What Vacuum Level Should a Transformer Oil Purifier Achieve?

The vacuum level is one of the most critical performance indicators of a vacuum oil purifier—especially for transformer oil dehydration and degassing. Vacuum can be expressed in several ways, and understanding these values can help you evaluate equipment quality more accurately.

1. Absolute Pressure (Most Common and Most Accurate)

The ultimate vacuum of an oil purifier is typically expressed in absolute pressure, measured in Pa (Pascal) or mbar (millibar). This value directly reflects how effectively the system can remove water and gases from transformer oil.

Typical Absolute Pressure Ranges

Standard / Economy Vacuum Oil Purifiers:

1000–500 Pa (10–5 mbar)

High-Efficiency Dual-Stage Vacuum Oil Purifiers

Common for transformer oil processing:

100–20 Pa (1–0.2 mbar)

High-Performance Deep Dehydration Units

Used for UHV transformers, new-oil preparation, or demanding applications:

<10 Pa (e.g., 5 Pa or 2 Pa)

These values directly answer questions such as: "What vacuum level can the oil purifier achieve?"

2. Relative Vacuum (“Negative Pressure” Reading)

In field operation, vacuum is sometimes expressed as relative vacuum, e.g., MPa or % vacuum.

Examples:

–0.099 MPa

“99% vacuum”

These readings correspond roughly to ~1000 Pa (10 mbar) absolute pressure.

However, this method is less accurate because atmospheric pressure varies by altitude and weather.

3. What Affects the Achievable Vacuum Level?

Several factors influence the vacuum value you see during operation:

✓ Vacuum Pump & System Performance

Type of pump (rotary vane, Roots pump), sealing quality, and condenser efficiency all affect the final vacuum level.

✓ Oil Condition

Water and gas released from oil under vacuum will temporarily reduce vacuum until removed.

✓ Operating Temperature

Heating oil to 50–65°C reduces the water's boiling point and allows the vacuum system to work more efficiently.

✓ System Leakage

Even tiny leaks in valves, seals, or pipelines can prevent the purifier from reaching high vacuum.

4. How to Check Your Oil Purifier’s Vacuum Level

A. Equipment Nameplate / Manual

Look for terms like “ultimate vacuum”or“working vacuum.” These are the most reliable factory specifications.

B. Vacuum Gauge Readings

Absolute pressure gauge:

Shows direct values such as Pa or mbar.

Negative pressure gauge:

Shows 0 to –0.1 MPa.

The closer to –0.1 MPa, the higher the vacuum (lower absolute pressure).

5. Recommended Vacuum Levels for Transformer Oil Treatment

For typical transformer oil dehydration and degassing:

50–200 Pa absolute pressure

→ Ideal for removing water to <10 ppm and gas content to <0.5%.

A well-maintained dual-stage high-vacuum oil purifier should stably achieve:

<100 Pa (1 mbar) during normal operation

20 Pa or lower for deep treatment applications

Conclusion

A high-quality transformer oil purifier must deliver a stable and deep vacuum to achieve effective dehydration and degassing. Understanding how vacuum is expressed—absolute pressure, relative vacuum, and influencing factors—helps ensure your equipment meets industry standards and application requirements.

Note: The above technical information is based on general industry knowledge and cannot ｒｅｐｌａｃｅ your equipment's official technical manual or the measurement results of a professional engineer. Please refer to your equipment's instruction manual or actual measurement results for the final parameters.