|
(Last update.... 7th
June 2013 ) |
6, 8, 25, 56, 45, 29 |
|
|
Motor not able to drive the load.. |
|
|
|
Some times,
motor draws good amount of armature current, but not able to drive the load connected
to it. Common reason for this observation is that the load is too much and is
beyond the capacity of motor to produce required torque. The dc drive is said
to have gone in “current limit”. This is visible on ammeter connected to the
drive. One will find that the motor starts drawing more and more current and
finally reaches a point where the ammeter appears to be stuck at one level.
If the ammeter is of analog type, the pointer becomes rock steady. If the
drive has not reached the current limit level, then the ammeter pointer
normally keeps on
moving up and down a bit. In such cases cause for no rotation
is not from excessive load. If the load is
mechanically not jammed or locked, and the drive goes in current limit, there
could be one more probable reason for this. It is possible that the “field
voltage” is absent and the mechanism to sense “field failure” condition is
bypassed! i.e. out of two magnetic fluxes produced by armature current and
field winding, required for production of torque, one is absent. If the filed voltage is also present and okay, there is another possibility, although remote, that the carbon brushes on the commutator are not making contact with commutator. In case of motors with 4 sets of brushes ( located at 90 degrees ) this situation is likely to occur. The armature current drawn by the motor is not at “electrical right angles” with respect to magnetic flux and therefore not able to produce any torque!
|
|
|
Download PDF version of these pages.
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Speed
control not satisfactory |
|
|
|
|
Your
comments and suggestions please |
|
Drive
stops all off a sudden.. |
|
|
|
|
|