An investigation of the transient behavior of an aluminum potline installation

OVER A PERIOD of several years, a number of transformers and induction regulators supplying energy to aluminum potlines and similar installations have been damaged by insulation failures; the failures were apparently due to abnormal overvoltages. The transformers used for these applications usually step down from 13.8 kv to a secondary voltage in the range 600 to 900 volts depending upon the installation. A basic impulse level of at least 40 kv is normal for the secondary winding; insulation failures occurring on these windings are an indication of the severity of the voltage transients. An excellent photograph showing typical coil damage appears in a paper by Pope, et al.1