For V/F control, when frequency is increased in transformer
a) Core loss component current increases, Magnetizing component current
decreases
b) Core loss component current increases, Magnetizing component current
increases
c) Core loss component current decreases, Magnetizing component current
decreases
d) Core loss component current decreases, Magnetizing component current
increases

1 Answer

Answer :

Ans: Core loss component current decreases, Magnetizing component
current decreases

Related questions

Description : A 220/440 V, 50 Hz, 5 KVA, single phase transformer operates on 220V, 40Hz supply with secondary winding open circuited. Then (A) Both eddy current and hysteresis losses decreases. (B) Both ... same but hysteresis loss increases. (D) Eddy current loss increases but hysteresis loss remains the same.

Last Answer : (A) Both eddy current and hysteresis losses decreases.

Description : The rating of the Transformer __ when the supply frequency is increased: a) Remains unchanged b) Increases c) Decreases d) None of the above

Last Answer : Ans: B

Description : The air gap provided in induction motors should be checked periodically with a feeler gage to detect an unequal air gap and _____________. A. decreased motor magnetizing current B. hysteresis loses C. increased power factor D. mechanical damage to the rotor

Last Answer : Answer: D

Description : Which of the following statements is true concerning a stepdown transformer in an operating AC power circuit? A. Voltage and current will both be increased. B. Voltage and current will both be decreased C. Voltage decreases as current increases. D. Voltage increases as current decreases.

Last Answer : Answer: C

Description : The magnetizing reactance of a 4 kV/ 400 V, 50 Hz single-phase transformer on low voltage side is 35 Ω. The magnetizing reactance on the high voltage side is (A) 0.35 Ω (B) 3.5 Ω (C) 350 Ω (D) 3500 Ω

Last Answer : 3500

Description : When the current in a power transmission line is increased, the power loss _____________. A. increases as the square of the current B. decreases as the square root of the current C. remains the same, as it is independent of current flow D. increases in direct proportion as the current

Last Answer : Answer: A

Description : In a single-phase transformer, the magnetizing current is (A) in phase with the no-load current (B) in quadrature with the no-load current (C) the product of no-load current and power factor (D) in phase with the flux in the core

Last Answer : In a single-phase transformer, the magnetizing current is in phase with the flux in the core

Description : Materials that retain a large part of their magnetization, after the magnetizing force is removed, are said to have _____________. A. low hysteresis loss B. high flux density C. high permanence D. high permeability

Last Answer : Answer: C

Description : The value of exciting or magnetizing current depends upon which of the following factors ? (a) Total m.m.f. required (b) The number of turns in the exciting winding (c) The way in which the winding is distributed (d) All of the above

Last Answer : (d) All of the above

Description : When the voltage remains constant and the resistance is increased in a series circuit, the flow of current _____________. A. increases by the square of the original value B. increases C. remains the same D. decreases

Last Answer : Answer: D

Description : The hook-on AC volt-ammeter consists essentially of a split-core and a rectifiertype instrument connected to the secondary winding of a _____________. A. potential transformer B. control transformer C. current transformer D. reactance transformer

Last Answer : Answer: C

Description : The voltage applied to the H.V. side of a transformer during S.C. test is 2% of the rated voltage. The core loss as the fraction of its rated core loss is (a) 4% (b) 0.4% (c) 0.25% (d) 0.04%

Last Answer : 0.04%

Description : In the heating process of the ________type a simple method of temperature control is possible by means of a special alloy which loses its magnetic properties at a particular high temperature and regains ... ) core type induction furnace (C) coreless induction furnace (D) high frequency eddy current

Last Answer : Ans: D Magnetic property of alloy changes with change of the temperature and Heat is produced due to eddy current = i2R and i α f2

Description : [53] The iron loss of the transformer is negligible during short circuit test because A. The entire input is just sufficient to meet Cu losses only B. Flux produced is a small fraction of the normal flux C. Iron core becomes fully saturated D. Supply frequency is held constant

