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What are the causes for the field failure in a dc shunt motor and how to troubleshot?
Wiki User
∙ 11y ago
the field winding is just a single magnet
a single pole motor has two usually in series
to start the motor full voltage is put on the field
ok failure modes almost always insulation problems
water, metal chips short to ground
an overloaded motor can induce a reverse polarity in the field causing higher current or voltage (extreme conditions) this also reverses the tempory magnet in all the metal parts and can burn out the winding
to troubleshoot isolate the field put on an ohm meter check the resistance
nameplate will tell the current so 250V 1 a is 250 Ohms
if this in anywhere close there is probably an insulation failure
so find a megohmmeter sufficient to test the insulation
(minimum for 250v 2*250V +1000V or 1500V megger)
100s of megohms is probably safe and with the 1500v it will see any air gaps or pinholes in insulation.
dc is very unforgiving with arcing
if an arc gets started it wont stop until fuses blow
even enclosed motors have brushes and the carbon dust will get on the field windings so they should be cleaned OFTEN.
Wiki User
∙ 11y ago
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