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![Page 1: Conducting Distribution Transformer Loss Evaluations IEEE Rural Electric Power Conference April 21, 2015 Troy Knutson P.E.](https://reader036.fdocuments.us/reader036/viewer/2022062516/56649d355503460f94a0c140/html5/thumbnails/1.jpg)
Conducting Distribution Transformer Loss
Evaluations
IEEE Rural Electric Power ConferenceApril 21, 2015
Troy Knutson P.E.
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1 of 11 coop-owners of Minnkota Power
Cooperative
•Service to 43,000 members•5,000 mi2 service area•4,700 miles of line•260 MW Peak
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How many use loss evaluated transformers?•What would your CEO/Manager say?•How about your CFO?•January 1st, 2016
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RUS Bulletin 61-16•Originally published 1983•Present worth analysis•Outdated estimates/averages•New method developed in late 80’s•Coupled with advent of computerized
spreadsheets•Revised as a part of NRECA T&DEC
committee activity
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New Bulletin•Uses A and B values for Total Ownership Cost (TOC) valuation•Goes through a step by step example•Adds an excel spreadsheet•Goal was to simplify!
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Total Ownership Cost• TOC = Purchase Price + Cost of Losses• Transformer manufacturer will bid a purchase price and
losses• NL and LL
• Putting a $ value on losses• TOC = Purchase Price + (“A”*NL + “B”*LL)• Evaluates strictly on cost• “A” and “B” will give most cost effective design• Based on assumptions
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“A” Factor
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“A” Factor•Related to core losses•Not dependent on loading•Cost in $/Watt will give an “A” value•Ways to reduce No-Load losses• Use higher grade core steel• Thinner laminations• Larger leg area
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“A” Factor Inputs• DC’ - levelized demand cost in
$/kW-year• EC’ - levelized energy cost in
$/kWh• HPY - Hours per year • FCR - Fixed Charge Rate or
carrying charge
in $/watt
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“A” Factor Inputs• Demand and Energy Cost determined from PPA• These will be base values to be levelized
• Hours per year (8760)• Fixed Charge Rate gives costs associated with owning a transformer• Interest• Depreciation• Insurance• Taxes• O&M
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“B” Factor
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“B” Factor•Related to windings•Dependent on loading•Also referred to as I2R losses•Cost in $/Watt will give a “B” value•Ways to reduce Load Losses• Copper over aluminum• Larger area conductor
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“B” Factor Inputs in $/watt • DC’ - levelized demand cost
• EC’ - levelized energy cost• Hours per year• Fixed charge rate• PL2 - levelized peak loading on
transformer• RF - peak loss responsibility factor• LSF - loss factor
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“B” Factor Inputs
• PLI = the anticipated peak load during the first year of installation • g = estimated annual percentage
increase in peak load during the life of the transformer• i = the average rate of interest borrower
is paying on loans • n = the number of years which the
transformer will be in service• p = the estimated average increase in
energy cost per year• = capital recovery factor
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“B” Factor Inputs• CRF = used to levelize the total present
worth• Converts the sum into a annual series
• i = interest rate• n = number of years
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“B” Factor Inputs• Peak Loss
Responsibility Factor (RF)• Differences between
peak on transformer vs. distribution system
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“B” Factor Inputs• Loss Factor (LSF)• Average transformer losses vs.
the peak transformer losses• Nonlinear relationship to load
factorWhere:
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Escalation and Inflation
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Energy Escalation and Inflation
• A and B values need provisions for increases over time• Due to inflation• Due to increasing costs
• This can be converted to an equivalent level cost “Levelized”• The levelized value is neither the first cost or the final cost• Levelized values will be used in the evaluation • denoted by a apostrophe (‘)
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Adjusting for Inflation• for r ≠ i• A = the cost adjusted for inflation• A = the base cost before inflation• n = the number of years in the
inflation period (life of transformer)• i = the average rate of interest
being paid on loans• r = the average year over year rate
of inflation for transformer life
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Adjusting for Escalation and Inflation
for r ≠ IWhere: for P ≥ ig
• r = The equivalent inflation rate• P = the rate of increase in costs
per kwh associated with G&T• ig = the inflation rate for the
economy as a whole expressed as a decimal
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Single phase 50 kVA comparison
Known• 30 year depreciation• DC = $120/kW-Yr• EC = $0.06/kWh• RF = .81• LSF = .532• FCR = 14.58%
Assumptions• PLI = 80%• Load growth (g) = 1.5%• Interest rate (i) = 4.5%• Energy escalation (p) = 3%• Inflation rate (ig) = 2.8%
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Single Phase 50 kVA Comparison
• A value is $4.54/Watt• B value is $2.45/Watt
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Single Phase 50 kVA Comparison
Transformer X
•Bid Price = $3,500•NL = 90 Watts• LL = 537 Watts
Transformer Y
•Bid Price = $4,200•NL = 63 Watts• LL = 221 Watts
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Single Phase 50 kVA Comparison
Transformer X
• TOC = $3,500 + ((4.54*90)+(2.45*537))= $5,224
Transformer Y
• TOC = $4,200 + ((4.54*63)+(2.45*221))= $5,027
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DOE Standard• DOE transformer efficiency standards• http://www1.eere.energy.gov/buildings/appliance_standards/rulemaking.asp
x/ruleid/44• Mention meeting this in your spec “10 CFR Part 431 for liquid-immersed
distribution transformers”• Manufacturer will be ultimately responsible but a large price increase may be
the surprise
• January 1, 2016• May be re-evaluated before
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DOE Rule Impact on Manufacturing
•Commodities markets• Higher grade grain oriented core steel• Amorphous core steel
•Production limitations• Increased weight and dimensions• Transportation cost
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Final Thoughts• Each utility needs to make several assumptions! • Each A and B is only for assumptions made
• Cost is not the only factor• Warranty• Service• Quality• Lead times
• May want to have separate A and B for different kVA ranges• Manipulate equations to find lowest cost kVA size