Grid Compatibility of a High Frequency Current Transformer Designed for Coupling to the Cable Central Conductor

The presented research lies in the field of partial discharge (PD) signal acquisition for testing and monitoring of high voltage AC and DC cable systems. A high frequency current transformer (HFCT) is a well-known device for coupling of PD signals at electrical equipment. In high voltage cable systems, the coupling is often carried out at shields of joints and terminations. The use of this position has the benefit of absence of rated current. However, this approach leads to a locally sensitive PD detection, resulting in the requirement to measure every critical component (e.g. every joint and termination). Coupling to PD signals in the cable core might be more effective for reaching a high global sensitivity. This is essential in respect of the ongoing rapid development of the long cable corridor projects. Available on the market HFCTs cannot be used for coupling to the cable core due to the low saturation currents and small apertures. In this paper, at first, the grid compatibility requirements for a cable-core-coupled HFCT were defined. According to them, the development and experimental validation of the prototype was performed. Particularly, the influence on the grid and the ability to withstand stationary as well as dynamic operating conditions while maintaining sufficient performance were investigated.