MIL-HDBK-1003/7
a)
ANSI C84.1 designates standard voltages as discussed in
Section 1.
b) Generator kVA rating for steam turbine generating units is standardized
as a multiplier of the turbine kW rating. Turbine rating for a condensing steam turbine
with controlled extraction for feedwater heating is the kW output at design initial
steam conditions, 3.5 inches Hg (12 kPa) absolute exhaust pressure, three percent cycle
makeup, and all feedwater heaters in service. Turbine rating for a noncondensing
turbine without controlled or uncontrolled extraction is based on output at design
initial steam conditions and design exhaust pressure. Turbine standard ratings for
automatic extraction units are based on design initial steam conditions and exhaust
pressure with zero extraction while maintaining rated extraction pressure. However,
automatic extraction turbine ratings are complicated by the unique steam extraction
requirements for each machine specified. For air-cooled generators up to 15,625 kVA,
the multiplier is 1.25 times the turbine rating, and for 18,750 kVA air-cooled and
hydrogen-cooled generators, 1.20. These ratings are for water-cooled generators with 95
degrees F (35 degrees C) maximum inlet water to the generator air or hydrogen coolers.
Open, self-ventilated generator rating varies with ambient air temperature; standard
rating usually is at 104 degrees F (40 degrees C) ambient.
c) Generator ratings for gas turbine generating units are selected in
accordance with ANSI Standards which require the generator rating to be the base
capacity which, in turn, must be equal to or greater than the base rating of the turbine
over a specified range of inlet temperatures. Non-standard generator ratings can be
obtained at an additional price.
d) Power factor ratings of steam turbine driven generators are 0.80 for
ratings up to 15,625 kVA and 0.85 for 17,650 kVA air-cooled and 25,600 kVA to 32,000 kVA
air/water-cooled units. Standard power factor ratings for gas turbine driven air-cooled
generators usually are 0.80 for machines up to 9,375 kVA and 0.90 for 12,500 to 32,000
kVA. Changes in air density, however, do not affect the capability of the turbine and
generator to the same extent so that kW based on standard conditions and generator kVA
ratings show various relationships. Power factors of large hydrogen cooled machines are
standardized at 0.90. Power factor for salient pole generators is usually 0.80. Power
factor lower than standard, with increased kVA rating, can be obtained at an extra
price.
e) Generator short circuit ratio is a rough indication of generator
stability; the higher the short circuit ratio, the more stable the generator under
transient system load changes or faults. However, fast acting voltage regulation can
also assist in achieving generator stability without the heavy expense associated with
the high cost of building high short circuit ratios into the generator. Generators have
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