EASA announces the publication of an update to AR200, now titled the Guide For The Repair Of Dry-Type Transformers. This guide outlines best practices for the repair of dry-type transformers.

EASA members adopt a customer service-centered mission encompassing various electrical apparatus repairs such as electric motors, transformers, controls, electrical troubleshooting and construction. EASA’s Technical Services Committee recently reviewed and extensively edited the AR200 guide in support of transformer repair services.

The previous version of AR200 (published in 2011) was titled Guide For The Repair Of Power And Distribution Transformers. Like preceding versions, it embraced a broad scope of transformer repair that included liquid-filled distribution or power transformers up to 10 MVA and 69 kV and dry-type distribution and power transformers up to 5 MVA and 25 kV.

In preparing this update, the Technical Services Committee chose to narrow the scope to the types of transformer repair activities usually found in EASA service centers (i.e., non-liquid-filled distribution dry-type transformers with high voltage windings up to 69 kV and rated less than 15,000 kVA). After all, liquid-filled transformer repair and service is a specialty few members offer, with many standards and best practices differing from those for dry-type transformers. In recognition of EASA’s international membership, the updated procedures in the new version now reference both IEEE and IEC standards.

Besides being helpful to the transformer repair and service efforts in many EASA service centers, it continues to position EASA as the definitive source for best practices in the electrical apparatus repair industry.

While the AR200 guide was an effort of the AR200 Task Group and EASA’s Technical Services Committee, thanks also go to EASA members who offered their comments and expertise. With a view of continual improvement as industry standards evolve, we welcome your feedback.

Table of Contents Summary

• Section 1 General
  • 1.1 Purpose
  • 1.2 Scope
  • 1.3 Identification
    • 1.3.1 Records
    • 1.3.2 Nameplate
    • 1.3.3 Service center labels
  • 1.4 Condition assessment and failure analysis
  • 1.5 Cleaning
  • 1.6 Terminals
    • 1.6.1 Leads
    • 1.6.2 Connections
    • 1.6.3 Enclosures
  • 1.7 Accessories
  • 1.8 Painting
  • 1.9 Packaging and transportation
• Section 2 Testing Transformers
  • 2.1 Safety considerations
  • 2.2 Instrument calibration
  • 2.3 Insulation condition test
    • 2.3.1 Insulation resistance test
    • 2.3.2 Polarization index test
    • 2.3.3 Insulation power factor test
  • 2.4 Other tests
    • 2.4.1 Winding resistance test
    • 2.4.2 Transformer turns ratio (TTR) test
    • 2.4.3 Polarity test
    • 2.4.4 No-load loss test
    • 2.4.5 Load loss test
    • 2.4.6 Single-phase impedance test
  • 2.5 High-potential tests
    • 2.5.1 50/60 Hz high-potential test
    • 2.5.2 DC high-potential test
    • 2.5.3 High frequency induced potential test
    • 2.5.4 Test levels, windings
• Section 3 Rewinding Transformers
  • 3.1 Investigation
  • 3.2 Gathering data
  • 3.3 Winding coils
  • 3.4 Core laminations
    • 3.4.1 Stacked cores, disassembly
    • 3.4.2 Stacked cores, assembly
    • 3.4.3 Wound cores, disassembly
    • 3.4.4 Wound cores, assembly
  • 3.5 Connections
    • 3.5.1 Connections in the winding
    • 3.5.2 External connections
    • 3.5.3 Insulating connections
  • 3.6 Leads
• Section 4 Transformer Repair
  • 4.1 Checking for service suitability
    • 4.1.1 Tests
    • 4.1.2 Equipment checks
    • 4.1.3 Summary of results
    • 4.1.4 Preparation for shipment
  • 4.2 Rewind
    • 4.2.1 Inspection, test and estimate
    • 4.2.2 Dismantle
    • 4.2.3 Winding new coils
    • 4.2.4 Reassembly
    • 4.2.5 Final tests
    • 4.2.6 Preparation for shipment
• Appendix A Electrical Testing Safety Considerations
  • A.1 Personal safety
    • A.1.1 Training
    • A.1.2 Personal protective equipment (PPE)
    • A.1.3 Supervision
    • A.1.4 First aid and CPR
  • A.2 Test area
    • A.2.1 Enclosure
    • A.2.2 Gates
    • A.2.3 Signs
    • A.2.4 Lighting
    • A.2.5 Safety equipment
    • A.2.6 Test unit clearance
  • A.3 Unit under test
    • A.3.1 Suitability for test
    • A.3.2 Exclusive attention
    • A.3.3 Grounding (earthing)
    • A.3.4 Base
  • A.4 Test panels
    • A.4.1 Construction
    • A.4.2 Voltages
    • A.4.3 Warning lights
    • A.4.4 Disconnect
    • A.4.5 Safety switch
    • A.4.6 Leads
  • A.5 High-potential ground (earth) test
• Appendix B Reference Information
  • Table b-1. Insulation resistance test voltages
  • Table b-2. Temperature correction factors for dry-type transformer insulation resistance tests
  • Table b-3. Recommended minimum insulation resistances for dry-type transformers
  • Table b-4. Recommended test levels for dry-type transformer new windings
• Bibliography
• Standards Organizations & Other Resources