Online Moisture monitoring & drying solutions for oil insulated transformers


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  • Increases life expectancy of transformers by drying the insulation
  • Maintain a safe and high breakdown voltage in oil
  • Online installation & operation – no shutdown
  • Cost effective solution – 24/7 continuous drying and monitoring
  • No operator required. Stand alone unit LV powered
  • Function

    TRANSEC is a system to monitor and extract the moisture in power transformers of all sizes. The problem of wet transformer is already well known. Due to high temperatures, moisture and oxygen, the insulation paper within the transformer is degrading. One of the by-products resulting from this chemical reaction is molecules of water (H2O). While only a small part of the moisture is dissolved in the transformer oil, more than 98% of the moisture becomes diffused in the tons of insulation paper. Depending on the percentage of moisture, the aging of the transformer increases faster and the breakdown voltage decreases. This can lead to failures such as flashovers between the windings. Oil temperature changes during the operation even increase the risk of an outage.

    Once the oil in the transformer gets dried by TRANSEC, it dehumidifies the insulation paper, hence slowing the aging process. Using this cycle effect, TRANSEC keeps the oil and the insulation paper permanently dry, ensures a faultless operation, and elongates the life expectancy of the transformer significantly. Comparing to other solutions, the transformer can be dried during its operation. There is no need for a maintenance outage.

    Operational Principle

    TRANSEC extracts moisture from the oil thanks to molecular sieves. An electrical pump circulates the transformer oil through the 3 TRANSEC cylinders containing a large amount of these molecular sieves. The molecules of water dissolved in the oil will remain in the TRANSEC cylinders. Two moisture and temperature sensors are placed at the beginning and end of the system in order to monitor the moisture level of the transformer and to control a proper filtration process. Oil particles filtration and air bubble removal is also ensured during this cycle.

    TRANSEC can either be mounted directly on the power transformer or can be installed on a stand-alone frame next to it. Two pipes are connected to the upper and lower valves of the transformer. Every TRANSEC unit includes sample/measuring points at the inlet and outlet.

    Technical characteristics



    in Frame

    in Cabinet

    In Frame

    Weight, kg




    Dimension (HxWxD), mm





    304 grade stainless steel

    Environmental Condition

    0°C to + 90°C

    Water capacity, litre

    3 x 4 = 12


    Transformer size

    > 10 MVA

    < 10 MVA

    Protection class of cabinet/frame

    Designed to comply with IP64 (in frame) / IP65 (in enclosure)

    Installation time, h

    5–6 (with two specialists)

    Max oil temp, C


    Pump capacity, l/hr


    Electrical supply for pump

    240V; 50Hz; 0.27kW / (120V; 60Hz - possible)


    Stainless steel pipes bent on site or hydraulic flexible pipes;

    Flange adaptors, non-return valves and bleed valve

    Modules (optional)

    Output : Analogue 0-20mA or 4-20mA for SCADA

    Temperature and Moisture probes at inlet and outlet with local LCD display

    Monitoring for ppm and temperature.

    IEC61850 SCADA integration via Ethernet or fibre optic

    Type Test

    System pressurised to 3 bar for 1 hour at 110ºC (pump not running) to prove leak free

    Routine Test

    Each unit is tested pressurised to 2 bar for 30 minutes at 60ºC to prove leak free.

    Product Selection guide


    Optional accessories

    Monitoring cabinet


    • Continuous monitoring of PPM, oil Temperature and % Relative Saturation at inlet and outlet
    • Analog outputs, ethernet or fibre optic communication
    • IEC 61850 compatible



    An additional pre-filter can be installed in case of a heavy-sludge transformer to extract solid impurities from the transformer oil before entering to the cylinder sieves.



    In the requirement of special protection and aesthetics, a metal enclosure made of either Aluminium or Stainless steel can be installed to cover the unit.

    What to do when the moisture extraction cylinders are saturated? 

    The first thing to do is to contact your local representative of Streamer Electric AG. Streamer make an effort to find companies close to you in order to support you efficiently. Local representatives are hold a stock of ready cylinders which they can provide to you.

    TRANSEC units can typically extract between 3 to 4 liters of water per cylinder before saturation. The rate of extraction is directly linked to the amount of water available in the transformer. The higher moisture content and the warmer the oil is, the faster the extraction will be. You can find typical saturation time below.

    The cylinder saturation can be determined either by the TRANSEC monitoring system or by comparing water PPM in 2 oil samples (inlet & outlet).

    A set of saturated cylinders can be removed and replaced while the transformer is online by new cylinders within 30 min. 


      Typical time for extraction of 10 litres of water 

    New transformer water content <1% 

     5 years
     Old/Wet transformer water content >3%  6-12 months
     Moderately wet transformer water content = 2% 2 years 

    More than 15 years of successful experience 

    A TRANSEC unit was installed in November 2017 on 40 MVA General Electric 3 phases transformers in the Dammam region, Saudi Arabia. This 115kV/13.2kV transformer from the 1970s had reached a very high water content in paper (above 5%) and needed urgent drying. 

    Once installed the TRANSEC started removing moisture from the oil immediately. It provided a positive effect on the breakdown voltage value. In a second step water started to get extracted from the paper as the oil got dried out after a few weeks. 

    Over the 1st year, you can see on the 2 graphs that the PPM inflow and the water content are dropping. 

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    Within that year the water content in paper went from 5% to about 3% (much more acceptable level). We can also see that during the second year of operation the PPM values of inflow and outflow were almost matching which is a sign of water saturation in the Transec unit. This is confirmed by the water content increasing again to 4% at the end of the second year. The saturated TRANSEC extraction cylinders are then replaced by new ones in order to restart the filtering process. 

    They had extracted about 12 litres of water from that transformer within 1 year.


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