Transformer loading, what is rule for loading

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pes

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what is the rule of thumb when it comes to loading a 3 phase 480 transformer or any tranformer. ie.. KVA30 480v 3phase HV amps 36 / LV amps 83. how high can I load??
 
If you're the utility you size them conservatively at the beginning and eventually load them to 105%:roll:
 
jdsmith said:
If you're the utility you size them conservatively at the beginning and eventually load them to 105%:roll:
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And there is a problem with that? :confused:

The utility is always there to replace a transformer when it goes bad, if it ever does.

Furthermore, it makes no sense to have large transformers that are lightly loaded which just sit there and waste power in "standby mode." (for lack of a better term) {eddy current, hysterises, I squared R losses}
 
pes said:
what is the rule of thumb when it comes to loading a 3 phase 480 transformer or any tranformer. ie.. KVA30 480v 3phase HV amps 36 / LV amps 83. how high can I load??
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The rule of thumb for loading a transformer is that the hotter it gets the shorter its life will be. They will operate just fine above their rating by quite a bit, but the more you do it the faster it ages. Temperature = age.
 
thanks for the info most helpful.

thanks for the info most helpful.

I just wanted to make sure I was not missing anything major before we add to the existing transformer.:) :)
 
drbond24 said:
The rule of thumb for loading a transformer is that the hotter it gets the shorter its life will be. They will operate just fine above their rating by quite a bit, but the more you do it the faster it ages. Temperature = age.
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Actually the rule of thumb for insulation life is more specific.

You will halve the life of insulation for every 10C* rise.
 
weressl said:
Actually the rule of thumb for insulation life is more specific.

You will halve the life of insulation for every 10C* rise.
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I've actually had occasion to use this rule of thumb and it worked out quite well. I estimated the age of our tranformer to be 19.5 years, 12 years of actual age plus 7.5 years for a 30 minute heating event. We did a furanic compound test on the oil to estimate tranformer age and they came up with 20 years. :smile:
 
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