Misalignment of Coaxial Conductors

Compressed gas insulated coaxial transmission lines are being developed which withstand 1200-kV rms phase-to-phase voltage and carry 3000 A continuous current. As a method of instrumenting the voltage on a single-phase of coaxial line, an isolated capacitive section approximately one meter in length is inserted between the conductors. The resulting displacement current due to line voltage is detected with low voltage electronics. In the present work, misalignment of the coaxial conductors is investigated theoretically and experimentally to determine the effect of small relative displacements on the amount of capacitance of the isolated section. Capacitance change due only to conductor misalignment is found not to restrict severely the metering accuracy of the isolated section, provided reasonable tolerances for the position of the isolated section are maintained. Forces due to imbalance of surface charge when the conductors are slightly misaligned are calculated and shown to be small, suggesting that a "voltage coefficient" of capacitance also should not severely restrict the metering accuracy of the isolated section.