How can the reactive power delivered by a synchronous generator be controlled?

1. By changing the prime mover input
2. By changing the excitation
3. By changing the direction of rotation
4. By changing the prime mover speed

Answer : By changing the excitation

A transformer has a percentage resistance of 2% and percentage reactance of 4%. What are its regulations at power factor 0.8 lagging and 0.8 leading , respectively?

1. 4% and -0.8%
2. 3.2% and -1.6%
3. 1.6% and -3.2%
4. 4.8% and -0.6 %

Answer :  4% and -0.8%

The full load copper loss and iron loss of a transformer are 6400 W and 5000 W respectively. the copper loss and iron loss at half load will be , respectively

1. 3200 W and 2500 W
2. 3200 W and 5200 W
3. 1600 W and 1250 W
4. 1600 W and 5000 W

Answer: 1600 W and 5000 W

A shunt generator has a critical field resistance of 200 ohms at a speed of 800 rpm. If the speed of the generator is increased to 1000 rpm. What is the change in critical field resistance of the generator

1.  Decrease to 160 ohm
2. Remains the same at 200 ohm
3. Increase to 250 ohm
4. Increase to 312.5 ohm

Answer: Increase to 250 ohm