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sauravbabu
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Transformer Fuses

06/21/2012 2:09 AM

Hi,
Is transformer LV fuse supposed to operate first than HV fuse?
Regards,sks
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Tornado
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#1

Re: transformer fuses.

06/21/2012 2:24 AM

That would be desirable, but I'm not sure whether it is required (which could vary by local Codes).

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sauravbabu
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#2
In reply to #1

Re: transformer fuses.

06/21/2012 2:37 AM

thanks,

i am considering a fault on LV side. Should a LV fuse operate for fault on HV side as well?

Regards,

sks
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PWSlack
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#4
In reply to #2

Re: transformer fuses.

06/21/2012 4:14 AM

No.

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tonykuphaldt
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#6
In reply to #2

Re: transformer fuses.

06/24/2012 9:29 AM

Fuses protect against excessive current. The only way a fuse will operate ("blow") is if the current through it is too great, for too long. If a transformer suffers a fault in its primary widing, this will cause excessive current on the primary (HV) side, but not on the secondary (LV) side. A fault in the secondary circuit, however, will cause current to increase for both the primary and secondary windings.

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nobodysomebody47
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#3

Re: transformer fuses.

06/21/2012 3:35 AM

Fault Analysis on LV & HV in Transformers

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V.I.Abraham
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#5

Re: Transformer Fuses

06/21/2012 8:33 AM

The protection in electrical systems are always graded. As far as possible the first protection whether it is fuse or breaker nearest to the fault must operate first to avoid the healthy circuits not to get affected by a fault on defective circuit. In case of failure of the nearest protective system with in the rated time the next above fuse or breaker should operate. The proper grading is essential to avoid undesired power outage at the same time provide proper protection to the system and life . So the LV fuse have to be defined to operate first before the fault current trips the transformer. In practical at times the transformer trips first in case of earth fault and short circuit because they are designed more sensitive and are very prompt in operation to avoid fire or accidents in line even if the LT protection fails.
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simbarashe gunzvenzve
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#7

Re: Transformer Fuses

06/26/2012 9:07 AM

If the fault is on the HV side, then the HV fuse blows: if on the LV, then the LV fuse. The idea is to isolate the transformer from the fault circuit. In the event of error (failure of fuse to blow)- then yes, a through fault on the HV side may cause the LV fuse to operate to take out the load.

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