Delta Star

Top Tier Manufacturing of Power Transformers and Mobile Substations

About the company

Delta Star Incorporated manufactures medium power transformers (5 through 300 MVA; 5 kV up through 345 kV class) and is the premier manufacturer of mobile substations in North America.  In Canada, Delta Star Transformer's facility is located in Saint-Jean-sur-Richelieu near Montreal, Quebec. In addition, Delta Star has 2 factories located in the United States.

St-Jean-sur-Richelieu, QC, Canada

  • Plant size: 4,500 m² (48,437 ft²)
  • Since 1989
  • 106 employees
  • Acquired in 2015
  • Capacity: 6 PTs per month
  • ISO-9001-2015 certified (1996)
  • Serves: Canada and Northern US

Lynchburg, VA, USA

  • Plant size: 24155 m² (260,000 ft²)
  • Since 1950
  • 450 employees
  • Capacity: 13 PTs per month
  • ISO-9001-2015 certified (2003)

San Carlos, CA, USA

  • Plant size: 11334 m² (122,000 ft²)
  • Since 1959
  • 205 employees
  • PT Capacity: PTs per month
  • Mobile Capacity: 2 MTs per month
  • ISO-9001-2015 certified (2003)


Delta Star takes quality down to the component level. As a result, Delta Star designs and manufactures their critical components in-house in order to meet our customer’s specific requirements. This is just another reason why utilities all over the world trust Delta Star for all their power needs.



Every steel tank is designed and manufactured at DSI factories, giving both flexibility and control over quality and lead time.



Delta Star’s commitment to building their own switches gives the ability to make the complex multiple voltage designs that are unique to their product.



DSI considers this a vital component of a load tap changing power transformer. While others purchase these components from third party providers,DSI designs and builds theirs in-house.



Delta Star’s decades of building mobile substations has led to a reliable nitrogen system that is considered the best in the industry. 



DSI builds lightweight, durable aluminum enclosures and control cabinets for entire substations. Unmatched engineering staff designs transformer protection and relaying systems on some of the most complex mobile substations on the market.



Over the years DSI has relied on an epoxy based primer with a polyurethane topcoat that they apply to every transformer.

Product range




Delta star power transformers

Delta Star power transformers are individually designed and manufactured to meet and exceed the highest industry standards and the exact specifications for the particular application involved. They are not stock units modified or customized to meet minimum specifications. Special options and features are planned into the original design and built into the unit. Delta Star power transformers are liquid-oil-immersed for the most efficient and reliable long-term operation in a wide variety of utility and industrial applications (transformer oil meets or exceeds ASTM D 3487 standards). Markets Served Utility Applications include power and distribution, system step up or step down transmission voltages, system tie, automatic voltage regulation, and many more. Industrial Applications include secondary load center, unit substation, distribution service, and power substation. Delta Star power transformers are manufactured in the medium to high voltage range from 5 kV up through 315 kV class in single and 3-phase ratings, 5 through 180 MVA (self cooled rating) with or without load tap change equipment. Power Generation Applications include generator step up, unit auxiliaries (UAT), and station service.


Each Delta Star power transformer core is designed to provide the accuracy and consistency necessary for high efficiency and superior performance. Only the highest quality grain-oriented electrical steel is used to make step-lap laminations cut to engineering design specifications. After the laminations have been precisely cut and assembled on a stacking table for accurate positions, experienced personnel assemble the core clamping structure so that the mass of steel is supported in a cradle-like method. The structure eliminates undue stress on the laminations while providing maximum strength to withstand the forces of shipping and short circuit.


Delta Star engineers custom design coils with the optimum winding configuration to meet the specific requirements of each application. Advanced engineering ensures high reliability, mechanical, and electrical integrity. Specific requirements such as non-standard loading conditions or low-impedance are accommodated in design. All Delta Star windings are designed and built with the inherent strength to withstand the axial and radial components of short circuit stress. The design calculations have been developed and proven by short circuit test results. Only the best grade electrical conductors and materials are used to make the coils of Delta Star power transformers.



Because long-term tank integrity is absolutely essential for the reliability and long life of a transformer, Delta Star fabricates transformer tanks to meet the highest standards of quality and craftsmanship. All tanks and covers are fabricated of high quality plate steel to withstand full vacuum. Tank corners are bent instead of welded to assure strength, reliability, and eliminate stress leaks. Welding is accomplished in a double shielded "mig" process that provides continuous welds. All tank seams are welded inside and outside to ensure leak-free construction. A leading paint manufacturer, after many years of research and development, has developed a special transformer paint formulated to withstand exposure to extreme weather conditions. Prior to painting, the metal surface is shot-blasted to provide superior cleanliness and paint bonding.


At Delta Star, the control panel is given special emphasis in design and construction as the critical part to monitor, control, and protect the whole power transformer unit. Delta Star produces a superior control panel that enables the user to accurately monitor and adjust the operation of the transformer. Sensors are located at various points in the transformer to accurately monitor temperature, fluid levels, and other conditions of the unit at all times. Alarms and visual instruments alert personnel in the event of an abnormal condition for correction or further troubleshooting. Remote monitoring is also available.


