Online Transformer Drying Solution


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    Every oil insulated transformer is facing the problem of moisture and oxygen upbuilding and insulation deterioration. This process leads to transformer life expectancy reduction. Also, wet transformers are becoming the source of failure risk because of insulating capacity reduction. To address this problem, Streamer introduced innovative online dehumidifying system TRANSEC.

    TRANSEC key features

    • Increase of oil transformer life expectancy over 30%
    • Decrease of transformer outage and accidents risks
    • Universal solution for all transformers. There is no upper limit of transformer parameters.
    • Maintenance without shutdown. Online drying solution keeps system dry without it’s outage for maintenance.
    • Smart monitoring of moisture level in oil and current status of the system
    • Stand-alone unit with low-voltage power supply.
    • Long life of the filters: up to 60 months (5 years) of operation on new dry transformers or up to 24 months on very wet transformers.
    • Easy installation: just 5 – 6 hours and two specialists needed. Transformer keeps running all the time.
    • Easy cylinder regeneration. Used filtering cylinders can be shipped back to us, and we’ll regenerate those.
    • Minimal service. Device needs about 30 minutes every 6 – 60 month to replace used filters. That’s all.

    How does TRANSEC works?

    The goal is to reduce moisture level in oil and paper used in transformer insulation.

    To reach this goal, device works this way:

    • Filtering system cuts in into transformer oil circuit by two pipes connected to upper and lower parts of transformer housing. As long as system connected by pipes, it can be easily positioned somewhere near the transformer.
    • Electric pump starts to circulate the oil, passing it through the array of filters.
    • Filtering cylinders are filled with zeolite ­– water absorbing material used to dehumidify oil. Also oil passes through deaerator. So after passing the cylinder oil comes back to the transformer cleaned from oxygen and water.
    • Before oil is getting inside the transformer it goes through additional filters designed to remove particles and impurities.
    • Dry oil is able to remove some moisture from insulation paper (about 2% of its volume) and this moisture again comes out from the device to filter.
    • Cycle after cycle water is being removed from insulation paper while transformer keeps running.

    So we get a results:

    • Protection from moisture buildup in new transformers. Installing a new transformer? We recommend to protect it with TRANSEC at once!
    • Increase of life expectancy and reduction of moisture in wet transformers.

    Filtering cylinder replacement and regeneration

    The principle of filtration implies saturation of the filters with water. Zeolites are being saturated, and filter capacity to remove water from oil deteriorates with time. To control this process system is equipped with monitoring system measuring moisture levels. When filter needs replacement, inbuilt monitor will notify about it.

    The procedure of filtering cylinders’ replacement takes up to 30 minutes and doesn’t require to shut down the transformer. Used cylinders can be shipped back to us in order to be regenerated. We will refill those filters with zeolites and remove moisture from them.


    TRANSEC is a system to dry Power Transformers of all sizes. The Problem of wet Transformer is already well known. Due to moisture and oxygen, the insulation paper within the Transformer degenerates. One of the products of this chemical process is H O. While only a small part 2 of the moisture is absorbed by the Transformer oil, more than 95% of the moisture becomes diffused in the tons of insulation paper. Depending on the percentage of moisture, the aging of the Transformer increases and failures such as flashovers between the windings, treeing, and creeping discharges occur. Temperature changes of the oil 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 and returns back again to the unit. Using this cycle effect, TRANSEC keep the insulation paper permanently dry, ensure 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 to transport or switch it off.

    Operational Principle

    TRANSEC is an online drying sieves. The unit consists of an electrical pump, special water absorber cylinders and measuring sensors to monitor the amount of removed water. The System can either be mounted directly on a Power Transformer or can be installed next to it. Two pipes are connected to the upper and lower part of the Transformer body. After the unit is installed and switched on, the pump continuously cycles the transformer oil through the cylinders. Within the cylinders, water absorbing material removes the moisture from the oil. After this process, the oil goes through a particle filter to ensure its cleanliness before it returns back to the Transformer. An inbuilt deaerator insures, that no air will enter the tank. Every TRANSEC unit includes sample / measuring points at the inlet and outlet (to check the moisture content in the oil). An additional prefilter and a monitoring system can be added to the unit as an option.

    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.



    • high capacity for moisture extraction (12 litre)
    • for transformer >10 MVA
    • long operation duration without maintenance
    • in frame or in cabinet
    • measuring and monitoring module available


    • low weight, easy to move
    • for transformer <10 MVA
    • cost effective and flexible to operate on different transformer
    • measuring and monitoring module available

    Optional accessories


    • LCD Display with Oil Temp, ppm INPUT and ppm OUTPUT
    • Analogue Output 0-20mA or 4-20mA for SCADA
    • Alarm on minimum pump current
    • Pump overload protection


    • For heavy sludged transformer
    • Filters coarse particles from the oil
    • Prevent obstruction of the cylinders


    • Protect the unit against outer influence (water, dust etc.)
    • Prevent damages due to vandalism
    • Made of stainless steal or aluminum

    Slam Shut Valve

    • Additional safety
    • Prevent oil leakage in case of pipe damage

    Cylinder regeneration

    When TRANSEC is retrofitted on an existing transformer with high percentage of moisture (>2% of moisture in paper), the filter-cylinders will extract their maximum capacity within 6 to 24 months depending of moisture level at installation date, of the transformer load and temperature. The filter-cylinders will have then to be replaced and a new cycle of filtration will start. The following regenerations will happen after a longer period of filtration as the overall moisture level in the transformer has decreased.

    On a new or very dry transformer (<1% of moisture in paper) the filtration time will be longer (at least a couples of years) before the filter-cylinders are saturated.

    Saturated cylinders can easily be identified by using the inbuilt measuring module or by measuring manually on the in- and output of TRANSEC. If the proportion of the water in the oil remains the same, the filter needs to be changed.

    The replacement of the Filter-Cylinders can be done on the installed device. Two valves, on the income and the outcome of TRANSEC need to be closed and the remained oil needs to be caught. The cylinders can directly be replaced by new types while the saturated cylinders can be shipped back to TRANSEC for the regeneration process.

    This operation takes approx. 30 min per cylinder and can be done while the Transformer is running and operational.