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VPI/VPE Power Transformer

Product Overview & Application


Vacuum Pressure Impregnated (VPI) power transformers utilize an open winding design, where the coil insulation is impregnated with an epoxy resin under vacuum and pressure, providing the windings a degree of protection against moisture and dirt, and improving the thermal conductivity of the winding which reduces localized hot spots. Furthermore, the VPI process removes air voids which deep within the windings, filling them with epoxy instead. These air voids, if not eliminated, can lead to higher partial discharges which can damage the transformer insulation over time, leading to premature failure. For a higher degree of protection, vacuum pressure encapsulated (VPE) coils can be utilized which involves repeated VPI and bake cycles. The VPE process builds a thick coat of epoxy over the windings which increases the windings resilience in humid and dirty environments.

Rex Vacuum Pressure Impregnated (VPI) dry type power transformers are primarily designed for stepping down high voltages from transmission and distribution systems to lower voltages which can be utilized in commercial, industrial, institutional or utility applications. They are ideally suited for both indoor and outdoor applications and require minimal maintenance to provide many years of reliable trouble free service. Unlike liquid filled transformers which are cooled with oil or a fire resistant liquid dielectric, dry type units utilize only environmentally safe, CSA and UL recognized high temperature insulation systems. Dry type designs provides a safe and reliable power source which does not require fire proof vaults, catch basins or the venting of toxic gasses. These important safety factors allow the installation of dry type transformers inside buildings close to the load, which improves overall system regulation and reduces costly secondary line losses.

Typical Configurations

Typically, dry type transformers are designed in one of the following three configurations:

1. General Purpose Power Transformer

General purpose power transformers are designed with primary and secondary bus stubs terminals suitable for side or bottom cable entry directly into the transformer enclosure. The terminals are mounted in a "stubs up" or "stubs down" configuration and electricians route the incoming and outgoing cables directly to these terminals. Optionally, the bus terminals can be routed to the either end of the enclosure to reduce the amount of internal cable routing required on site. For top cable entry applications, the terminals may be routed to an air terminal chamber (ATC).

2. Unit Substation Transformer

UnitSubstationUnit substation transformers are designed for close coupling with primary and/or secondary equipment. Transformer terminals are bussed to the either end of the transformer, and their exact location is coordinated with the equipment the transformer will be integrating with. The enclosure end walls feature openings which line up with the primary and/or secondary equipment, and flex connector can be utilized to connect the transformer with the other equipment. Unit substations are ideal for reducing the required space in an electrical room as the equipment can be installed right up against one another without the need for transition cells.

3. Pad Mounted Transformer

PadMountPad mounted transformers feature a compartmentalized design with front accessible and pad lockable primary and secondary air terminal chambers. These configurations are particularly well suited for outdoor areas with underground incoming and outgoing power service where the general public may be present. Transformer voltage taps are accessible from the rear via a removable panel or pad lockable door and tamperproof enclosure hardware is utilized to deter forced entry.

Rex Power Magnetics has over 30 years of experience designing and manufacturing medium voltage power transformers to meet various requirements and applications which include:

  • Zig Zag Grounding Transformers
  • Single Phase Neutral Grounding Transformers
  • Triplex Configuration Transformers
  • Transformers for Mining, Pulp and Paper Application
  • Corrosion Resistant Transformers for Marine Applications
  • Low Electromagnetic Field Emission Transformers For Hospital and Institutional Use
  • Traction Power Rectifier Transformers for Transit Systems
  • Motor Starting & Drive System Applications
  • High Harmonic and Intermittent Load Applications

Our technical team is always ready to find a solution and design a custom transformer for the most challenging applications. 

