This chapter organises the lightning interactions with power transmission lines from the simple consequences of a direct stroke attachment to an unshielded line, to the complex consequences of a stroke attachment to shielded line with multiple groundwires, including the UBGW effects from phases with TLSA protection. It builds on the information in Chapters 1 and 2 of this volume to develop important measures in transmission line lightning performance: N L , the number of fl ashes (100 km) -1 year -1 of line length per year, and the number of those fl ashes that bypass an OHGW, giving a Shielding Failure Flashover Rate (SFFOR) with the same units. Simplified models from industrial standards are then used to illustrate important principles and concepts such as the 'critical current' that just causes backflashover from a normally earthed component to a phase conductor. Matrix methods are used to manage the self and mutual surge impedance, with sample calculations shown using Microsoft Excel Tm as a common language. Specialised computer programs to calculate BFR on lines with OHGW and full or partial application of TLSA are described further in Chapter 12 of this volume.

Chapter Contents:

• 3.1 Lightning attachment to overhead transmission lines
• 3.1.1 Overhead line attachment rates using ground flash density and typical dimensions
• 3.1.2 Local voltage rise from lightning attachment to transmission line phase conductor
• 3.1.2.1 Surge impedance of single conductor over earth
• 3.1.2.2 Surge impedance response of short conductor over earth
• 3.1.2.3 Surge impedance response of long conductor over earth with no corona
• 3.1.2.4 Interaction of lightning channels with long conductors
• 3.1.2.5 Surge impedance response of long, single conductor over earth including corona
• 3.1.2.6 Surge impedance response of bundle of conductors over earth with no corona
• 3.1.3 Role of span length and nearby arresters on peak insulator voltage
• 3.1.4 Shielding of transmission line phase conductors using overhead groundwires
• 3.2 Lightning impulse flashover of power transmission line insulation
• 3.2.1 Lightning impulse voltage test waveshapes
• 3.2.2 Single gap full-wave flashover strength for dry arc distance of 0.5 to 10 m
• 3.2.2.1 Full lightning impulse waveshape for first stroke
• 3.2.2.2 Volt–time curve for standard lightning impulse waveshape
• 3.2.2.3 Full lightning impulse waveshape for subsequent strokes
• 3.2.2.4 Effects of nonstandard voltage waves
• 3.2.3 Strength of multiple air gaps in parallel under shielding failure conditions
• 3.2.4 Strength of multiple air gaps in series
• 3.2.5 Evolution of surge protective devices for insulation coordination
• 3.2.6 Design and performance of unshielded power transmission lines
• 3.2.6.1 Critical current for first return stroke to phase
• 3.2.6.2 Critical current for subsequent return stroke to phase
• 3.2.6.3 Probability of exceeding critical current with any stroke in a flash
• 3.2.6.4 Predicted and observed flashover rates of unshielded lines
• 3.3 Bonding, earthing and equalisation of potential differences on transmission lines
• 3.3.1 Analysis of transient voltage rise on connections from OHGW to earthing electrodes
• 3.3.1.1 Conical antenna surge impedance
• 3.3.1.2 Surge impedance from capacitance
• 3.3.1.3 Surge impedance of prisms, triangular plates and bow-tie antennas
• 3.3.1.4 Surge impedance of antennas of arbitrary shape
• 3.3.2 Analysis of transient voltage rise on earthing electrodes
• 3.3.2.1 Surge impedance of earth plane
• 3.3.2.2 Surge impedance of counterpoise
• 3.3.2.3 Soil resistivity and low-frequency, low-current resistance
• 3.3.2.4 Soil ionisation and effect on high-current lightning impulse impedance
• 3.3.2.5 Frequency dependence of soil resistivity and effect on lightning impulse impedance
• 3.3.2.6 Combined effects: simplified modelling of transient impedance
• 3.3.2.7 Combined effects: measuring transient impedance and resistivity
• 3.3.3 Analysis of transient voltage reduction from adjacent phases
• 3.3.4 Analysis of transient voltage rise on insulated phases from surge impedance coupling
• 3.3.5 The backflashover from OHGW to phase
• 3.3.6 Design and performance of shielded power transmission lines
• 3.3.7 Methods for increasing the backflashover critical current
• 3.3.7.1 Improvements to earthing impedance
• 3.3.7.2 Improvements to insulation
• 3.3.7.3 Improvements to tower surge impedance
• 3.3.7.4 Improvements to overhead groundwire systems
• 3.3.8 Methods for improving the equalisation of potential differences
• 3.3.8.1 Transmission line surge arresters on selected conductors, direct and indirect aspects
• 3.3.8.2 Under-built ground wires including OPGW retrofit projects, aerial and buried counterpoise
• 3.3.8.3 Co-located infrastructure with reduced insulation strength
• 3.3.8.4 Co-located infrastructure with arrester protection
• 3.4 Considerations in the design trade-off: arresters versus earthing
• References

Inspec keywords: power transmission lines; lightning protection; matrix algebra; power transmission reliability; flashover; power transmission protection

Other keywords: matrix methods; Microsoft Excel; lightning interaction; TLSA protection; SFFOR; shielding failure flashover rate; power transmission lines

Subjects: Power line supports, insulators and connectors; Power system protection; Reliability; Linear algebra (numerical analysis)