Last Answer : B. Flux produced is a small fraction of the normal flux

Description : The harmonic currents in a power transformer does not cause increase in: a) Secondary voltage b) Core loss c) Copper loss d) Magnetic interference with protective relays

Last Answer : Ans: A

Description : The reaction rate almost gets doubled for 10°C rise in temperature. This is due to the fact that the (A) Increased temperature reduces the activation energy (B) Fraction of molecules having threshold energy increases (C) Collision frequency increases (D) Value of threshold energy decreases

Last Answer : (B) Fraction of molecules having threshold energy increases

Description : A source produces sound waves under water. Waves travel through water and then into air. Which of the following statements about the frequency (f) and the wavelength () is correct and sound passes from ... increases. (3)  remains unchanged but f decreases. (4)  remains unchanged but f increases.

Last Answer : 3)  remains unchanged but f decreases.

Last Answer : If the supply frequency to the transformer is increased, the iron loss will increase.

Description : 43 The purpose of providing an iron core in a transformer is to A.Provide support to windings B. Reduce hysteresis loss C. decrease the reluctance of the magnetic path D. reduce eddy current losses

Last Answer : C. Decrease the reluctance of the magnetic path

Description : 19 Transformer cores are built up from laminations rather than from solid metal so that A. Oil penetrates the core more easily B. Eddy current loss is reduced C. Less lamination is required for the windings D. Turn ratio is higher than voltage ratio

Last Answer : B. Eddy current loss is reduced

Description : In dielectric measurement, the dielectric loss is proportional to a) F b) V c) I d) Vsqr

Last Answer : Ans: Vsqr

Description : In the illustrated electronic governor, the circuit card connected to the potential and current transformers is for ________. EL-0046 A. increasing the signal strength to the governor to ... from motorization D. conditioning the load through the use of a magnetic amplifier current transformer

Last Answer : Answer: A

Description : 72 Harmonics in transformer result in A. Increased core losses B. Increased I2R losses C. Magnetic interference with communication circuits D. All of the above

Last Answer : D. All of the above

Description : In the illustrated 450 VAC system, what should be provided between the bus and the device labeled 'F'? EL-0003 A. a potential transformer B. a current transformer C. an emergency disconnect device D. an audible alarm and indicating light

Last Answer : Answer: A

Description : Which of the following losses is/are present in every direct current generator armature? A. Winding copper loss B. Core eddy current loss C. Magnetic hysteresis loss D. All of the above.

Last Answer : Answer: D

Description : 25 A step up transformer increases A. voltage B. current C. power D. frequency

Last Answer : A. Voltage

Description : 16.step-up transformer increases A. voltage B. current C. power D. frequency

Last Answer : A. Voltage

Description : The primary turns of a 444 V/222 V, 50 Hz single-phase transformer with a core cross-sectional area of 100 cm2, and a maximum flux density of 1.0 T is (A) 100 (B) 200 (C) 222 (D) 400

Last Answer : The primary turns of a 444 V/222 V, 50 Hz single-phase transformer with a core cross-sectional area of 100 cm2, and a maximum flux density of 1.0 T is 200

Description : The threshold frequency is the frequency below which – (1) photo current increases with voltage (2) photo current decreases with voltage (3) photo electric emission is not possible (4) photo current is constant

Last Answer : (3) photo electric emission is not possible Explanation: The photoelectric effect is the emission of electrons by substances, especially metals, when light falls on their surfaces. The photoelectric ... gain sufficient energy to overcome the electrostatic barrier of the work function of the metal.

Description : The threshold frequency is the frequency below which - (1) photo current is constant (2) photo current increases with voltage (3) photo current decreases with volt (4) photo electric emission is not possible

Last Answer : (4) photo electric emission is not possible

Description : The threshold frequency is the frequency below which – (1) photo current increases with voltage (2) photo current decreases with voltage (3) photo electric emission is not possible (4) photo current is constant

Last Answer : (3) photo electric emission is not possible Explanation: The photoelectric effect is the emission of electrons by substances, especially metals, when light falls on their surfaces. The photoelectric ... gain sufficient energy to overcome the electrostatic barrier of the work function of the metal.

