If the primary line voltage rating is 3.3 kV (Y side) of a 25 kVA, Y-Δ transformer (the per phase turns ratio is 5: 1), then the line current rating of the secondary side (in Ampere) is _________.
Concept:
In a three-phase system,
- The current passing through any two lines of supply is called as line current
- The current passing through a supply line is called as phase current
- The voltage across any single phase is called as phase voltage
- The voltage difference between any two phases is called as line voltage
Important Point:
In a star-connected three-phase system,
VL = √3 × Vph
And IL = Iph
\({I_{ph}} = \frac{{{V_L}}}{{\surd 3Z}}\)
In a delta connected three-phase system,
VL = Vph
IL = √3 × Iph
\({I_{ph}} = \;\frac{{{V_L}}}{Z}\)
Where,
VL is line voltage
Vph is phase voltage
IL is line current
Iph is phase current
Explanation:
Primary side rating: 3.3 kV(Y), 25 kVA
Phase current in primary side \(= \frac{{25}}{{\sqrt 3 \times 3.3}} = 4.37{\rm{\;A}}\)
Phase turns ratio = 5 : 1
Phase current in secondary side = 5 × 4.374 = 21.87 A
Line current in secondary side \(= 21.87 \times \sqrt 3 = 37.88{\rm{\;A}}\)
Important Questions from Three Phase Transformer Basics
Three-phase transformer contains-
Which type of connection is used for both large voltage and low voltage rating transformers?
In Three Phase Transformer, The load Current is 139.1 A, and Secondary Voltage is 415 V. The Rating of the Transformer would be:
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.
