The per-unit power output of a salient-pole generator which is connected to an infinite bus

Q. The per-unit power output of a salient-pole generator which is connected to an infinite bus, is given by the expression, 𝑃 = 1.4 sin 𝛿 + 0.15 sin 2𝛿, where 𝛿 is the load angle. Newton- Raphson method is used to calculate the value of 𝛿 for 𝑃 = 0.8 pu. If the initial guess is 30°, then its value (in degree) at the end of the first iteration is

(A) 15°                       (B) 28.48°                  (C) 28.74°                  (D) 31.20°

Ans: 28.74°  

Sol: