Lecture Notes: Cast Epoxy Resin Transformers

Introduction

• Speaker: Richard Wolff, VP of Business Development at JST Power Equipment, Carlstadt, New Jersey
• Topic: Cast epoxy resin transformers for medium voltage applications
• Objectives:
  • Discuss transformer evolution
  • Overview of dry type transformers
  • Company introduction and installation base commentary
  • Q&A session

Transformer Evolution

• Focus on medium voltage power transformers
• Historical context:
  • Oil-filled transformers:
    • Used for cooling via insulating fluid
    • High maintenance and environmental concerns prompted shift to dry-type transformers
  • Dry-type transformers development:
    • Continuous improvement in mechanical robustness and dielectric properties
    • Key processes:
      • Open wound construction dipped in varnish
      • Vacuum Pressured Impregnation (VPI)
      • Vacuum Pressure Encapsulation (VPE)
      • Encapsulated transformers: open wound dipped and baked or VPI + protective epoxy coating

Cast Coil Transformers

• Windings solidly cast in epoxy resin
• Process involves:
  • Molding windings in epoxy in a vacuum chamber
• Comparative features:
  • VPI/VPE: Environmentally friendly, lower cost, but weaker dielectric properties, higher heat, less reliability in harsh conditions
  • Cast Coil:
    • Environmentally friendly, high reliability, better performance
    • BIL ratings up to 200 kV, typical partial discharge < 10 picocoulombs
    • Cooler operation than varnish systems, but hotter than oil filled
    • Superior mechanical strength
• Cost considerations: Cast coil typically has a higher purchase price

Application Guidelines

• Oil-filled transformers:
  • Suitable for outdoor, less populated areas, easy access for maintenance
• VPI/VPE:
  • Best for indoor applications with less critical performance needs
• Cast coil transformers:
  • Versatile for both indoor/outdoor applications in urban and harsh environments

Focus on Cast Resin Transformers

• Structure: core and coil assembly with high and low voltage coils
• Benefits:
  • Higher reliability, performance, environmental safety
  • Lower cost of ownership than liquid-filled transformers
  • Design life: typically 25 years, often exceeds this
  • Less prone to contamination and moisture issues
  • Simplified waste disposal during decommissioning

Applications of Cast Resin Transformers

• Suitable for:
  • Urban developments (subways, hospitals, airports, offices)
  • Commercial sectors (factories, processing plants, data centers)
  • Electrical power generation and renewable energy (wind energy)

Manufacturing Process Overview

• Facility: 25,000 sq ft in Carlstadt, NJ; North American and European HQ
• Key processes:
  • Coil winding: Conductors wrapped, wound on mandrel
  • Casting: Epoxy injected under vacuum conditions
  • Core cutting and stacking: Sheets of electrical grade silica steel
  • Final assembly and testing: Core and coil assembly into enclosures for testing

Installation Examples

• Representing various applications in the U.S.:
  • Data centers, hospitals, manufacturing plants, urban infrastructure projects
  • Notable projects: Freedom Tower at One World Trade Center

Summary

• Cast epoxy resin transformers provide:
  • Better reliability, performance, lower ownership costs, and environmental benefits
  • Optimal for indoor/outdoor applications in urban and harsh environments
• JST Power Equipment's commitment to modern production and extensive experience ensures high-quality manufacturing.

Q&A Session Highlights

• Cost Comparison:
  • Cast resin transformers generally 15-20% more expensive than oil-filled, ~10% more than VPI.
• Temperature Ratings:
  • Cast: Typically 80°C rise (up to 115°C available); VPI: 150°C rise
  • Headroom crucial for extending transformer life.
• Dielectric Properties:
  • Cast transformers have superior dielectric properties over VPI/VPE; lower partial discharge and higher BIL ratings.
• Application Limitations:
  • Dry-type transformers (including cast) not typically used in high voltage applications beyond 34.5 kV.
  • Cost limitations: Use depends on performance necessity.
• Useful Life:
  • Commonly specified as 20-25 years; actual operational life may exceed specifications with proper maintenance.