# Give some typical value of generated voltage in a power station. Why is it necessary to step up the...

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Give some typical value of generated voltage in a power station. Why is it necessary to step up the voltage further before transmitting?

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In a hydel power station, the number of poles of an alternator is 24. At what rpm the alternator must be driven to produce 50 Hz voltage?

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State the types of radioactive waste generated in a nuclear power station. Explain the methods employed for their disposal.

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The duty ratio of a step-up chopper with an output voltage of 200 V from a 80 V dc source, is (A) 0.4 (B) 0.5 (C ) 0.6 (D) 1.5

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D.C. motor is to drive a load which has certain minimum value for most of the time and some peak value for short duration. We will select the?

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A sine wave voltage is applied across an inductor. When the frequency of the voltage is decreased, the current decreases.

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In an alternator at lagging power factor the generated voltage per phase as compared to that at unity power factor?

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Explain why potential difference is necessary to produce current in a circuit.

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What is a pole mounted substation? At what voltage levels are the found in a power system?

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A standard AM broadcast station is allowed to transmit modulating frequencies up to 5 kHz. If the AM station is transmitting on a frequency of 980 kHz, compute the maximum and minimum upper and lower sidebands and the total bandwidth occupied by the AM station : (A) 10 kHz (B) 975 kHz (C) 990 kHz (D) 20 kHz

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What is the most effective way to reduce the cost of power generation in a power station?  (A) By increasing the diversity factor and decreasing the load factor (B) By increasing both the diversity factor and the load factor (C) By decreasing both the diversity factor and the load factor (D) By decreasing the diversity factor and increasing the load factor

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A diesel power station spends 0.25 kg/kWh fuel. If the calorific value is 10,000 kcal/kg then overall efficiency of the power station will be   (a) 25% (b) 30% (c) 34.4% (d) 100%

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A menu driven operating system is one which allows you to pick up from the menu of choices it displays on the screen. What is the name given to the images which are used in such image oriented menus?  (1) Model (2) Figure (3) Symbol (4) Icon

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Draw a neat labeled diagram to show protective system for AC traction and give the function of each relay used in it.

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A transistor has a typical value of β = 200 , If the collector current is 15 mA, then base current will be

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Three phase step-up transformer installed at power house, just before commencement of transmission line, have:

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Explain the term reactive power. Why it is sometimes essential to measure reactive power?

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For a fixed value of complex power flow in a transmission line having a sending and voltage V, the real power loss will be proportional to  A) V B) v2 C) 1/V2 D)1/V

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A step voltage E is applied to a series R-L circuit. The rate of change of current is maximum at t = _:  (1) Zero (2) Infinity (3) L/R (4) R/L

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In a three-phase supply floating neutral is undesirable because it way give rise to?

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If it takes a transmitted signal 1m sec to go up to the target and come back after reflection, how far is the transmitter from the target? A) 150 Km B) 150 m C) 15 Km D) 1500 m

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To turn a conducting SCR to off state, it is necessary to make : -  a) anode current less than holding current b)gate current zero  c) anode voltage less than break over voltage  d) gate voltage zero

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The typical ratio of latching current to holding current in a 20A thyristor is : (A) 5.0 (B) 2.0 (C) 1.0 (D) 0.5

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Three single phase transformers are connected in delta-delta to step down a line voltage of 138 kV to 4160 V to supply power to a production plant. The plant draws 21 MW at a lagging power factor of 86 %. Calculate the apparent power furnished by the HV line.  (A) 24.4 MVA (B) 48.8 MVA (C) 12.2 MVA (D) 6.1 MVA

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At an industrial sub-station with a 4 MW load, a capacitor of 2 MVAR is installed to maintain the load power factor at 0.97 lagging. If the capacitor goes out of service, the load power factor becomes (A) 0.85 (B) 1.00 (C) 0.80 lag (D) 0.90 lag

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Why is it cheaper to transmit electrical energy at high voltage?

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Which of the following connection of transformers will give highest value of secondary voltage ? (A) Delta primary delta secondary (B) Delta primary star secondary (C) Star primary star secondary (D) Star primary delta secondary

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Overall thermal efficiency of a steam power station in India is in the range: A) 18-24 percent B) 30-40 percent C) 44-62 percent D) 68-79 percent

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The input voltage to an OP AMP is a large voltage step. The output is an exponential waveform that changes to 0.25 V in 0.1µs (microsecond). The slew rate of the OP AMP is : -  a) 5V/µs b) 2.5 V/ µs c) 3V/µs d) 4.5V/ µs

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A power station supplies the peak load of 60 Mw, 40 MW and 70 MW to three localities. The annual load factor is 0.50 p.u. and the diversity factor of the load at the station is 1.55. The maximum demand on the station and average load respectively will be

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A 1:5 step-up transformer has 120V across the primary and 600 ohms resistance across the secondary. Assuming 100% efficiency, the primary current will be:  (A) 0.2 Amp. (B) 5 Amps. (C)10 Amps. (D) 20 Amps

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Are different power stations interconnected? If so, why?

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Why are batteries used in a substation?

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Typical value of SCR for modern turbo alternator is (1) 1 (2) 1.2 (3) 0.5 (4) 1.5

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In a power station, the cost of generation of power reduces when (A) diversity factor alone increases (B) both diversity factor and load factor increase. (C) load factor alone increases. (D) both diversity factor and load factor decrease,

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A unit step voltage is applied at t = 0 to a series RL circuit with zero initial conditions  A) It is possible for the current to be oscillatory B) The voltage across the resistor at t = 0+ is zero C) The energy stored in the inductor in the steady state is zero D) Theresistor current eventually falls to zero

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A moving coil meter has a resistance of 3 Ω and gives full scale deflection with 30 mA. To measure voltage up to 300 V, the external resistance to be connected in series with the instrument is (A) 9997 Ω (B) 10000 Ω (C) 997 Ω (D) 10003 Ω

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In a series RLC circuit, the rms value of voltage across the resistor is 30 V, across the inductor is 60 V and across the capacitor is 20 V. The rms supply voltage would be (A) 110 V (B) 10 V (C) 220 V (D) 50 V

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If a self excited d.c. generator after being installed, fails to build up voltage on its first trial run, the first thing to do is (a) reverse the field winding connections (b) increase the field resistance (c) decrease the speed of prime mover (d) increase the speed of prime mover

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A typical Solder composition used in component assembly to PCB is