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Power Transformers

Online Monitoring of Moisture in Power Transformers

​Moisture reduces the insulating properties of transformer oil and quickens the ageing of the transformer. Traditionally oil moisture readings have been checked at periodic intervals. However, moisture levels can change rapidly rendering periodic sampling methods insufficient. To protect the transformer, timely and cost-efficient maintenance needs to be ensured with a permanently online monitoring system.

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 long-term stability is ensured by the Vaisala-designed HUMICAP® sensor, the first sensor ever to measure moisture in oil online. Today, Vaisala has 15 years of experience monitoring transformer oil moisture in thousands of transformers world-wide. Industry-leading customers in over 30 countries use Vaisala's equipment to monitor moisture in transformers online.

Measuring the Dew point during Insulation Drying

When building a new transformer or overhauling an installed transformer the cellulose insulation is dried by applying heat and a vacuum to remove water. After the drying procedure the tank is purged with dry nitrogen. Measuring the dew point is a widely used method of 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 


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