A three-phase, three winding Δ/Δ/Y (1.1 kV/6.6 kV/400 V) transformer is energized from AC mains at the 1.1 kV side. It supplies 900 kVA load at 0.8 power factor lag from the 6.6 kV winding and 300 kVA load at 0.6 power factor lag from the 400 V winding. The RMS line current in ampere drawn by the 1.1 kV winding from the mains is ___________. (Give the answer up to one decimal place.)
Concept:
Power balance equation,
input kVA = output kVA
Explanation:
Equivalent circuit is given as,
using power balance equation,
input kVA = output kVA
kVA1 = kVA2 + kVA3
kVA1 = 900 ∠-36.87° + 300 ∠-53.13°
kVA1 = 720 - j 540 + 160 - j 240
kvA1 = 900 + j 780
kvA1 = 1190.9 ∠-40.9° kVA
We know that,
kVA = √3 Vl Il
where,
Vl = line voltage
Il = line current
Now,
\(\rm kVA=\sqrt{3}V_{l_1}I_{l_1}=1190.9\angle-40.9^\circ\)
⇒ \(I_{l_1}=\frac{1190.9\angle-40.9\ \rm kVA}{\sqrt{3}\times1.1\ \rm kV}\)
⇒ \(\rm I_{l_1}=625.09\angle-40.9^\circ\ \rm A\)
Hence,
RMS line current drawn by the 1.1 kV winding from the mains is 625.09 A
Important Questions from Three Phase Transformer Basics
Three-phase transformer contains-
Consider three transformers in Δ - Δ, supplying their rated load. If one transformer is removed, then each of the remaining two transformers is overloaded. The overload on each transformer is given as
The core of a three-phase, 50 Hz, 1000/400 V delta/star: 300 kVA core type transformer operated with a flux of 0.04 wb. Find the EMF per turn.
A three-phase transformer has 600 primary turns and 200 secondary turns. If the supply voltage is 1000 V, find the secondary line voltage on no-load when the windings are connected in star–delta.
The most familiar application of zigzag transformer is
