Oil-Sealed Rotary Vane Vacuum Pumps in Transformer Manufacturing: A Complete Guide

Transformer manufacturing is one of the most demanding industrial processes where vacuum technology plays a decisive role. Power transformers, distribution transformers, and instrument transformers all contain large amounts of non-metallic components such as insulation paper, wood, oil, and resin that can absorb moisture from the atmosphere. Even trace amounts of moisture can drastically reduce dielectric strength, leading to partial discharges, electrical breakdown, and catastrophic failure.

This is where oil-sealed rotary vane vacuum pumps become indispensable. As industry leaders like Leybold confirm, oil-sealed rotary-vane pumps have been "typically used for all drying steps of transformer production," offering a cost-effective and proven solution for this critical application.

Why Vacuum is Critical in Transformer Manufacturing

The Problem: Moisture is the Enemy

Transformers rely on a dual insulation system: solid insulation (cellulose paper and pressboard) and liquid insulation (transformer oil). Both are hygroscopic — they naturally absorb moisture from the air.

The consequences of moisture contamination are severe:

To prevent these failures, residual moisture content in high-performance transformers must not exceed 0.1–0.3%.

The Solution: Vacuum Processing

Vacuum technology addresses this challenge through two key stages:

1. Dehydration and Degassing

The transformer tank is subjected to a deep vacuum for an extended period. Under low pressure, the boiling point of water is significantly lowered, causing trapped moisture to vaporize and be drawn out. Simultaneously, dissolved gases (oxygen, nitrogen) are removed from the oil and solid materials.

2. Impregnation with Insulating Oil

After dehydration, the tank must be filled with insulating oil under vacuum. The vacuum created inside the microscopic pores of cellulose insulation allows degassed oil to be "sucked" into every tiny space. This eliminates air pockets that could cause partial discharges and ensures the oil and solid insulation work as a single, unified dielectric system.

The Role of Oil-Sealed Rotary Vane Pumps

Why Oil-Sealed Rotary Vane Pumps?

Oil-sealed rotary vane pumps are the most widely used vacuum technology in transformer production. Here's why:

Proven Technology – Oil-sealed rotary vane pumps have been the industry standard for transformer drying for decades. They are "well-proven, highly-efficient and cost-effective" solutions widely used for all transformer production drying steps.

Deep Vacuum Capability – These pumps achieve ultimate pressures as low as 0.5 mbar (single-stage) and even lower with two-stage configurations, meeting the stringent vacuum requirements of transformer drying processes.

Cost-Effectiveness – Compared to dry vacuum technologies, oil-sealed rotary vane pumps offer a lower initial investment and proven reliability, making them the most economical choice for many transformer production lines.

Water Vapor Handling – Transformer drying generates considerable water vapor outgassing. Oil-sealed rotary vane pumps equipped with gas ballast valves can effectively handle condensable vapors, preventing moisture from contaminating the pump oil.

Typical System Configuration

In transformer manufacturing, oil-sealed rotary vane pumps are typically used in combination with Roots pumps (mechanical boosters):

Primary/Backing Pump: A high-flow oil-sealed rotary vane pump (such as the Wordfik PVX series) establishes the initial vacuum and serves as the backing pump

Main/Booster Pump: A Roots vacuum pump increases pumping speed and improves the ultimate vacuum of the entire system

This combination delivers the high pumping speeds and deep vacuum levels required for efficient transformer drying.

Wordfik PVX Series: Engineered for Transformer Manufacturing

Wordfik's PVX series oil-sealed rotary vane vacuum pumps are specifically designed to meet the demanding requirements of transformer production. Here's how they deliver:

Key Features for Transformer Applications

Deep Vacuum Performance – PVX series pumps achieve an ultimate vacuum of 0.5 mbar, ensuring thorough dehydration of transformer insulation. For the most demanding applications, the PVX630 and PVX750 models reach 0.1 mbar.

