from no load to full load. On these units,
the cooling water temperature is varied by
mixing warm discharge water with fresh
cool water as required to minimize
temperature variations.
the cooling water temperature is varied by
mixing warm discharge water with fresh
cool water as required to minimize
temperature variations.
13. SUPPLEMENTAL COOLING
For air/water-cooled units, when not limited by the
mechanical capability, the capacity may be
increased by using colder water, or by increasing
the quantity of water circulated through the coolers.
Open-type units depend on the surrounding air for
the removal of heat. By increasing circulation of
the air, or by cooling the air in some manner,
capacity of open-type machines can be increased,
but temperature rise limitations of
mechanical capability, the capacity may be
increased by using colder water, or by increasing
the quantity of water circulated through the coolers.
Open-type units depend on the surrounding air for
the removal of heat. By increasing circulation of
the air, or by cooling the air in some manner,
capacity of open-type machines can be increased,
but temperature rise limitations of
must be
kept in mind. Ventilating fans may be used to direct
air toward the machine. Advantage should be
taken of windows and doors to admit outside air. In
several instances, cooling has been improved by
building a duct to bring outdoor air directly into the
turbine pit and eliminating the possibility of warm
air exhausted from the generator being recirculated
into the machine, if artificial cooling of the air is
attempted, care should be taken to prevent
moisture or dusty air from being drawn into the
generator.
air toward the machine. Advantage should be
taken of windows and doors to admit outside air. In
several instances, cooling has been improved by
building a duct to bring outdoor air directly into the
turbine pit and eliminating the possibility of warm
air exhausted from the generator being recirculated
into the machine, if artificial cooling of the air is
attempted, care should be taken to prevent
moisture or dusty air from being drawn into the
generator.
14. KEEPING MACHINES CLEAN
Another factor which should be watched in
machines, especially if they are to be overloaded,
is accumulation of dust and dirt. Dust and dirt
hinder heat dissipation and can adversely affect
the voltage grading system; therefore, internal
cleanliness of the machine is important to assure
proper cooling and retention of the voltage grading
should be cleaned regularly to assure maximum
heat transfer. When generator temperatures
appear to be getting higher, temperature data
should be compared with log sheet data of past
years, or cleaned to determine the amount of
temperature when the machine was new, or just
after being rise due system. Particular attention
should be given to field winding because dirt is
more apt to deposit on irregular surfaces.
Inspection should be made of ventilating passages
of the stator core for dirt accumulations. For
machines having recirculating systems, the cooler
should be cleaned regularly to assure maximum
heat transfer. When generator temperatures
appear to be getting higher, temperature data
machines, especially if they are to be overloaded,
is accumulation of dust and dirt. Dust and dirt
hinder heat dissipation and can adversely affect
the voltage grading system; therefore, internal
cleanliness of the machine is important to assure
proper cooling and retention of the voltage grading
should be cleaned regularly to assure maximum
heat transfer. When generator temperatures
appear to be getting higher, temperature data
should be compared with log sheet data of past
years, or cleaned to determine the amount of
temperature when the machine was new, or just
after being rise due system. Particular attention
should be given to field winding because dirt is
more apt to deposit on irregular surfaces.
Inspection should be made of ventilating passages
of the stator core for dirt accumulations. For
machines having recirculating systems, the cooler
should be cleaned regularly to assure maximum
heat transfer. When generator temperatures
appear to be getting higher, temperature data
should be compared with log sheet data of past
years, or when the machine was new, or just after
being cleaned to determine the amount of
temperature rise due to accumulation of dirt and
estimate the benefit obtainable by cleaning.
Reduction of approximately 10 °C in the stator
temperature of of an open-type Bureau generator
resulted from a thorough cleaning and enable the
plant to carry more load during a critical period.
Where possible, suction should be used to clean
machines, since with this method the grit and
dust is not merely moved from one resting place
to another. Clean, dry compressed air at a
pressure of not over 276 kPa (40 lb/in
years, or when the machine was new, or just after
being cleaned to determine the amount of
temperature rise due to accumulation of dirt and
estimate the benefit obtainable by cleaning.
Reduction of approximately 10 °C in the stator
temperature of of an open-type Bureau generator
resulted from a thorough cleaning and enable the
plant to carry more load during a critical period.
Where possible, suction should be used to clean
machines, since with this method the grit and
dust is not merely moved from one resting place
to another. Clean, dry compressed air at a
pressure of not over 276 kPa (40 lb/in
2
) may be
used to blow dust out of the wound section or
other places not accessible to the suction
attachment. If dust is allowed to accumulate on
the windings, it not only prevents proper
dissipation of heat and circulation of cooling air
through ducts, but also tends to hold moisture and
oil against insulation. In the cleaning process, slip
rings and commutators should be cleaned of dust
to prevent abrasion. Oil should never be allowed
anywhere on machines except where it is required
for lubrication. Oil harms commutators by
carbonizing mica insulating segments between
bars. Oil on windings catches dirt and dust and
the resulting gummy compound hastens ultimate
failure of insulation. Flammable or highly toxic
cleaning mixtures such as carbon tetrachloride
should not be used. Several satisfactory
commercial solvents are now available for this
purpose. Windings should not be allowed to soak
in any solvent, but just enough solvent should be
used to loosen grease so that it can be wiped off.
Ample ventilation should be supplied for
workmen. Any oil leaks should, of course, be
promptly repaired.
other places not accessible to the suction
attachment. If dust is allowed to accumulate on
the windings, it not only prevents proper
dissipation of heat and circulation of cooling air
through ducts, but also tends to hold moisture and
oil against insulation. In the cleaning process, slip
rings and commutators should be cleaned of dust
to prevent abrasion. Oil should never be allowed
anywhere on machines except where it is required
for lubrication. Oil harms commutators by
carbonizing mica insulating segments between
bars. Oil on windings catches dirt and dust and
the resulting gummy compound hastens ultimate
failure of insulation. Flammable or highly toxic
cleaning mixtures such as carbon tetrachloride
should not be used. Several satisfactory
commercial solvents are now available for this
purpose. Windings should not be allowed to soak
in any solvent, but just enough solvent should be
used to loosen grease so that it can be wiped off.
Ample ventilation should be supplied for
workmen. Any oil leaks should, of course, be
promptly repaired.
15. TEMPERATURE OF OLD MACHINES
For older machines, special care should be taken
in determining the temperature of all parts if
operation at overload is contemplated. Many older
machines have stator core laminations of poor
quality steel and inadequate ventilating systems
for taking care of losses in the area close to the
air gap. Increased load or operation above normal
voltage means more leakage flux and even higher
temperatures for these machines. During
underexcited operation, some machines are
subject to above normal temperatures on end
and finger plates or laminations at each end of
in determining the temperature of all parts if
operation at overload is contemplated. Many older
machines have stator core laminations of poor
quality steel and inadequate ventilating systems
for taking care of losses in the area close to the
air gap. Increased load or operation above normal
voltage means more leakage flux and even higher
temperatures for these machines. During
underexcited operation, some machines are
subject to above normal temperatures on end
and finger plates or laminations at each end of
9 (FIST 1-4 3/9)