Transformer Vacuum Pumping System for Vacuum Drying & Evacuation

A Transformer Vacuum Pumping System is specialized equipment designed to create a high-vacuum environment inside power transformers before vacuum oil filling and commissioning. By removing moisture, air, and other gases from the transformer tank and insulation system, it helps improve dielectric performance, extends insulation life, and reduces the risk of partial discharge or insulation failure. Widely used during transformer installation, maintenance, and factory testing, these systems are suitable for 220kV, 500kV, 750kV, and 1000kV high-voltage transformers. They are commonly deployed in substations, transformer manufacturing factories, power plants, renewable energy projects, and other high-voltage electrical facilities. YUNENG Transformer Vacuum Pumping Systems combine high pumping efficiency, reliable vacuum performance, and intelligent controls to support safe, efficient transformer evacuation and preparation for long-term, reliable operation.

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Why Vacuum Pumping Is Essential Before Transformer Oil Filling

Vacuum pumping is one of the most critical steps in transformer installation, manufacturing, and maintenance. Before insulating oil is injected into a transformer, the internal tank, windings, and cellulose insulation must be thoroughly evacuated to remove moisture, air, and dissolved gases. Without a proper vacuum process, contaminants can remain trapped inside the transformer, reducing insulation performance and increasing the risk of premature failure. A high-performance transformer vacuum pumping system ensures that the transformer is fully prepared for vacuum oil filling and reliable long-term operation.

How a Transformer Vacuum Pumping System Works

A transformer vacuum pumping system removes moisture, air, and dissolved gases from the transformer tank before insulating oil is injected. By creating a deep and stable vacuum, the system ensures that transformer oil fully penetrates the winding insulation while preventing air pockets that could reduce dielectric performance. The entire evacuation process is fully automated through a PLC control system and typically follows six key steps.

Step 1 – Connect the Vacuum Pumping System

The vacuum pumping unit is connected to the transformer through vacuum-rated pipelines and sealed valves. All connections are inspected to ensure the system is completely leak-free before evacuation begins.

Step 2 – Start the Rotary Vane Vacuum Pump

The rotary vane pump starts first to remove the majority of air inside the transformer tank. This initial evacuation rapidly lowers the internal pressure and prepares the system for deep vacuum operation.

Step 3 – Activate the Roots Booster Pump

Once the required pre-vacuum level is reached, the Roots booster pump automatically starts. Working together with the rotary vane pump, it dramatically increases pumping speed and enables the system to reach a much lower ultimate vacuum within a shorter period.

Step 4 – Achieve the Required High Vacuum

The PLC continuously monitors the vacuum level using precision vacuum gauges. During this stage, residual moisture, oxygen, and dissolved gases are extracted from the transformer tank, windings, and cellulose insulation until the specified vacuum level is achieved.

Step 5 – Perform Vacuum Oil Filling

After the target vacuum is reached, degassed transformer insulating oil is introduced into the transformer while the vacuum is maintained. Vacuum oil filling allows the oil to completely impregnate the insulation, eliminating trapped air and ensuring uniform insulation throughout the transformer.

Step 6 – Maintain Vacuum and Complete Commissioning

Following oil filling, the transformer remains under vacuum for a specified holding period to stabilize internal pressure and verify system integrity. Once all vacuum and pressure requirements are satisfied, the transformer is ready for electrical testing, commissioning, and long-term operation.

Vacuum Pumping System vs. Transformer Oil Purifier

Although a Transformer Vacuum Pumping System and a Transformer Oil Purifier are both essential transformer maintenance equipment, they serve different purposes. A vacuum pumping system evacuates air, moisture, and gases from the transformer tank before oil filling or commissioning, while an oil purifier restores the quality of insulating oil by removing water, dissolved gases, and solid contaminants during operation or maintenance.

Understanding the difference between these two systems helps engineers and maintenance teams select the right equipment for each stage of a transformer’s lifecycle.

Transformer Vacuum Pumping System	Transformer Oil Purifier
Removes air, moisture, and gases from the transformer tank	Removes moisture, dissolved gases, and particles from transformer oil
Creates a high vacuum for transformer drying	Purifies and regenerates insulating oil
Used before vacuum oil filling and transformer commissioning	Used during routine maintenance and transformer servicing
Treats the internal transformer environment	Treats the transformer insulating oil
Protects cellulose insulation before energization	Restores oil dielectric strength and extends oil service life
Commonly used for new transformer installation and major overhauls	Commonly used for preventive maintenance and in-service transformers

Which One Do You Need?

