From: Kenneth Winder [mailto:kwinder@mleainc.com]  

Sent: Friday, October 07, 2011 7:16 PM

To: Robert Berman

Cc: Gaytan Cavazos, Carlos (GE Energy, Non‐GE); Richard Parker; ahoffman@publicpower.org;

pkumar@publicpower.org; Aaron Meyers; Andrew Delaski; Art Rosenfeld; Bob Saint; Brian Coffey; Bruce

R Hirsch; Bruce Smith; Caitlin Johnson; Charlie Drexler; Chris Bolduc; Chuck Simmons; Dan Cohen; Daniel

Young; Dave Millure; Eric.Petersen@aksteel.com; Gary Fernstrom; Greg Coulter; Greg Rosenquist; James

Lass; Jeremiah Freeman (CONTR); Jerry Corkran; Jerry Hodge; Jerry Schoen; Jim Creevy; Joanna Mauer;

John Caskey; John Cymbalsky; jrossetti@mlgw.org; kcoughlin@lbl.gov; Mahesh P. Sampat; Meg Waltner;

Michael Hyland; Michael Rivest; Paul Ryan; Phil Hopkinson; Raymond Polinski; Rick Anderson; Rob

Greeson; Robin Roy; Scott Beck; Steve Nadel; Steve Rosenstock; Tim Ballo; Tom Eckman; Wes Patterson;

Zhimei Luo

Subject: Re: MV Working Group: Follow‐up to Sept 15/16 Mtg

Dear Mr. Parker and Colleagues:  The following information may be of interest to or helpful to the

Rulemaking Committee, and therefore, I am forwarding it to everyone.

     Moon Lake Electric is a Rural Electric Cooperative serving in Northeastern Utah and Northwestern

Colorado.  We have approximately 20,000 meters.  Most of our load is three‐phase associated with the

oil and gas industry in our service area.  Our distribution system is 7.2/12.5 kV and 14.4/24.9 kV.  

Subtransmission lines are 69 and 138 kV.  We have 43 substations and over 3,700 miles of line.  Most of

our distribution lines are overhead except within subdivisions in communities, recreational areas or in

environmentally sensitive areas.   

     We are winter peaking.  We are located in a high desert climate in valleys (5,000 feet above sea level)

surrounded by mountains that top out over 13,500 feet above sea level. Temperatures throughout the

year are moderate except they can be below zero for periods of time during the winter months.  Our

system load factor is near 90% on a monthly basis.        

    We are located in an isokeruanic level of approximately 45 thunderstorm days per year.  The system

area has a lightning flash density of 1 per square km per year.  The lightning exposure factor is in the

range of 250 to 600 per RUS Bulletin 1751F.801 Figure 2.  Since lightning seems to be involved with most

of our transformer failures, we apply lightning protection on the primary and secondary of our

transformers.  

    We feel that we have a good record keeping process for our transformers and believe the information

herein is accurate.  From the time we receive transformers, we keep records of when they were

purchased and most of their nameplate information, no‐load and full‐loss loss values, where they are

located on the system by GPS coordinates and pole numbers or which warehouse if they are on a dock,

customers serviced by them (current and even some historical records of this), etc.  We review loading

of distribution transformers periodically to see if we need to exchange them for a different capacity

unit.  If the units are removed from service due to failure, we keep track of when they left the system

and who purchased them, shipping information, etc..

    We have prepared information about the number of overhead distribution transformers purchased by

year, and have determined how many of these are still in service or on warehouse docks ready to be

placed in service.  We have records identifying those transformers that we no longer own.  None of the

units discussed herein contain or contained PCB's.

    We have separated the information about transformers into two (2) types based upon their core

material i.e. amorphous core or steel core.  We also have subclasses for this information based upon the

secondary voltage rating of the transformers.  The transformers with secondary voltage of 240/480 or

277 probably serve the high load factor loads.  Others probably serve small commercial and residential

consumers.
   Moon Lake Electric purchased 1,771 amorphous core distribution transformers between 1990 and

1996.  We had a very high loss evaluation during those years due to our power supply costs and that

situation was projected into the future. Our A and B factors supported purchase of these distribution

transformers during that period of time.  We only purchased overhead amorphous core transformers.  

During that same period, we also purchased steel core transformers.  In 1996, our power supply costs

changed, and our A and B factors no longer economically justified the purchase of amorphous core

transformers.  

    The summary of this information is attached.

    The spreadsheet shows that we have 94.47% of the amorphous core transformers still in service.  

Some of those have been in service for over 20 years.  The spreadsheet also shows that we have 97.28%

of steel core transformers purchased during the same period of time we were purchasing the

amorphous core transformers that are still in service.  Transformers no longer in service are failed units

that have been sold to buyers of failed transformers.

    There are probably two (2) immediate observations that can be made from these records.  The first

being that the percentage of distribution transformer failures Moon Lake Electric has experienced is low

for the length of time in service according to information being discussed in the Committee.  The other

observation is that the percentage of failed units for amorphous core transformers is just over two (2)

times the percentage of failed steel core transformers (5.53% vs 2.72%) purchased during the same

period of time (percentages are used for comparison recognizing that the sampling sizes differ).  

    We have 24 amorphous core units that are on warehouse docks that are ready to be placed in service.

Our linemen prefer to install a physically‐smaller transformer than the amorphous core transformers

when they have a choice.  That situation is being rectified because these highly efficient units should be

in service.

    For your interest we have also shown on the spreadsheet the steel core transformers purchased over

the period of 1982 through 1996 and the number of those units that are still in service or on warehouse

docks ready to be placed in service.  We have 93.18% of those transformers still in service on our

system. Some of them are approaching 30 years of service.  It is interesting to recognize the number of

steel core transformers purchased between 1982 and 1996 is very similar to the number of amorphous

core transformers purchased between 1990 and 1996.  Furthermore, the percentage of steel core

transformers still in service for that whole period is approximately equal to the percentage of

amorphous core transformers during a shorter period of service.

    This information represents the experience of Moon Lake Electric regarding our overhead distribution

transformers.  It may or may not be similar to the experience of other utilities.   

Kenneth A. Winder, PE

Moon Lake Electric Assn., Inc.