Description : 4] In operating a 400hz transformer at 50Hz A. Only voltage is reduced in the same proportion as the frequency B. Only KVA rating is reduced in the same proportion as the frequency C. Both voltage and KVA rating are reduced in the same proportion as frequency D. None of the above
Last Answer : B. Only KVA rating is reduced in the same proportion as the frequency
Description : Why Transformer rating is given in kVA?
Last Answer : Because of core losses and iron losses as core losses are measured in amps and cu losses in voltage ....this is definatly reason for the rating Or kVA is the unit for apparent power. Apparent ... shift between voltage and current). So a transformer has to be rated (and selected) by apparent power.
Description : Define kVA rating of transformer.
Last Answer : kVA rating of transformer is defined as the product of voltage (V) and current (I) on primary side of transformer or secondary side of transformer divided by 1000. On both side the VA rating remains ... Mathematically kVA rating is given by, kVA rating of transformer = V1I1/1000 =V2I2/1000
Description : The kVA rating of Three-phase transformer with Voltage = 200V and Current = 100A will be : (A) 34.64 kVA (B) 75 kVA (C) 20 kVA (D) None of the above
Last Answer : The kVA rating of Three-phase transformer with Voltage = 200V and Current = 100A will be : 34.64 kVA
Description : Transformer generally rated in KVA
Last Answer : The power of transformer is apparent power because it has no power factor and it is the product of voltage and current.
Description : Can Transformers be Reconnected as Autotransformers to Increase Their KVA Rating?
Last Answer : ANSWER: Several of standard single phase transformers can be connected as autotransformers. The KVA capacity will be greatly increased when used as an Autotransformer, in comparison to the ... This voltage is normally used for operating fluorescent lamps or similar devices requiring 277 volts
Description : 47 Cross over windings are used in A. Low voltage side of high kVA rating transformers B. Current transformers C. High voltage side of high kVA rating transformers D. High voltage side of low kVA rating transformers
Last Answer : D. High voltage side of low kVA rating transformers
Description : 4 Helical coils can be used on A. Low voltage side of high kVA transformers B. High frequency transformers C. High voltage side of small capacity transformers D. High voltage side of high kVA rating transformers
Last Answer : A) low voltage side of high KVA transformer
Description : 64)During the short-circuit test on a small transformer the frequency is increased from 50-200Hz. The copper losses will increase by a factor of A. 16 B. 4 C. 1 D. 1/4
Last Answer : A) 16
Description : If an insulating material is operated beyond the maximum allowable temperature, its life is (a) drastically increased (b) drastically reduced (c) unaffected (d) none of the above
Last Answer : (b) drastically reduced
Description : The transformer ratings are usually expressed in terms of A. Volts B. Amperes C. kW D. kVA
Last Answer : D) KVA
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 : A 4000 kVA, 11 kV/132 kV delta-star connected 3-phase transformer has reactance, x1 = 0.12 p.u. The actual value of x1 referred to the low voltage side is (A) 0.85 Ω (B) 3.63 Ω (C) 36.3 Ω (D) 252 Ω
Last Answer : A 4000 kVA, 11 kV/132 kV delta-star connected 3-phase transformer has reactance, x1 = 0.12 p.u. The actual value of x1 referred to the low voltage side is 3.63 Ω
Description : If a transformer is continuously operated the maximum temperature rise will occur in?
Last Answer : If a transformer is continuously operated the maximum temperature rise will occur in windings.
Description : 56 Which of the following does not change in a transformer? A. Current B. Voltage C. Frequency D. All of the above
Last Answer : C. Frequency
Description : The rating of transformer may be expressed in ____________. (A) kVAR (B) kW (C) kVA (D) Horse power
Last Answer : The rating of transformer may be expressed in kVA .
Description : The kVA rating required for a transformer that must handle a maximum load current of 8 A with a secondary voltage of 2 kV will be: A. 4 kVA B. 0.25 kVA C. 16 kVA D. 8 kVA
Last Answer : The kVA rating required for a transformer that must handle a maximum load current of 8 A with a secondary voltage of 2 kV will be: 16 kVA
Last Answer : When a given transformer is run at its rated voltage but reduced frequency, its core flux density is increased.
Description : How the leakage reactance of the transformer is reduced?
Last Answer : In transformers the leakage reactance is reduced by interleaving the high voltage and low voltage winding.
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 : 7 The main advantage of auto transformer over a two winding transformer is A. Hysteresis losses are reduced B. Saving in winding material C. Copper losses are negligible D. Eddy losses are totally eliminated
Last Answer : A) hysteresis losses is reduced
Description : why transformers are rated in kVA ?
Last Answer : A:Copper loss of a transformer depends on current and iron loss on voltage . Hence total losses depends on Volt- Ampere and not on the power factor. That is why the rating of transformers are in kVA and not in kW.
Description : [75] Two transformers are connected in parallel. These transformers do not have equal percentage impedance which results A. Short-circuiting of the secondaries B. Power factor of one of the ... have negligible core losses D. Loading of the transformers not in proportion to their kVA ratings.
