This dataset supports the study “Temporal Observability and Techno-Economic Assessment of Temporary and Permanent Partial Discharge Monitoring for Underground Distribution Cables.” It provides a synthetic, reference-informed cable population used to evaluate how short-term inspection and permanent monitoring affect partial discharge (PD) observability, alarm outcomes, residual failure exposure, and economic performance. The dataset contains 1000 underground distribution cable records. Each cable is described by asset- and condition-related variables, including age, joint count, termination count, installation environment, load level, previous PD indication, defect type, condition state, and a derived risk score. The population includes 800 cables without PD issues, 100 cables with occasional PD activity, and 100 cables with actionable PD trends. For each cable, the dataset provides a 365-day PD-amplitude timeline. Cables without PD issues have zero PD amplitude, occasional-PD cables include sparse PD pulses after a randomized onset day, and trend-PD cables include exponential, step, or linear PD development. The file also includes summary quantities such as active PD days, maximum PD amplitude, mean PD amplitude, representative outage duration, affected customers, and failure-cost assumptions. The dataset is synthetic and does not contain real utility, customer, or personally identifiable data. It is intended for reproducibility of the monitoring-comparison calculations and for testing temporal-observability, PD-alarm, trend-alarm, and cost-benefit evaluation methods.