3.10 ground flash density (GFD)(Ng): The average number of lightning flashes per unit area per unit time
at a particular location.
3.11 guy insulator: An insulating element, possibly with elongated form and transverse holes or slots, for
the purpose of insulating two sections of a guy or provide insulation between structure and anchor and also
to provide protection in case of broken wires.
3.12 guy wire: A stranded cable used for a semi-flexible tension support between a pole or structure and
the anchor rod, or between structures.
3.13 induced voltage (lightning strokes): The voltage induced on a network or electric installation by a
nearby stroke.
3.14 lightning first return stroke: A lightning discharge to ground initiated when the tip of a downward
stepped leader meets an upward leader from the earth.
3.15 lightning flash: The complete lightning discharge, most often composed of one or more leaders from
a cloud followed by one or more return strokes.
3.16 lightning subsequent stroke: A lightning discharge that may follow a path already established by a
first stroke.
3.17 lightning outage: A power outage following a lightning flashover that results in system fault current,
thereby necessitating the operation of a switching device to clear the fault.
3.18 line lightning performance: The performance of a line expressed as the annual number of lightning
flashovers on a circuit kilometer or tower-line kilometer basis.
3.19 metal-oxide surge arrester (MOSA): A surge arrester utilizing valve elements fabricated from nonlinear
resistance metal-oxide materials.
3.20 nearby stroke: A lightning stroke that does not terminate directly on any part of a network but
induces a significant overvoltage in it.
3.21 overhead groundwire (OHGW): Grounded wire or wires placed above phase conductors for the
purpose of intercepting direct strokes in order to protect the phase conductors from the direct strokes. They
may be grounded directly or indirectly through short gaps. An OHGW also functions as a shield wire.
3.22 shielding angle: The angle between the vertical line through the overheadground wire and a line
connecting the overhead ground wire with the shielded conductor.
3.23 shield wire: Grounded wire(s) placed near the phase conductors for the purposes of: a) Reducing the
incidence of direct lightning strokes to phase conductors, b) Reducing induced voltages from external
electromagnetic fields, c) Lowering the self-surge impedance of an overhead groundwire (OHGW) system,
or d) Raising the mutual surge impedance of an OHGW system to the protected phase conductors. A
grounded neutral beneath a phase conductor functions as a shield wire (functions b,c,d) but not as an
OHGW (function a).
3.24 spark gap: Any short-air space between two conductors electrically insulated from or remotely
electrically connected to each other.
3.25 surge arrester: A protective device for limiting surge voltages on equipment by diverting surge
current and returning the device to its original status. It is capable of repeating these functions as specified