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It is common practice to install only phase to ground surge arresters for transformer insulation protection against electrical stresses. However, this may not adequately protect the delta connected transformer phase to phase winding insulation. High phase to phase overvoltages at the transformer terminals, due to capacitor switching, have been reported. This paper describes the excessive phase to phase overvoltages that can also occur due to wave propagation and surge transfer through transformers. This paper points out the need for surge arrester arrangements that protect both, phase to phase and phase to ground transformer insulations. Surge arrester arrangements, selection criteria, installation practices, and application considerations are discussed in this paper.

American Electric Power conducted field tests to study transient overvoltages and overcurrents on a 12.47 kV distribution line. A separate paper (1) has reported on the field test results. This paper covers the computer modeling and simulation of the field tests. The paper describes the adaptation and refinement of the transformer, load and line models. Computer simulation of the field tests using the Electromagnetic Transients Program (EMTP) give results which are very close to the actual field tests. Also reported in the paper are the results from a parametric study which were utilized to develop a simplified computer model.

The paper reports on field tests conducted by American Electric Power (AEP) on a 12.47 kV distribution line. The results cover capacitor switching and load dropping tests. The highest overvoltage recorded of 2.43 p.u. was during capacitor switching with arresters disconnected. At the line end, a maximum of 2.16 p.u. was measured during the line reenergization with the capacitor bank disconnected. The results give both overvoltage and overcurrent transient waveshape, magnitude and dominant frequency. Spectrum analysis of selected test shots provided the information on the extent of transient nonlinearity. Also, information is given on the field test instrumentation setup.