Abstract: Tangent delta measurements using very low frequency (VLF) sinusoidal waveform in aged cable system have been proved sensitive to water tree degradation and insulation aging. Whereas, the application of VLF in acceptance tests on new cable systems of medium voltage is still on research and development. In this paper, the validity of the main VLF diagnostic test methods on condition assessment for newly installed 10kV XLPE cables is discussed based on laboratory and field tests results. Firstly, simulation models of six typical defects in new cables were made in laboratory. Based on the comparable tests results of the experiment cables performed with 0.1Hz AC, 50Hz AC and oscillation wave excitation, the applicability and effectiveness of non-monitored (simple), monitored withstand, tangent delta and partial discharge measurement using 0.1Hz sinusoidal or cosine-rectangular waveforms were studied. In addition, the practice of withstand and tangent delta tests in acceptance of newly installed cables in a certain distribution grid is introduced. The results analysis showed that monitored VLF withstand with tangent delta measurement during a 30 min to 60 min test procedure is more than an alternative to withstand at power frequency, for its distinctive ability of detection of a wet or lossy accessory in new cable systems. The combination of monitored VLF withstand with tangent delta measurement and oscillatory wave test system (OWTS) or VLF cosine-rectangular partial discharge is proved currently to be the most suitable method in acceptance test.