Last Answer : D. Loading of the transformers not in proportion to their kVA ratings
Description : When two transformer of different kVA rating are connected in parallel they share the load in proportion to their respective kVA rating only when their:
Last Answer : When two transformer of different kVA rating are connected in parallel they share the load in proportion to their respective kVA rating only when their: P u impedance are equal
Description : What should be kVA rating of each transformer in V-V bank when three phase balanced load is 40 kVA ? (A) 19 (B) 28 (C) 37 (D) 23
Last Answer : What should be kVA rating of each transformer in V-V bank when three phase balanced load is 40 kVA ? (A) 19 (B) 28 (C) 37 (D) 23
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
Last Answer : If the supply frequency to the transformer is increased, the iron loss will increase.
Description : Can 60 Hz transformers be operated at 50 Hz?
Last Answer : The transformers rated below 1 KVA can be used on 50 Hz service. Transformers 1 KVA and larger, rated at 60 Hz, should not be used on 50 Hz service, due to the higher losses and resultant heat ... designs are required for this service. However, any 50 Hz transformer will operate on a 60 Hz service.
Description : Can Transformers be Operated at Voltages other than Nameplate Voltages?
Last Answer : In some cases, transformers can be operated at voltages below the nameplate rated voltage. In NO case should a transformer be operated at a voltage in excess of its name- plate rating unless taps are ... 10 KVA, the reduced rating would be 5 KVA, or in direct proportion to the applied voltage.
Description : Can transformers be operated at voltages other than nameplate voltages?
Last Answer : In some cases, transformers can be operated at voltages below the nameplate rated voltage. In NO case should a transformer be operated at a voltage in excess of its nameplate rating, unless taps are ... 10 kVA, the reduced rating would be 5 kVA, or in direct proportion to the applied voltage.
Description : 29.In transformer terminology, the ratio 20:1 indicates that A. there are 20 turns on primary one turn on secondary B. secondary voltage is 1/20th of the primary C. primary current is 20 times greater than the secondary current D. for every 0 turns on primary, there is one turn on secondary
Last Answer : A. there are 20 turns on primary one turn on secondary
Description : 28.In a two winding transformer, the emf /turn in secondary winding is always......the induced emf power turn in primary A. equal to k times B. equal to 1/k times C. equal D. greater than
Last Answer : C. equal
Description : What is the reduced fraction of 56 and 64?
Last Answer : If you mean 56/64 then it is 7/8
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 : How is magnetic leakage reduced to a minimum in commercial transformers?
Last Answer : By interleaving the primary and secondary windings.
Description : Two transformers are to be operated in parallel such that they share load in proportion to their kVA ratings. The rating of the first transformer is 500 kVA ratings. The rating of the first transformer is 500 kVA and its pu ... its pu leakage impedance is (A) 0.20 (B) 0.10 (C) 0.05 (D) 0.025
Last Answer : Two transformers are to be operated in parallel such that they share load in proportion to their kVA ratings. The rating of the first transformer is 500 kVA ratings. The rating of the first transformer is ... .05 pu. If the rating of second transformer is 250 kVA, its pu leakage impedance is 0.10
Description : Does the transformer draw any current when its secondary is open?
Last Answer : Yes, no-load primary current.
Description : What is tertiary winding? What is Three Winding Transformer? What are its advantages?
Last Answer : A. In some high rating transformers, one winding, in addition to the primary and secondary winding, is used. This is known as Tertiary Winding of Transformer. Because of this third winding, the ... it assists in limitation of fault current in the event of a short circuit from line to neutral.
Description : What current flows in the transformer primary when its secondary is open?
Last Answer : A. When the secondary is open, there is no current in the secondary of the transformer. The primary takes a small current I0) from the source called no-load current which has a magnetizing ... ) producing the magnetic flux and a working component (I0 cosθ0) supplying real power for iron losses.
Description : 57 In a transformer the resistance between its primary and secondary is A. Zero B. 1Ω C. 1000 Ω D. Infinite
Last Answer : D. Infinite
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 : 24 Transformer cores are laminated in order to A. simplify its construction B. minimise eddy current loss C. reduce cost D. reduce hysteresis loss
Last Answer : B. Minimise eddy current loss
Description : Define Dielectric Strength for transformer oil. State its value for new transformer oil.
Last Answer : Dielectric strength is defined as the maximum voltage that can be applied to across to the Fulid with out electrical breakdown is called Dielectric strength.
Description : A single phase transformer has resistance and reactance of 0.2 pu and 0.6 pu respectively. Its pu voltage regulation at 0.8 pf lagging would he
Last Answer : A single phase transformer has resistance and reactance of 0.2 pu and 0.6 pu respectively. Its pu voltage regulation at 0.8 pf lagging would he 0.52
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 : A transformer operates 24 hours day at full -load. It's full -load efficiency is : (A) equal all day efficiency (B) more than all -day efficiency (C) less than all -day efficiency (D) equal to maximum efficiency
Last Answer : A transformer operates 24 hours day at full -load. It's full -load efficiency is : equal all day efficiency
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 : In a transformer the resistance between its primary and secondary should be?
Last Answer : In a transformer the resistance between its primary and secondary should be infinity.
Description : The maximum load that a power transformer can carry is limited by its?
Last Answer : The maximum load that a power transformer can carry is limited by its voltage ratio.
Description : Explain the single pass transformer design procedure step by step by giving its flowchart.
Last Answer : single pass transformer design procedure step by step by giving its flowchart: