5.3.1 Relative temperature monitoring
The recommended generic guidelines for setting the thresholds based on the relative
change are:
T
Advise
= 10°C increase
T
Maintenance
= 15°C increase
T
Failed
= 20°C increase
Assuming that the ambient temperature is 25°C, when operating at steady-state, you have
determined that the normal temperature at this point on your equipment is 55°C. Your
"baseline" relative difference is 30°C. Using these guidelines, you should choose the Advise,
Maintenance, and Failed levels for a difference of 40°C, 45°C, and 50°C, respectively.
Assuming the ambient temperature is constant at 25°C, this means the thresholds
become 65°C, 70°C, and 75°C for Advise, Maintenance, and Failed, respectively. Then, as
the ambient temperature changes, the thresholds should be changed accordingly (e.g., a
5°C increase in ambient temperature raises the alert thresholds by 5°C).
5.3.2
Absolute temperature monitoring
For monitoring a driven component (such as a pump or fan), there are no generic rules to
determine the default levels without some prior knowledge of the steady-state baseline
(good) value. In general, the Advise level should be set about 10°C to 20°C above this
baseline, with the Maintenance level about 10°C above Advise and the Failed level about
10°C above Maintenance.
There are equations that define the suggested generic thresholds for monitoring motor
(driver) temperature. These are based on characteristics of the motor as well as
knowledge of the ambient temperature.
The first step is to determine the estimated winding temperature, which is dependent on
the following variables:
• Insulation type
• Motor type
• Ambient temperature
• Altitude
The estimated winding temperature, T
W
, is the rise in temperature, T
rise
, for the
appropriate type of motor adjusted for high ambient temperature (T
a
) effects.
T
rise
=
• 65°C + serv_fact_temp; for class A insulation
• 85°C + serv_fact_temp; for class B insulation
• 110°C + serv_fact_temp; for class F insulation
• 130°C + serv_fact_temp; for class H insulation
• 150°C + serv_fact_temp; for class N insulation
where serv_fact_temp =
User Guide Overall Velocity, PeakVue, and temperature
MHM-97927-PBF July 2020
MHM-97927-PBF, DRAFT 61
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