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A balanced 3-phase system consists of positive sequence currents.

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Description :

The line current in a balanced delta system is 30 A. The load current is (A) 30√3 A (B) 30/√3 A (C) 10 A (D) 30/√2 A

Answer :

The line current in a balanced delta system is 30 A. The load current is 30/√3 A

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Description :

The sequence components of current of a single-phase load connected to a 3-phase system are (A) equal positive and negative sequence components (B) equal positive, negative and zero sequence components (C) vector sum of sequence currents is zero (D) algebraic sum of sequence currents is zero

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The sequence components of current of a single-phase load connected to a 3-phase system are equal positive, negative and zero sequence components

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Description :

A balanced three phase Delta connected load consists of three resistances each of four ohm's connected to a 400 V 3 phase 50 Hz supply. Find 1) phase voltage, 2) phase current, 3) line current, 4) power consumed.

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Description :

At a particular instant, the R-phase voltage of a balanced 3-phase system is + 30 V, and the Y-phase voltage is – 90 V. The voltage of B-phase at that instant is (A) + 120 V (B) – 120 V (C) – 60 V (D) + 60 V

Answer :

At a particular instant, the R-phase voltage of a balanced 3-phase system is + 30 V, and the Y-phase voltage is – 90 V. The voltage of B-phase at that instant is + 60 V

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Description :

Total instantaneous power supplied by a 3-phase ac supply to a balanced R-L load is

Answer :

Total instantaneous power supplied by a 3-phase ac supply to a balanced R-L load is constant

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Description :

Define balanced 3 phase load.

Answer :

Balanced 3 phase Load: Balanced three phase load is defined as star or delta connection of three equal impedances having equal real parts and equal imaginary parts. It takes same current of equal magnitude and equal phase angle.

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Description :

A balanced Delta connected load supplied with 440 V 50 Hz three phase AC supply has R=10 Ohm and L=0.6 mH in is each arm. Calculate line and phase current, active power.

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Description :

A balanced three phase star connected load is supplied from a three phase 400V 50 Hz supply. The resistance for per phase is 10 Ohm. Find the value of phase current, line current, power factor and total power consumed.

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Description :

Define balanced and unbalanced load in three phase circuit.

Answer :

Balanced Load: When all the imedances of 3 phases are equal in magnitude and of same nature then load is said to be balanced.  Unbalanced Load: When all the imedances of 3 phases are not equal in magnitude and of different nature then load is said to be unbalanced.

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Description :

The power consumed by a balanced 3-ph load is measured by two-wattmeter method. The meter readings are 8 kW and 4 kW. The power factor of the load is (A) zero (B) 0.5 (C) between zero and 0.5 (D) between 0.5 and unity

Answer :

The power consumed by a balanced 3-ph load is measured by two-wattmeter method. The meter readings are 8 kW and 4 kW. The power factor of the load is between 0.5 and unity

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Description :

Define for polyphase circuit (i) Balanced load (ii) Unbalanced load. Draw one example circuit for each type of load.

Answer :

i) Balanced Load: Balanced three phase load is defined as star or delta connection of three equal impedances having equal real parts and equal imaginary parts.  Example circuit:  ii) ... satisfy the condition of balance, then it is called as unbalanced load.  Example circuit:

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Define balanced supply and unbalanced supply.

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Description :

Which of the following 3-phase connection of a transformer causes interference with the neighbouring communication lines:  (A) Delta-Star (B) Star-Delta (C) Delta-Delta (D) Star-Star

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Which of the following 3-phase connection of a transformer causes interference with the neighbouring communication lines: Star-Star

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Description :

A 3-phase voltage source inverter operates in 180° conduction mode with a star connected resistive load. If input dc voltage is 100 V, then the peak to peak output line voltage is :

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A 3-phase voltage source inverter operates in 180° conduction mode with a star connected resistive load. If input dc voltage is 100 V, then the peak to peak output line voltage is : 200 V