Product Specification

Capacity  100 to 5,000 kVA Single Phase and 300 to 15,000 kVA Three Phase 
Voltage Class  up to 46kV (250kV BIL) 
Cooling  Self Cooled (ANN) [Optional Forced Air Cooled (AFN/AF)]
Frequency  60Hz [50/60Hz Optional]
Conductors  Copper (Cu) or Aluminum (Al) Windings 
Insulation System  220°C (150°C Temperature Rise) [Optional 115°C & 80°C Rise Available]
Impregnation  Epoxy Vaccum Pressure Impregnated (VPI) and Baked [Optional VPE]

 Meets North American Energy Efficiency Standards:

  • U.S. - (DOE 2016) DOE 10 CFR Part 431
  • Canada - (NRCan 2019) SOR/2018-201, Amd. 14 & ON Reg. 404/12
Primary Taps  Typically +/-2 x 2.5% taps
Sound Level  Meets IEEE C57.12.01
Configuration  Terminal Bus Stubs Suitable For Cables [Optional Unit-Substation or Padmount Configuration]
Enclosure Type  Type 1 Indoor [Type 2, 3R, 4, 4X & 12 Optional]
Enclosure Finish  ANSI 61 Grey Powder Coat

 Std Production Tests (per IEEE C57.12.91)

  • Winding Resistance
  • Turns Ratio
  • Polarity and Phase Relation 
  • No-Load Loss and Excitation Current
  • Load Loss & Impendance
  • Applied Potential
  • Induced Potential

 Optional Type Tests 

  • Basic Insulation Level (BIL)
  • Temperature Rise (Heat Run)
  • Sound Level 
  • Partial Discharge

 Other Optional Tests

  • RIV 
  • Power Factor
Warranty  18 Months (See Warranty and Limitations)
Quality System  ISO 9001:2015 Quality Management System 
  • CSA Certified
  • UL Listed
Reference Standards
  • CSA C22.2 No 47
  • CSA C9
  • IEEE C57.12.01
  • IEEE C57.12.91
Optional Features & Accessories
  • Provision for Future Fans or Fan Packages (AFN) completely installed with or without Control Power
  • Buss Co-ordination with primary and secondary switchgear (Unit-Substation configuration)
  • Dial (Analog) or Digital Thermometers to monitor winding temperatures
  • Neutral Ground Resistors (NGR) and Monitoring
  • Anti-Condensation Strip Heaters
  • Switching surge mitigating R.C. Snubbers (with or without ground current monitoring)
  • Ground Fault Protection Relays (GFR)
  • Anti-Vibration mounting to reduce transformer hum (sound level)
  • Provision for Seismic mounting or complete Seismic Snubbers and Restraints
  • Distribution, Intermediate or Station Class Surge Arrestors
  • Provision for Buss Duct Entry
  • Fully Insulated Buss
  • Mimic Buss
  • Kirk-Key Interlock

Typical Drawings of Medium Voltage Power Transformers (Nema-1 Enclosed)

