Research, software programs best way to determine transformer sizing
Editor's note: The Energy Services Bulletin features real answers to real questions posed to our staff at the Energy Services Power Line. We hope you find it useful.
Question: Is there a "rule of thumb" for utilities to use in determining transformer sizing of residential distribution loads? Something based on monthly kWh usage, or house size, etc....something our lineman can use in the field. We have a large electric heat load, so that type of load must be factored in also.
Answer: According to retired Electrical Distribution Engineer Dennis Greys, no "rule of thumb" would accurately provide this information. Many utilities do a series of correlation studies for the most loaded months—in your case, winter. This is done every three or four years for different groups, i.e. residential, light commercial, etc. A simple regression analysis is studied and data collected for the energy and capacity. Utilities use this information to size transformers for residential loads. Your current transformer suppliers may also have information on this topic.
You should definitely consider the use of high-efficiency transformers, which include both amorphous core and high-efficiency silicon-steel core transformers, both of which can play an important role in reducing energy losses. The EPA Energy Star Transformer Program is a good starting point to find out more about this.
Also, consider integrating software programs into your electrical distribution group to make better transformer decisions. Considering that residential transformers can last 45 years and commercial transformers 35 years, this would be a prudent strategy in the long run. The Energy Star Program offers two choices:
- Optimal Transformer Sizing Model — Working jointly with Edison Electric Institute, EPA has developed software to help electric utilities in selecting the optimal rating of distribution transformers. You can also download the zip file directly.
- Distribution Transformer Cost Evaluation Model. EPA developed DTCEM to assist utilities in considering both the economic and environmental benefits of energy-efficient distribution transformers. The comprehensive tool assists in evaluating multiple transformer bids. It generates reports that present an analysis of the total owning cost, cost of saved energy, simple payback, emission reduction potential and other factors that should be considered in transformer purchasing decisions. The program is in two separate zip files and a pdf manual.
Here are some additional resources on distribution transformers:
