How you can achieve a permanently high dielectric strength, secure the filling volume in transformer pits and increase operational safety
CJC® Filter for transformers: longer service life for transformers and more automation
How you can achieve a permanently high dielectric strength, secure the filling volume in transformer pits and increase operational safety
CJC® Filter for transformers: longer service life for transformers and more automation
Challenge
The cellulose insulation of transformers is prone to molecular decay as a result of chemical ageing processes. This creates water in the cellulose insulation, which is released into the transformer oil where it can adsorb to suspended particles in the oil. Water molecules act as conductivity bridges, which reduces the dielectric strength and thus the operational reliability of the transformer. The risk of short circuits and partial discharges increases. The chemical ageing of the insulating oil also leads to deposits and an increase in acidity. Water, acids and oxygen are the primary accelerators for further ageing of the transformer insulation (oil and cellulose). Therefore, the aim of sustainable transformer maintenance should be the permanent and gentle drying of the cellulose insulation, as well as the continuous removal of water, suspended solids, ageing products and acids from the insulating oil. Oil changes and temporary oil drying only lead to a short-term improvement.
But also ensuring the functionality of transformer pits is one of the challenges. Water can accumulate in the oil catch basins due to rain and snow, which means that there is insufficient capacity in the event of an oil spill. The water must therefore be regularly removed from the basins and, if contaminated with oil, disposed of in accordance with environmental guidelines – typically creating high personnel costs and high disposal costs.
Consequences of water in the transformer insulation and the transformer pits
During the natural decomposition of the cellulose molecules (depolymerization), water molecules are released. The water collects in the windings of the transformer cores. The more water accumulates in the cellulose insulation, the faster the further decomposition of the cellulose molecules and the accumulation of water in the transformer insulation. Up to 100 times more water is retained in the cellulose insulation than is measured in the transformer oil:
Example. Transformer with 20 tons of oil weight and 40 ppm oil moisture (0.004 %):
- Only 0.8 liters of water is in the insulating oil
- approx. 100 liters is in the cellulose insulation
The diffusion of water molecules from the cellulose insulation to the surrounding oil takes a very long time and depends on where the water has formed and accumulated in the cellulose. When the water molecules diffuse from inside the cellulose insulation to the oil, the water has to diffuse in and out of numerous cellulose fibers and this process takes time. The rate of diffusion, i.e. the slow rate at which water comes out of the insulation, can be clearly seen in the diagram. In the example, a transformer weighing 20 tons of oil is continuously and gently dried with a CJC® filter (flow rate: 270 litres/hour). After 6 days, all the water has been removed from the cellulose insulation.
Water molecules act as conductive bridges in the insulating system of cellulose and oil, which reduces the dielectric strength of the transformer. If the water molecules diffuse into the transformer oil, they bind to suspended solids due to the polar attraction (e.g. cellulose fibers from the insulation). If the aggregate state of the water molecules changes to steam due to heat, the volume of the water molecules increases abruptly (steam = approx. 1000 times more volume than water), creating a gas channel. For this reason, fibers and suspended solids in the insulating oil increase the risk of short circuits and partial discharges.
Water, oxygen and heat accelerate the chemical ageing and decomposition of the transformer oil (oil ageing). As the oil ages, soft contaminants are formed which lead to sludge-like, sticky deposits (e.g. on the transformer cores) and the acid content in the insulating oil increases. The longer the oil is in use, the higher the oil temperature/operating temperature and the more contaminated the oil is (water, particles), the faster the acidity increases. A high acid content lowers the interfacial tension and increases the dielectric loss factor of the transformer oil.
Contamination in the insulating oil due to abrasion, e.g. from the slip rings, and oil ageing products not only reduce the insulation resistance, but also lead to deposits on the transformer cores and other oil-wetted components. Time-consuming cleaning work, frequent oil changes and downtimes are the result.
Discharging any oil-contaminated water into the environment or into the public sewage system is only permitted under strict environmental guidelines (oil content < 5 ppm). The SIPP™ Node is permanently installed at transformer stations and has been developed for the automatic, environmentally safe, quality-controlled and documented drainage of transformer pits. The SIPP™ Node makes economic and ecological sense: dewatering via the SIPP Node is possible in over 90% of cases.
Disadvantages of conventional methods
Discontinuous transformer drying and oil change:
Changing the oil only removes a fraction of the water, because most of the water inside a transformer is in the cellulose insulation (windings). In a transformer with, for example, 20 tons of oil weight and 40 ppm oil moisture, only 0.8 liters of water are retained in the insulating oil, but around 100 liters in the cellulose insulation. It is therefore crucial to dry the cellulose insulation and not just the oil.
