From: Robert Berman [mailto:bermaneconomics@gmail.com] 

Sent: Tuesday, December 13, 2011 10:24 PM 

To: Corkran, Jerry L 

Cc: jerry.schoen@aksteel.com; Andrew Delaski; Alex Hofmann; Aris Marantan; Art Rosenfeld; Robert 

Berman; Brenda Edwards; Brian Coffey; Hirsch, Bruce R; Bob Smith; Chris Bolduc; Caitlin Johnson; Carlos 

Gaytan; Charlie Drexler; Chris Brown; Simmons, Chuck; Clark Silcox; Charlie Stevens; Dan Cohen; Millure, 

Dave; David Flaten; Dan Mulkey; Daniel Young; Emily Marchetti; Eric Peterson; Gary Fernstrom; Greg 

Rosenquist; Greg Coulter; James Lass; Jennifer Tiedeman; Freeman, Jeremiah; Jerry Hodge; Creevy, Jim; 

Jim Raba; Joanna Mauer; Caskey, John; John Cymbalsky; John Rossetti; Katie Coughlin; Ken Winder; 

Mahesh P. Sampat; Matthew Nardotti; Maxine Savitz; Michael Hyland; Michael Rivest; Meg Waltner; 

Pamela Costello; Ryan, Paul; Phil Harter; Phil Hopkinson; Puesh Kumar; Polinski, Raymond; Rob Greeson; 

Richard Parker; Rick Anderson; Bob Saint; Robert van Buskirk; Robin Roy; Scott Beck; Steve Nadel; Steve 

Rosenstock; Tim Ballo; Tom Eckman; Ted Johnstone; Thomas Petrosino; Wes Patterson; Zhimei Luo 

Subject: Re: Distribution Transformer loading 

Actually the opposite is true. With increasing emphasis on energy conservation, loads will likely 

continue to fall. This is especially true if you assume that system peaks are weather driven and 

transformer capacity must be there to maintain system reliability even (or especially) on hot 

summer days. 

Regards,

Robert A. Berman, Principal

Berman Economics

www.BermanEconomics.com

1915 Grand Court

Vienna, VA 22182

703‐281‐0490

703‐655‐8398 (cell)

BermanEconomics@gmail.com

On Dec 13, 2011, at 9:36 PM, Corkran, Jerry L wrote: 

Jerry,

The memo called attention to the PG&E practices, because we believe that what they are doing is what

most of the other utilities will do soon, because it is an intelligent way to use the smart meter

capabilities.  It is smart not just for the transformers, but also for the cable capacities.
The DOE study locked in a 50% target for the maximum efficiency, likely because that is what the 2007

study used for the maximum efficiency point.  The 50% maximum efficiency target is wrong now for new

transformers purchased by PG&E and it is either wrong now or it will sooner or later be wrong for the

entire industry.  It is logical that the industry will follow the PG&E lead and load their transformers to a

load which gives them maximum utilization of their equiptment.   If a 70% average RMS load  is the

expected target when smart meters are in widespread use, then the DOE should target the maximum

transformer efficiency at 70%.

Another reason we encourage the DOE to use the correct average RMS load is so that the transformer

efficiency payback calculations will be more accurate.  If the predicted average transformer loads are

incorrect, then the payback calculations  are incorrect such that they distort the actual efficiency

performance of the designs evaluated.   

Thanks to Katie Coughlin who sent out the email which is copied below.  It explains the percentages of

full load  for the transformer evaluations used in the DOE calculations.  Katie’s sample population was

10,000 transformers while the PG&E population data was 6 million transformers.   

Hello all,

Load losses are calculated based on the annual average of the squared load, i.e. the RMS. The 

LCC analysis sums the results from a sample population of 10,000 transformers, each of which 

is loaded differently, so we work with a distribution of RMS loadings. 

The shape of this distribution is approximately triangular. The shape of the distribution was 

developed based on an analysis of hourly building loads for several hundred commercial, 

residential and industrial buildings. 

The building load data can give us the average load is relative to the peak load. For the 

transformer analysis we also need to know what is the peak load relative to the transformer 

capacity. In the LCC, this "peak load factor" is also chosen from a distribution. 

Uncertainty about how transformers are sized relative to their peak loads is handled by defining 

an additional parameter that scales the entire RMS load distribution up or down. The value of 

this parameter determines the average RMS loading, relative to transformer capacity, for the 

transformer population. 

