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A balanced star-delta connected purely capacitive load is at the secondary of a star-delta synchronous motor which is in unsync of induction motor

Electrical Engineering

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A balanced star-delta connected purely capacitive load is at the secondary of a star-delta synchronous motor which is in unsync of induction motor. The ventilating ducts have been provided by stator core. The field excitation of 100 A in a certain level results in armature current of 200A in short circuit and a terminal voltage of 400V on open circuit.

1. Design the characteristic equation of the developed impedance.

2. Draw the circuit diagram of the whole system.

3. Find and active and reactive system

4. The per unit saturated synchronous reactance.

5. The magnitude of the internal voltage drop.

6. The effective impedance of equivalent generator.

7. The per unit characteristics of whole system.

 

 

 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?