300kva useable amp Calculation hv 480 3p to 240v 3p delta

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Zaster

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How many amp at 240v are available total and to use? Also when using a meter with CT’s like myeyedro how many amps per phase on the 480v line side are available total and useable and per phase?


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If 240 is a secondary of a 300kva transformer, then solve for Amps

300,000 / 240 / 1.732 / Power factor from utility and/or connected loads
 
This is what is confusing me when I look at the my eyedro ct reading, it adds the amp reading per phase but does that total correspond to the actual total amps I have available? Because it appears as though I’m already over on useable amps but I know I’m not. The CT’s are 600A rated that why it Is in there like that.

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'Total' amps is rarely used because it is only indirectly related to a measurement of interest.

Circuits are rated by the phase amp rating. A 300A circuit is rated for 300A on each phase conductor. A 300A breaker has a 300A trip element on each pole. So your eyedro is correctly reported the value for each phase.

Devices like generators and transformers are rated for total kVA assuming a balanced load, and something like a generator prime mover will be rated for total kW. 'Total amps' can be used to approximately calculate total kVA being used. But since you are also limited by the assumption of balanced loading, you can't simply use the total amp number and assume you are fine.

A 300kVA 480V three phase system is nominally 360A. This could be expressed as 1080 total amps, but if you had 500A on phase A and 500A on phase B (total 1000A) then the system would still be overloaded. Better to ignore total amps and just look at individual phase amps.

More useful would be if the eyedro could be configured to report neutral current. Is it possible that the unit is trying to do this but is somehow misconfigured?

Jon
 
I don’t believe it is misconfigured it may be a limitation of the product itself. The only variables that can be set in this product are in the photos (power factor and amp multiplier and both are set = 1.) I have attached screenshots below. Let me know what you think.

When I take the total number of amps on the 480 volt side or calculate by phase to determine how much of the 300kva transformer is being used (480v x amps = kva) am I able to safely use the full 300kva or do I need to derate it by .8? Asking because the available kva/amps will differ depending on whether it can be used closer to 100% or 80% of the 300kva.


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Also, is the 300kva 3P 480v to 3P 240v delta xfmr able to be used up to 300kva or is it advised to use upto 80%? I have found conflicting information regarding this.


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