Drawings for 150°C or 115°C Rise, Stubs Up, Max. 600V/10kV BIL on L.V.
BIL 10kV 30kV 45kV 60kV 95kV 125kV 150kV
Rating 1.2kV Class 5kV Class 8.7kV Class 15kV Class 18kV Class 25.0kV Class 34.5kV Class
225kVA 225KVA-BIL10 225KVA-BIL30 225KVA-BIL45 225KVA-BIL60 225KVA-BIL95 Consult Eng. Consult Eng.
300kVA 300KVA-BIL10 300KVA-BIL30 300KVA-BIL45 300KVA-BIL60 300KVA-BIL95 Consult Eng. Consult Eng.
450kVA 450KVA-BIL10 450KVA-BIL30 450KVA-BIL45 450KVA-BIL60 450KVA-BIL95 450KVA-BIL125 450KVA-BIL150
500kVA 500KVA-BIL10 500KVA-BIL30 500KVA-BIL45 500KVA-BIL60 500KVA-BIL95 500KVA-BIL125 500KVA-BIL150
600kVA 600KVA-BIL10 600KVA-BIL30 600KVA-BIL45 600KVA-BIL60 600KVA-BIL95 600KVA-BIL125 600KVA-BIL150
750kVA 750KVA-BIL10 750KVA-BIL30 750KVA-BIL45 750KVA-BIL60 750KVA-BIL95 750KVA-BIL125 750KVA-BIL150
1,000kVA 1000KVA-BIL10 1000KVA-BIL30 1000KVA-BIL45 1000KVA-BIL60 1000KVA-BIL95 1000KVA-BIL125 1000KVA-BIL150
1,250kVA 1250KVA-BIL10 1250KVA-BIL30 1250KVA-BIL45 1250KVA-BIL60 1250KVA-BIL95 1250KVA-BIL125 1250KVA-BIL150
1,500kVA 1500KVA-BIL10 1500KVA-BIL30 1500KVA-BIL45 1500KVA-BIL60 1500KVA-BIL95 1500KVA-BIL125 1500KVA-BIL150
1,750kVA 1750KVA-BIL10 1750KVA-BIL30 1750KVA-BIL45 1750KVA-BIL60 1750KVA-BIL95 1750KVA-BIL125 1750KVA-BIL150
2,000kVA 2000KVA-BIL10 2000KVA-BIL30 2000KVA-BIL45 2000KVA-BIL60 2000KVA-BIL95 2000KVA-BIL125 2000KVA-BIL150
2,250kVA 2250KVA-BIL10 2250KVA-BIL30 2250KVA-BIL45 2250KVA-BIL60 2250KVA-BIL95 2250KVA-BIL125 2250KVA-BIL150
2,500kVA 2500KVA-BIL10 2500KVA-BIL30 2500KVA-BIL45 2500KVA-BIL60 2500KVA-BIL95 2500KVA-BIL125 2500KVA-BIL150
3,000kVA 3000KVA-BIL10 3000KVA-BIL30 3000KVA-BIL45 3000KVA-BIL60 3000KVA-BIL95 3000KVA-BIL125 3000KVA-BIL150
3,500kVA Consult Eng. 3500KVA-BIL30 3500KVA-BIL45 3500KVA-BIL60 3500KVA-BIL95 3500KVA-BIL125 3500KVA-BIL150
3,750kVA Consult Eng. 3750KVA-BIL30 3750KVA-BIL45 3750KVA-BIL60 3750KVA-BIL95 3750KVA-BIL125 3750KVA-BIL150
4,000kVA Consult Eng. 4000KVA-BIL30 4000KVA-BIL45 4000KVA-BIL60 4000KVA-BIL95 4000KVA-BIL125 4000KVA-BIL150
4,500kVA Consult Eng. 4500KVA-BIL30 4500KVA-BIL45 4500KVA-BIL60 4500KVA-BIL95 4500KVA-BIL125 4500KVA-BIL150
4,750kVA Consult Eng. 4750KVA-BIL30 4750KVA-BIL45 4750KVA-BIL60 4750KVA-BIL95 4750KVA-BIL125 4750KVA-BIL150
5,000kVA Consult Eng. 5000KVA-BIL30 5000KVA-BIL45 5000KVA-BIL60 5000KVA-BIL95 5000KVA-BIL125 5000KVA-BIL150

Typical Drawings of Medium Voltage Power Transformers (Nema-3R Enclosed)

