Last Answer : The main reason for generation of harmonics in a transformer could be saturation of core.
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 : 49 The open circuit test is carried out in a transformer to find the A. Cu loss B. Core loss C. Total loss D. Insulation resistance
Last Answer : B. Core loss
Description : Which of the following properties is not necessarily desirable in the material for transformer core? A. Mechanical strength B. Low hysteresis loss C. High thermal conductivity D. High permeability
Last Answer : C) high thermal conductivity
Description : Explain the effect of Harmonics on the Transformer.
Last Answer : Effect of Harmonics on the Transformer: 1. Core loss: Harmonic voltage increases the hysteresis and eddy current losses in the lamination. The amount of the core loss depends on ... small core vibrations. 5. Saturation problem: Sometimes additional harmonic voltage causes core saturation.
Description : 61 The degree of mechanical vibrations produced by the laminations of a transformers depends on A. Tightness of clamping B. Gauge of laminations C. Size of laminations D. All of the above
Description : A 40 kVA transformer has a core loss of 400 W and a full load copper loss of 800 W. The proportion of full load at maximum efficiency is
Last Answer : A 40 kVA transformer has a core loss of 400 W and a full load copper loss of 800 W. The proportion of full load at maximum efficiency is 0.707
Description : 69 In case there are burrs on the edges of the laminations of the transformer, it is likely to result in A. Vibrations B. Noise C. Higher eddy currents loss D. Higher hysteresis loss
Last Answer : C. Higher eddy currents loss
Description : The main purpose of using core in a transformer is to (A) decrease iron losses (B) eliminate magnetic hysteresis (C) reduce reluctance of the common magnetic circuit (D) prevent eddy current loss
Last Answer : Reduce Relucatnce of the common magnetic circuit.
Description : What are the necessary tests to determine the efficiency, voltage regulation, and temperature rise of winding & insulation of transformer?
Last Answer : 1.Direct loading test 2.Open circuit test 3. Short circuit test 4. Sumpner's or back to back test
Description : The area of the yoke in a transformer is taken 15 to 20% larger than that of the core. Why?
Last Answer : By keeping yoke area 15-20% higher ,the flux density in the yoke is reduced, resulting into reduction in iron losses for yoke. The reduced core area results working flux density and needed to increase the number of turns.
Description : What is the purpose of laminating the core in a transformer?
Last Answer : In order to minimize eddy current loss.
Description : Where is core type and shell type construction suitable for a transformer?
Last Answer : Core type transformers are popular in High voltage applications like Distribution transformers, Power transformers, and obviously auto transformers. Where as, Shell type transformers are ... voltage applications like transformers used in electronic circuits and power electronic converters etc
Description : What are the advantages of shell type transformer over core type transformers?
Last Answer : In shell type transformers the coils are well supported on the all sides and so they can withstand higher mechanical stresses developed during short circuit conditions. Also the leakage reactance will be less in shell type transformers.
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 : 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
Description : 45 The function of conservator in a transformer is A. To protect against internal fault B. To reduce copper as well as core losses C. To cool the transformer oil D. To take care of the expansion and contraction of transformer oil due to variation of temperature of surroundings
Last Answer : D. To take care of the expansion and contraction of transformer oil due to variation of temperature of surroundings
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 : 27] In a transformer, the leakage flux of each winding is proportional to the current in that winding because A. Ohm's law applies to magnetic circuits B. Leakage paths do no saturate C. the two windings are electrically isolated D. mutual flux is confined to the core
Last Answer : B. Leakage path do not saturate
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 : 8 The transformer core is laminated to A. Reduce the copper losses B. Reduce the core losses C. Reduce the eddy current losses D. None of the above
Last Answer : C. Reduce the eddy current losses
Description : 13) In an ideal transformer A. windings have no resistance B. core has no losses C. core has infinite permeability D. all of the above
Description : 12] Which is not the basic element of the transformer? A. core B. primary winding C. secondary winding D. mutual flux
Last Answer : D. Mutual flux
Description : Material used for construction of transformer core is usually A. 0.4mm to 0.5 mm B. 4mm to 5 mm C. 14mm to 15 mm D. 25mm to 40 mm
Last Answer : d) 25mm to 40mm
Description : State any four characteristics of core type transformer.
Last Answer : Characteristics of core type transformer: i) It has one window. ii) It has one magnetic circuit. iii) Core surrounds the winding. iv) Average length of core is more. v) Area of cross ... Better cooling for winding. vii) Mechnical strength is comparatively less. viii) Repair and maintenance is easy.