Initially the Department's estimates for the population-average RMS loading were taken from the 

previous rulemaking. For the current rulemaking, the utility representatives on the committee 

have provided us with data on transformer loads, primarily for single-phase, smaller capacity 

units connected to residential loads. Based on their input, our current assumptions are: 

- for smaller capacity transformers the average RMS is about 32% 

- for smaller capacity transformers in low population density areas the average RMS is 25% 

These assumptions apply to design lines 1 and 2. Note that these design lines also serve small 

commercial and multi-family loads, but we do not have data on average loading for those 

customer classes. 

For the larger capacity transformers and 3-phase transformers, the loading is currently set to 

about 40% population-average RMS. We also do a sensitivity with the RMS load set equal to 
50%. We do not currently have data for the larger capacity range. 

regards, 

Katie 

Recommendations: The DOE should correct the average and peak load factors used for all lines

anticipating that the good judgment of the utility managers will lead them to follow the PG&E lead to

result in an electric utility industry loaded at about the 70% of full load level chosen by PG&E.  The

payback calculations and the maximum efficiency target points should also be corrected.

Thanks for reading this,

Jerry Corkran

From: jerry.schoen@aksteel.com [mailto:jerry.schoen@aksteel.com]

Sent: Tuesday, December 13, 2011 3:06 PM 

To: Corkran, Jerry L 

Cc: Andrew Delaski; Alex Hofmann; Aris Marantan; Art Rosenfeld; Robert Berman; Brenda Edwards; 

Brian Coffey; Hirsch, Bruce R; Bob Smith; Chris Bolduc; Caitlin Johnson; Carlos Gaytan; Charlie Drexler; 

Chris Brown; Simmons, Chuck; Clark Silcox; Charlie Stevens; Dan Cohen; Millure, Dave; David Flaten; 

Dan Mulkey; Daniel Young; Emily Marchetti; Eric Peterson; Gary Fernstrom; Greg Rosenquist; Greg 

Coulter; James Lass; Jennifer Tiedeman; Freeman, Jeremiah; Corkran, Jerry L; Jerry Hodge; Creevy, Jim; 

Jim Raba; Joanna Mauer; Caskey, John; John Cymbalsky; John Rossetti; Katie Coughlin; Ken Winder; 

Mahesh P. Sampat; Matthew Nardotti; Maxine Savitz; Michael Hyland; Michael Rivest; Meg Waltner; Pam 

Costello; Ryan, Paul; Phil Harter; Phil Hopkinson; Puesh Kumar; Polinski, Raymond; Rob Greeson; Richard 

Parker; Rick Anderson; Bob Saint; Robert van Buskirk; Robin Roy; Scott Beck; Steve Nadel; Steve 

Rosenstock; Tim Ballo; Tom Eckman; Ted Johnstone; Thomas Petrosino; Wes Patterson; Zhimei Luo 

Subject: Re: FW: Distribution Transformer loading

 

Jerry. 

Thank you for a most interesting submission. In the analysis of watts loss versus load that you and Phil 

Hopkinson developed and sent out on 31 October 2011 showed that above a 60% load factor, the lower 

conductor losses for silicon steel units resulted in lower total losses. In my earlier discussions with 

Navigant, I suggested they look at evaluating efficiency at two points, 50% and something higher like 

80%. 

What PG&E is saying is that they are going to design their unit selections to -- essentially -- rely on 

overloading transformers during peak demand times. Is that correct? If so, neglecting the issue of higherload-factor efficiency should be reconsidered by the rulemaking team. 
<image001.gif> 

Thanks. Very interesting. 

Jerry 

Jerry W. Schoen 

Principal Engineer 

Product Development & Applications Engineering 

AK Steel Research 

Middletown, OH USA 45043-0001 

From: "Corkran, Jerry L" <Jerry.Corkran@CooperIndustries.com> To: "Dan Mulkey" <dhm3@pge.com>, "Phil Hopkinson" <phopkinson@hvolt.com>, "Aris Marantan" <amarantan@navigant.com>, "Katie 

Coughlin" <kcoughlin@lbl.gov>, "Richard Parker" <richardparkerdc@gmail.com>, "Brenda Edwards" <Brenda.Edwards@ee.doe.gov>, 

