A nitrogen gas pressure system shall include a nitrogen cylinder installed as
described below, with a three-stage pressure regulating system, a pressure vacuum
gauge, pressure relief valves, and alarm contacts to indicate high and low nitrogen
pressure in the transformer tank and low nitrogen pressure in the cylinder. The
cylinder shall be furnished with the U.S. standard outlet connection for nitrogen
gas, designated by the Compressed Gas Association as CGA 580. The thread
specification is 0.965−14 NGO−RH−INT (0.965-inch [24.5 mm] diameter, 14
threads per inch, National Gas Outlet form, right-hand internal thread).
This system shall be furnished in two parts. The first part shall consist of a
weatherproof compartment that contains the active parts, such as, but not limited
to: the pressure regulator, gauges, high/low alarm contacts and empty cylinder
alarm contact, space heaters, and gas sampling parts. This compartment shall not
be located such that the top of the compartment is more than 6′ 0″ above the base
of the transformer. The second part of the insulating liquid preservation system is
a provision to secure the full-sized gas cylinder. This provision shall secure the
cylinder to the side of the transformer tank by means of chains or clamps.
The base of the cylinder shall rest either on the transformer foundation, or on
grating furnished by the customer that is on top of the crushed rock oil
containment. This grating could be as much as 12 inches below the transformer
base. The provisions (two minimum) to secure the cylinder shall be adjustable
such that the cylinder is plumb when it is secured. A flexible connection shall be
supplied to connect the cylinder to the regulating and alarm equipment.
All bracings on the transformer tank walls used for gas space shall be stenciled
with a warning to not drill, and shall be equipped with oil drain plugs