Energy dissipation by partial discharge in cryogenic cables

In general the two contributions to aging in lapped tape insulated cables are partial discharge and thermal heating. At cryogenic temperatures, thermal aging is expected to be negligible, leaving partial discharge as the primary aging mechanism. Using data obtained with a digital partial discharge detector, the energy dissipated by PD can be determined from the product of the apparent charge of each PD pulse times the instantaneous applied voltage and summing over ail pulses. This can be shown to be equivalent to the product of actual charge and the internal voltage at the site of PD. It can also be shown that the slope, n, of the log plot of energy dissipation versus voltage is the same, n, in the exponent of the power law used in aging studies. We will show data on energy dissipation versus voltage for lapped tape insulated cable in pressurized liquid nitrogen and compare the n from that data with aging data reported in the literature.