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 4.5.2
Grounding. Provide protection for smokestacks as described in
para. 4.8, and ground all steel columns, beams, trusses, and equipment frames
at their lowest points to a low resistance station grounding system.
4.6
Outdoor Substations or Switching Stations. All overhead feeders
shall be provided with surge arresters at the station which shall be connected
to their own ground rod system. The ground rod system shall be connected
below grade to the station ground mat. Refer to IEEE 80, Guide for Safety in
Substation Grounding, and IEEE 81, Guide for Measuring Earth Resistivity,
Ground Impedance, and Earth Surface Potentials of a Ground System. Additional
protection shall be as described in paras. 4.6.1 through 4.6.3.
4.6.1
Air Terminals. On distribution metal station structures, provide
lightning
rods at each corner of the station, extending rods above the
structure
and the electric conductors. Connect the structure and all
equipment
frames, transformers, tanks, and bases to a low resistance grounding
system.
4.6.2
Grounded Aerial Conductors. In areas where lightning storms are
prevalent, install overhead ground conductors above the transmission and
distribution system conductors to form a ground wire network over distribution
stations. Extend the overhead ground wires out over transmission lines for a
minimum of 1/2 mile (0.8 km). Aerial ground wires shall be grounded at the
station and at each pole.
4.6.3
Grounding. Provide a ground system of No. 2/0 AWG (67.4 mm)
copper cable, welded to the columns and equipment frames and connected to a
ground system. Provide a ground mat for stations supplying distribution
voltages and a counterpoise for substations supplying utilization voltages.
A ground mat shall consist of a system of bare conductors located on or below
grade throughout the station and connected to a counterpoise to provide
protection from dangerous touch voltages.
4.7
Transmission and Distribution Lines. Overhead aerial lines shall be
provided with lightning protection coordinated with NFGS-16302 and in
accordance with standard utility practice at the project location. Acceptable
shielding results when a perpendicular line from grade to the ground wire and
when a line from the ground wire to the conductor protected do not result in
an angle greater than 30. Overhead ground wires may be steel, copper,
aluminum, or copper clad steel, with sizes dependent upon mechanical
requirements but not smaller than No. 1/0 AWG (53.5 mm) copper-equivalent.
Ground the overhead ground wires at each pole. Where an overhead electric
transmission and distribution line transitions to underground, the underground
cable shall be provided with lightning protection.
4.7.1
Distribution Line Clearances. The towers or poles supporting
distribution lines operating at less than 69 kV, and unmanned electric
substations operating at less than 69 kV, shall not be closer to ordnance
facilities than public traffic route distances as defined in DOD-STD-6055.9.
4.7.2
Transmission Line Clearances. For transmission lines operating at
69 kV and
above, and for electric substations operating at 69 kV and above
which are
part of a system serving a substantial off base area, both the
towers or
poles supporting the lines and the stations shall not be closer to
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