A 20 kVA , 2000/220 V single-phase transformer has a primary resistance of 2.1 ohms and a secondary resistance of 0.026 ohms. The corresponding leakage reactance are 2.5 and 0.03 ohms. Estimate the regulation at full load under power factor condition of a) Unity b) 0.5 (lagging) and c) 0.5 (leading)
Given
kVA = 20
V1 = 2000
V2 = 220
R1 =2.1
R2 = 0.026
X1 = 2.5
X2 = 0.03
To find
Estimate the regulation at full load under power factor condition of
a) Unity
b) 0.5 (lagging)
c) 0.5 (leading)
Solution
We know that turn ratio = N1/N2 = V1/V2
So Turn ratio = 2000/220 = 9.09
Full load secondary current I2 = VA/V
= 20000 / 220
= 90.9 A
Equivalent resistance, R2' = R2 + R1 x (N2/N1)2
= 0.026 + 2.1 x (1/9.09)2
= 0.026 + 0.0255
= 0.0515 ohm
Equivalent reactance, X2' = X2 + X1 x (N2/N1)2
= 0.03 + 2.5 x (1/9.09)2
= 0.03 + 0.0302
= 0.0602 ohm
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