Frequently Asked Questions 3M Liquid-Filled Transformer Insulation
Frequently Asked Questions What configurations are available for 3M Liquid-Filled Transformer Insulation (LFT Insulation) layer insulation? LFT insulation is available in calendered 3-5-, 7- and 10- mil (0.13, 0.18 & 0.25mm) configurations, with and without diamond dot adhesive in 36" (914mm) widths. The roll diameters are 12.75" (324mm) and 20.5" (521mm). For applications that require additional material flexibility, a 5-mil (0.13mm) crepe paper configuration is available that can be formed into tubes and used to insulate lead wires. What is the difference between low-density and high-density boards? The LFT insulation low-density board has a 1.0 to 1.1 g/cm 3 density and is designed for core tube and window insulation applications. It has a slight texture to the surface finish. The LFT insulation high-density board starts as the low density board and is densified to 1.5 to 1.7 g/cm 3 using a calendaring process. The finished board has a very smooth surface finish with a higher mechanical strength, which is optimal for structural applications. What board sizes are available? The low-density boards are available in 30, 60, 90, 120 and 180 mil (0.76, 1.5, 2.3, 3.0 & 4.6 mm), up to 48" x 48" (1.2m x 1.2m) sizes. High density boards are available in 30, 60, 90 and 120 mil (0.76, 1.5, 2.3, & 3.0 mm), up to 48" x 48" (1.2m x 1.2m) sizes. What samples are available? The layer insulation is available in 8.5" x 11"/ A4 sheets with and without adhesive. For low-density and high-density board, the samples are available in 4" x 4" (100mm x 100mm). Please contact your 3M representative. Is it possible to procure the layer insulation and apply the diamond dot adhesive myself? Yes. Please contact your 3M representative for more information. 3
3M Liquid-Filled Transformer Insulation Frequently Asked Questions Is the 3M Liquid-Filled Transformer Insulation available in flexible tube, insulated lead wire, and cooling duct configurations? Yes. Please contact your 3M representative for more information about where to obtain them. How is LFT insulation different from existing cellulose-based solutions? LFT insulation is an inorganic-based material which provides higher thermal stability, less moisture absorption and better resistance to degradation due to moisture, along with higher thermal conductivity. What is the thermal class of LFT insulation and how does it compare to existing insulation solutions? LFT Insulation: 155 C Cellulose/ Kraft: 105 C Cellulose/ Thermally Upgraded Kraft: 120 C How was the LFT Insulation Thermal Class determined? Testing was performed in accordance to IEEE Std C.57.100-2011 Standard Test Procedure for Thermal Evaluation of Insulation Systems for Liquid-Immersed Distribution and Power Transformers and was used to define the particular Thermal Class for LFT Insulation. The IEEE Std. C.57.154-2012 Standard for the Design, Testing, and Application of Liquid-Immersed Distribution, Power, and Regulating Transformers Using High-Temperature Insulation Systems and Operating at Elevated Temperatures specifies which thermal classes are required for different classifications for high-temperature transformers. These standards are very similar to IEC Std. 62332-2 and IEC Std. 60076. Why would a utility want to deploy a higher temperature transformer? If a transformer is designed for a higher thermal class, the size of the transformer can be reduced and can potentially lower the overall transformer material cost. A higher thermal class/ temperature stability can increase the overload capability of the insulation system without damage and can increase the overall life of the insulation system. 4
If a transformer is designed for a higher Thermal Class, will other materials in the transformer need to be changed? Yes, if a high-temperature insulation system is used. IEEE Std. C.57.154-2012 sets the guidelines for different combinations of solid insulation and liquid that can be used for different thermal classes. Conventional insulation systems consisting of Thermally Upgraded Kraft (TUK) and mineral oil, the TUK has a thermal class of 120 C while the mineral oil has a maximum temperature rise of 65 C. If an ester or silicone liquid is used with a high-temperature solid insulation, instead of mineral oil, the transformer can be designed to allow higher temperature operation, per Table 4 (below) from IEEE Std. C.57.154-2012. This standard also describes hybrid transformer designs where a combination of conventional and high-temperature solid insulation, such as 3M Liquid-Filled Transformer Insulation, can be used in higher thermal class designs. Other materials, such as magnet wire may need to be changed for a higher thermal class. This needs to be verified with the material suppliers. Table 4 - Maximum continuous temperature rise limits for transformers with high-temperature insulation systems a,b Liquid Type Ester Silicone Minimum required high-temperature solid insulation thermal class c 130 140 155 180 130 140 155 180 Top liquid temperature rise, ( C) Average winding temperature rise, ( C) 90 90 90 90 115 115 115 115 75 85 95 115 75 85 95 115 Hottest spot temperature rise, ( C) 90 100 115 140 90 100 115 140 a The temperature rises shown are based on a 30 C average cooling air temperature as defined in IEEE Std C57.12.00. If the specified cooling air temperature is different from 30 C, the temperature rise limits shall be adjusted accordingly to meet the suggested limits of Table 6. b Essentially oxygen-free applications where the liquid preservation system effectively prevents the ingress of air into the tank. c The high-temperature insulation may include different temperature classes, all above conventional. In a mixed hybrid insulation winding, per IEEE Std. C.57.154-2012, other materials may not need to be changed. In this case, the higher thermal class insulation is used in regions operating at temperatures above conventional cellulose limits. However, the majority of the insulation is conventional. For more information on this and other configurations, refer to IEEE Std. C.57.154-2012. 5
3M Liquid-Filled Transformer Insulation Frequently Asked Questions How much moisture does 3M Liquid-Filled Transformer Insulation absorb compared to cellulose and meta-aramid? Cellulose based materials absorb a substantial amount of water, approximately five percent moisture content at room temperature and 50 percent relative humidity (RH) and up to 25 percent, when subjected to 95 percent RH. Meta-aramid insulation absorbs enough moisture to expand up to two percent in the cross direction at 95 percent. The LFT Insulation typically has less than one percent moisture content at 50 percent RH and about six percent content at 95 percent RH. With less moisture absorption across a wide range of environments, the insulation exhibits stability in all dimensions including material thickness. Additionally, lower moisture absorption relative to cellulose-based paper can reduce the time needed to dry a coil. Why is insulation thermal conductivity important? The higher the electrical insulation thermal conductivity, the faster heat is transferred away from the hottest temperature spot in the coil, thus reducing the hottest temperature in the transformer coil. Based upon thermal aging studies, a lower temperature increases the insulation life expectancy. The LFT Insulation has approximately 10 percent higher thermal conductivity than cellulose. Using this improved thermal conductivity, hot spots could be reduced or a transformer manufacturer could redesign the coil to maintain the same temperature rise, but reduce the cooling channels. This enables the coil to be reduced in diameter and the total amount of conductor length decreased. With what oils and liquids is the LFT Insulation compatible? LFT insulation is compatible with mineral oil and ester oil fluid. The insulation was successfully tested in mineral oil per ASTM D3455 Standard Test Methods for Compatibility of Construction Material with Electrical Insulating Oil of Petroleum Origin by 3M and by Doble Engineering. The same test was conducted with ester oil and the LFT insulation had similar results. The dielectric properties of the LFT insulation were tested in ester oil with results being very similar to mineral oil results. 6
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