Question

Three coils are connected in delta to a 30,
3 wire, 415 V, 50 Hz supply and take a line
current of 5 A, 0.8 p.f lagging. Calculate the
resistance and inductance of the coils.
R=90 0, L = 0.3 H
R=115.03 Q. L=0.274 H
R=40 0, L = 0.3 H
R=2000, L = 0.623 H​

Answer 1

The resistance is 90 ohms and inductance is 0.3H.

Given,

Voltage supply(V) =415V

Frequency(f)= 50Hz

Current (I)=5A

To find,

The resistance(R) and inductance(L) of the coils.

Solution,

In LR circuit:

V =$\sqrt{Vr^{2} + (VL^{2} ) }$

(Where Vr is voltage across resistance and VL is voltage drop across inductor coil.)

I= V/ $\sqrt{R^{2} + XL^{2} }$

XL is inductive reactance =2πf L

5 = 415/ √(R²+ XL²)..........eq1

Now,

tan∅ = XL / R

0.8 = XL/R

∴XL = 0.8R

Putting this value in eq 1

5 = 415/ √(R²+ 0.8R²)

R =90 ohm

XL= 0.8*90

XL= ωL =2πfL

L =0.3H

Hence, Resistance is 90 ohms and inductance is 0.3H.

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