Self-Powered On-Line Signal Injection Based on a Current Transformer

An on-line signal injection approach based on a special current transformer is proposed as part of a solution for improving the test set-up of transfer function diagnostics of transformers. However, the method is general and applicable to many types of sub-system equipment, such as breakers and transmission lines. The system allows a high-power, high-frequency test signal to be injected directly on a high-voltage bus of an energised system. Due to the self-contained nature of the system, no external power supplies or signal generators are needed and the design does not need to be ground-referenced. The system can be at the bus potential. In conjunction with wireless communication for control, no isolator bushings are required and the device can be constructed as a sleeve to be mounted around the bus-bar. This allows for economical retro-fitting to existing installations. In this paper, the operational need for such an injection device is discussed, followed by the theory behind the proposed concept. An example injection core for a 512 kV system is designed to show the practical validity of the concept and numerical simulations are performed for validation. It is shown that the injection concept is a viable, high-power, wide-band signal source for on-line equipment testing.