Reactive Compensation Needs for Superconducting Transmission Systems

Replacing conventional ac transmission lines with superconducting cables provides many potential advantages, including strengthening the dynamic coupling of the power system since superconducting cables have much lower series inductance than overhead lines in addition to the greatly reduced resistance. This will make the transmission lines appear electrically shorter and can eliminate the need to install shunt capacitors for transmission voltage support or the need to install series capacitors to make lines appear electrically shorter to improve system performance. The superconducting cable performance characteristics will be dominated by shunt parasitic capacitance charging affects, much as is the case with conventional underground cables. However, the low series impedance of the cable improves the voltage regulation across the cable. As a result, ac superconducting cables could face less severe distance limits than conventional cables before reactive compensation is required in the middle of the cable to correct for the effects of this capacitance. However, the capacitive current will still need to be compensated at the end point terminations. In addition, superconducting systems have less inherent damping for electromechanical disturbances. The compensation scheme will need to address these needs as well.