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Insulating Liquids

Insulating liquid particle testing standards are published by IEC and ASTM. The IEC standard covers methods for counting and sizing particles, and ASTM publishes documents on standards practices and test methods for sampling electrical insulating liquids, particle count in mineral insulating oil, and determination of elements in insulating oils.

ASTM D923-15

Standard Practices for Sampling Electrical Insulating Liquids

1.1 These practices cover sampling of new electrical insulating liquids including oils, askarels, silicones, synthetic liquids, and natural ester insulating liquids as well as those insulating liquids in service or subsequent to service in cables, transformers, circuit breakers, and other electrical apparatus. These practices apply to liquids having a viscosity of less than 6.476 10 -4 m 2 /s (540 cSt) at 40 C (104 F). 1.2 Representative samples of electrical insulating liquids are taken for test specimens so that the quality pertinent to their use may be determined. The quality in different portions of a given container, or the average quality of the whole bulk may be ascertained if desired. 1.3 The values stated in SI units are regarded as the standard where applicable. Inch pound units are used where there is no SI equivalent. 1.4 These practices also include special techniques and devices for sampling for dissolved gases-in-oil (DGA) ( D3612 ), water ( D1533 ) and particles ( D6786 ).

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IEC 60970 Ed. 2.0 b:2007

Insulating liquids - Methods for counting and sizing particles

"Describes the sampling procedures and methods for the determination of particle concentration and size distribution. Three methods are specified. One uses an automatic particle size analyser, working on the light interruption principle. The other two use an optical microscope, in either the transmitted light or incident light mode, to count particles collected on the surface of a membrane filter. The optical microscope methods are described in ISO 4407. All three methods are applicable to both used and unused insulating liquids. Annex A contains an alternative sampling procedure using a syringe and Annex B reports a reference for the calibration of automatic particle counters. The significant technical changes with respect to the previous edition are as follows: - new calibration procedures for automated laser particle; - three figures contamination code; - new procedure of sample pre-treatment when automated laser counter method are used. "

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ASTM D6786-15

Standard Test Method for Particle Count in Mineral Insulating Oil Using Automatic Optical Particle Counters

1.1 This test method covers the determination of particle concentration and particle size distribution in mineral insulating oil. It is suitable for testing oils having a viscosity of 6 to 20 mm 2 /s at 40 C. The test method is specific to liquid automatic particle analyzers that use the light extinction principle. 1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard. 1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

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ASTM D7151-15

Standard Test Method for Determination of Elements in Insulating Oils by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES)

1.1 This test method describes the determination of metals and contaminants in insulating oils by inductively coupled plasma atomic emission spectrometry (ICP-AES). The specific elements are listed in Table 1 . This test method is similar to Test Method D5185 , but differs in methodology, which results in the greater sensitivity required for insulating oil applications. 1.2 This test method uses oil-soluble metals for calibration and does not purport to quantitatively determine insoluble particulates. Analytical results are particle size dependent, and low results are obtained for particles larger than several micrometers. 2 1.3 This test method determines the dissolved metals (which can originate from overheating or arcing, or both) and a portion of the particulate metals (which generally originate from a wear mechanism). While this ICP method detects nearly all particles less than several micrometers, the response of larger particles decreases with increasing particle size because larger particles are less likely to make it through the nebulizer and into the sample excitation zone. 1.4 This test method includes an option for filtering the oil sample for those users who wish to separately determine dissolved metals and particulate metals (and hence, total metals). 1.5 Elements present at concentrations above the upper limit of the calibration curves can be determined with additional, appropriate dilutions and with no degradation of precision.

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