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Power Transformers

Online Monitoring of Hydrogen and Moisture in ​Oil of Power Transformers

Power transformers are critical components in any electricity grid. Age, increased load levels, and network failures all take their toll on transformers, leading to an increased risk of unpredictable faults and outages.

Online and real-time condition monitoring of power transformers can keep them operating safely and with maximum efficiency, while supporting the planning of timely maintenance actions that can extend operational lifetime and prevent unexpected and costly outages.

  • Moisture reduces the insulating properties of transformer oil, resulting in more rapid aging of the transformer. Traditionally, oil moisture readings have been taken at periodic intervals. However, because moisture levels can change rapidly, periodic sampling is not sufficient.
  • Hydrogen levels in transformer oil indicate the existence of a fault and the rate of change in these levels can be used to determine its severity.

The Vaisala HUMICAP® Moisture and Temperature Transmitter Series for Oil, MMT330, accurately measures online the moisture in transformer oil, giving a real-time picture of the oil's condition, an indicator of how well the transformer is operating. The transmitter monitors the moisture levels at all ambient and operating conditions and is compatible with any insulating oil. The measurement can be connected to the substation data-collection system directly. For temporary spot-checks we recommend the lightweight Vaisala HUMICAP® Hand-held Moisture Meter for Oil MM70.

The Vaisala Moisture, Hydrogen, and Temperature Transmitter MHT410 provides reliable monitoring of insulating oil in power transformers. Unlike conventional solutions, the MHT410 sensors take measurements directly from representative oil in order to provide reliable trend data. Using non-membrane hydrogen technology, the MHT410 can handle under pressure and overpressure conditions, and never depletes. The transmitter can be installed in minutes by a single person, and its robust design – with no pumps, hoses, or valves – ensures long-term stability.    

Vaisala HUMICAP® sensors are the first ever sensors that can measure moisture in oil online. Vaisala has over 15 years of experience monitoring transformer oil moisture in thousands of transformers around the world. Industry leaders in over 30 countries use Vaisala equipment for online monitoring of transformer oil.

Measuring the Dew Point During Insulation Drying

When building a new transformer or overhauling an existing unit, the cellulose insulation is dried by applying heat and a vacuum. After drying, the tank is purged with dry nitrogen. Measuring the dew point is a widely used method for monitoring the drying process and confirming the final dryness after the nitrogen purge.

Vaisala offers both fixed and portable dew-point instruments that offer fast response time, enabling quick and reliable verification that acceptable moisture levels have been achieved.

Transformer oil testing: online monitoring of transformer oil with moisture and temperature transmitters from Vaisala

Transformer Oil Moisture Monitoring 


New product: MHT410 Moisture, Hydrogen, and Temperature Transmitter for Online Transformer Condition Monitoring 

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