Introduction to Transformer Moisture Absorbers

• core functionality: Isolates and removes moisture and impurities from the air entering the transformer oil conservator to maintain the high dielectric strength of the insulating oil and to slow down the aging process of the solid insulating material.

• Working Principle: Utilizes the "breathing" effect produced by the thermal expansion and contraction of the insulating oil inside the transformer due to changes in operating conditions and ambient temperature. Moisture absorber in the transformer "inhalation" when the incoming gas for efficient drying and filtration.

• Key Components: It consists mainly of a desiccant (usually color-changing silica gel) and an oil seal for filtering impurities.

• technological evolution: From the traditional humidity absorber that relies on manual inspection and regular replacement of desiccant, it has developed into an intelligent and maintenance-free humidity absorber with on-line monitoring, automatic heating and regeneration, and remote communication functions.

• applied valueAs a basic protection accessory to ensure long-term safe and reliable operation of the transformer, its performance status directly affects the insulation level and overall service life of the transformer.

I. Physical mechanism and hazards of transformer respiration

Oil-immersed power transformers with oil conservator tanks are not completely insulated from the atmosphere. Insulating oil, as a liquid, changes its volume significantly with temperature:

• Expansion process (exhalation): When the transformer load rises or the ambient temperature rises, the oil temperature increases and the volume expands, causing the oil level in the oil conservator to rise, and the gas above the cabinet to be squeezed and discharged through the moisture absorber.

• Contraction process (inhalation): When the load decreases or the ambient temperature drops, the oil temperature decreases, the volume shrinks, the oil level in the oil conservator decreases, and a negative pressure is formed inside, so that the outside air is sucked in through the hygroscope in order to balance the pressure difference between inside and outside.

This periodic gas exchange process is known as the "respiration" of the transformer. Without effective protection, moisture and suspended particulate matter contained in the inhaled air will directly enter the oil conservator and eventually penetrate into the insulating oil of the transformer body. The presence of moisture will sharply reduce the breakdown voltage of the insulating oil, and is the main catalyst to accelerate the hydrolysis of cellulose insulating paper aging; and solid particulate impurities may form conductive paths in the strong electric field, triggering internal discharge. Therefore, it is crucial to dry and purify the inhaled air.

II. Traditional Silicone Moisture Absorber

Conventional hygroscopes are the most widely used basic protection devices and are relatively simple in structure and principle.

1. Structural components.

• casings: Transparent glass or high-strength polycarbonate materials are usually used to facilitate external observation of the state of the silicone inside.

• desiccant:: Internally filled with highly effective moisture-absorbing materials -Color Changing SiliconeThe

  • Cobalt-free and environmentally friendly (mainstream): Orange color when dry, gradually turns to dark green when saturated with moisture.

  • Cobalt-containing (phased out): Blue when dry, turns pink when saturated with moisture.

• oil seal: An oil cup is provided at the bottom of the unit, which is filled with an appropriate amount of insulating oil to form an oil seal.

2. Workflow.
During "suction", the outside air first passes through the oil seal at the bottom. The oil seal can effectively filter most of the dust and solid impurities in the air. Subsequently, the air enters the shell upwards and passes through the silica gel desiccant layer, where the water molecules in the air are physically adsorbed by the porous structure of the silica gel, thus realizing dryness. Finally, the clean, dry air enters the transformer oil conservator.

Intelligent maintenance-free moisture absorber

Traditional moisture absorbers rely on manual periodic inspections and maintenance, with the risk of untimely maintenance leading to protection failure. Intelligent, maintenance-free moisture absorbers achieve automated operation by integrating sensors, controllers and regeneration systems.

1. Principles of operation.
The heart of the device is the "online monitoring and automatic regeneration" cycle.

• Online monitoring: Built-in high-precision humidity sensor to measure in real time the relative humidity of the air that has been dried and processed in preparation for entering the oil conservator.

• intelligent control: When the controller monitors that the humidity of the outlet air exceeds the preset safety threshold (indicating a decrease in the moisture absorption capacity of the silica gel), the regeneration process is automatically initiated.

• auto-regeneration: The controller activates an internal electrical heating system (e.g. PTC heater) to heat the moisture-saturated silica gel. Under the effect of high temperature, the moisture adsorbed in the silica gel is evaporated and expelled to the atmosphere. Once regeneration is complete, the silica gel regains its dryness and moisture absorption capacity.

• Bypass and Isolation: During regeneration, an internal valve system ensures that water vapor from heating is vented to the outside world and does not enter the transformer. At the same time, the transformer can still breathe normally through a spare drying chamber or bypass channel.

• telecommunication: The device is usually configured with RS-485 or Ethernet interface, which can upload the operation status, humidity data, and alarm information to the substation automation system to realize remote monitoring under unattended operation.

IV. Comparison of technical performance

Frequently Asked Questions (FAQ)

1. How can I tell when the silicone in a conventional humidifier needs to be replaced?
Usually, when more than 2/3 of the volume of silica gel in the moisture absorber changes from dry color (orange) to saturated color (dark green), it indicates that its moisture absorption capacity has been significantly reduced, and it should be immediately arranged for replacement or offline drying and regeneration of silica gel.

2. What is the purpose of the oil cup at the bottom of the dehumidifier? What are the oil level requirements?
The oil cup has two main functions: one is to carry out preliminary filtration of the inhaled air to remove dust and other particulate impurities; the other is to form an oil seal to prevent direct and continuous contact between the silica gel and the external atmosphere and slow down the speed of its natural moisture. The oil level should be kept between the graduation lines marked on the oil cup, too low will lose the filtering and sealing effect, too high may suck the oil into the desiccant cavity when a large amount of air is inhaled.

3. Why is blue silicone being phased out?
Conventional blue silica gel uses cobalt chloride as a color developer. Cobalt chloride has been shown to be potentially harmful to the environment and human health. Therefore, for environmental and occupational health and safety reasons, there has been a complete shift to the use of cobalt-free orange silicone.

4. Do all oil-immersed transformers have moisture absorbers installed?
No. Only transformers with oil storage cabinets need to be fitted with moisture absorbers. And the fully sealed structure of the transformer (such as the use of corrugated oil tank or built-in nitrogen bladder) its internal and atmospheric isolation, through the tank's own elastic deformation to compensate for the volume change of the oil, so there is no need for moisture absorber.