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Pearl Electric's VPI Dry Type Transformer is a ventilated dry-type transformer featuring Vacuum Pressure Impregnated windings and a robust air-cooled construction.
During the VPI manufacturing process, transformer windings are placed under vacuum to remove air and moisture before insulating resin is introduced. Controlled pressure is then applied to help the resin penetrate the winding insulation structure. After curing, the impregnated winding forms a mechanically stable and electrically reinforced insulation system.This creates a dense, protective insulation layer that renders the unit virtually impervious to moisture, dust, salt spray, and common industrial pollutants.
This construction provides a practical alternative to liquid-filled transformers in applications where oil containment, fire protection, or environmental considerations are important.
The transformer can be supplied with aluminum or copper windings and designed with natural-air cooling (AN) or forced-air cooling (AF) according to the required load profile. Forced-air cooling can also be configured to increase the transformer's available capacity where project conditions require additional thermal capability.
Coupled with a 220°C insulation system, the transformer maintains stable, reliable performance regardless of the average temperature rise rating. With proper installation and maintenance, this series delivers long-term, maintenance-free, and highly reliable operation.
For demanding industrial environments, Pearl Electric can provide customized enclosure, coating, temperature monitoring, electrostatic shielding, noise reduction, space-heater, and other accessory options.
Parameter Range | Value |
Rated Capacity | 500 kVA – 10,000 kVA |
Rated Voltage | 6 kV / 10 kV / 13.8kV /15 kV / 25 kV / 34.5 kV / 35 kV |
Cooling Method | AN (Natural Air Cooling) / AF (Forced Air Cooling) |
Insulation System | 220°C (Class H) |
Average Temperature Rise | 80°C / 115°C / 150°C |
Frequency | 50 Hz / 60 Hz |
Phases | Three-phase |
Winding Material | Copper / Aluminum |
Tap Range | ±2 × 2.5% (Full-capacity taps or Customized) |
Enclosure | Customized |
Advanced Vacuum Pressure Impregnation Technology
The VPI process uses controlled vacuum and pressure cycles to iResin fully permeates windings and insulation gaps, eliminating air bubbles and voids .This helps create a compact and mechanically reinforced winding structure with consistent insulation performance.
220°C Insulation System
A high-temperature insulation system can be selected for demanding operating conditions. 220°C (Class H) insulation system High thermal rating, adaptable to various average temperature rise requirements (options: 80°C / 115°C / 150°C).The insulation system is designed to provide adequate thermal margin while supporting reliable transformer operation under continuous and variable loads.
Copper or Aluminum Windings
Pearl Electric VPI transformers can be manufactured with copper or aluminum conductors depending on electrical requirements, weight considerations, cost targets, and customer specifications.
Oil-Free Construction
The dry-type VPI design does not use conventional mineral insulating oil. This eliminates the need for oil containment systems and reduces the maintenance requirements associated with liquid insulation.
High overload capacity
The standard self-cooled configuration uses natural air circulation. Forced-air fans can be added when higher load capacity or improved thermal performance is required.
For selected designs, forced-air cooling can provide approximately 33% additional capacity compared with the self-cooled rating, subject to transformer design and thermal calculations.
Moisture and Contaminant Resistance
The VPI resin system helps protect the windings from moisture, dust, and common industrial contaminants. Additional enclosure and coating configurations can be selected for more demanding environments.
High Mechanical Strength
The impregnated winding structure provides improved mechanical stability and resistance to the electromagnetic forces generated during transformer operation and short-circuit events.
Flexible Enclosure Configuration
The transformer can be supplied as an open ventilated design or equipped with an enclosure suitable for indoor or outdoor installation. NEMA 1 and NEMA 3R-type configurations can be considered according to project requirements.
Enhanced Fire Safety
Because VPI transformers do not contain conventional mineral oil, they eliminate the fire and environmental risks associated with oil leakage and liquid-filled transformer installations. This makes them attractive for buildings and other locations where fire protection is a major consideration.
Lower Routine Maintenance
Oil testing, oil filtration, and oil replacement are not required. Routine maintenance can instead focus on electrical connections, cooling equipment, ventilation, insulation condition, and general cleanliness.
Suitable for Indoor Installation
The compact dry-type construction makes VPI transformers suitable for electrical rooms, industrial facilities, commercial buildings, data centers, transportation infrastructure, and other indoor substations.
Strong Thermal Performance
The VPI insulation system combined with AN or AF cooling provides reliable thermal management. Forced-air cooling can be added for applications with higher continuous loading or temporary capacity requirements.
Excellent Mechanical Stability
Vacuum pressure impregnation helps bond the winding insulation system and improve mechanical integrity, supporting stable performance under thermal cycling, vibration, and electrical stresses.
Flexible Application Design
VPI transformers can be customized for different voltage levels, capacity ratings, frequencies, winding materials, insulation systems, temperature rises, enclosure types, sound requirements, and environmental conditions.
Suitable for Harsh Industrial Environments
With appropriate enclosure, coating, ventilation, and insulation configurations, VPI transformers can be adapted for industrial plants, mining facilities, transportation systems, renewable energy installations, and other demanding environments.