"Brian Coffey" <brian.coffey@navigant.com>, "Caitlin Johnson" <Caitlin.Johnson@navigant.com>, "Dan Cohen" 

<daniel.cohen@hq.doe.gov>, "Jennifer Tiedeman" <Jennifer.Tiedeman@hq.doe.gov>, "John Cymbalsky" <john.cymbalsky@ee.doe.gov>, 

"Chris Bolduc" <cabolduc@lbl.gov>, "Freeman, Jeremiah" <Jeremiah.Freeman@ee.doe.gov>, "Emily Marchetti" 

<Emily.Marchetti@ee.doe.gov>, "Zhimei Luo" <zhimei.luo@navigant.com> Cc: "Puesh Kumar" <pkumar@publicpower.org>, "Alex Hofmann" <ahofmann@publicpower.org>, "Andrew Delaski" 

<adelaski@standardsasap.org>, "Art Rosenfeld" <artrosenfeld@gmail.com>, "Bob Saint" <robert.saint@nreca.coop>, "Bob Smith" 

<bsmith@federalpacific.com>, "Carlos Gaytan" <carlos.gaytan@ge.com>, "Caskey, John" <john.caskey@nema.org>, "Charlie Drexler" 

<charlied@uus.org>, "Charlie Stevens" <cstephens@neea.org>, "Chris Brown" <chris.brown@cogentpowerinc.com>, "Clark Silcox" 

<clark.silcox@nema.org>, "Creevy, Jim" <Jim.Creevy@nema.org>, "Daniel Young" <DYoung@energy-solution.com>, "David Flaten" 

<david.l.flaten@xcelenergy.com>, "Eric Peterson" <Eric.Petersen@aksteel.com>, "Gary Fernstrom" <gbf1@pge.com>, "Greg Coulter" 

<greg.coulter405@gmail.com>, "Greg Rosenquist" <GJRosenquist@lbl.gov>, "Hirsch, Bruce R" <bruce.r.hirsch@bge.com>, "James Lass" 

<James.Lass@cleco.com>, "Corkran, Jerry L" <Jerry.Corkran@CooperIndustries.com>, "Jerry Hodge" <jhodge@howard.com>, "Jerry 

Schoen" <jerry.schoen@aksteel.com>, "Jim Raba" <Jim.Raba@ee.doe.gov>, "Joanna Mauer" <jmauer@standardsasap.org>, "John 

Rossetti" <jrossetti@mlgw.org>, "Ken Winder" <kwinder@mleainc.com>, "Mahesh P. Sampat" <maheshsampat@bellsouth.net>, "Matthew 

Nardotti" <matthew.nardotti@navigant.com>, "Maxine Savitz" <maxinesavitz@aol.com>, "Meg Waltner" <mwaltner@nrdc.org>, "Michael 

Hyland" <mhyland@appanet.org>, "Michael Rivest" <mrivest@navigant.com>, "Millure, Dave" <dave.millure@metglas.com>, "Pam Costello" 

<pamela.costello@navigant.com>, "Phil Harter" <phil@pjharter.com>, "Polinski, Raymond" <Raymond.Polinski@atimetals.com>, "Rick 

Anderson" <rick.anderson@faypwc.com>, "Rob Greeson" <rgreeson@federalpacific.com>, "Robert Berman" 

<bermaneconomics@gmail.com>, "Robert van Buskirk" <Robert.VanBuskirk@ee.doe.gov>, "Robin Roy" <rroy@nrdc.org>, "Ryan, Paul" 

<Paul.Ryan@hitmet.com>, "Scott Beck" <ScottB@lvmetals.com>, "Simmons, Chuck" <chuck.simmons@pgnmail.com>, "Steve Nadel" 

<snadel@aceee.org>, "Steve Rosenstock" <srosenstock@eei.org>, "Ted Johnstone" <ted.johnstone@cogentpowerinc.com>, "Thomas 

Petrosino" <tpetrosino@carolina.rr.com>, "Tim Ballo" <tballo@earthjustice.org>, "Tom Eckman" <Teckman@nwcouncil.org>, "Wes 

Patterson" <wes.patterson@us.abb.com> 

Date: 12/13/2011 03:30 PM Subject: FW: Distribution Transformer loading

Dan Mulkey and Phil Hopkinson – the attached loading data and the explanation of how PG&E loads their new

transformers at a targeted 70% of the nameplate rating is very factual and the most accurate explanation I have

heard about how the utilities load their new transformers.  We have all heard the terms “Smart Grid”.  This

appears to be an example of a smart customer using the latest technology to lead the way on efficient use of new

transformers.   

