Monitoring moisture in oil

Moisture in transformers Q&A eBook

The definitive eBook on the subject, this companion to our renowned webinar series is full of the latest practical and scientific advice on measuring moisture in power transformers. Filled with your actual questions answered by Vaisala's experts, this nearly 40-page eBook is a versatile manual for anyone whose business it is to maintain guard against and understand the effects of moisture in power transformers.

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Your key benefits for transformers

Real-time measurement of relative saturation (%RS) e.g. for dielectric strength monitoring

  • Real Time PPM output for absolute moisture measurement in transformer oils
  • Excellent long-term stability
  • Highly selective to water molecules
  • Insensitive to additives or contaminants in oil

Picture: Effect of relative moisture saturation (%RS) on dielectric strength of transformer insulation oils. 

Your key benefits for lubrication

  • Real time relative saturation measurement helps plan maintenance advance and minimize unplanned maintenance
  • Real-time measurement helps minimize damage to critical machinery and also to optimize dryer usage 
  • Excellent long term stability ensures a trouble free operation and reliability of readings. 
  • Insensitive to additives and contaminants ensures suitability for numerous lubrication oil applications.

Get all the gains

Robust reliability


Accurate water saturation and PPM measurements in rapidly changing conditions.

All equipment comes with NIST or Accredited calibration and is field calibratable.

No moving parts in transmitters.


Long-term stability


Thin film polymer sensor designs protect from contamination and are highly selective to water  only .

Capacitive technology provides long term stable measurement.

Insensitive to additives or contaminants in oil.

Auto-recovery from full saturation.


Rapid Response


In situ, real time measurement of moisture in oil as true relative saturation (%RS).

Eliminates need for sampling and lab analysis for moisture.

Easy installation via ball valve. 

Installable even in energized transformers.


Protect your machinery and minimize downtime

From power transformers to lubrication, and from maritime to pulp and paper Vaisala leads the leap into knowledge. With sensors built in our own cleanrooms, our robust technology offers long-term stable and precise measurements. 
Download our eBook and get a full overview of moisture in oil.

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Uniquely robust sensors

Vaisala’s HUMICAP® were the first ever capacitive sensors used to measure moisture in oil online, and have since become a virtual industry standard.

The sensors have specifically been developed to measure even very low moisture levels in oils — mineral, vegetable and synthetic. The HUMICAP® sensors, manufactured in Vaisala’s own cleanrooms, have seen use in all corners of the Earth and even Mars.

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What is water activity (aw)?

Water activity is the amount of water in a substance relative to the total amount of water it can hold. It is defined in our application note, which you can download from the link below.

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Insights, webinars and more


Practicalities of measuring moisture in transformers online

Vaisala's Senja Leivo and Riku Rantala go head to head to discuss practicalities and real-life lessons learned, tackle audience questions and offer highly valuable, directly applicable insights into measuring moisture in transformers.

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Expert Q&A: moisture in oil and transformers (ep. 3/3)

Take a deep dive into the latest industry insights, answer the most topical audience questions asked during the series and present some of our latest findings.

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Extra Q&A episode: moisture in transformers (ep. 4)

Entirely devoted to answering topical questions we have received throughout the series, this is a must-watch for all in the transformer industry.

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The art and practice of measuring moisture in oil (ep. 2/3)

In this second episode, we cover the more practical side of measuring moisture in oil and transformers, with practical, tried and tested tips.

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The science of moisture in transformers

In four episodes, you'll get a deep dive into both the science and practice of moisture in oil and measuring it, culminating in a two Expert Q&A sessions with your insights & questions answered by the experts.

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From the depths of space to the heart of your transformer — we lead the leap.

While one sensor is on Mars, its cousin is right here on Earth — taking its readings from the heart of your transformer.

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Customer case

Moisture management in power transformers

TRANSEC UK Ltd. provides first-rate on-line moisture management for oil-filled power transformers – with a little help from Vaisala’s online moisture and temperature monitoring.

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Your most pressing questions related to moisture in transformer oil

Vaisala power transformer monitoring experts, Senja Leivo and Steven Jiroutek answered the most pressing questions from the audience related to moisture in transformer oil in our Q&A webinar.

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Moisture in oil products

Power Industry Solutions

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Contact us

Interested to receive more information on a specific application or product? Drop us a line, and we'll get back to you!

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