Insulation life is affected by many other factors, such
as cyclical loading duty, cleanliness, and rate of
loading. so general conclusions on effect of
temperature on insulation life are difficult to make.
as cyclical loading duty, cleanliness, and rate of
loading. so general conclusions on effect of
temperature on insulation life are difficult to make.
5. HOTTEST SPOT ALLOWANCE
Insulation deterioration at a given temperature is
approximately proportional to the length of time that
the temperature is above the limiting value. Hottest
spot temperatures shown in
approximately proportional to the length of time that
the temperature is above the limiting value. Hottest
spot temperatures shown in
are not directly
measurable values in actual machines and are,
therefore, not used in machine ratings. Usual
methods for measuring winding temperatures are
embedded RTD's (resistance temperature detectors)
or by measuring the winding resistance. The latter
method is dated and is not used with newer
machines; new machines have RTD's to measure
winding temperatures and RTD's are being phased
in to replace old temperature measuring methods as
older machines are rewound or uprated. The
measurable or "observable" temperature indicated
by these devices will be less than the hottest spot
temperature by an amount known as "temperature
gradient" or "hottest spot allowance.' The actual
hottest spot allowance varies with machine design,
and, therefore, the limiting temperature rise is not
the same for all machines. Values of limiting
observable temperature are shown in
therefore, not used in machine ratings. Usual
methods for measuring winding temperatures are
embedded RTD's (resistance temperature detectors)
or by measuring the winding resistance. The latter
method is dated and is not used with newer
machines; new machines have RTD's to measure
winding temperatures and RTD's are being phased
in to replace old temperature measuring methods as
older machines are rewound or uprated. The
measurable or "observable" temperature indicated
by these devices will be less than the hottest spot
temperature by an amount known as "temperature
gradient" or "hottest spot allowance.' The actual
hottest spot allowance varies with machine design,
and, therefore, the limiting temperature rise is not
the same for all machines. Values of limiting
observable temperature are shown in
apply only to
insulating materials themselves and not to
equipment in which they are used. To provide a
reasonable service life for insulation in equipment,
rated temperature rise should be used as the
machine base allowable temperature.
equipment in which they are used. To provide a
reasonable service life for insulation in equipment,
rated temperature rise should be used as the
machine base allowable temperature.
6. LIMITING TEMPERATURE RISE
Observable temperature rise of each of the various
parts of a rotating machine above the temperature of
the cooling air should not exceed values given in
parts of a rotating machine above the temperature of
the cooling air should not exceed values given in
factor, voltage, and kVA (hereafter called rated
load). For open machines and for parts of enclosed
machines which are cooled by open ventilation, such
as collector rings, cooling air temperature is the
average temperature of the external air at entrances
to the ventilation opening of the machine. For totally
enclosed machines, cooling air temperature is the
average temperature of air leaving the coolers. In no
event should cooling air temperature exceed 40 °C.
Machines whose observable temperature rise at
rated load exceeds values given in
machines which are cooled by open ventilation, such
as collector rings, cooling air temperature is the
average temperature of the external air at entrances
to the ventilation opening of the machine. For totally
enclosed machines, cooling air temperature is the
average temperature of air leaving the coolers. In no
event should cooling air temperature exceed 40 °C.
Machines whose observable temperature rise at
rated load exceeds values given in
should be
considered to have a reduced operational capacity
to correspond to a loading value which does not
exceed temperature rise values given in the table.
to correspond to a loading value which does not
exceed temperature rise values given in the table.
7. OPERATION OF MACHINES UNDER
WARRANTY
WARRANTY
New, newly uprated, or newly rewound machines
operating under the manufacturer's warranty should
not be loaded above design values. If the results of
acceptance tests or the observation of station
instruments should show that a machine will exceed
temperature rise limitations of specifications, the
machine should not be operated above these
limitations until the contractor has had the
opportunity to make the necessary corrections to the
equipment. This is necessary to avoid nullifying
contractual warranties on equipment as well as to
permit a period of close observation of performance
of new equipment to evaluate the desirability of
allowing increased loading. After acceptance of the
machine and analysis of heat runs, the Denver
Office will prepare and issue capability curves for
subsequent operational use (par.20).
operating under the manufacturer's warranty should
not be loaded above design values. If the results of
acceptance tests or the observation of station
instruments should show that a machine will exceed
temperature rise limitations of specifications, the
machine should not be operated above these
limitations until the contractor has had the
opportunity to make the necessary corrections to the
equipment. This is necessary to avoid nullifying
contractual warranties on equipment as well as to
permit a period of close observation of performance
of new equipment to evaluate the desirability of
allowing increased loading. After acceptance of the
machine and analysis of heat runs, the Denver
Office will prepare and issue capability curves for
subsequent operational use (par.20).
8. OPERATION UP TO RATED CAPACITY
Hydroelectric generators fail into the following of
the five categories:
the five categories:
a. Old machines that have not been rewound or
uprated.
b. Old machines that have been rewound.
3
(FIST 1-4 3/91)