Electrical Model of Phase-to-Woodpole Bird Electrocution

The electrocution of large birds such as eagles and vultures when making simultaneous contact between a phase conductor and the top of a pole on medium voltage woodpole distribution lines is addressed. System (phase-to-phase) voltages of 11 kV, 22 kV and 33 kV are covered. This phenomenon has been investigated by measurement of the resistance of poles used in the field, as well as measurement of the impedance of recently deceased birds. This has previously been used to compile a simple electrical model for 22 kV systems. This paper compiles a detailed model that is used to estimate the risk posed to large birds by this mode of electrocution for all three voltage levels. The results show that only a few scenarios exist whereby a bird may be at risk, which ties in with field experience. Details of how the wood and bird resistance was measured are also included, as are details of calculations performed.