UPSC ESE Electrical Engineering Solved Papers

Consider the following advantages of hydrogen cooling of alternators in steam power generation:

1. Less noise due to the lower density of hydrogen
2. Ventilation losses (fan power absorbed) are higher by 10%
3. The heat transfer is more than that of air

Which of the above advantages is/are correct?

Match the following Lists regarding Surge Impedance Loading (SIL) of AC lines:

Select the correct answer using the code given below:

If d is the distance between the conductors and e is the Euler's number, then the maximum critical disruptive voltage occurs when the radius (r) of the conductors is

Match the following Lists regarding cable conductors:

Select the correct answer using the code given below:

Match the following Lists regarding percentage distribution of faults in various elements of a power system:

Select the correct answer using the code given below:

For a 735 kV line with a fault current of 4 kA, what is the arc resistance? (Assume no resistance in the ground return path)

Consider the following statements regarding static relays compared with electromechanical relays:

1. In static relays, frequent operations cause deterioration.
2. In static relays, there is a quick resetting and absence of overshoot.
3. Static relays are sensitive to voltage transients.

Which of the above statements is/are correct?

What is the maximum value of restriking voltage across the contacts of the circuit breaker in a 132 kV system?

Consider the following statements regarding radial distribution system:

1. Distributor far away from the substation is highly loaded.
2. Severe voltage variation to the consumers nearest to the substation is due to load variations.
3. Consumers are dependent on a single feeder and a single distributor, and a fault on either of them causes interruption of supply to all the consumers away from the fault.

Which of the above statements is/are correct?

Match the following Lists regarding bus classifications:

Select the correct answer using the code given below:

Consider the following statements with respect to the change in torque angle whenever a disturbance occurs:

1. There is no change in torque angle when the speed of the rotor is the synchronous speed.
2. The angle decreases in case of a motor, if $P_s > P_e$, i.e., the mechanical output is more than the electrical input and the speed goes down.
3. The angle increases, if the speed is more than the synchronous speed.

Which of the above statements is/are correct?

Which one of the following is not a feature of ideal control system for an HVDC converter?

Consider the following statements regarding Static Synchronous Compensator (STATCOM):

1. It is insensitive to transmission system harmonics.
2. It has difficulty in operating with a very weak AC system.
3. It can be used for small amount of energy storage.

Which of the above statements is/are correct?

A diode circuit consists of a diode in series with switch ($S_1$), resistance ($R = 44\,\Omega$) and capacitance ($C = 0.1\,\mu\text{F}$). The capacitor has an initial voltage $V_{C0} = V_C(t=0) = 220\text{ V}$. If switch $S_1$ is closed at $t = 0$, what is the energy dissipated in the resistor R?

Which of the following is not a limitation of MOSFET?

Two BJTs are connected in parallel to share the total current 25 A. The collector-to-emitter voltage of $T_1$ and $T_2$ are 1.5 V and 1.75 V respectively. What is the difference in emitter current sharing by the two transistors, when the current-sharing series resistances are $R_{E1} = 0.25\,\Omega$ and $R_{E2} = 0.35\,\Omega$?

The typical upper ratings of power transistor (MOSFET) are

The firing frequency of relaxation oscillator is varied by changing the value of charging resistance R. What are the maximum and minimum values of R? (Assume $\eta = 0.65,$ $I_p = 0.65\text{ mA},$ $V_p = 12\text{ V},$ $I_v = 2.0\text{ mA},$ $V_v = 1.5\text{ V},$ $V_{BB} = 20\text{ V}$ and $C = 0.047\,\mu\text{F}$)

The capacitance ($C_{J2}$) value of reverse-biased junction J2 of a thyristor is independent of off-state voltage. The limit value of the charging current to turn the thyristor is about 15 mA. If the critical value of $dv/dt$ is $750\text{ V/}\mu\text{s}$, what is the value of the junction capacitance ($C_{J2}$)?

A single-phase, half-wave controlled rectifier with R load is supplied from a 230 V, 50 Hz AC source. When the average DC output voltage is 50% of maximum possible average DC output voltage, what are the firing angle of thyristor and average DC output voltage respectively?

A single-phase semi-converter is supplied by 200 V, 50 Hz and it is connected with an R-L-E load, where $R=15\,\Omega$, $E=80\text{ V}$ and L is very large so that the load current is ripple-free. What is the average output current at $\alpha=90^\circ$?

A step-down chopper has a load resistance of $20\,\Omega$ and input DC voltage is 200 V. When the chopper switch is 'on', the voltage across semiconductor switch is 2 V. If the chopping frequency is 1.5 kHz and duty ratio is 40%, what is the average DC output voltage?

What is the expression for distortion factor (DF) in inverters?

A separately excited DC motor is controlled by a single-phase full converter which is supplied from 440 V, 50 Hz AC supply. If the field circuit is fed through a single-phase full converter with $0^\circ$ firing angle, the delay angle of armature converter is $30^\circ$ and load current is 20 A, what is the field current? (Assume that the armature resistance $R_a=0.5\,\Omega$, field resistance $R_f=140\,\Omega$ and the current waveforms are ripple-free)

Consider the following statements regarding AC drives:

1. AC drives require simple control algorithms than DC drives.
2. Power converters used in AC drives are relatively simple and less expensive.
3. VSI, CSI, AC voltage controllers, PWM inverters are used in variable speed induction motor drives.

Which of the above statements is/are correct?