(3) In the case of the unit system, to provide startup power to each
unit auxiliary power system until the generator is up to speed and
voltage and is synchronized with the distribution system.
b) The startup and standby transformer and switchgear will be sized to
accomplish the above three functions and, in addition, to allow for possible future
additions to the plant. Interconnections will be provided between the common and unit
switchgear. Appropriate interlocks will be included, so that no more than one auxiliary
Type. Generators for power plant service can be generally grouped according
to service and size.
a) Generators for steam turbine service rated 5,000-32,000 kVA, are
revolving field, non-salient, two-pole, totally enclosed, air-cooled with water cooling
for air coolers, direct connected, 3,600 rpm for 60 Hz frequency (sometimes connected
through a gear reducer up to 10,000 kVA or more). Self-ventilation is provided for
generators larger than 5,000 kVA by some manufacturers, but this is not recommended for
steam power plant service.
b) Similar generators rated 5,000 kVA and below are revolving field, non-
salient or salient pole, self-ventilated, open drip-proof type, sometimes connected
through a gear reducer to the turbine with the number of poles dependent on the speed
selected which is the result of an economic evaluation by the manufacturer to optimize
the best combination of turbine, gear, and generator.
c) Generators for gas turbine service are revolving field, nonsalient or
salient pole, self-ventilated, open drip-proof type, sometimes connected through a gear
reducer, depending on manufacturer's gas turbine design speed, to the gas turbine power
takeoff shaft. Non-salient pole generators are two-pole, 3,600 rpm for 60Hz, although
manufacturers of machines smaller than 1,500 kVA may utilize 1,800 rpm, four-pole, or
1,200 rpm, six-pole, salient pole generators. Generators may be obtained totally
enclosed with water cooling, if desired, because of high ambient temperatures or
d) Generators for diesel service are revolving field, salient pole, air-
cooled, open type, direct connected, and with amortisseur windings to dampen pulsating
engine torque. Number of poles is six or more to match low speeds typical of diesels.
Standards. Generators shall meet the requirements of ANSI C50.10, C50.13, and
C50.14. These are applicable as well as the requirements of National Electrical
Manufacturers Association (NEMA) SM 23, Steam Turbines for Mechanical Drive Service, and
SM 24, Land Based Steam Turbine Generator sets 0 to 33,000 KW.