Energy utilities need on-site AC high-voltage acceptance tests on their cable systems and switchgear, in order to ensure the quality of their transmission systems; such tests need to be performed on site with special equipment as well as remarkable measurement technology and diagnosis at voltages of up to 500 kV. Complete acceptance tests such as on-site AC high-voltage tests combined with Partial Discharge measurements serve to prove the performance of the laid cable systems by timely detecting the faults. They also serve to increase the efficiency of the network, help to minimise technical failures and save long-term costs, thus increasing the reputation of the network operators. Furthermore the measurement of partial discharge (PD) contribute to the increase of system safety and to ensure quality during the assembly of terminations and joints. PD measurement results allow early intervention during the test in the case of a failure and they can be of help to avoid future disruptive discharges during system operation and to have an early start of repair work at minimum expenditures. CESI-IPH owns state of the art equipment such as AC high-voltage resonant systems for the on-site testing of XLPE-insulated cables, cable accessories and gas-insulated transmission lines (GIL). One single test unit is able to do tests on 110-kV and 220-kV cable systems and it allows the testing of 400-kV and 500-kV cable systems and GIL when used in series connection. Parallel connection doubles the testable length, e. g., from 5.5 km to 12 km in the case of 220-kV cable lines. It is also possible to test short cables with capacitance magnitudes below 20 nF by using additional capacitors. High-sensitivity measurement, e. g., partial discharges on accessories of installed cables with sensitivity below 10 pC, is possible even under heavy-disturbance conditions by means of CESI-IPH’s variable center frequency and bandwidth that allows to carry out the complete acceptance tests for detecting faults on time, help increasing the efficiency of the network and minimizing technical failures so that long-term costs can be saved by the network operators and the utilities.​