Delta Star engineers conduct all routine tests, in accordance with ANSI/IEEE on every transformer manufactured. In addition to these routine tests, the Quality Control team performs ANSI/IEEE design tests including switching surge impulse, zero-phase sequence impedance, temperature rise, and sound level. Knowing that load and no-load losses over time can be a primary cost consideration, Delta Star provides certified test reports on every transformer and supports it with an instrument calibration program traceable to standards (NIST).


tapChangerDSW (1).jpg

Tap changing equipment used on Delta Star transformers are available for off-load or load applications. Both type units have been developed and improved to exceed the highest industry standards and to provide long service life with minimum maintenance requirements. Off-load DETC units feature silver plated contacts and operate under spring-pressure to ensure positive contact. The tap changing control lever is operated externally. It clearly indicates the tap position and can be pad locked in the locked position. Load LTC units maintain the voltage at the load to the required level, automatically utilizing advanced technical design and the most durable high efficiency, long contact life, and maintenance-free operation (vacuum-reactor or resistor types are available).

Mobile substations

Delta Star mobile transformers and mobile substations provide the capabilities to quickly restore electrical service following an outage caused by a storm or other disaster, provide temporary new service while permanent facilities are being constructed and replace existing equipment during regularly scheduled maintenance. Delta Star engineers determine specific customer needs and exact equipment integration requirements prior to the design and manufacture of each quality mobile unit. Custom designed and built to order, each unit also has a wide variety of accessories and equipment options available to provide even greater capability and operating flexibility. Quick response installation time and equipment reliability are just two of the reasons why Delta Star units place far ahead of the competition. 



  • Quickly restore electrical service
  • Rapid response to outage due to ice storms
  • Natural disaster relief support


  • Reliable service during construction
  • Immediate electrical service on new sites
  • Commercial and industrial applications


  • Substitute during regular maintenance
  • Service to temporary sites
  • Remote area support

Read more about Delta Star's mobile capabilities on our blog:


The Delta Star product list goes far beyond power transformers. They have a strong reputation for providing the flexibility to build Auto and Ground Transformers, Voltage Regulators, Mobile Circuit Protectors and Mobile and Portable Substations. As a result, Delta Star is the only North American transformer manufacturer with the breadth of products to meet all your power needs.



Field Service has always been a hallmark of Delta Star, providing the best and most comprehensive service available to ensure that your transformers operate at optimum performance. Delta Star Field Service offers full-service packages which include installation, processing, standard maintenance, and specialized services. Delta Star Field Service focuses on preventive maintenance that minimizes future unscheduled maintenance and optimizes the life of the transformer.


  • Installation, Removal and Relocation
  • Testing (Including standard and diagnostic testing)
  • Repair and Preventive Maintenance
  • Turnkey Installation
  • LTC Maintenance
  • Engineering Services
  • Oil Processing (Dehumidify & Degas)
  • Regasketing
  • Relocation Services
  • Transformer Replacement Parts



DSI trained employees offer over 300 years combined experience in the field providing quality support to help significantly lengthen the operational life of your transformer. Our customers can be assured that Delta Star technicians are always there to assist you with experience and technical competence. This experience, quality equipment, and up-to-date training allows us to install over 100 transformers a year.



Delta Star uses professionally maintained and calibrated equipment for every step of the process. From installation to oil processing to testing, we use the latest technology. This allows us to perform field service to the highest standard.

  • 30 – 50 GPM Oil Processing Trailers
  • Full Degassing capabilities
  • Dual 170 CFM Vacuum Pumps
  • 224 Kilowatt Heating Systems
  • Inhibitor injection system


DSI professional technicians use the latest technology in test sets to ensure high levels of accuracy and repeatability.
Field testing capabilities include:

  • Power Factor Bushings
  • Power Factor Transformer
  • 10 kV Excitation
  • Megger Winding and Core Ground
  • Functional Testing of Protection and Control Circuits

In addition to standard testing, Delta Star offers advanced testing and diagnostics including: Sweep Frequency Response Analysis (SFRA), CT’s (Ratio, Resistance, Saturation Curves), Winding Resistance, Ultrasonic Leak Detection, Leakage Reactance, Thermal Imaging, Dewpoint, Dielectric Frequency Response, and Oil Testing.


Delta Star provides logistical service and support to transport, relocate, and install transformers. Electronic Impact Recorders with GPS and automated notification of events are used to track transformers during shipments and ensure that your transformer arrives protected and on time. Delta Star has extensive experience with railcar, truck, and shipments.


DSI professional technicians receive extensive technical and safety training. The technicians are outfitted with proper Personal Protective Equipment (PPE) and are trained in accordance to OSHA requirements. Other safety courses include: Safe Work Practices, Hazardous Materials, Forklift Safety (Operator’s Permit), Overhead Crane (Operator’s Permit), Scaffold, Ladders, and Fall Protection, Heat Stress, Fire Safety, Safe Electrical Practices, NFPA 70E 8-hour Electrical Safety, Lockout/Tagout, Confined Space Safety and Rescue, First Aid/CPR, and Bloodborne Pathogens.

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