Delta Star

Visit Website »

Who We Are:

Power transformers are considered the most important capital asset in a substation. Delta Star is proud to offer stationary transformers, mobile, portable and skid mounted transformers, substations, circuit switchers and breakers, and mobile cable trailers. Delta Star is the most experienced manufacturer of mobile substations and mobile transformers in North America. All of the Company’s transformers are designed and manufactured to customer specifications.

Delta Star is capable of constructing transformers that are 230,000 volts and below in both single and three phase ratings through 900 kV BIL rating. These units could include tap-changing equipment and are utilized in both utility and industrial applications. Utility applications include power, distribution, generator step up, UAT, grounding units, voltage regulators and autotransformers. Delta Star’s industrial transformers are used for secondary load centers, unit substations, distribution services, power substations, and hazardous locations. The fundamental technology involved in manufacturing and operating a transformer has basically not changed since the early to mid-1900’s indicating a mature product category.

Delta Star constructs mobile transformers that can be used for a number of different purposes, which include serving as temporary substations during emergencies or as a safeguard against power outages resulting from malfunctioning transformers. Additionally, mobile transformers are used in remote locations until permanent transformers are in place and for planning routine maintenance of permanent substations. Delta Star’s mobile transformers can be built up to a capacity of 100 MVA rating and up to 230,000 volts depending on states’ DOT regulations. DSI can provide multiple voltage requirements for use on both the high and low sides. Additionally, load tap changer equipment can be installed for the secondary voltage regulation. All of the mobile transformers are welded to their trailers.

Our Roots:

Delta-Star Electric was founded in Chicago in 1908 to manufacture devices required by the electrical industry in the generation, transmission, and distribution of electrical energy. Some of its early products included a complete line of high-voltage indoor and outdoor switches including disconnects, transfers, interrupters, and disrupters for single and group operation.

In 1950,Delta-Star Electric Company was purchased by H. K. Porter Company and was subsequently renamed the Delta-Star Electric Division of H. K. Porter Company. On October 13, 1959, H. K. Porter purchased Hill Transformer and moved it to Belmont, California. Shortly after the purchase of Hill Transformer, H. K. Porter built a transformer plant in Lynchburg, Virginia and became operational in 1962. In 1980, the Chicago plant was closed and its assets liquidated. Subsequent to the closure of the Chicago plant, the Delta Star name (without the hyphen) was used by the transformer plants in Belmont and Lynchburg.

On November 23, 1988, Delta Star was sold, in entirety, to the Delta Star Employee Stock Ownership Plan and to certain key personnel. At the time of the transaction, the ESOP acquired 986,302 or 98.63% of the Company’s outstanding common stock while several members of the management team purchased the remaining shares.

Products and Services – Summary:

  • Power Transformers
  • Generator Step Up Units
  • Autotransformers
  • Mobile Transformers
  • Auxiliary Transformers
  • Voltage Regulators
  • Grounding Devices
  • Cable Trailers
  • Field Services
  1. Oil Processing & Analysis
  2. Full Testing service
  3. Parts
  4. Maintenance
  5. Installation
  6. Engineering

Power w/o LTC (PT) 10-60 15/110 230/900 4/75 115/550
Power w/LTC (PTL) 10-45 15/110 230/900 4/75 115/550
Auto & TV w/o LTC (AT) 15-90 69/350 230/900 25/150 161/650
Auto & TV w/LTC (ATL) 15-60 69/350 230/900 25/150 138/550
Voltage Regulators
(Through put rating)
20-50 15/110 115/550 +/- (10-15%) Regulation +/- (10-15%) Regulation
Grounding Device Zig-Zag,
or Wye-Delta
15/110 115/550 Zero Sequence Impedance on Request Zero Sequence Impedance on Request
Generator Step-up (UT) 10-60 15/110 230/900 4/75 115/550
Unit Auxiliaries (UAT) 5-60 15/110 34.5/200 2.4/60 25/150
Mobile Substation &
Portable Transformer
5-100* 25/150 230/650 2.4/60 69/350

* Mobile units are generally designed with ODAF ratings.


Delta Star, Inc.’s manufacturing capability is limited by weight and size restrictions. Many factors influence the above criteria, such as:

  • Impedance
  • Sound Level
  • Loss Evaluation
  • Temperature Rise
  • Basic Impulse Level (BIL)
  • Limiting Dimension
  • State Highway Road Limits (Mobile Transformers)


The specification listing on this page is a general guide. Requests for transformers below and above the limits set in the listing will be evaluated individually, and would be dependent on the factors mentioned above.

If you have any questions, please call us at 949-852-1006