IEEE C57.121-1996 pdf download IEEE Guide for Acceptance and Maintenance of Less Flammable Hydrocarbon Fluid in Transformers
1. Overview
1.1 Scope
This guide recommends tests” and evaluation procedures, as well as criteria and methods of maintenancefor less fammable hydrocarbon (LFH) transformer insulating fluids. These liquids are also known as highmolecular weight hydrocarbon (HMWH) fuids. HMWH dielectric fluids are hereby defined as those fiuidshaving an ASTM D92 fire point of 300 °C or greater, being primarily composed of, but not restricted to.hydrocarbons. These fluids meet the requirements of the National Electrical Code@ (NECO) (NFPA 701999). Article 450-23, as a less flammable dielectric for use in indoor applications when used in properlydesigned and installed transformers. Ester- and silicone-based fluids are not covered by this guide. Methodsof reconditioning LFH fluids are also described. It is not the intent of this guide to address retrofilling trans-formers with LFH fluids. Any such substitution of fuids should be performed only after consultation withthe manufacturers of fluid and equipment. Where instructions given by the transformer or fluid manufactur-ers differ from those given in this guide, the manufacturer’s instructions are to be given preference.
1.2 Purpose
The purpose of this guide is to assist the transformer operator in evaluating and processing LFH fluidsreceived in new transformers, as received from the fluid manufacturer for filling transformers, and as processed into such equipment. It also assists the operator in maintaining the fuid in serviceable condition. Thisguide, therefore, recommends standard tests and evaluation procedures, methods of reconditioning andreclaiming LFH fluids, and the analysis results at which these processes become necessary. It will alsoaddress the routines for restoring resistance to oxidation, where desired. by the addition of inhibitors.
1.3 System design
The reliable performance ofL.FH flids in an insulation system depends upon certain basic fuid characteristicsthat can affect overall apparatus characteristics. Such flid characteristics are integral to equipment design folwhich the manufacturer has final responsibility. The reliable operation of the equipment in service, for whichthe transformer operator has final responsibility, also depends on maintaining certain basic fuid characteristicsAdherence to the recommended fuid characteristics will assist in obtaining the desired equipment characteristics. Other tests or verification of the integrity of the insulation system are often necessary.
The essential properties of insulating fluids used in transformers must be maintained if the fuid is to performits multiple role as an electrical insulating and heat transfer agent. It must have adequate dielectric strengthto withstand the electric stresses imposed in service. It must have a certain combination of thermal conduc.tivity, specific heat, and viscosity so that its ability to transfer heat is sufficient for the particular equipmentIt must have sufficiently high flash point and fire point to meet safety requirements. The fluid’s dielectriclosses should not become excessive. The L.FH fuid should not be allowed to become so deteriorated or contaminated that it adversely affects other materials in the apparatus, nor should deterioration products(sludge) impair its circulation through cooling ducts. If the purpose of using an HMWH is to comply withNEC Article 450-23 requires that less fammable transformer liquids have an ASTM D92 fire point of notless than 300 °C and that the installation complies with all restrictions provided for in the listing of the fluid
1.4 Background information
1.4.1 Mixtures of LFH fluids with other liquids
LFH fluids are miscible and compatible with other hydrocarbon insulating liquids as well as with halogenated hydrocarbons. Mixtures with conventional transformer oil will lower the flash and fire points of theLFH fluid. If the fire point (ASTM D92) of the contaminated LFH fluid is less than 300 C, the transformeiwill not meet the requirements of NEC Article 450-23.
1.4.2 Mixtures of different types of LFH fluids
Although in many cases different types of LFH fluids are miscible (e.g., synthetic hydrocarbons, petroleum.based hydrocarbons), such ixtures should generally be avoided in transformers and fuid processing equipment due to a possible unacceptable decrease in flash and fire points. Consult the manufacturer of each fuidfor advice if mixing has occurred or is necessary
2.References
The following references should be used in conjunction with this guide. When any of the following stan·dards is superseded by an approved revision, the revision shall apply.
ASTM D5222-92, Standard Guide for High Fire-Point Electrical Insulating Oils of Petroleum Origin.
IEEE C57.121-1996 pdf download
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