1. When a sinusoidal voltage is applied across R-L series circuit having R XL, t
ID: 2292894 • Letter: 1
Question
1. When a sinusoidal voltage is applied across R-L series circuit having R XL, the phase angle will be a. 90 degree lagging b. 45 degree lead c, 45 degree lag d. 90 degree lead 2. Three identical impedances are connected in delta to a 3-phase supply of 400 V. The line-current is 34.65 A and the total power taken is 14.4 kW. The resistance of the load in each phase (in ohm) is a. 20 b. 12 d. 10 3. A 3-phase star connected symmetrical load consumes P watts of power from a balanced supply. If the same load is connected in delta to the same supply, the power consumption will be a. c. 3P d. Not determined from the given data.Explanation / Answer
1] phase angle = tan ?¹( X/R)
if X=R, then phase angle = tan ?¹(1) = 45 degree lagging(as ckt is inductive)
2] line current = 34.65 A
In delta connection, Phase current = line current/ ?3
So, phase current = 34.65/?3 = 20 A
Total power taken = 3* (phase current)2 * R = 14400
R = 14400 / (3*202 ) = 12 ohm.
3] 3 phase power = 3* (V phase)2 / R
In Star connection: Power= Pstar =3 * (V line/?3)2/R = V line2 / R (as in star conn :V phase = V line=?3)
In Delta connection: Power = Pdelta = 3* (V line)2 / R = 3*Pstar (as in star conn :V phase = V line)
option c is correct.
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