The answer depends on your application. If you are installing a new transformer, replacing windings, or carrying out a major overhaul, a Transformer Vacuum Pumping System is required to achieve the deep vacuum necessary before vacuum oil filling. If your transformer is already in service and the insulating oil contains moisture, dissolved gases, or contaminants, a Transformer Oil Purifier is the appropriate solution to restore oil quality without replacing the oil.

Many Projects Use Both Systems Together

In transformer manufacturing plants, substations, and power plants, these two systems are often used together to achieve the best maintenance results. The vacuum pumping system first evacuates the transformer tank and insulation, creating the required high vacuum. Degassed and purified transformer oil is then processed by the Transformer Oil Purifier before being injected under vacuum. For projects requiring exceptionally dry insulation, a Dry Air Generator can also be used after maintenance to supply clean, low-dew-point dry air, preventing moisture from re-entering the transformer during assembly or shutdown.

Technical Standards and Compliance

YUNENG Transformer Vacuum Pumping Systems are designed to support transformer manufacturing, installation, commissioning, and maintenance in accordance with internationally recognized industry standards. The following standards are commonly referenced for transformer vacuum drying, oil filling, quality management, and equipment safety.

Transformer Vacuum Pumping Systems – Standards Compliance

Standard	Standard Title & Scope	Specific Technical Requirements & Parameters	Application to Vacuum Systems
IEC 60076	Power Transformers (Parts 1–22)	Defines general requirements, insulation levels, dielectric tests, and temperature rise limits. Specifies permissible moisture limits in solid insulation (< 0.5%) and oil (< 10 ppm).	Governs the allowable residual moisture and vacuum drying endpoints required to meet transformer dielectric design criteria.
IEC 60422	Mineral insulating oils in electrical equipment – Supervision and maintenance	Provides guidelines for handling, conditioning, and testing of insulating liquids. Sets maximum allowable water content limits in service (≤ 3 to 30 ppm depending on voltage class) and breakdown voltage thresholds.	Directs vacuum system oil-degassing and dehydration performance parameters during transformer oil processing and maintenance.
IEEE C57	IEEE Power and Distribution Transformer Standards (e.g., C57.12.00, C57.637)	Establishes North American standards for liquid-immersed transformers, guide for reclamation of mineral insulating oil, and vacuum-degassing procedures. Recommends vacuum levels of < 1 Torr (133 Pa) or lower during processing.	Ensures compliance with North American utility practices, system pressure metrics, leak-rate testing (< 0.1%/hour of test volume), and safety margins.
ISO 9001	Quality Management Systems – Requirements	Mandates a robust quality management framework covering design, manufacturing, factory acceptance testing (FAT), calibration control, and traceability of components.	Ensures consistency, reliability, and precision calibration of vacuum gauges, sensors, pumps, and valves used in the pumping system.
CE Mark	European Conformity Directives (Machinery, EMC, LVD)	Compliance with Machinery Directive (2006/42/EC), Low Voltage Directive (2014/35/EU), and Electromagnetic Compatibility Directive (2014/30/EU). Mandates fail-safe interlocks, emergency stops, and IP protection ratings (≥ IP54).	Mandatory certification for commercial deployment in the European Economic Area, guaranteeing electrical safety, mechanical safety, and EMC immunity.

Transformer Vacuum Pumping Systems – Engineering Specifications

Parameter Category	Engineering Specification / Limit	Testing & Verification Method
Ultimate Vacuum Pressure	P ≤ 1 Pa (with Roots-Rotary Piston/Screw combination)	Pirani vacuum meter measured at cold trap inlet.
Pumping Speed	Nominal displacement rate matching transformer volume (e.g., 250 m³/h to 4000 m³/h)	Volumetric flow rate test per PNEUROP / ISO standards.
Electrical & Control	PLC-controlled automation (Siemens, HMI touch screen, automatic pressure regulation, phase failure protection	Functional loop testing, insulation resistance test (≥ 20 MΩ), high-voltage withstand test (2.5 kV, 1 min).

Frequently Asked Questions about Vacuum Pumping Systems