Drawings of 150°C or 115°C Rise, Stubs Up, Max. 600V/10kV BIL on L.V.
BIL 10kV 30kV 45kV 60kV 95kV 125kV 150kV
Rating 1.2kV Class 5.0kV Class 8.7kV Class 15.0kV Class 18.0kV Class 25.0kV Class 34.5kV Class
225kVA 225KVA-BIL10-3R 225KVA-BIL30-3R 225KVA-BIL45-3R 225KVA-BIL60-3R 225KVA-BIL95-3R Consult Eng. Consult Eng.
300kVA 300KVA-BIL10-3R 300KVA-BIL30-3R 300KVA-BIL45-3R 300KVA-BIL60-3R 300KVA-BIL95-3R Consult Eng. Consult Eng.
450kVA 450KVA-BIL10-3R 450KVA-BIL30-3R 450KVA-BIL45-3R 450KVA-BIL60-3R 450KVA-BIL95-3R 450KVA-BIL125-3R Consult Eng.
500kVA 500KVA-BIL10-3R 500KVA-BIL30-3R 500KVA-BIL45-3R 500KVA-BIL60-3R 500KVA-BIL95-3R 500KVA-BIL125-3R 500KVA-BIL150-3R
600kVA 600KVA-BIL10-3R 600KVA-BIL30-3R 600KVA-BIL45-3R 600KVA-BIL60-3R 600KVA-BIL95-3R 600KVA-BIL125-3R 600KVA-BIL150-3R
750kVA 750KVA-BIL10-3R 750KVA-BIL30-3R 750KVA-BIL45-3R 750KVA-BIL60-3R 750KVA-BIL95-3R 750KVA-BIL125-3R 750KVA-BIL150-3R
1,000kVA 1000KVA-BIL10-3R 1000KVA-BIL30-3R 1000KVA-BIL45-3R 1000KVA-BIL60-3R 1000KVA-BIL95-3R 1000KVA-BIL125-3R 1000KVA-BIL150-3R
1,250kVA 1250KVA-BIL10-3R 1250KVA-BIL30-3R 1250KVA-BIL45-3R 1250KVA-BIL60-3R 1250KVA-BIL95-3R 1250KVA-BIL125-3R 1250KVA-BIL150-3R
1,500kVA 1500KVA-BIL10-3R 1500KVA-BIL30-3R 1500KVA-BIL45-3R 1500KVA-BIL60-3R 1500KVA-BIL95-3R 1500KVA-BIL125-3R 1500KVA-BIL150-3R
1,750kVA 1750KVA-BIL10-3R 1750KVA-BIL30-3R 1750KVA-BIL45-3R 1750KVA-BIL60-3R 1750KVA-BIL95-3R 1750KVA-BIL125-3R 1750KVA-BIL150-3R
2,000kVA 2000KVA-BIL10-3R 2000KVA-BIL30-3R 2000KVA-BIL45-3R 2000KVA-BIL60-3R 2000KVA-BIL95-3R 2000KVA-BIL125-3R 2000KVA-BIL150-3R
2,250kVA 2250KVA-BIL10-3R 2250KVA-BIL30-3R 2250KVA-BIL45-3R 2250KVA-BIL60-3R 2250KVA-BIL95-3R 2250KVA-BIL125-3R 2250KVA-BIL150-3R
2,500kVA 2500KVA-BIL10-3R 200KVA-BIL30-3R 2500KVA-BIL45-3R 2500KVA-BIL60-3R 2500KVA-BIL95-3R 2500KVA-BIL125-3R 2500KVA-BIL150-3R
3,000kVA 3000KVA-BIL10-3R 3000KVA-BIL30-3R 3000KVA-BIL45-3R 3000KVA-BIL60-3R 3000KVA-BIL95-3R 3000KVA-BIL125-3R 3000KVA-BIL150-3R
3,500kVA Consult Eng. 3500KVA-BIL30-3R 3500KVA-BIL45-3R 3500KVA-BIL60-3R 3500KVA-BIL95-3R 3500KVA-BIL125-3R 3500KVA-BIL150-3R
3,750kVA Consult Eng. 3750KVA-BIL30-3R 3750KVA-BIL45-3R 3750KVA-BIL60-3R 3750KVA-BIL95-3R 3750KVA-BIL125-3R 3750KVA-BIL150-3R
4,000kVA Consult Eng. 4000KVA-BIL30-3R 4000KVA-BIL45-3R 4000KVA-BIL60-3R 4000KVA-BIL95-3R 4000KVA-BIL125-3R 4000KVA-BIL150-3R
4,500kVA Consult Eng. 4500KVA-BIL30-3R 4500KVA-BIL45-3R 4500KVA-BIL60-3R 4500KVA-BIL95-3R 4500KVA-BIL125-3R 4500KVA-BIL150-3R
4,750kVA Consult Eng. 4750KVA-BIL30-3R 4750KVA-BIL45-3R 4750KVA-BIL60-3R 4750KVA-BIL95-3R 4750KVA-BIL125-3R 4750KVA-BIL150-3R
5,000kVA Consult Eng. 5000KVA-BIL30-3R 5000KVA-BIL45-3R 5000KVA-BIL60-3R 5000KVA-BIL95-3R 5000KVA-BIL125-3R 5000KVA-BIL150-3R