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Anonymous Poster #1

HRC Fuse Blow

11/15/2019 6:03 PM

I have came across many incidences when a 3 phase motor insulation fails in one winding (winding to body) with the other two windings are ok (winding to winding as well as winding to body). But always noticed that two fuses blow together. Why so?
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Brave Sir Robin
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#1

Re: HRC fuse blow

11/15/2019 7:10 PM

Draw a schematic of a three-phase winding with a fuse in each of the lines. Then show a short circuit from one winding to the body (earth). You will see the answer.
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raghun
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#2

Re: HRC fuse blow

11/16/2019 12:11 AM

Could it be Delta connected motor!!

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Stef
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#3

Re: HRC Fuse Blow

11/17/2019 2:31 AM

Two of the windings in delta connection will both feed the fault that is why the fuses blow because the resistance between the ends of the faulty winding is decreased by the earth fault making the winding two parallel paths via the earthed neutral connection.

I believe that if one winding shorts to earth then both the other windings will show a low resistance to earth. For the other two windings not to show a low earth resistance then the winding with the fault has blown clear or the method of testing is inadequate for the supply voltage unless the terminal box has been opened and all the winding leads separated from each other.

Anyway it doesn't matter for when the new motor is installed all the fuses should be changed not just the failed ones because the other fuse may/will have been stressed.

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vimal76
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#4

Re: HRC Fuse Blow

03/10/2020 11:14 PM

The two phases feed the fault that is why the two fuses blown off when there is insulation failures in any of the winding.
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