UL / CSA / cUL certification (optional)
Average temperature rise rating: 80°C / 115°C / 150°C (selectable)
Operating frequency: 50Hz / 60Hz
220°C insulation system
Copper or aluminum windings (selectable)
ANSI standard grounding terminals
Core grounding copper busbar
Indoor ventilated enclosure (NEMA 1 / IP20 rating)
ANSI 61 standard finish (light gray)
Lifting provisions
Removable front and rear panels
Anti-vibration rubber pads
HV side taps: 2 × 2.5% full-capacity taps (above and below nominal)
Compliant with NEMA, ANSI, and IEEE standards
Electrostatic shield
Space heater (anti-condensation)
Temperature monitor / automatic fan controller
Dedicated thermostat for space heater
Forced-air cooling fans (increases capacity to 133% AF)
Pre-wired fan connections and control circuits
Full-length copper grounding busbar
Mechanical shock recorder
Outdoor enclosure (NEMA 3R / IP33; higher ratings available)
Polyurethane topcoat
Ventilation opening protective screens
Hinged access panels
Low-noise design (3–10 dB reduction below standard sound levels)
Enclosure: The standard indoor enclosure features a NEMA 1, Type C construction, supporting installation via hoisting, jacking, or rolling; ANSI-standard grounding terminals are provided on both the high-voltage and low-voltage sides. The enclosure surface undergoes degreasing, derusting, and impurity removal before being finished with ANSI 61 light gray paint, ensuring excellent corrosion resistance; a NEMA 3R weather-resistant enclosure is available as an option for outdoor installations.
Coils: Low-voltage windings (below 2400V) typically utilize stranded conductors or foil-wound structures, offering cost advantages for lower-capacity applications; high-voltage windings (2400V and above) may employ single-section barrel, multi-section barrel, or disc-type configurations. For units rated up to 2000kVA, coils may be circular, elliptical, or rectangular; units above 2000kVA generally utilize circular windings to ensure mechanical strength during short-circuit events, except where specific dimensional constraints apply.
Core: Constructed from stacked high-permeability, low-loss grain-oriented silicon steel laminations, with magnetic flux density maintained below the saturation point; laminations undergo rigorous deburring and are tightly stacked without gaps. A mitered step-lap (STEPLAP) core structure is available as an option to reduce no-load losses and noise. Apart from the factory-installed grounding copper busbar, the core remains electrically isolated from external components.
Forced Air Cooling: Units rated 750kVA and above can be equipped with a forced air cooling system, increasing capacity by approximately 33% over self-cooled ratings. Automatic fan start/stop control is enabled via a temperature control relay; control cabling and wire identification markers are included as standard.
VPI dry-type transformers are suitable for applications where reliable medium-voltage power conversion is required together with low fire risk, reduced maintenance, and flexible installation.
VPI transformers can provide medium-voltage power distribution for factories, machinery, production lines, motors, drives, and industrial automation systems.
Data centers require highly reliable electrical infrastructure with strict fire-safety requirements. VPI transformers can be installed in indoor electrical rooms and integrated with utility, UPS, and backup power systems.
Shopping malls, office buildings, hotels, hospitals, and other commercial facilities can use VPI transformers for indoor medium-voltage distribution.
VPI dry-type transformers can be used in solar PV, wind power, battery energy storage, and other renewable energy projects for voltage conversion and auxiliary power distribution.
Mining operations often involve dust, vibration, variable loads, and demanding operating environments. VPI transformer designs can be customized with appropriate insulation, cooling, enclosure, and environmental protection.
Railway stations, metro systems, tunnels, and transportation infrastructure can benefit from oil-free dry-type transformer technology where fire safety and reliable power distribution are important.
VPI transformers can be considered for industrial facilities where environmental conditions, fire safety, and reliable electrical power distribution require careful transformer selection. Hazardous-area installation must be evaluated separately according to the applicable site classification and equipment requirements.
Water treatment plants and pumping stations require continuous electrical power for motors, pumps, control systems, and auxiliary equipment. VPI transformers provide a low-maintenance solution for indoor and protected outdoor installations.
Airports, tunnels, public facilities, universities, hospitals, and other infrastructure projects can use VPI dry-type transformers where oil-free construction and indoor installation are preferred.
Pearl Electric provides customized transformer solutions for industrial, commercial, renewable energy, infrastructure, and utility applications.
For VPI dry-type transformers, Pearl Electric can support customers with:
Customized Electrical Design
Transformer capacity, voltage ratio, frequency, impedance, vector group, insulation level, temperature rise, and cooling method can be configured according to project requirements.
Flexible Mechanical Configuration
Enclosure, terminal arrangement, lifting structure, ventilation, cable connection, and installation dimensions can be customized for different substations and electrical rooms.
International Project Support
Transformer designs can be developed according to IEC and other applicable international or local standards, depending on the destination market and project specification.
Complete Testing Support
Routine testing and selected special tests can be provided according to the technical specification and applicable standards.
OEM & Project-Based Manufacturing
Pearl Electric can provide transformer solutions for EPC contractors, electrical distributors, utilities, industrial companies, renewable energy developers, and infrastructure projects.
VPI stands for Vacuum Pressure Impregnation. A VPI transformer is a dry-type transformer whose windings are impregnated with insulating resin using controlled vacuum and pressure processes.
Both are dry-type transformer technologies, but their winding insulation structures differ. VPI transformers use resin impregnation to saturate the winding insulation, while cast resin transformers use epoxy resin to encapsulate the windings.
VPI is often selected where a robust, ventilated winding construction and good heat dissipation are required, while cast resin transformers may be preferred for applications requiring fully encapsulated windings and enhanced environmental protection.
Yes. VPI transformers can be manufactured with copper or aluminum windings. The appropriate conductor material is selected according to electrical performance, current rating, project cost, weight, and customer requirements.
Yes. VPI transformers are suitable for data centers where indoor installation, fire safety, reliable power distribution, and reduced maintenance are important considerations.
Yes. Forced-air cooling can increase the available capacity of a VPI transformer by improving heat dissipation. A commonly used design target is approximately 133% of the self-cooled rating, subject to the specific transformer thermal design. VanTran's published VPI documentation specifies this option for selected units.
Please contact the Pearl Electric sales engineering team to obtain detailed product selection manuals, quotations, or customized solutions.
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