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The speed of a 2-pole, 3-phase stepper motor operated by 1200 pulses/min (A) 100 rpm (B) 200 rpm (C) 400 rpm (D) 800 rpm

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The speed of a 2-pole, 3-phase stepper motor operated by 1200 pulses/min 200 rpm

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Description :

In a 3-phase converter circuit during commutation when one SCR in one phase is turned on to turn-off an SCR in another phase, results in (A) voltage notching (B) harmonic distortion (C) voltage sag (D) voltage swell

Answer :

In a 3-phase converter circuit during commutation when one SCR in one phase is turned on to turn-off an SCR in another phase, results in voltage notching

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Description :

Answer :

In a dynamometer 3-phase power factor meter, the planes of the two moving coils are at 120°.

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Description :

Two 3-phase transformers cannot be operated in parallel, if their :  (A) kVAs are different (B) phase sequences are different (C) % impedances are different (D) voltage ratios are different

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Two 3-phase transformers cannot be operated in parallel, if their : phase sequences are different

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Damper winding is provided in 3 phase synchronous motors to :

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Damper winding is provided in 3 phase synchronous motors to : provide starting torque and prevent hunting

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The direction of rotation of an inverter fed 3-phase ac motor is reversed by (A) a mechanical reversing switch (B) reversing the input dc link voltage (C) operating the inverter as a rectifier (D) changing the sequence of switching

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The direction of rotation of an inverter fed 3-phase ac motor is reversed by changing the sequence of switching

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Description :

Define phase sequence of three phase supply with waveforms. What is normal phase sequence? Which 3 standard colours are used to denote the phase sequence?

Answer :

It  is  sunnosoidal  sequence.

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Draw the phasor diagram for Star connected balanced system.

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For a 15-bus power system with 3 voltage controlled buses, the size of Jacobian matrix is

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For a 15-bus power system with 3 voltage controlled buses, the size of Jacobian matrix is 25 x 25

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A lightening arrester connected between the line and earth in a power system  (1) protects the terminal equipment against travelling surges (2) protects the transmission line against direct lightening strokes (3) suppresses high frequency oscillations in the line (4) reflects back the travelling wave approaching it

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A lightening arrester connected between the line and earth in a power system protects the terminal equipment against travelling surges

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With fault clearing time, the transient stability of a power system

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With fault clearing time, the transient stability of a power system decreases

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In a single bus-bar system there will be complete shut down when fault occurs on the bus itself.

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In quadrilateral speed-time curve of electric traction system, the accelerations during successive time periods are ______ respectively.  (A) positive, negative and negative (B) positive, zero and negative (C) positive, positive and negative (D) positive, negative and zero

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In quadrilateral speed-time curve of electric traction system, the accelerations during successive time periods are positive, negative and negative respectively. 

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The steady state stability of the power system can be increased by connecting lines in parallel.

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Air blast circuit breakers for 400 kV power system are designed to operate in 50 millisecond.

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Ungrounded neutral transmission system is not recommended because of system insulation being overstressed due to over voltages, insulation overstress may lead to failure and subsequent phase to phase faults, being inadequately protected against ground fault.

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The contacts of high voltage switches used in power system are submerged in oil. The main purpose of the oil is to extinguish the arc.

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Write short notes on 3 phase AC system.

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A single core cable is designed to work for a single phase system with a peak voltage of 220 kV. The maximum permissible stress in the dielectric is not to exceed 20 kV/mm. For economical size, the overall core diameter of the cable is (A) 28.2 mm (B) 26.4 mm (C) 24.4 mm (D) 22.0 mm

Answer :

A single core cable is designed to work for a single phase system with a peak voltage of 220 kV. The maximum permissible stress in the dielectric is not to exceed 20 kV/mm. For economical size, the overall core diameter of the cable is 22.0 mm

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When a V-V three phase transformer system is converted into a Δ-Δ system, increase in capacity of the system is (A) 86.6% (B) 50% (C) 57.7% (D) 73.2%

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When a V-V three phase transformer system is converted into a Δ-Δ system, increase in capacity of the system is 73.2%

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Explain following techniques related to energy conservation in transmission and distribution system. (i) By balancing phase currents (ii) Variable technical losses (I2R losses).

