Midterm Examination

NPC supplies energy to Clark Development Corporation at 69 kV from a 50 MVA transformer whose impedance is 4%. the short circuit MVA at the primary of the transformer is 600 MVA. To limit the fault current, a three phase limiting reactor is connected on the secondary of the transformer. What is the reactance of the reactor required to limit the short circuit MVA at the secondary to 200 MVA.

• 0.167 pu

• 0.127 pu

• 0.173 pu

• 0.139 pu

A transmission line with an impedance of 4 + j7.5 ohms is supplying a load of 1000 kW at 80% lagging. What is the sending end power factor for a receiving end voltage equal to 13.2 kV?

• 0.8

• 0.635

• 0.471

• 0.785

The current in pure capacitor?

• lags behind the voltage by 90⁰

• is in phase with the voltage

• lags behind the voltage by 45⁰

• leads the voltage by 90⁰

One sine wave has a positive peak at 75⁰, and another has a positive peak at 100⁰. How much is first sine wave shifted in phase from the 0⁰ reference?

• leads reference angle by 10⁰

• lags reference angle by 10⁰

• leads reference angle by 15⁰

• lags reference angle by 15⁰

For reactive load, the power factor is equal to?

• 0

• 1

• 2

• 3

The value from positive to negative peak of the sine wave is called?

• effective value

• average value

• peak value

• peak to peak value

The power factor is the ratio of ________ power to the ______ power.

• average, apparent

• apparent, reactive

• reactive, average

• apparent, average

If power factor = 0, then the current to a load is ______ with the voltage.

• in phase

• out of phase

• 45⁰ out of phase

• 90⁰ out of phase

A filter which passes without attenuation all frequencies up to the cut-off frequency f_c and attenuates all other frequencies greater than f_c is called?

• high pass filter

• low pass filter

• band elimination filter

• band pass filter

The transfer bus scheme has the following characteristics except one. Which one is it?

• It allows the disconnection of circuit breaker for maintenance without interrupting the service.

• It is more flexible.

• It allows better continuity of service as compared with the single bus.

• It is more costly than that of the single bus system.