The validity of short time screening tests in evaluation of general-purpose transformer insulation systems

Users of Proposed Test Procedure, IEEE 259, "Evaluation of Systems of Insulation for Specialty Transformers," have become aware of the need for a low cost screening test of short duration to be conducted prior to manufacture of test transformers. A quick and simple screening test is needed to indicate insulation incompatabilities and faults in an insulation system under consideration. This will serve an economic need by making more certain that labor and material required to produce and life test actual transformers results in meaningful data. This paper proposes a test piece and method. The test piece is described and can be easily assembled by hand with readily available materials. The components of the test piece are of low cost and dimensions are not critical — conditions which promote acceptability and reproducible results at different laboratories. These are prime requirements if a screening procedure is to become a supplement to IEEE 259. A comparison of the data obtained with actual transformers using IEEE 259 procedure and the proposed test piece, both constructed with the same insulation system is shown as well as with twisted pair tests IEEE No. 57 using the same enameled wire. When sufficient background data has been developed using the subject test piece, it is anticipated that a base performance life line would be established for a 105 °C rise system as was done in the case of the transformer test procedure.