On-line cleaning of trans.former oil boosts reliability, dielectric properties

June 24, 2008 at 7:08 am | Posted in Power Plant | Leave a comment
A technology called balanced-charge agglomeration (BCA) has proven its ability to restore oil to cleaner-than-new conditions in a variety of applications. BCA accelerates particulate agglomeration and removal of sub-micron material, eliminates the water-holding particles upon which emulsions form, and allows for faster and more complete water removal.

Oil condition data published in 2001 makes reference to the first application of this technology on steam-turbine lube oil. The research trial ran for more than five years and concluded that the lube oil tested at 16 times cleaner than new oil specifications (Figure 1). The technique essentially supercharges the filtration process by electronically removing sub-micron material and products of oxidation together, for removal by standard and proprietary filters.

1. Close-up of a compressor bearing

The balanced-charge agglomeration process, which removes sub-micron contamination, has proved its ability to restore lubricating oil in rotating machinery. The on-line cleaning process is now applied to transformer fluids to boost dielectric resistance.

Source: ISOPur Fluid Technology

This process also can be applied to high-voltage transformer fluid, where it can increase the dielectric resistance of insulating fluids to better-than-new standards. In fact, recent studies suggest that particulate contamination may be as significant as water contamination in reducing the reliability of transformers and tap changers. As effective as water removal is in improving electrical resistance, removing these fine particles boosts dielectric strength even higher and blocks the pre-varnish discoloration that often is seen forming in tap-changer oil and on the contacts. During a typical on-line clean-up cycle, transformer oil was restored from 20 kV to 75 kV, preventing transformer downtime and improving equipment performance.

During a typical clean-up of transformer fluid for an industrial environment, particle count was reduced to such a low level that the dielectric strength was improved from 35 to 90 kV. This increase in kV resistance is much better than new oil specs, with the net result that the useful life of the oil is dramatically extended. Using a combination of the fluid technology process to remove sub-micron material together with a vacuum distillation process to reduce water contents to below 10 ppm and gas to less than 0.08% by volume results in fluid that has the maximum kV value attainable (Figure 2).

2. Extending oil life

Varnish that normally forms in fluid systems plates out in the fluid-collection cartridge. Because the spaces in the collection cartridge range from 50 to 300 microns, a large amount of sub-micron material and products of oxidation can be eliminated from the fluid.

Source: ISOPur Fluid Technology

From hydraulic fluid at a major auto parts manufacturer to tap-changer switchgear, turbines, and compressors, dramatic reductions in particulates and the products of oxidation have documented the effectiveness of the BCA process. The process induces reformation of varnish within a fluid-collection cartridge, depositing varnish and sludge onto the proprietary depth media cartridge. Previous early indicators of films forming on switchgear in tap changers does not appear in the BCA-protected apparatus.

Recently, a new system incorporating a low-maintenance PetroTech vacuum dehydrator was installed at a major utility site in the Northeast. In addition to the significantly reduced particle counts, water and gas quickly dropped to extremely low levels (Figure 3). The proven ability to address all aspects of transformer oil condition using one cost-effective portable system has motivated ISOPUR Fluid Technology Inc (Rocky Hill, Conn.) to design smaller, permanent units with remote monitoring capabilities for installation on critical or troubled (high-maintenance) equipment.

3. PetroTech vacuum dehydrator

During a typical clean-up of transformer fluid in an industrial environment, particle count was reduced to such a low level that the dielectric strength improved from 35 to 90 kV.

Source: ISOPur Fluid Technology

Standard mechanical filtration can remove larger particles but has no impact on the millions of smaller particulate matter that can easily pass through the filter and accumulate in critical equipment. These small particles pick up a low uniform static charge, causing the formation of varnish and sludge due to their attraction to grounded internal surfaces. The BCA process can gather together particles below the one-tenth micron size and remove them from the fluid. Because most soot particles range from one-tenth to three-tenths micron, the normal drop in kV resistance over time is eliminated. By creating floods of equal and opposite-charged particles, the BCA process eliminates net static charge and blocks varnish formation.

Essentially, the varnish that normally forms in machines plates out in the fluid-collection cartridge due to the BCA process. Because the spaces in the collection cartridge range from 50 to 300 microns, a large amount of sub-micron material and products of oxidation can be collected before change-out is required. A typical cartridge life is one year. Typical fluid life is expected to be measured in decades, even with troubled systems.

By Gerald Munson and C. Wesley Mitchell, ISOPUR Fluid Technology, and R. Haig Hachadoorian, Petroleum Technology Inc

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