Sent: Tuesday, December 13, 2011 5:27 PM 

To: Phil Hopkinson 

Cc: Robert Berman; Corkran, Jerry L; Dan Mulkey; Aris Marantan; Katie Coughlin; Richard Parker; Brenda 

Edwards; Brian Coffey; Caitlin Johnson; Dan Cohen; Jennifer Tiedeman; John Cymbalsky; Chris Bolduc; 

Freeman, Jeremiah; Emily Marchetti; Zhimei Luo; Puesh Kumar; Alex Hofmann; Andrew Delaski; Art 

Rosenfeld; Bob Saint; Bob Smith; Carlos Gaytan; Caskey, John; Charlie Drexler; Charlie Stevens; Chris 

Brown; Clark Silcox; Creevy, Jim; Daniel Young; David Flaten; Eric Peterson; Gary Fernstrom; Greg 

Coulter; Greg Rosenquist; Hirsch, Bruce R; James Lass; Jerry Hodge; Jerry Schoen; Jim Raba; Joanna 

Mauer; John Rossetti; Ken Winder; Mahesh P. Sampat; Matthew Nardotti; Maxine Savitz; Meg Waltner; 

Michael Hyland; Michael Rivest; Millure, Dave; Pamela Costello; Phil Harter; Polinski, Raymond; Rick 

Anderson; Rob Greeson; Robert van Buskirk; Robin Roy; Ryan, Paul; Scott Beck; Simmons, Chuck; Steve 

Nadel; Steve Rosenstock; Ted Johnstone; Thomas Petrosino; Tim Ballo; Tom Eckman; Wes Patterson 

Subject: Re: Distribution Transformer loading 

Sorry, the average load factor is what it is -- striving notwithstanding. All the striving in the 

world is not going to boost the load factors of a rural electric, for example, regardless of what 

they want or how much they want it. That's why Dan reports the annual average load at 39% and 

the peak day load at 70%. I suspect that his guidance is to make the average load of the 

transformer on the peak day equal to 70% of the nameplate rating. That would make sense as 

opposed to larger, historical oversizing factors, and would also lower transformer purchase costs. 

Dan does, indeed, buy a very large number of 15 kVa transformers for his E1 rate class (not load 

class). This is for residential customers in rural mountainous areas. PG&E buys so many in large 

part because the casualty rate due to lightening is quite high. 

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 5:07 PM, Phil Hopkinson wrote: 

Good afternoon Robert and all:
1. No that is not the correct interpretation.  I spoke extensively with Dan Mulkey, the PG&E Transformer

Engineer. The 39% load factor is on a per meter basis and is the average load for that meter divided by

the maximum load for that meter.  Since all meters of the same class are averaged it is the average load

divided by the maximum load for all of the meters of that class.

2. The transformer loading is a different calculation.  Effectively, PG&E under Dan Mulkey’s

guidance strives to make the average load on the transformer equal to 70% of the Nameplate rating of

the transformer.

3. Transformers are chosen for the application based on achieving 70% RMS equivalent load on the

transformer and on remaining within acceptable flicker and load regulation.  He often times chooses a

15 kVA transformer for 10‐15 meters of load class E1.

I have spoken with Ameren UE this afternoon as well and they have within the last 5 years modified

their transformer sizing policy to go to much heavier loading so as to minimize their transformer

purchase budget.

Best regards,

Phil

Philip J Hopkinson, PE 

President & CEO HVOLT Inc. 

3704 High Ridge Rd. 

Charlotte, NC 28270 

phopkinson@hvolt.com

Ph 704-846-3290 

Fx 704-845-2520 

Cell 704-236-3320 

www.hvolt.com

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

Sent: Tuesday, December 13, 2011 4:17 PM 

To: Corkran, Jerry L 

Cc: Dan Mulkey; Phil Hopkinson; Aris Marantan; Katie Coughlin; Richard Parker; Brenda Edwards; Brian 

Coffey; Caitlin Johnson; Dan Cohen; Jennifer Tiedeman; John Cymbalsky; Chris Bolduc; Freeman, 

Jeremiah; Emily Marchetti; Zhimei Luo; Puesh Kumar; Alex Hofmann; Andrew Delaski; Art Rosenfeld; Bob 

Saint; Bob Smith; Carlos Gaytan; Caskey, John; Charlie Drexler; Charlie Stevens; Chris Brown; Clark 

Silcox; Creevy, Jim; Daniel Young; David Flaten; Eric Peterson; Gary Fernstrom; Greg Coulter; Greg 

Rosenquist; Hirsch, Bruce R; James Lass; Jerry Hodge; Jerry Schoen; Jim Raba; Joanna Mauer; John 

Rossetti; Ken Winder; Mahesh P. Sampat; Matthew Nardotti; Maxine Savitz; Meg Waltner; Michael 

Hyland; Michael Rivest; Millure, Dave; Pam Costello; Phil Harter; Polinski, Raymond; Rick Anderson; Rob 

Greeson; Robert Berman; Robert van Buskirk; Robin Roy; Ryan, Paul; Scott Beck; Simmons, Chuck; Steve 

Nadel; Steve Rosenstock; Ted Johnstone; Thomas Petrosino; Tim Ballo; Tom Eckman; Wes Patterson 

Subject: Re: Distribution Transformer loading

 

It appears that the 70% load factor occurs only on the peak day. The annual load factor for 80% 

of the meters is reported as 39%. This is consistent with 38% implied load factor PG&E filed in 

it's 2007 rate case (A=$7.268, B=$1.063). These results are not inconsistent with the national 

distribution of loads used by LBNL. 

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 3:26 PM, Corkran, Jerry L wrote: 

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. <image001.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

<Electric Rate Schedules.xls><2006 Load Profile.xls>