Description : The threshold frequency is the frequency below which - (1) photo current is constant (2) photo current increases with voltage (3) photo current decreases with volt (4) photo electric emission is not possible

Last Answer : (4) photo electric emission is not possible

Description : The threshold frequency is the frequency below which : (1) photo current increases with voltage (2) photo current decreases with voltage (3) photo electric emission is not possible (4) photo current is constant

Last Answer : photo electric emission is not possible

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

Last Answer : The question seems to be wrong. Increase in frequency would actually decrease the current through the Inductor. This happens because inductive reactance Xl is directly proportional to frequency. And if frequency increases the value of Xl would ... vice versa. Xl= 2*pi*f*L I=E/Z Z=sqrt(R^2+Xl^2)

Description : What is represented by the two parallel lines within component 'A' of the circuit shown in the illustration? EL-0081 A. A ground connection B. An iron core C. Ventilation openings D. A mounting base

Last Answer : Answer: B

Description : The torque and current curves for a three-phase induction motor with a cage rotor, are shown in the illustration. Which of the following statements is true concerning the depicted curves? EL-0056 A. As slip ... D. If the motor is loaded to the point where 40% slip has resulted, it will stall.

Last Answer : Answer: D

Description : When the voltage remains constant, and the resistance increases in a series circuit, current flow _____________. A. decreases B. remains the same C. increases D. increases by the square

Last Answer : Answer: A

Description : When Alternator excitation increases and machine is operating at lagging power factor then a) I increase b) I decreases c) No effect on current d) None

Last Answer : Ans: I increase

Description : A dc cumulatively compounded motor delivers rated load torque at rated speed. If series field is short circuited, then the armature current and speed will a) Both increases b) Both decreases c) Increases and decreases d) Decreases and increases

Last Answer : Ans: Both increases

Description : What are the advantages of V/F control?

Last Answer : 1. Smooth speed control 2. Small input current and improved power factor at low-frequency start 3. Higher starting torque for low case resistance

Description : What is meant by V/F control?

Last Answer : When the frequency is reduced, the input voltage must be reduced proportionally so as to maintain constant flux. Otherwise the core will get saturated resulting in excessive iron loss and magnetizing current. This type of induction motor behaviour is similar to the working of dc series motors.

Description : A switchboard for an AC electrical system requires the use of which of the following devices? A. Frequency meter. B. Ohmmeter. C. Induction voltage regulator. D. Current transformer governor.

Last Answer : Answer: A

Description : 46 The core used in high frequency transformer is usually A. Copper core B. Cost iron core C. Air core D.Mid steel core

Last Answer : C. Air core

Last Answer : The core used in high frequency transformer is usually air core .

Description : Which of the listed electrical devices is represented by the symbol shown in the illustration? EL-0055 A. Fixed resistance resistor B. Coil with magnetic core C. DC motor or generator shunt field D. Transformer

Last Answer : Answer: D

Description : In replacing a defective transformer with a new one, which of the following actions must be carried out to insure proper operation of the equipment it serves? A. The secondary leads must be grounded ... magnetize it. D. The iron core must be grounded for 10 minutes to remove any residual magnetism.

Last Answer : Answer: B

Description : When a transformer is used to step down voltage, the low voltage winding is _____________. A. part of the core B. the primary coil C. not insulated D. the secondary coil

Last Answer : Answer: D

Description : If a transformer is connected to a DC source, the transformer will overload at the ____________. A. contacts B. primary coil C. secondary coil D. core

Last Answer : Answer: B

Description : Figure 'B' shown in the illustration represents a/an ____________. EL-0091 A. magnetic amplifier B. Scott-T transformer C. saturable-core reactor D. oil-filled toroid

Last Answer : Answer: A

Description : Figure 'A' shown in the illustration represents a/an _______________. EL-0091 A. magnetic amplifier B. Scott-T transformer C. saturable-core reactor D. oil-filled toroid

Last Answer : Answer: C