Investigation of the effect of repetitive voltage surges on epoxy insulation

The aging of epoxy electrical insulation by unipolar, repetitive voltage surges has been investigated to determine whether such surges can precipitate premature failure of high-voltage motor windings and gas insulated switchgear spacers. A full factorial statistical test was devised and performed on 180 pure epoxy insulation specimens to examine the effect of voltage magnitude, polarity, and surge repetition rate on the life of unfilled epoxy specimens containing a needle-plane electrode geometry. All factors and interactions were determined to have a significant effect on the life, and life prediction equations were estimated. Increasing the voltage magnitude or repetition rate, decreased or increased the life, respectively. Aging was found to occur at as low a stress as 2 MV/cm. Gradual aging of the epoxy does occur under repetitive voltage surges. Based on a realistic number of surges with typical voltage amplitudes which can normally occur from vacuum switchgear during service, gradual deterioration of the epoxy turn insulation in motor stator windings is possible in some situations. Situations where surge aging may occur are identified. >

[1]  H. W. Ng,et al.  Effects of voltage impulses on extruded dielectric cable life , 1989 .

[2]  G. Stone,et al.  The Statistical Analysis of a High Voltage Endurance Test on an Epoxy , 1979, IEEE Transactions on Electrical Insulation.

[3]  O. M. Nassar,et al.  Motor Insulation Degradation Due to Switching Surges and Surge Protection Requirements , 1986, IEEE Transactions on Energy Conversion.

[4]  A. Bulinski,et al.  Evidence of near‐ultraviolet emission during electrical‐tree initiation in polyethylene , 1987 .

[5]  T. Lebey,et al.  Charge injection and electroluminescence as a prelude to dielectric breakdown , 1990 .

[6]  G. Stone,et al.  Electroluminescence in epoxy insulation , 1992 .

[7]  T. W. Dakin,et al.  The voltage endurance of cast epoxy resins , 1978, 1978 IEEE International Conference on Electrical Insulation.

[8]  H. Zeller,et al.  Electrofracture mechanics of dielectric aging , 1984 .

[9]  Y. Sekii,et al.  Deterioration by Treeing of Rubber- and Plastic-Insulated Cables Caused by Impulse Voltage , 1971 .

[10]  D. K. Sharma,et al.  Degradation of turn insulation in motor coils under repetitive surges , 1990 .

[11]  G.C. Stone,et al.  Turn Insulation Capability of Large AC Motors Part 2 - Impulse Strength , 1987, IEEE Transactions on Energy Conversion.

[12]  J. H. Mason.  Breakdown of Solid Dielectrics in Divergent Fields , 1955 .

[13]  R. Bartnikas,et al.  Electrical aging and electroluminescence in epoxy under repetitive voltage surges , 1992 .

[14]  Luciano Simoni.  General Equation of the Decline in the Electric Strength for Combined Thermal and Electrical Stresses , 1984, IEEE Transactions on Electrical Insulation.