Product Overview

When a dry-type transformer winding fails, replacing the winding coil is often faster, more economical, and far less disruptive than replacing the entire transformer. Our custom High Voltage (HV) and Low Voltage (LV) winding coils are manufactured according to your original drawings, transformer nameplate data, or OEM specifications to ensure perfect compatibility and reliable long-term performance.

Whether you require a single replacement HV coil for an aging transformer or a complete HV and LV coil set for transformer refurbishment, every coil is precisely wound, insulated, vacuum cast, and factory tested to match—or improve upon—the original transformer design.

Who This Product Is For

Maintenance engineers replacing failed, burned, or degraded transformer windings in existing dry-type transformers.

Transformer repair workshops sourcing precision replacement coils for third-party transformer overhaul and refurbishment projects.

OEM manufacturers and panel builders requiring custom-built winding coils with exact electrical and dimensional specifications.

Utilities, substations, and industrial plants extending transformer service life without the high cost and downtime of full transformer replacement.

High Voltage (HV) Winding Coils

High voltage windings handle incoming medium voltage power, typically 6kV, 10kV, or 35kV, and require precise insulation control to withstand impulse voltage, overvoltage stress, and long-term dielectric aging.

HV Coil Construction

HV coils are manufactured using multi-layer helical winding or segmented layer winding techniques on CNC-controlled winding machines. Conductors are selected based on voltage class and current rating, using fine enameled copper wire or fiberglass-wrapped rectangular copper conductors.

Inter-layer insulation adopts prepreg epoxy glass cloth or Nomex® insulation paper according to the specified insulation class and thermal requirements.

After winding, HV coils undergo vacuum epoxy resin casting. The vacuum process removes trapped air and moisture before resin injection, creating a void-free, crack-resistant structure with excellent short-circuit resistance and long-term thermal stability.

Tap positions such as ±2.5%, ±5%, or customized requirements are reproduced exactly according to the original drawing or transformer nameplate data. Tap leads are terminated using copper lugs or busbar connections to match the original installation layout.

Low Voltage (LV) Winding Coils

Low voltage windings carry the full load current at 0.4kV output, where conductor cross-sectional area is the most critical factor. A poorly designed LV coil leads to excessive resistive losses, overheating, and uneven current distribution that significantly shortens transformer life.

LV Coil Construction

LV coils are manufactured using precision foil winding machines with wide copper foil or aluminum foil conductors. The foil width matches the full winding height, naturally creating balanced current distribution and superior short-circuit withstand capability.

Cooling ducts are formed between winding layers during production to maintain temperature rise within design limits and improve heat dissipation during continuous operation.

Inter-layer insulation uses epoxy-impregnated insulation film, while terminal ends and mechanical support points are reinforced with fiberglass epoxy end caps to prevent axial displacement during short-circuit fault conditions.

Copper foil is recommended for higher efficiency and compact transformer dimensions, while aluminum foil provides a cost-effective solution for projects with sufficient installation space.

Main Features

Built to Your Drawing or Nameplate

Simply provide your original engineering drawing, CAD file, or transformer nameplate data. Our engineering team reviews all specifications and confirms the winding design before production begins to ensure accuracy without approximation.

Vacuum Epoxy Casting for Void-Free Construction

All HV coils use thermosetting epoxy vacuum casting reinforced with fiberglass cloth. This void-free structure eliminates internal partial discharge points, which are the primary cause of insulation failure in long-service transformer coils.

Class F or Class H Insulation

Standard production uses Class F insulation rated at 155°C. Class H insulation rated at 180°C is available for high ambient temperature environments and overload-prone applications.

Copper or Aluminum Conductors

Both HV and LV coils are available in oxygen-free copper or high-grade electrical aluminum. Conductor cross-sections are calculated according to rated current and current density safety margins.

Exact Dimensional Interchangeability

Replacement coils are dimensioned to fit the existing transformer core without modification. Window height, winding height, inner diameter, outer diameter, and terminal positions are matched precisely for direct installation.

Low Partial Discharge Performance

HV coils undergo partial discharge testing after casting. Typical PD values are below 10 pC at 1.2 times rated voltage, fully meeting IEC 60076-11 requirements for cast resin dry-type transformers.

Technical Specifications

Winding Type Reference

Different transformer applications require different winding structures. We manufacture all common dry-type transformer winding configurations.

Applicable Standards

All winding coils undergo strict factory testing before shipment, including winding resistance measurement, turns ratio verification, insulation resistance testing, power frequency withstand voltage testing, and partial discharge measurement for HV coils.

How to Order

Option A – From Original Drawing

Provide the original winding assembly drawing in PDF, DWG, or DXF format. Please include conductor specification, insulation class, and terminal arrangement if not clearly shown.

Option B – From Nameplate Data

Provide the transformer nameplate details including rated capacity, HV voltage, LV voltage, vector group, impedance voltage, frequency, and insulation class. Our engineers calculate the complete winding design from these parameters.

Option C – From Failed Coil Sample

Send the failed coil to our factory for reverse engineering. We perform dimensional and electrical analysis to manufacture an exact replacement and return both the original sample and the new coil.

Additional information such as conductor preference, insulation class, tap positions, terminal direction, and delivery schedule helps speed up quotation and production.

Why Choose Custom Coil Replacement Instead of Full Transformer Replacement

Replacing a complete transformer involves long procurement cycles, civil work, switchgear shutdown coordination, transportation, and disposal of the old unit. In contrast, custom replacement winding coils can be installed much faster using the existing core, structure, and terminal system.

For transformers with healthy cores and structural integrity, winding replacement restores full rated performance, renews insulation life, and significantly reduces total project cost compared to purchasing a new transformer.

This approach minimizes downtime, shortens maintenance schedules, and provides a practical long-term asset management solution for industrial plants and utilities.

Contact Us for Custom Coil Solutions

Submit your original drawing, transformer nameplate photo, or failed coil description to our technical team. We will review the feasibility, confirm the winding design, and provide a detailed quotation within 2 business days.