Superior Water Vapor Handling – Equipped with high-quality gas ballast valves, PVX pumps effectively handle the considerable water vapor outgassing during pre-drying and final drying stages. For example, the PVX202 offers a water vapor handling capacity of 4 kg/h, while larger models handle even higher loads.

Heavy-Duty Cast-Iron Construction – Built with robust cast-iron bodies and precision-machined components, PVX pumps are designed for 24/7 continuous operation in demanding industrial environments.

Low Operating Temperature – Efficient cooling systems maintain low oil temperatures, extending oil change intervals and pump service life.

Easy Maintenance – With accessible service points and simplified maintenance procedures, PVX pumps minimize downtime and reduce total cost of ownership.

Model Selection for Transformer Applications

Vapor Phase Drying (VPD): The Gold Standard

The most effective drying method for transformer insulation is Vapor Phase Drying (VPD) , developed in the 1960s and still the industry standard today.

How VPD Works

In VPD, kerosene or alcohol is injected into the drying chamber as a heat transfer medium. The process involves:

1. The transformer or its windings are placed in a drying chamber (up to 1,000 m³ volume)

2. The chamber is heated to approximately 105–110°C

3. Kerosene vapor penetrates the insulation material due to its low density and surface tension

4. The vapor condenses on the cooler insulation, releasing latent heat and driving out moisture

Why VPD with Oil-Sealed Pumps?

50-60% Faster Drying – VPD dries windings within days (at most a week), compared to weeks with conventional hot air methods

Superior Quality – VPD achieves residual moisture below 0.1–0.3%, ensuring maximum dielectric strength

Extended Insulation Life – The process significantly reduces the depolymerization factor, extending the life of insulating materials

Proven Compatibility – Oil-sealed rotary vane pumps have been the backbone of VPD systems for decades, providing the deep vacuum and high water vapor handling capacity this demanding process requires

Case Study: Wordfik Vacuum Systems in Transformer Production

Wordfik provides complete vacuum solutions for transformer manufacturers, including customized Roots + rotary vane vacuum systems specifically designed for kerosene vapor phase drying and high-vacuum evacuation.

Typical System Components

• Primary Pump: Oil-sealed rotary vane pump (PVX series) for establishing and maintaining base vacuum
• Booster Pump: Magnetic Roots vacuum pump (LCVS series) for increased pumping speed
• System Integration: Pre-assembled, pre-piped systems with intelligent controls

Benefits for Transformer Manufacturers

• Faster Cycle Times: Optimized pump combinations reduce drying and evacuation times
• Higher Quality: Deep, stable vacuum ensures thorough moisture removal
• Lower Operating Costs: Energy-efficient designs and extended maintenance intervals
• Reliability: Heavy-duty construction for 24/7 operation in demanding environments

Maintenance Considerations for Transformer Applications

Transformer drying applications are demanding on vacuum pumps due to:

High water vapor loads that can contaminate pump oil

Organic solvent vapors during VPD processes

Acidic byproducts from insulation material degradation

Best Practices

Regular Oil Changes – Monitor oil condition and change at recommended intervals to maintain performance and protect the pump.

Gas Ballast Operation – Use the gas ballast valve during drying processes to prevent moisture from condensing in the pump oil.

Oil Mist Filtration – Install exhaust oil mist filters to capture oil aerosols and protect the working environment.

Anti-Suck Back Protection – Ensure pumps are equipped with integral anti-suck back valves to prevent oil from flowing back into the transformer tank during power interruptions.

Conclusion

Oil-sealed rotary vane vacuum pumps remain the backbone of transformer manufacturing — a proven, cost-effective, and reliable technology for removing moisture and gases from transformer insulation.

Wordfik's PVX series offers transformer manufacturers:

l Deep vacuum down to 0.1 mbar for thorough drying

l Superior water vapor handling with gas ballast valves

l Heavy-duty construction for 24/7 continuous operation

l Proven reliability in the most demanding applications

Whether you're drying instrument transformers, distribution transformers, or large power transformers, Wordfik has the vacuum solution to ensure your products meet the highest quality standards.