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Motor gets overheated with no apparent reason....
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Motor can run hot for any of the
following reasons : 1. cooling inadequate due to air
leakages in the blower gasket 2. blower direction wrong 3. bearings faulty 4. gain adjustment of the drive
incorrect 5. Four quadrant dc drives which
have two sets of thyristors ( Two bridges connected in back to back manner )
can casue overheating of motor if the gain is not adjusted properly.
Monitoring Current waveform will show that both the thyristor bridges are
firing ( becoming on ) alternately at a fast rate. Torque is thus applied in
alternate directions. However, mechanically this is not felt due to inertia.
Net effect of torques in both directions is what is rotating the motor in one
direction. It is like saying that we
get a torque of say 3 units but it is as a result of two opposite torques of
unnecesarily high values. ( 23-20 =3, or 56-53=3 !) Torque of +56 and –53
units cause overheating of the winding, but it is 3 units which is driving
the load. 5. If motor runs normally at low
speeds, reduce the diameter of the pulley on the motor shaft. This will reduce the current
drawn for the same load, thus reduce the heating. |
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Download PDF
version of these pages.
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Speed control not satisfactory
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