An oil change due to a high level of contamination and/or acidity can also normally be avoided, as the oil can be treated with adequate fine filtration and can continuously used for many months and even years.
Vacuum drying:
Temporary vacuum drying has significant disadvantages in terms of time and costs. The drying process cannot usually be carried out on site. The costs and effort involved in transporting the transformer are enormous. The longer the drying process takes, the greater the increase in costs due to the resulting loss of use. Shorter drying processes, on the other hand, reduce efficiency: only the oil is dried, but not the cellulose insulation, as the water only diffuses slowly from the insulation into the oil.
In addition, the vacuum process puts a strain on the cellulose insulation, which is already affected by chemical ageing, as compression is reduced, which can damage the winding during further operation. The gas-in-oil analysis, which is crucial for assessing the functionality and safety of a running transformer, is also impaired by the vacuum process, as gases are removed, making it difficult to accurately assess the safety status.
Your solution: an efficient filter for transformers
Efficient filtration in transformer stations means, on the one hand, installing a system that gently and thoroughly dries the cellulose insulation of the transformer in continuous operation and simultaneously removes impurities, suspended solids and deposits from the oil, and on the other hand, installing a system that ensures the functionality of the oil catch basins — at all times. Fact is, only with efficient and proofed systems you …
Less oil consumption
Less maintenance
Higher reliability
Better protection of resources
CJC® Filter for transformers: more efficiency and automation
Does the dielectric strength and acid number of the insulating oil increase briefly after the transformer has dried? Do you frequently replace the oil and do deposits prolong the cleaning procedure during the revision? The cost of emptying the collection basins is disproportionately high? Then the CJC® Transformer Oil Filter and the SIPP™ Node are exactly the right solution for your transformer stations.
The transformer oil filter ensures continuous drying of the cellulose insulation and maintenance of the insulating oil, and the SIPP™ Node ensures the automated drainage of water from the catch basins. Everything can be documented using the integrated sensor technology. Both solutions impress with their innovative approaches and high separation efficiency and precision.
The CJC® Transformer Oil Filter is a stationary drying system that is permanently installed on your transformer and is designed for continuous operation on the running transformer (24/7/365). This means that transformers can be dried without any loss of use or transportation costs. In addition, the cellulose insulation is given the necessary time to release the retained water into the insulating oil — this process is not only thorough, but also gentle.
The pump of the CJC® Transformer Oil Filter draws in the humid, contaminated transformer oil and passes it through one to three filter housings. The integrated CJC® Fine and Depth Filter Insert removes water, suspended solids, oil ageing products and acids from the oil. Dried and cleaned the insulating oil is lead back to the transformer.
Two sensors in the filter inlet and outlet measure the water content in the oil during operation. The difference between the measured values indicates the quantity of the removed water. A necessary filter replacement of the filter insert is indicated on the PLC display.
The CJC® Filter for transformers removes all impurities:
Water
Reduce water content to < 10 ppm.
Oil ageing products
Remove soft contaminants before they deposit
Stabilize the oxidation rate
Particles / suspended solids
Achieve cleanliness classes up to ISO 12 (ISO 4406).
Acids
Absorb / neutralize and prevent acids for a permanently stable acid number (TAN).
CJC® Fine Filter Inserts are depth filters with a filtration degree of 3 µm absolute and a retention rate of < 1 µm. The whole volume of the insert is made of finely ramified fibres that offer an outer and, in addtion, an inner surface — from 120 to 150 m² per gram. That enables the extremely high dirt holding capacity — the higher, the longer the lifetime of the filter insert.
Fact is, our dirt holding capacity is the market leader.
Contact your regional contact now
Let’s talk: about your transformer pit, your transformers and catch basins and the specific challenges. We ensure optimum drying and maintenance of transformer oil and enable the automated, environmentally safe draining of water from transformer pits. Together with you we maximize the service life of your insulating oils and transformers and increase the automation level of your processes.
Receive a personal consultation and a non-binding offer for a CJC® Transformer Oil Filter and a SIPP™ Node.
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That say our customers
” […] SIPP has the necessary technical approvals, while the company has the capacity and expertise to adapt and develop the system to meet different needs. The SIPP Node also gives us the necessary freedom to use our employees for complex tasks that cannot be automated. Using the SIPP Node also gives us greater and consistent accuracy in sampling the collected water, which helps us achieve our high environmental protection requirements. The basic prerequisite remains that the approval authorities agree to its use. This in turn depends on the legal framework and applicable limits.”
“The biggest advantage is that we now have an automated monitoring system, which in practice means that we no longer have to think much about measuring and emptying our transformer pits. Instead of regularly sending out an electrician to monitor the transformer pits, we now have full control at each time. Occasionally, the filters and measuring cells have to be changed, but otherwise most of it is automatic.”