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Conducting Distribution Transformer Loss
Evaluations
IEEE Rural Electric Power ConferenceApril 21, 2015
Troy Knutson P.E.
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
How many use loss evaluated transformers?•What would your CEO/Manager say?•How about your CFO?•January 1st, 2016
RUS Bulletin 61-16•Originally published 1983•Present worth analysis•Outdated estimates/averages•New method developed in late 80’s•Coupled with advent of computerized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
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!
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
“A” Factor
“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
“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
“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
“B” Factor
“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
“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
“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
“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
“B” Factor Inputs• Peak Loss
Responsibility Factor (RF)• Differences between
peak on transformer vs. distribution system
“B” Factor Inputs• Loss Factor (LSF)• Average transformer losses vs.
the peak transformer losses• Nonlinear relationship to load
factorWhere:
Escalation and Inflation
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 (‘)
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
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
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%
Single Phase 50 kVA Comparison
• A value is $4.54/Watt• B value is $2.45/Watt
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
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
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
DOE Rule Impact on Manufacturing
•Commodities markets• Higher grade grain oriented core steel• Amorphous core steel
•Production limitations• Increased weight and dimensions• Transportation cost
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
