Experience of withstand testing of cable systems in the USA
High voltage withstand tests are used within manufacturing plants to ensure the quality of completed cable system components from MV to EHV. Thus, it is quite natural for utilities to also use withstand tests as commissioning and maintenance tests for cable systems in the field. The goal of these tests is the same as in the factory test, namely to have any weak components of the cable system fail in a controlled manner, such that the minimum number of customers are affected. In fact a recent study has shown that withstand tests are among the most routinely employed diagnostic tests in the USA; this study has also shown that the most preferred withstand tests use Very Low Frequency (VLF: 0.02 to 0.1 Hz) AC methods. This paper describes the collation and analysis of data from a wide range of on going utility VLF withstand program conducted on medium voltage distribution systems. A significant feature of this study is that the data are not from research or pilot programs. As a result of the analysis described herein the authors conclude that: It is beneficial to collate and compare VLF test experiences across a range of utilities. VLF tests are very practical for a utility to perform and d not require specialized services. The Survivor rates are high for these tests with expected values, based on 1,000 ft (305 m) cable system segment lengths, in the range of 0.2 to 4 % for 30 min tests performed at the IEEE Std. 400.2 voltage levels. IEEE Std. 400.2 provides appropriate time and voltage test levels (determining optimal times and voltages was outside the scope of the work reported here). VLF tests at IEEE Std. 400.2 test levels d not significantly damage cable systems as would be manifested by cascading (or multiple) failures on test or shortened times to failure in service. Data have been collected using both of the commonly used VLF waveforms, there is little evidence of a significant difference in outcomes that can be ascribed to the voltage waveform. A number of areas for further technically useful work have been identified.
43rd International Conference on Large High Voltage Electric Systems 2010, CIGRE 2010
author list (cited authors)
Hampton, R. N., Perkel, J., Hernandez, J. C., Begovic, M., Hans, J., Riley, R., ... Linte, G. C.
complete list of authors
Hampton, RN||Perkel, J||Hernandez, JC||Begovic, M||Hans, J||Riley, R||Tyschenko, P||Doherty, F||Murray, G||Hong, L||Pearman, MG||Fletcher, CL||Linte, GC