International specifications of liquid dielectrics under use in power equipment with a special focus on very high voltage transmission systems and high ambient temperature based tropical countries

The specification for liquid dielectric has undergone changes over the years. Conventionally used mineral oil based on acid-clay treatment has been changed to hydrocraking/iso dewaxing/ hydrofinishing combinations. The power equipment being a precious system in the power system network, needs to be assured for its reliable performance and any failure of this equipment can cause serious system failure. Such failures will lead to revenue losses, not only due to the loss of equipment but also due to disruption of power system network. Present investigation, reviews various aspects of the dielectric nature and property evaluation for various characteristics such as dielectric loss, oxidation stability, inhibitors and their level of inhibition, sulphur levels and their limiting values, dibenzyl disulphide, metal passivators, stray and general gassing tendency, electro static charging tendency, viscosity and pourpoint characteristics and others. Applicability and significance of these characteristics under HVAC and HVDC systems. Severity of conditions under which dielectric has to perform has been analysed. Role of each characteristic under the severe conditions and their consequences have been evaluated. Necessity of change of limiting values for these characteristics for the tropical countries based on utility and essentiality pertaining to sulphur compounds, DBDS, Gassing tendency has been discussed with experimental data based on laboratory conditions.