IEEE Std C57.139 pdf free download
IEEE Std C57.139 pdf free download.Dissolved Gas Analysis in Transformer Load Tap Changers.
For the purposes of this document, the following terms and detinitions apply. The IEEE Standards Dictioiiari’ Online should be consulted for terms not defined in this clause.4
arcing gases: Hydrogen and acetylene gases may be referred to as arcing gases. Hydrogen is the primary gas generated during low-intensity discharges. Acetylene is the primary gas generated during high-intensity arcing faults in the 700 C to 1800 C temperature range.
coking: The formation of a hard carbonized deposit on the contacts of a tap changer. This process occurs due to the breakdown of oil from heat and arcing across the tap changer contacts that are immersed in oil.
continuous on-line filtration: Removal of oil insoluble contaminants by use of a permanently installed online filter and continuous circulation of the oil.
desiccant breather unit: An oil-filled free-breathing load tap changer (LTC) compartment with the addition of a dehydrating breather to remove moisture from the air that is in contact with the oil. Typically, the internal pressure inside a desiccant breather is slightly higher than atmospheric.
dissolved gas analysis (DCA): The measurement and interpretation of dissolved gas concentrations in the insulating liquid of electrical equipment. The interpretation can identify certain kinds of faults, sometimes in very early stages, and provide a rough indication of severity.
free breather unit: An oil-filled load tap changer (LTC) compartment mounted on the transformer in which the air space above the tap changer oil freely exchanges gases with the outside atmosphere.
heating gases: Methane, ethane, or ethylene gases are referred to as healing gases since they are generated when insulating liquid is exposed to higher than normal operating temperatures generated by hot metallic surfaces in the 150 C to 500 C temperature range.
non—invasive method: Any method of testing a load tap changer (LTC) that does not alter the properties of the oil, components. or insulating materials. Such methods may include, but arc not limited to, DGA, fluid quality, thermography, and ultrasonics.
sealed tank unit: An oil-filled load tap changer (ITC) compartment that is totally sealed to the atmosphere that vents upon reaching a predelined pressure setting. Typically the compartment contains a one-way valve. This arrangement can result in development of a partial vacuum in the compartment when the oil temperature drops.
total dissolved heating gas (TDHG): The sum of the concentrations of heating gases methane, ethane, and ethylene, in tL/L (ppm), in the oil.
4. Nature, purpose, and basis for DGA for LTCs
4.1 Nature of LTC DGA
Dissolved gas analysis ([)GA) for LTCs is a process of measurement, identification, and interpretation of gases dissolved in the LTC oil. Usually at regular intervals, a small sample of oil is drawn according to ASTM D923 (see DGA sampling), and the sample is sent to an analytical laboratory. which measures the dissolved gas concentrations with a gas chromatograph according to ASTM D36 12 and sends back a report. Alternatively, the analysis may be done on-site with a portable gas analyzer instead of sending the sample to a laboratory. An on-line dissolved gas monitor attached to an LTC is another possible source of DGA data (see Soundarrajan [B9]). The process of sample collection, transportation. and analysis of its gas content is subject to various hazards, discussed as follows, that can affect the quality and usefulness of the data produced.IEEE Std C57.139 pdf download.
