From: Hirsch, Bruce R [mailto:Bruce.R.Hirsch@bge.com] 

Sent: Wednesday, December 14, 2011 1:21 PM 

To: 'Richard Parker'; Wes Patterson 

Cc: Meyers, Aaron; Andrew Delaski; Alex Hofmann; Aris Marantan; Art Rosenfeld; Robert Berman; 

Brenda Edwards; Brian Coffey; Bob Smith; Chris Bolduc; Caitlin Johnson; Carlos Gaytan; Charlie Drexler; 

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Anderson; Bob Saint; Robert van Buskirk; Robin Roy; Scott Beck; Steve Nadel; Steve Rosenstock; Tim 

Ballo; Tom Eckman; Ted Johnstone; Thomas Petrosino; Zhimei Luo 

Subject: RE: Dry Type Transformers 

Dry Type Transformers – Commonwealth Edison uses dry type transformers in high rise buildings. I have

copied some of their comments and attached documents covering size and weight restraints as part of

this email. The issue is in the replacement market. If an existing transformer needs to be replaced, there

may not be room for a larger transformer or the ability to transport a heavier transformer to upper level

transformer rooms.  

                                                                                                                                                                                            

                    Bruce

ComEd installs medium voltage dry-type transformers in building vaults and building electrical closets as 

follows: 

 Single phase – 75 kVA – 833 kVA, 7200/12470GrdY – 120/240 V and 7200/12470GrdY – 

277/480Y V 

 Three phase – 112.5 kVA – 2500 kVA, 12470 – 208Y/120 V and 12470 – 480Y/277 V 

The usage over the last five years is as follows: 

 Single phase – 671 transformers (approx. 134 per year) 

 Three phase – 454 transformer (approx. 91 per year) 

I have attached an e-mail with a letter that ComEd submitted earlier this year to the DOE regarding the 

potential impact of increased efficiencies. The following is an excerpt from that letter regarding dry-type 

and network transformers installed in buildings. ComEd has very specific limiting dimensions and weights 

in its dry-type and network transformer specifications. 

The building vaults are designed on an individual basis. The equipment opening is 

designed to meet the customer's ultimate transformer capacity requirement. 

ComEd utilizes a table of dimensions and weights based on historical transformer 

designs of different sizes used as a guide to determine the size of equipment opening 

needed to meet the ultimate transformer capacity requirement. 

The building vault structure is owned by the customer. The customer typically provides 

the smallest vault possible that still meets the ComEd requirements in order to reduce 

costs. The equipment opening is designed to meet the ultimate transformer capacity 
requirement with a typical clearance of only a few inches. Additionally, larger 

transformers may not be able to be maneuvered through building hallways. 

A slightly larger transformer as a result of increased efficiency would potentially cause 

severe problems when replacing an existing transformer with respect to the equipment 

opening. A slightly larger transformer as a result of increased efficiency installed in an 

existing building vault may violate certain company operating clearances inside the vault 

and possibly be deemed a safety issue. A slightly heavier transformer as a result of 

increased efficiency may cause severe problems if it exceeds the loading capacity of 

floors and elevators used to transport the transformer to the vault. 

The customer would have the burden of providing a larger opening and facilities 

(elevators and floors) needed to support a larger and heavier transformer which may 

result in an extended outage and a large cost incurred by the customer. 

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