1-phase dry-type xfmrs

[jojo]

hello good day.. want to ask advice. there's an existing 75kva single-phase transfomer 13.2kV/240v supplying a residential bldg. the owner wants the existing 6 circuits to be feed from an individual LV/LV dry-type transformer 240V/120V; 5- 3kva's(240Vpri/120Vsec) for 5 receptacle circuits and 1-10 kva(240Vpri-240/120Vsec) for 8000W range. im planning to separate the 5 circuits from the existing panel and place it in a new panel (100A). so there will be individual protection for the 6 transformers.. what im not sure if it's okay to connect this new panel to the existing distribution transformer? is there an available 120Vsec (only) for the LV/LV dry-type transformer? and also, should the transformer be loaded to 70% or 80% of the demand load?.. i need your advice. thanks.

 

[boboelectric]

Does your area go under the National Electric Code,2008?

 

[mickeyrench]

230v motor

230v motor

removing post in the wrong place, sorry for inconvienace.

 

[jojo]

yes, our area is also adopting the NEC.. aside from the PEC (Philippine Electrical Code)

 

[augie47]

most of the LV transformers I've sen can be wired so the secondary can be 240/120 or straight 120 depending on how you connect the leads.
I know of no Code reason you can't connect the transformers at 100%.

 

[jojo]

thanks augie47.. maybe i'll load the trnsformer up to 70% or 80% for its long lifespan and for reserve capacity. for the LV/LV dry-type transformer primary and secondary feeders, i used 1.25 times the trnsformer full-load current. for their corresponding protection: for the the primary i use again 1.25 times IFL primary (20AT for 3kVA, 240V primary), and for the secondary i selected 20AT (IFL sec=25A at 120V) for effective overload protection. because if i use 30AT for the secondary, its secondary windings might burn (Ifl sec=25A).

 

[augie47]

you may need to increase your primary protection to avoid an inrush problem. with you secondary protection at 1.25 your primary can be 2.5

 

[jojo]

thanks gus.. NEC Table 450.30(A).