help with power factor calculations 1

[bigheadted]

The main transformer that feeds our plant is a 100kva transformer that feeds a 1600kva breaker at 433v
how can i work out the maximum line current that i can pull on each phase before triping the breaker?

IL=(KVA.1000)/(VL.1.73)= 2135A per phase is this correct?

is it also true to say that if i have witnessed the plant running at full load of with a 0.98 pf p1=1659A
p2=1635A and P3 =1626A then i can use the figures as a rough guide to how much energy the press requires to turn at unity power factor and then calculate the affects of a lower power factor

KW= (IL.VL.1.73.PF)/(1000) taking the highest line current 1659A pf0.98 = 1218kw

Now if the power factor drops to 0.8

IL=(KW.1000)/VL.1.73.0.8= 2032A

am i along the right lines here because if i am thats very close to the breaker rating

The power factor correction we use consists of 15 banks of 46kvar delta connected three phase capacitors.
After checking it recently we found the yellow phase fuses blown on 12 of the 15 banks.
on the next production we lost the main breaker
How can i calculate the affects this would have had using the above data? could someone plese help me with the more complicated formulas
so that i can work it out for myself

 

[wareagle]

What you did looks ok. Using the information you have
caculate the PF with the cap off line. You don't have to guess at a PF. That the worst case condition. I did a quick check and with the caps off the load is 2086 amps.
You breaker is at 2135 amps. Close. Any unbalance may trip it.

 

[davidbeach]

The main transformer that feeds our plant is a 100kva transformer that feeds a 1600kva breaker at 433v

Huh? What? I've never heard of a breaker rated in kVA, and even if such exists, I would think that a 100kVA transformer would be a bit small, certainly too small for the currents you are listing.

Any breaker I've ever seen for use at low voltage works entirely and only on current, doesn't give a rip about power factor. 2135A would be a rather peculiar rating (but then so is 13A or 16A ;-)), but what ever it is, it would be a current rating that would be independent of voltage.

 

[bigheadted]

ok point taken 1600kva transformer and i can only go on what is written on the reaker label '1600kva' its the curent rating that i was trying to calculate

 

[bigheadted]

i realise that the breaker doest care about pf but the net effect of the power factor lowering as far as i knew was that the equipment would need to draw more current through that breaker in order to generate the power required to run,therefore a lowering in power factor may cause the breaker to trip being that we are so close to the limit anyway