Answer :

(i) Balancing Phase currents: Proper (healthy balanced) three phase loads always draw equal currents in all lines but single phase loads in the 3 phase 4 wire system or loads connected between two ... . 11) Minimize I2R losses. 12) Balance the load currents. 13) Regulate the system voltages.

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Phase margin is the amount of angle to make the system  (1) Oscillatory (2) Stable (3) Unstable (4) Exponential

Answer :

Phase margin is the amount of angle to make the system Unstable 

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write short notes on single phase system.

Answer :

A "phase" in an electrical system is often referred to as the waveform (may be voltage or the current) of the power supply. The waveform in an AC system is typically ... domestic household or commercial supplies and street lighting. Industrial supplies requires three phase electrical supply .

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Two wattmeter method is employed to measure power in a 3 -phase balanced system with the current coil connected in the A and C lines. The phase sequence is ABC. If the wattmeter with its current coil in A -phase line reads zero, then the power factor of the 3 -phase load will be

Answer :

Two wattmeter method is employed to measure power in a 3 -phase balanced system with the current coil connected in the A and C lines. The phase sequence is ABC. If the wattmeter with its current coil in A -phase line reads zero, then the power factor of the 3 -phase load will be 0.5 lagging.

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Two wattmeters are used to measure the power in a 3 -phase balanced system. What is the power factor of the load when one wattmeter reads twice the other ?  (a) 0 (b) 0.5 (c) 0.866 (d) 1

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Two wattmeters are used to measure the power in a 3 -phase balanced system. What is the power factor of the load when one wattmeter reads twice the other ?  0.866

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The clock frequency of an 8085 microprocessor based system is 3 MHz. What should be the minimum pulse width of the INTR signal so that it is recognized successfully? A) 5.6 µs B) 5.7 µs C) 5.8 µs D) 5.9 µs

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The clock frequency of an 8085 microprocessor based system is 3 MHz. What should be the minimum pulse width of the INTR signal so that it is recognized successfully? A) 5.6 µs B) 5.7 µs C) 5.8 µs D) 5.9 µs

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In a three-phase system, when the loads are perfectly balanced, the value of neutral current is equal to: A. Zero B. One-third of the maximum value C. Two -third of the maximum value D. The maximum value

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In a three-phase system, when the loads are perfectly balanced, the value of neutral current is equal to: Zero

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requirements of a distribution system

Answer :

Following requirements of a distribution system.  1. Layout should be simple in design. 2. It should have less initial cost 3. The distribution system should have minimum distribution ... stability of existing distribution system. 15. Time required for completion of work should be less. 

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List and explain the components of a hydraulic system.

Answer :

Components Hydraulic: Hydraulic pump- Supply fluid to the components in the system. Pressure in the system develops in reaction to the load. Hence, a pump rated for 5,000 ... mechanical components and need to be removed along with other contaminants.  Seals, fittings and connections.

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Why solar system is preferred now a days ? Justify your answer. 

Answer :

Since availability of fossil fuels like coal are limited in future so there is more importance of solar power in the energy deficient because of following advantages of solar power Fuel is ... .  10. solar system technology are ideally suited to distributed applications ( Decentralized system)

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With a neat diagram, explain back pressure steam turbine co-generation system.

Answer :

Back pressure steam turbine co-generation system: In this type steam enters the turbine chamber at High Pressure and expands to Low or Medium Pressure. Enthalpy difference is used for generating power / work. ... , the overall thermal efficiency of the system could reach as much as 90 percent.

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State the functions of fuel system and exhaust system of a diesel power station.

Answer :

Fuel system: It supplies fuel to engine for combustion purpose. It consists of Fuel Pump: - It supplies fuel to engine for combustion purpose. Strainer: - Are provided to remove suspended impurities and ... most of the noise. Chimney:- To exhaust gases in the atmosphere as high as possible. 

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