEFITS OF USING HIGH(ER)
EFFICIENCY TRANSFORMERS IN LOW
LOAD CONDITIONS
Florida Electrical Cooperative Association Statewide Engineers Conference
Clearwater, Florida
June 11, 2014
David Nathasingh & Paul Ryan
Metglas Inc
INTRODUCTION
• Transformer Efficiency Varies As a Function
of Load Conditions
• Low No Load Loss (Core Loss) Transformers
Perform Best When Loading is <50%
• DOE Compliant Amorphous Metal and
Silicon Steel Transformers Have Different
Efficiency Levels When Loading <50%
• *Low No Load Loss Transformers May Cost
More But are More Economical to Operate in
Both the Short and Long Term
*Depending on specification level, first-cost can be lower or higher
Core Materials Used in High(er) Efficiency
Transformers
Core Losses
2.0
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
50Hz
M2
Core loss (W/kg)
B (T)
Saturation Magnetization
M2
HB1
SA1
1.5
HB1
1.0
0.5
SA1
0.0
0
20
40
60
80
H (A/m)
Silicon Steel
1.0
1.2
1.4
1.6
Induction (T)
Amorphous Metal
Amorphous Metal
1.8
2.0
CASE 1
TOBACCO FARM – South Carolina
•Two Curing Barns
•Curing Period – August Thru September
•DOE 75 kVA Single Phase Polemount Amorphous Metal and Silicon Steel Transformers
•Transformers Idle for 10 months; Loaded for 2 months
•Average Load of Transformers <50%
CASE 2
WINDFARM – California
•Farm With 70 Turbines
•2600 kVA Generator Step Up Amorphous Metal and Silicon Steel Transformers
•83% Annual Turbine/Transformer Loading ≤37.5%
DEFINITIONS
•DOE Transformer – Transformer manufactured to meet DOE Minimum Efficiency Standards 72CFR-58190. Designed for an
average loading of 50%.
•Generator Step Up Transformer (GSU) – Used on Wind Farms to step up turbine voltage of 690V to 34,500V. They are sized
to meet peak turbine output and NOT governed by DOE Minimum Efficiency Standards.
•Higher Efficiency Transformer – Transformer optimized to minimize core losses – no load losses. Efficiency higher than DOE
current Standards.
•Capitalized Losses – Cost of losses over the life of the transformer.
•Total Owning Costs – Capitalized Losses + Purchase Price of Transformer.
• Present Value of Losses – Future cost of losses in today’s dollars.
CASE 1 – TOBACCO FARM
Test Procedure
•Use Amorphous Metal and Silicon Steel
Transformers Made To DOE Standards
•Record load Currents and Voltages For
Parts of Curing Period And Idle Period
•Use One Curing Period Data to Calculate
Losses During Entire Curing Period
•Use 2 Week Idle Period Data to Calculate
Losses During Rest of Year
The efficiency levels in each TSL can be characterized as follows:
•
Baseline is our existing required efficiency.
•
TSL 1 represents an increase in efficiency where a diversity of electrical steels
are cost-competitive and economically feasible for all design lines. (DOE settled
on this)
•
TSL 2 represents EL1 for all design lines
•
TSL 3 represents the maximum efficiency level achievable with M3 core steel.
•
TSL 4 represents the maximum net present value (NPV) with 7 percent
discounting.
•
TSL 5 represents EL 3 for all design lines. (Advocates wanted this)
•
TSL 6 represents the maximum source energy savings with positive NPV with 7
% discounting.
•
TSL 7 represents the maximum technologically feasible level.
