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It is the intent
of a thermograph inspection to survey a number of pieces of electrical
and mechanical equipment, as selected by you, the customer, with the objective
of locating potential problems and determining their priority. |
| Background; |
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Thermal radiation
(heat) is constantly being emitted by all objects around us and is converted
into a television like picture by specialized infrared scanners. |
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This technique
for imaging and measuring heat is called Thermography. |
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The thermal images
produced by the infrared scanner allows for meaningful interpretation of
the thermal properties of various objects and at the same time makes it
possible to pinpoint potential problems at a stage where damage can still
be prevented and costly heat related problems can be identified. |
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Results; |
| The
results are presented in the form of a thermal image in the report. The
data with the resultant temperature differential(s) is given with the thermal
image. In the particular case of the electrical inspections, a temperature
differential at the hot phase to a normal phase is usually presented, called
temperature rise. As a rule of thumb guide, excess temperature measured
directly on the faulty part itself are divided into four categories, relating
to 50% of the maximum load. (see chart) |
| Ideally,
thermograph electrical inspections should be carried out under full load.
Since this is not often practical we apply a correction to the excess temperature
to estimate temperature rise under a 50% load condition. Otherwise the
magnitude of the problem can be seriously understated. |
| In
order to assess excess temperature at a load which is less than 50%, a
modified Joule's Law is used for re-calculation to 50%. |
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This gives a
corrected classification of the faults. However, the temperature change
and severity classification must be viewed along with type of equipment. |
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Temperature
Rise -
Phase to Phase |
Classification; |
| A:
Greater than 75 c |
Acute
overheating. Should be repaired at once. |
| B:
30 c - 75 c |
Developed
overheating. Should be repaired as soon as possible |
| C:
10 c - 29 c |
Second
stage of overheating. Should be attended to at the first opportune moment. |
| D.
Less than 10 c |
First
stage of overheating. Should be kept under control and repaired at the
next scheduled maintenance. |
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There are no
rules for the assessment of excess temperatures which are measured on indirectly
overheated surfaces. Indirect overheating can be caused by hidden faults,
e.g.: cracks inside a breaker where the temperature is measured from the
outside.
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Experience shows
that oil insulated transformers and breakers with internal faults where
an approximate temperature rise of 10% has been measured on the surface
are considerably hotter inside. Very often faulty parts are severely burnt. |
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