High current low voltage versus low voltage high current

[KasseemF]

Can someone explain to me what effects the following setup will have.

I am working for the first time with high voltage, I have a resort with a calculated load of 3500kVA that by simple calculation dy deviding by the 13.8kW and root3 give you just about 145A for the system.

Is there an issue if after the stepdown transformwer takes the voltage to 460V that the first overcurrent protection is 2000A? What effects could this have on the system?

Is that really how scurrent works from between high voltage and low voltage setups? Does the voltage increase that much just via a transformer?

and is it ok for the primary overcurrent protection on this property to be 200A?

 

[charlie b]

The problem with using a 2000 amp overcurrent device on the secondary is that it would be wasting more than half the capacity of the transformer. Take the same 3500 KVA, divide by 460 and divide again by root 3, and you get nearly 4400 amps. You can have secondary protection as high as 125% of that value, so the first OCPD can be close to 5500 amps.

Yes, that is how transformers work. Ignoring a small percentage of losses within the transformer, the 3500 KVA you put into the primary at 13,800 volts will give you 3500 KVA out of the secondary at 460 volts (are you sure it is not 480, by the way?).

You can protect the primary of any transformer at a value at least 125% of the primary current, and this particular transformer (over 600 volt primary side voltage) can be higher still. 125% of 146 amps is 182. The next standard overcurrent rating is 200, and so yes you can use that. You can even use a higher size, if needed.

 

[KasseemF]

strangely eneough though ,... the first overcurrent is a 200A but there is 600 amp transfer switch in front of that ... considerable waste of money.