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Cast Coil Power Transformer

Product Overview & Application

castcoilCast coil power transformers feature primary and secondary windings which are vacuum cast inside a solid block of epoxy resin. The epoxy resin is introduced under vacuum in order to penetrate all the spaces within the winding, ensuring a void free casting with minimal partial discharges. The sold casting provides the highest degree of protection to the windings, making them ideally suitable for harsh environmental conditions which include airborne dust & high humidity. Furthermore, the fiberglass reinforcement which is incorporated into the casting provides the transformer with the highest mechanical strength which makes it resiliant to short circuit forces.

Rex cast coil 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 cast coil transformers units utilize only environmentally safe, CSA and UL recognized insulation systems, providing 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 cast coil 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. 

Features & Benefits of Cast Coil Power Transformers

Suitable For Harsh Environments - Cast coil transformers offer the greatest degree of protection against the presence of atmospheric pollutants effecting the performance and life expectancy of a power transformer.

High Short Circuit Strength - The fiberglass reinforced solid cast construction provides superior mechanical strength with the highest short circuit withstand capability of all types of transformers.

High Overload Capability - Due to the longer thermal time constant of cast coil transformers, higher short time overload capabilities are possible in comparison with traditional resin impregnated or encapsulated dry type transformers.

Environmentally Friendly - Rex cast coil transformers contain only chemically non-hazardous materials.

High Impulse Voltage Strength - The impulse voltage withstand capability of cast coil transformers is higher than conventional dry type and is comparable to liquid filled transformers.

Maintenance And Resistance To Temperature Fluctuations - Cast coil transformers are virtually maintenance free due to their smooth, crevice free construction. Cast coil transformers can be installed at ambient temperatures as low as -50°C and can be energized from cold starts at full rated load.

Product Specification

Capacity  100 to 3,333 kVA Single Phase and 300 to 10,000 kVA Three Phase 
Voltage Class  up to 46kV (250kV BIL) 
Cooling  Self Cooled (ANN / AN) 
Frequency  60Hz (50/60Hz Optional)
Conductors  Copper (Cu) or Aluminum (Al) Windings 
Insulation System  180°C (115°C rise) (Optional 80°C Rise Available) 

 Meets North American Efficiency Standards:

  • U.S. - DOE 10 CFR Part 431 (Jan 1, 2017)
  • Canada - SOR/2016-311, Amd. 14 (Dec. 9, 2016) & ON Reg. 404/12 Standard
Primary Taps  Typically +/-2 x 2.5% taps
Sound Level  Meets IEEE C57.12.01
Enclosure Type  Type 1 Indoor (Type 2, 3R, 4, 4X & 12 optional)
Enclosure Finish  ANSI 61 Grey

 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 
  • Partial Discharge

 Optional Type Tests 

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

 Other Optional Tests

  • RIV 
  • Power Factor
Warranty  18 months (See Warranty and Limitations) 
Quality System  ISO 9001:2015 Quality Management System 
  • CSA Certified - File # LR34493
  • UL Listed - File # E108255
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
  • Dial (Analog) or Digital Thermometers to monitor winding temperatures
  • Neutral Ground Resistors (NGR) and Monitoring
  • Anti-Condensation Strip Heaters
  • Ground Fault 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