Transformer rating with single phase loads
Transformer rating with single phase loads
(OP)
Hi.
Assume that the single phase load is connected as follows (balanced):
L1-L2 = 23 kVA
L2-L3 = 23 kVA
L3-L1 = 23 kVA
All loads are resistive.
Based on the above load, what will be the kVA rating for a 3 phase supply transformer? The network is 230 V i.e. 3 wire system with isolated neutral. (Phase-earth voltage is 230/sqrt(3))
Best Regards
Murtaza
Assume that the single phase load is connected as follows (balanced):
L1-L2 = 23 kVA
L2-L3 = 23 kVA
L3-L1 = 23 kVA
All loads are resistive.
Based on the above load, what will be the kVA rating for a 3 phase supply transformer? The network is 230 V i.e. 3 wire system with isolated neutral. (Phase-earth voltage is 230/sqrt(3))
Best Regards
Murtaza






RE: Transformer rating with single phase loads
Muthu
www.edison.co.in
RE: Transformer rating with single phase loads
Ntr =Nmono * sqrt(3) => 39.84 kVA
RE: Transformer rating with single phase loads
If it were line currents that you start with, then something like what odlanor did would apply.
RE: Transformer rating with single phase loads
But the current in L1-L2 is 100 A, similiary in the other loads. Shouldnt the the rating be: S = sqrt(3)*230*100 = 39.8 kVA? That is 13.3 kVA in each phase?
RE: Transformer rating with single phase loads
RE: Transformer rating with single phase loads
I calculated 0.1A.
If is 100A so loads are 23MVA.
So, with a 3-phase transformer of 39.84 MVA you get in Y connection:
Iline-line=Iline-neutral = 39.84 *1000/(230*1.732) = 100 A
RE: Transformer rating with single phase loads
Current between L1-L2 will be the phase current in the load, connected in delta. The current in the formula you used is the line current, which will be 1.732*100=173A in a balanced phase system.
L1 is involved in feeding both L1-L2 and L1-L3 loads and so on.
Rafiq Bulsara
http://www.srengineersct.com
RE: Transformer rating with single phase loads
When you state that each load is 23kVA conservation of energy is going to demand the transformer feeding the three loads to transform the same total kVA. (23kVA x 3).
That would even go for single phase.
Three single phase 23kVA loads would still demand the same (23kVA x 3) transformer capacity.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Transformer rating with single phase loads
If you use LN voltage with line currents you will get the same result.
RE: Transformer rating with single phase loads
Yes, I agree. With Lavoisier I do not discuss!
ronaldo
RE: Transformer rating with single phase loads
Thanks everybody. Appreciate it.