Grid-Connected Low-Voltage Power Supply to Equipment on Transmission Line Structures

Electrical equipment installed on high-voltage (HV) transmission structures may require low-voltage (LV) electrical supply from the distribution network. For example, cell sites for communication antennas and warning lights are the most common applications in BC Hydro's system. Bringing the LV supply to the HV structures introduces a number of electrical concerns. The first concern is the transfer of ground potential rise (GPR) from the HV system to the LV system during a ground fault on the transmission structure. The second concern is the induction in the LV system due to the proximity to the HV transmission line. In addition, there could be system impacts that require special attention, such as reduction in circuit-to-circuit separation in multiple-circuit corridors, pole fire on the LV wood poles, etc. This paper discusses technical solutions to mitigate the identified concerns and system impacts. Amongst the possible recommendations, addition of appropriately rated isolation transformers to the LV feeder and improving the electrical grounding on the HV transmission structure are shown to be the most effective methods for preventing the transfer of hazardous potentials to the customers connected to the same LV feeder. The proposed isolation circuit has been tested in a HV laboratory to confirm its effectiveness.