 

For the 30 year time frame that is being considered for the DOE transformer efficiency rules, it seems logical that

most utilities will adopt a similar smart process as is being used by PG&E to size the transformers and that a

loading target similar to the 70% loading target used by PG&E will be adopted by the utility industry.  This is
expected to result in load levels much higher than the 25% to 40% loads used by the DOE to calculate the pay

backs for the various loss levels considered.  The key question is what loading will be used on new transformers to

be installed and not what loading exists on some unit installed long before the smart meters existed. 

 

Dan – Are you available to answer emails if the DOE WG has additional questions? 

 

Members of the DOE WG who are utility employees: Please comment about the practice that PGE is using to load

their new transformers.  What does your company currently do to size transformers and what will your company

do  in the future to efficiently load the new transformers installed on your systems? 

 

Members of the DOE and Navigant who are involved in the evaluations of the transformer designs: Please

comment ‐ Would the DOE and Navigant consider using a higher load factor in the DOE payback calculations?   

Based on the 70% load factor targeted by PG&E for 6 million customers,  it seems that the DOE study payback

results are not accurate and that they should be revised to some load factor that reflects the latest technology that

the utilities will routinely be using based on the future 30 year  time frame being considered. 

 

Regards, 

                Jerry Corkran 

 

 

From: Mulkey, Dan [mailto:DHM3@pge.com]

Sent: Tuesday, December 13, 2011 1:42 PM

To: Phil Hopkinson

Cc: Corkran, Jerry L; Meyers, Aaron; Trujillo, Antonio

Subject: RE: Distribution Transformer loading 

 

Phil: 

 

It is good to hear from you again as I missed attending the last IEEE Transformers Committee Meetings in Boston.   

 

You have asked about load cycles at Pacific Gas & Electric and in fact we have public information that is readily

available on our website.  There are approximately 5.1 million meters on the PG&E system. The average data

from test meters for each rate class from residential to commercial and industrial is displayed on an hourly basis

for all 8760 hours in a year.  Multiple years of data are available on the public website. The attached EXCEL

spreadsheet is an extract of the data for 2006.  The rate classes are defined in the second attachment. 

 

This data is not organized by transformer type but there are a number of factors that are significant to

understanding the displays: 

 

1.       The summary data by rate class is shown at the very bottom of the spreadsheet. 

2.       A snapshot of the summary data is shown below: 

3.       <image002.png> 

4.       The hourly readings are the kWHrs consumed which is also the average kW load during that hour. 

5.       Rate class E1 is the most abundant class. I estimate that it accounts for approximately 80% of the meters. 

6.       Rate class E7 is also residential but is Time of Use service, and probably accounts for ~5% of the meters.  This

class is most often advantageous for homes where people can shift their energy consumption to off‐peak times. 

7.       The various other rate classes are also defined in attachment 2. 

8.       The yearly load factor is equal to the average load divided by the max load. 
9.       For PG&E the average transformer is loaded to approximately 70% of nameplate. While the peak loads are

normally within the capability of the transformer, the peak loads will often exceed the nameplate rating of the

transformer. 

10.   It is usually the physical location and grouping of the customer service points that determines the needed

transformer. 

11.   For most transformer installations the limiting factor is usually the voltage or flicker drop rather than the kVA

size of the transformer.

12.   A given transformer can be placed into service for a wide variety of loads. For instance, the same 25 kVA

single‐phase pad‐mount could be used to supply everything from a single signal light, to a single isolated

residential customer, to  fifteen or so residential customers in a subdivision in a coastal area. 

13.   While the average distribution transformer serves 5 customers, the range is from one to several hundred. 

14.   PG&E attempts to take advantage of the full capability of our transformers to achieve favorable economics

for our ratepayers. 

 

I hope that this explanation helps. 

 

Best regards, 

 

Dan Mulkey 

Sr Consulting Electrical Engineer 

DHM3@PGE.COM 

415‐973‐4699 office 

415‐264‐9260 cell[attachment "Electric Rate Schedules.xls" deleted by Jerry W Schoen/AKSTEEL] [attachment

"2006 Load Profile.xls" deleted by Jerry W Schoen/AKSTEEL]

 

 

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