A study on analysis of defects for hydro generator power transmission cables using VLF testing and diagnostic measurements

For decades DC (Direct Current) has been used to assess the condition of medium and high voltage power cables. There are several advantages using this DC test due to its low weight, portability, usability, and being cost-effective. Meanwhile, this DC method has its limitations including possible destructive consequences [1]. It has caused cable failures due to `charges´ trapped in the insulation. This induced local field stress when AC power reenergized and accelerated the growth of water-trees. Therefore, recently the Very Low Frequency (VLF) test has been recommended to use as an installation test of XLPE insulated cables according to IEEE standards. In this paper the VLF cable test will be studied in detail for testing XLPE power cables using the Tan δ and Partial Discharge measurements. The focus is to detect any existing fault, defects, or irregularities at the inspection of the cables before any breakdowns occur. The test data on service aged XLPE cables used in hydro power generators will be analyzed.