Partial discharge testing of unshielded cables

The power, control, and instrumentation cables can be critical components of a plant life extension program, especially for nuclear stations. However, in many situations, especially for older plants, the cables are unshielded. A major challenge in applying diagnostic tests to these cables is the lack of a well-defined, stable ground plane. In recognition of this difficulty, recent work at Ontario Hydro has sought to determine whether an adequate ground plane for testing such cables can be defined. Analytical and experimental studies have been carried out into the feasibility of grounding adjacent conductors to form a testable configuration. The results of impedance analyses and numerical calculations of the electric field distribution using finite element techniques have shown that a ground plane, although not completely uniform, can be formed using this method. Partial discharge was detected with high probability on unshielded cables in which adjacent conductors were grounded