High-frequency impacts in a converter-based back-to-back tie; the eagle pass installation

Abstract

Voltage sourced converter-based transmission controllers, which use gate turn off switching components, introduce a new type of high voltage stress on insulation systems and materials. Fast switching components like IGBTs may generate or cause high-frequency voltages, which are superimposed upon the power frequency (50/60 Hz) voltage. Insulation within the station may thereby be continuously exposed to a new type of voltage stress, for which it has not been designed or tested. The high-frequency voltages may, under special circumstances, cause insulation damages at magnitude levels, which are well below the dielectric voltage withstand at power frequency. Compact insulation systems with resistive/refractive grading of the electrical field are particularly critical. Several compact type cable terminations rated 24 kV with resistive/refractive stressgrading have failed in the voltage soured converter-based back-to-back installation at Eagle Pass substation in the State of Texas. Through field measurements, laboratory tests, and simulations, the root cause of the failures has been identified. The compact cable terminations have been replaced by another type of termination, which is not sensitive to high-frequency voltages. The voltage sourced converter-based back-to-back installation in Eagle Pass is a joint ABB, EPRI, and AEP field demonstration project, which has been commissioned.