Online Moisture monitoring & drying solutions for oil insulated transformers

TRANSEC - Moisture monitoring & drying

  • TRANSEC -  Moisture monitoring & drying
  • TRANSEC -  Moisture monitoring & drying
  • TRANSEC -  Moisture monitoring & drying
  • TRANSEC -  Moisture monitoring & drying
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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


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.

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1. Outflow to transformer
2. Deaerator
3. Outflow sample valve
4. Outflow PPM/Temp sensor
5. In-line particle filter
6. Intermediate air bleed valve
7. Quick release connection
8. Molecular Sieve removal cylinders
9. Optional moisture monitoring box
10. Outlet air bleed valve
11. Optional particle pre-filter
12. Inflow PPM/Temp sensor
13. Oil Flow indicator
14. Pump
15. Inflow sample valve
16. Inflow from transformer
17. Optional standing frame

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 

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