Transfomer faults

[mbrooke]

Does typical NEC over current protection protect transformers from turn to turn faults? Are turn to turn faults appreciable in transformers under 5 MVA? When would I need to consider differential protection under the NEC- or in general?

 

[Bugman1400]

Does typical NEC over current protection protect transformers from turn to turn faults? Are turn to turn faults appreciable in transformers under 5 MVA? When would I need to consider differential protection under the NEC- or in general?

No and no. Use diff for 20MVA (base rating) and above.

 

[mbrooke]

No and no. Use diff for 20MVA (base rating) and above.

Why the change at 20MVA (just curious)?

 

[NewtonLaw]

When to use Transformer Differential Protection?

When to use Transformer Differential Protection?

Why the change at 20MVA (just curious)?

The answer comes down to the cost of failure and subsequent damage due to it. This includes the transformer that has failed, possible personnel hurt or killed due to the explosion, possible fire, environmental oil spill, projectile emission of steel, hot copper, bushing porcelain, etc.

Consider a set of four transformers set close enough to each other that the failure and fire on one could easily place the remaining three in danger of damage and failure. Consider these serve a hospital where lives depend on having adequate power available, or a production facility that for loss of primary power supply will mean shut and loss of product and production that could run in to millions. Trans Diff clears the failed transformer long before any eruptive failure. TD along with sudden pressure relays usually cover almost everything not protected by some thermal relay system.

Size of the transformer is a small consideration and transformer differential protection may be added to any transformer, so it comes down to what is the justification?

Hope this helps.

 

[mbrooke]

The answer comes down to the cost of failure and subsequent damage due to it. This includes the transformer that has failed, possible personnel hurt or killed due to the explosion, possible fire, environmental oil spill, projectile emission of steel, hot copper, bushing porcelain, etc.

Consider a set of four transformers set close enough to each other that the failure and fire on one could easily place the remaining three in danger of damage and failure. Consider these serve a hospital where lives depend on having adequate power available, or a production facility that for loss of primary power supply will mean shut and loss of product and production that could run in to millions. Trans Diff clears the failed transformer long before any eruptive failure. TD along with sudden pressure relays usually cover almost everything not protected by some thermal relay system.

Size of the transformer is a small consideration and transformer differential protection may be added to any transformer, so it comes down to what is the justification?

Hope this helps.

No it helps As is Id think differential might drive the cost up a tad on a 75kva unit. :lol:

 

[jim dungar]

Does typical NEC over current protection protect transformers from turn to turn faults?

There is almost no protective device that will protect a transformer from developing a turn-turn fault. That is not what typical protective devices do.
The commonly used protection schemes, including transformer differential, are there to remove faulted equipment from service, in order to reduce the amount of additional damage both to the equipment and the 'system'.

 

[mbrooke]

There is almost no protective device that will protect a transformer from developing a turn-turn fault. That is not what typical protective devices do.
The commonly used protection schemes, including transformer differential, are there to remove faulted equipment from service, in order to reduce the amount of additional damage both to the equipment and the 'system'.

I know, but my question is what happens when a transformer does develop a turn to turn fault.

 

[jumper]

I know, but my question is what happens when a transformer does develop a turn to turn fault.

Well it's kinda technical.......

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