Solved Anna University Question Paper with Answer - 2 (PART C)

PART C - (1 × 15 = 15 Marks)

(Application/Design/Analysis/Evaluation/Creativity/Case study question)

16. (a) Calculate the readings of the two wattmeters (W1 and W2) connected to measure the total power for a balanced star-connected load shown in Fig. 6, fed from a three-phase, 400 V balanced supply with phase sequence as R-Y- B. The load impedance per phase is 20 +  j 15. Also find the line and phase currents, power factor, total power, total reactive VA and VA.

VL =  400 V balanced (star)  I_L,I_ph,Pf,VAR,VA

Z_P = 20 + j 15

P = √3 V_L I_L cos ϕ = √3 × 400 × 9.2376 cos (36.87)

= 5719.99 W

Q  = √3 V_L I_L sin ϕ = √3 × 400 × 9.2376 sin (36.87)

= 3840.01 VAR

cos ϕ = cos 36.87° = 0.81

S  = √3V_L I_L =  √3 × 400 × 9.2376

= 06399.99 VA

W₁ = V_L I_L cos (30 + ϕ)

= 400 × 9.2376 cos (30+ 36.87)

= 1451.48 W

W₂ = V_L I_L COS (30 - ϕ)

= 400 × 9.2376 cos (30-36.87)

= 3668.51 W

Or

(b) Calculate the readings of the wattmeter (W) connected as shown in Fig. 7. The load is the balanced star-connected one, with impedance of per phase fed from a three-phase, 400 V, balanced supply, with the phase sequence as R-Y-B.

Refer Page No: 4.24 Section No: 4.7.3