75 kVA TRANSFORMERS USED IN STUDY
DOE Standard 72 CFR 58190
Average Loading 50%
Minimum Efficiency 99.17%
Core
Material
No Load
Loss
(Watts)
Load
Loss
(Watts)
%IX
%IR
DOE Efficiency
(%)
Est
Transformer
Price ($)
Amorphous
34
1181
2.85
1.58
99.20
1550
Silicon Steel
128
704
1.79
0.94
99.23
1400
AMORPHOUS METAL TRANSFORMER
No Load and Load Loss During Idle Time
Load Loss and No Load Loss in Watts vs. Time
60
50
Losses in Watts
40
30
20
Load Loss
No Load Loss
10
0
1
705
1409 2113 2817 3521 4225 4929 5633
6337 7041 7745 8449 9153 9857 10561
Time in Minutes
SILICON STEEL TRANSFORMER
No Load and Load Loss During Idle Time
Load Loss and No Load Loss in Watts vs. Time
160
140
Losses in Watts
120
100
80
Load Loss
60
No Load Loss
40
20
0
1
1258 2515 3772 5029 6286 7543 8800 10057 11314 12571 13828 15085 16342 17599 18856
Time in Minutes
AMORPHOUS METAL TRANSFORMER
No Load and Load Loss During Typical Curing Cycle
Load Loss and No Load Loss in Watts vs. Time
1600
1400
Losses in Watts
1200
1000
800
Load Loss
600
No Load Loss
400
200
0
1
909
1817 2725 3633 4541 5449 6357 7265 8173 9081 9989 10897 11805 12713
Time in Minutes
SILICON STEEL TRANSFORMER
No Load and Load Loss During Typical Curing Cycle
Load Loss and No Load Loss in Watts vs. Time
600
500
Losses in Watts
400
Load Loss
No Load Loss
300
200
100
0
1
682
1363 2044 2725 3406 4087 4768 5449 6130 6811 7492 8173 8854 9535 10216
Time in Minutes
ANNUAL LOSSES
kWh
kWh
kWh
Core
Coil
Idle
Coil
Loaded
AM
311
5.9
870
1187
SiFe
1162
3.7
576
1742
AM-Sw
311
6.1
957
1274
SiFe-Sw
1162
3.6
523
1689
Sw – Transformers rotated between Loads
kWh
Total
Loss Ratio
AM/SiFe
0.68%
0.75%
ANNUAL LOSSES
kWh
Core
AM
311
kWh
kWh
kWh
Coil-Idle Coil-Loaded Total
5.9
870
1187
SiFe
1162
3.7
576
1742
AM-Sw
311
6.1
957
1274
SiFe-Sw
1162
3.6
Sw – Transformers rotated between Loads
523
Delta
1689
555
kWh
415
kWh
TOBACCO STUDY CONCLUSION
• DOE Amorphous Metal Transformer had 25-32% less losses over
one year
•
DOE Amorphous Transformer saves 0.68-0.75% of the total load
delivered to Curing Barns
• Both DOE Transformers have the same efficiency at 50% Load.
BUT at Loads <50%, Amorphous Transformer exhibits higher
efficiency than Silicon Steel. NOTE: 50% AVG load is not realistic.
DOE data indicated the national AVG to be 33%.
•
Savings equate to about $1,500 over 30 year Transformer life.
Simple Payback ~ 2.5 Years.
CASE 2 – WIND FARM
Financial Analysis
• Amorphous Metal and Silicon Steel
Transformers Designed for Lowest Total
Owning Costs (TOC)
•Use Transformer Average Loading Data
from California Wind Farm Analysis
•Use Average Loading of 37.5% to
Calculate Economic Benefit
No established Wind Farms
---- Wind Maps---Source : American Wind Energy Association (AWEA)
Wind Power Installations
Production Tax Credit
Expired ($0.02 kWh)
Source: American Wind Energy Association (AWEA)
690v to 34.5kV
Wind Energy Case Study
Generation Profile
83% annual turbine
Base case generation
profile based on
actual wind site in
the United States
output < 37.5%
83% generation hours
at or less than
37.5% of generation
capacity
It’s been reported that
most wind sites
operate on average
at less than 50% of
capacity during the
year (EIA Data)
Buying power from the grid @
3 times wholesale to keep
Collector network energized.