Description : The core construction is like spokes of a wheel in following transformer: (A) Berry Type Transformer (B) Core Type Transformer (C) Shell Type Transformer (D) None of the above
Last Answer : The core construction is like spokes of a wheel in following transformer: Berry Type Transformer
Description : The desirable properties of transformer core material are (1) low permeability and low hysteresis loss. (2) high permeability and high hysteresis loss. (3) high permeability and low hysteresis loss. (4) low permeability and hysteresis loss.
Last Answer : The desirable properties of transformer core material are high permeability and low hysteresis loss.
Last Answer : The purpose of providing an iron core in a transformer is to decrease the reluctance of the magnetic path.
Last Answer : The purpose of providing iron core in a step-up transformer is to decrease the magnitude of magnetizing current.
Last Answer : Material used for construction of transformer core is usually silicon steel.
Last Answer : The core used in high frequency transformer is usually air core .
Description : When secondary of a current transformer is open-circuited its iron core will be?
Last Answer : When secondary of a current transformer is open-circuited its iron core will be hot because of heavy iron losses taking place in it due to high flux density.
Description : The size of a transformer core will depend on?
Last Answer : The size of a transformer core will depend on frequency and area of the core.
Description : Reduction in core losses and increase in permeability are obtained with transformer employing?
Last Answer : Reduction in core losses and increase in permeability are obtained with transformer employing core built-up of laminations of cold rolled grain oriented steel.
Description : Why does the core of a transformer need to be laminated?
Last Answer : Transformer cores are laminated to reduce eddy current loss.
Last Answer : Transformer core is laminated to reduce Eddy current losses.
Description : During No load why the power factor of the transformer is very low ?
Last Answer : Current flowing through the transformer consists of two components. Magnetizing current (Im) which is in quadrature (90 0 ) to the applied voltage and in phase current which is in phase to the applied voltage ... power factor of transformer during no load condition will by in the order of 0.1 to 0.2
Last Answer : A. Current flowing through the transformer consists of two components. Magnetizing current (Im) which is in quadrature (900) to the applied voltage and in phase current which is in phase to the applied voltage ... factor of transformer during no load condition will by in the order of 0.1 to 0.2
Description : How much is the no load current of transformer?
Last Answer : No load curent of transformer is 3 to 5% of rated current in transformer.
Description : What are two components of no load current in transformer?
Last Answer : i) IM (Magnetizing/reactive /wattless) current. It magnetizes core ii) Iw (Coreloss/ active/wattful ) current. It supplies hysteresis and eddy current loss and negligible I² R loss.
Description : What are the functions of no-load current in a transformer ?
Last Answer : No-load current produces flux and supplies iron loss and copper loss on no-load.
Description : 62)The no-load current drawn by transformer is usually........percent of the full-load current? A. 0.2 to 0.5 % B. 2 to 5% C. 12 to 15 % D. 20 to 30 %
Last Answer : B) 2 to 5%
Description : 51 A transformer has negative voltage regulation when its load power factor is A. Zero B. Unity C. Leading D. Lagging
Last Answer : C. leading
Description : 40 No load test on a transformer is carried out to find A. Copper loss B. magnetising current C. Magnetising current and loss D. Efficiency of the transformer
Last Answer : C. Magnetising current and loss
Description : 6 In a two winding transformer, the primary and secondary induced emf E1 & E2 are always A. equal in magnitude B. anti phase with each other C. in phase with each other D. determined by load on transformer secondary
Last Answer : C. In phase with each other
Description : 22 No load test on a transformer is carried out to find A. copper loss B. magnetising current C. Magnetising current and no load loss D. Efficiency of the transformer
Last Answer : C. Magnetising current and no load loss
Description : During short circuit test iron losses are negligible because A. The current on secondary side is negligible B. The voltage on secondary side does not vary C. The voltage applied on primary side is low D. Full-load current is not supplied to the transformer
Last Answer : C) the voltage applied on primary side is low
Description : A transformer has negative voltage regulation when its load power factor is (1) Zero (2) Unity (3) Leading (4) Lagging
Last Answer : 0
Description : The inrush current of a transformer at no load is maximum if the supply voltage is switched on (1) at peak voltage value (2) at zero voltage value (3) at half voltage value (4) at 0.866 time voltage value
Last Answer : At 0.866 time voltage value