MIL-DTL-3124E(SH)
3.3.25 Electrical insulation. Class F systems, or greater, in accordance with UL 1446 shall be constructed for
250- to 1,000-volt generators.
3.3.25.1 Electrical insulation varnish. At least one vacuum pressure impregnation (VPI) process shall be used,
followed by two times dip-and-bake varnishing. Varnishing procedures for either VPI or dip-and-bake processes
shall not be used without prior approval from NAVSEA. When the VPI method is used, the type of coil or winding
shall be as specified (see 6.2).
3.3.25.2 Air dry varnish. Air dry insulating varnish shall not be used without prior approval from NAVSEA.
3.3.26 Totally enclosed generators. Totally enclosed generators rated 500 kilowatts and more shall be cooled
by one of the following methods as specified (see 6.2):
a.
Air-cooled with an air-to-water heat exchanger as specified in 6.2.
b.
Liquid-cooled with a liquid-to-water heat exchanger.
3.3.26.1 Air-cooled generators. Air-cooled generators with air-to-water heat exchangers shall be as specified in
3.3.26.1.1 through 3.3.26.1.3.
3.3.26.1.1 Air cooler. The generator air cooler shall be in accordance with MIL-C-19836. Protective zincs
shall not be required when fresh water cooling is specified (see 6.2). Unless otherwise specified (see 6.2),
construction shall be based on the following:
a.
Coolant inlet temperature range of 34 to 95 °F (1.11 to 35 °C).
b.
Coolant pressure drop in accordance with MIL-C-19836.
Coolant system design pressure of 150 pounds per square inch (lb/in2) gauge.
c.
d. Operation of the turbine generators and cooler at design coolant flow with no throttling required over the
specified range of coolant inlet temperatures.
e.
Water coolant flow as specified in applicable equipment specifications.
f.
Heat transfer capability as specified in applicable equipment specifications.
3.3.26.1.1.1 Water connections. Water connections to cooler heads or waterboxes subject to design or
operating pressure in normal operation shall be integral or welded to the heads in accordance with
S9074-AR-GIB-010/278; brazing of pipe connections to cooler heads shall be prohibited. Connecting flanges shall
be in accordance with 810-1385861. Flanges shall be edge drilled and tapped for Military standard threaded
pressure tap connections. If cooler heads or waterboxes have existing, accessible, Military standard threaded vent or
drain connections, flanges need not be drilled and tapped. After completion of pressure drop testing plugs, in
accordance with SAE-J1926/1, with O-ring seals, shall be installed.
3.3.26.1.1.2 Vent and drain connections. Vent and drain connections shall be in accordance with SAE-J1926/1,
¾-16 UNF-2B.
3.3.26.1.2 Condensation drain. Condensation liquid shall drain to the outside of the machine without
contacting electrical windings.
3.3.26.1.3 Generator air temperature measurement. The generator air temperature RTEs shall be located to
measure the temperature of air to and from the generator air cooler. Air temperature RTEs shall be removable
without the removal of the complete air cooler cover.
3.3.26.2 Liquid-cooled generators. Liquid-cooled generators shall provide a cooling liquid-to-water heat
exchanger with construction as specified in 3.3.26.1.1.
3.3.26.3 Electric heaters. Electric heaters, in accordance with MIL-H-22577, shall be provided. The size and
number of heaters shall prevent condensation of moisture on the windings. The heaters shall be readily removable
for replacement from the outside of the generator without removing more than the access covers.
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