© ABB Group
GENERATOR STEP UP (GSU) TRANSFORMERS USED IN STUDY
SILICON STEEL
kVA
2,600
V1, V2
34,500
690
No Load
Losses
(W)
3,966
Load
Losses
(W)
20,816
Average Effective Load
Loading
Losses
(%)
(W)
100
20,816
87.5
15,937
62.5
8,131
37.5
2,927
12.5
325
0
0
Total
Losses
(W)
24,782
19,903
12,097
6,893
4,291
3,966
% No
Load
of Total
Losses
16
19.9
32.8
57.5
92.4
100
AMORPHOUS METAL
kVA
2,600
Data Courtesy ABB Group
V1, V2
34,500
690
No Load
Losses
(W)
745
Load
Losses
(W)
22,194
Average Effective Load
Loading
Losses
(%)
(W)
100
22,194
87.5
16,992
62.5
8,670
37.5
3,121
12.5
347
0
0
Total
Losses
(W)
22,939
17,737
9,415
2,866
1,092
745
% No
Load
of Total
Losses
3.2
4.2
7.9
19.3
92.4
100
COSTS of LOSSES - Annual & PV 6% and 20 Year Life
Silicon Steel Transformer
Load Factor
%
Total Losses
W
kWh/yr
Energy Costs ($) Present Value
@$0.065/kWh
$
100
87.5
62.5
24,782
19,903
12,097
217,090
174,352
105,972
14,111
11,333
6,888
161,851
129,988
79,007
37.5
12.5
6,893
4,291
60,385
37,591
3,925
2,443
45,020
28,026
0.0
3,966
34,742
2,258
25,902
Amorphous Metal Transformer
Load Factor
%
Total Losses
W
kWh/yr
100
87.5
62.5
22,949
17,737
9,415
200,946
155,379
82,471
13,061
10,100
5,361
149,814
115,842
61,486
37.5
12.5
3,866
1,092
33,866
9,564
2,201
622
25,249
7,130
0.0
745
6,526
414
4,866
Data Courtesy ABB Group
Energy Costs ($) Present Value
@$0.065/kWh
$
$0.065/ kWh estimated to Generate,Transmit and Distribute
FINANCIAL ANALYSIS
(Average Loading 12.5-37.5%)
ABB 2600 kVA GSU
• Simple Payback
Price Difference
$6,400
Annual Energy Savings $1,724 – 1,821
Payback
~3.5 YRS
• Present Value 6%, 20 YRS
Silicon Steel COL
$25,249 – 45,020
Amorphous Metal COL $ 7,130 – 28,026
Difference
$19,771 – 20,896
Amorphous Metal Transformer Price : $38,400
Silicon Steel Transformer Price
: $32,000
Price Difference : $ 6,400
2011 Pricing
Δ Transformer Price
-$6,400
Amorphous Metal Costs $13,371 - 14,496
Less to Operate in Today’s Dollars
Wind Farm Study Conclusion
• Transformer Efficiency Determined by Turbine Output - Loading
Profiles Show Average Loading ≤ 50%. Actual US Avg 12.5%.
• Low Core Loss Amorphous Metal Transformers Are More Efficient
Than Silicon Steel Transformers Under These Low Load Conditions.
• Amorphous Metal Transformers May Have a Higher Initial Cost But
Payback is ~3.5 Years.
• Annual savings equivalent to about 2% of expired Federal
Production Tax Credit.
• Not Economical to Purchase ‘Off The Shelf’ Transformers When
Average Loading ≤ 50%.
FINAL THOUGHTS
• COOPs tend to have Lower Loading profiles than MUNIs or IOUs.
Higher Efficiency (Low Core Loss) transformers should be
considered as part of installation mix.
• The Rural Utility Service (RUS) will offer 30 year loans @2% to
purchase Amorphous Metal transformers.
• Generation of Renewable Energy tend to be more expensive. Use
of Higher Efficiency transfomers during distribution would improve
economics.
• Transformer Efficiency is the starting point. Average Loading takes it
to the next economic level.
Thermal Parameters During Curing Cycle
Winding Gradiants, Oil Rises and Ambient Temperatures in Degrees C vs. Time
60
Temperatures or Temperature Differences in
Degrees C
Ambient Temperature
Average Oil Rise-No Time Constant
50
Average Winding Gradiant-No Time Constant
40
30
20
10
0
1
856
1711 2566 3421 4276 5131 5986 6841 7696 8551 9406 10261 11116 11971 12826
Time in Minutes
Load Current During Curing Cycle
Load Current vs. Time
400
350
Load Current in Amps
300
250
200
Channel 1
Channel 2
150
100
50
0
1
853
1705 2557 3409 4261 5113 5965 6817 7669 8521 9373 10225 11077 11929 12781
TIme in Minutes