A 3- phase, 50 Hz, 415 V, Synchronous machine operates at rated voltage and at a leading power factor of 0

Subject:Electrical EngineeringPrice:4.89 Bought3

Share With

A 3- phase, 50 Hz, 415 V, Synchronous machine operates at rated voltage and at a leading power factor of 0.95. Shaft power is 35 KW and the excitation emf is 440 V. If the per phase reactance is 1.5 pu. (i) Find the mechanical power delivered by the motor, including all losses? (ii) if for the same load on the motor, the excitation is reduced to generate an emf of 100%, what would be the input KVA? (iii) With its excitation emf adjusted to 1.3 pu, the alternator delivers an output of 0.75 pu.(including all losses)?(iv) Find the excitation voltage, load angle and the power factor?(v) Determine the load angle, armature current in per unit? (vi) With alternator output remaining constant, the alternator excitation is improved by 15%, find the new value of armature current, load angle and power deliver to bus?

A 3-phase 9-pole,50Hz, star connected induction motor has an emf 520 V(L-L). The stator winding has a synchronous reactance of 2.5 Ohms/phase. Induction machine operates at rated voltage and at a leading power factor of 0.85. Shaft power is 15 Kw and the excitation emf is 500 V.

(a). Determine the load angle, armature current in per unit and the power factor of the alternator.

(b). The alternator is now made to operate at another value of excitation emf which results in the same values of power output and armature current. Under these conditions, find the excitation voltage, load angle and the power factor.

(c) If the excitation in (a) and that obtained in (b), which is more likely to be used in practical situations and and why?

(d) With the alternator output remaining constant, the alternator excitation is increased by 15%. Find the new values of armature current, load angle and pf?

(e) Calculate the total steam output of the alternator delivered to the prime mover?

(f) Draw the phasor diagram under the conditions specified above?

(g)Find the total power transfer between the alternator and the motor? And calculate the maximum power transfer?

(h) Determine the maximum reactive power Q,the machine can deliver with fixed excitation?

(i) If the prime-mover torque is increased by 1% by how much will the synchronous power P and reactive power Q change?

(j)If the machine field current is increased, load angle δ must decrease to meet the demand of the load, find the maximum excitation voltage and the minimum load-angle for the given load?

A 4-pole 500 KVA,6.6 KV, star connected synchronous motor has synchronous reactance of (0.5 + j20) runs at a speed N rpm with all field coil in series. Determine the speed when the two halves of the field winding are connected in parallel? If an additional resistance of 20 ohms is inserted in the armature circuit, compute the motor speed and the line current in case load torque varies as the square of the speed? If the excitation is reduced to 75% of the initial value and the total torque developed by the armature remains unaltered, calculate new speed.? Also calculate the value of resistance to be inserted in series with the armature to reduce the operating speed to 800 rpm?(Assume linear sinusoidal magnetization characteristic). Also calculate the armature voltage and current at rated torque? Draw the external characteristics of the machine with the assumption of same rated terminal voltage and the same rated load current?