ASTM_D_2759_-_00_2010.pdf

Designation:D275900(Reapproved 2010)Standard Practice forSampling Gas from a Transformer Under Positive Pressure1This standard is issued under the fixed designation D2759;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This practice covers the sampling of gas above theinsulating liquid of a transformer.A gas sampling bottlecollects the gas sample from the gas space that is at a positivepressure.1.2 Representative samples of gas are taken for analysis todetermine their compositions.1.3 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.1.4 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Significance and Use2.1 A gas sample from above the insulating liquid intransformers and other electrical power apparatus can be usedto give an early indication of developing fault conditions.Combustible gases are formed from the breakdown of theinsulating materials under thermal and electrical stress.Exces-sive concentrations of combustible gases indicate the need totake appropriate action.2.2 It is important that gas samples from equipment be takenfrom the gas space directly above the liquid level,and not fromremote expansion compartments,such as tank bracing bands.2.3 The procedure described should be carefully followed toensure that the sample is not diluted by air or nitrogen,orcontaminated by residual materials in the sampling bottle.3.Apparatus3.1 Gas Sampling Bottlestainless steel,Monel metal,orglass,of at least 250-cm3capacity,with a valve and a hoseconnector on each end.3.1.1 The gas sampling bottle must be free of dirt,moisture,oil,or other contaminants.It should be cleaned by washingwith anhydrous isopropyl alcohol,or other suitable cleaningagent that is free from residue upon evaporation.The bottleshould then be dried by blowing out with dry air or nitrogen,oven baking,or be dried under vacuum.3.2 Plastic BagThe bag should have only one openingarranged to fit over one of the hose connectors on the samplingbottle.The plastic bag should have a volume,when fullyexpanded,of approximately 15 times the volume of thesampling bottle.4.Procedure4.1 Before connecting the sampling bottle to the trans-former,purge the outlet valve on the transformer by exhaustinga small amount of gas to remove any moisture,oil,or othercontaminants.4.2 Attach one end of the gas sampling bottle by plastichose to the transformer outlet valve,and the other end of thesampling bottle to the plastic bag,making sure that a leakproofconnection is obtained.4.3 Purge the sampling bottle and hose of air by firstopening both valves of the sampling bottle and then slightlyopening the outlet valve on the transformer.As the gas flowsthrough the sampling bottle,the plastic bag will expand.4.4 When the bag has expanded to its full volume,first closethe valve adjacent to the bag;then close the valve at the otherend of the sampling bottle;and,finally,close the transformergas outlet valve.Remove the hose and plastic bag from thesampling bottle.5.Marking5.1 Attach a tag to the gas sampling bottle showing thefollowing:5.1.1 Serial number of transformer,5.1.2 Date of sample,5.1.3 Transformer oil temperature,and5.1.4 Location of transformer.6.Precision and Bias6.1 This is a sampling method,and as such precision andbias do not apply.1This practice is under the jurisdiction of ASTM Committee D27 on ElectricalInsulating Liquids and Gases and is the direct responsibility of SubcommitteeD27.07 on Physical Test.Current edition approved Nov.1,2010.Published November 2010.Originallyapproved in 1968.Last previous edition approved in 2005 as D2759 00(2005).DOI:10.1520/D2759-00R10.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 7.Keywords7.1 gas;positive pressure;sampling gas;transformerASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard.Users of this standard are expressly advised that determination of the validity of any such patent rights,and the riskof infringement of such rights,are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised,either reapproved or withdrawn.Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters.Your comments will receive careful consid