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Star/star transformers work satisfactorily when load is balanced .

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Answer : Delta/star transformer works satisfactorily when on balanced as well as unbalanced loads.

Description : State and justify which of the following two transformers is better:  Transformer A = 4% voltage regulation  Transformer B = 6% voltage regulation

Answer : Transformer A with 4% voltage regulation is better.  Justification: Voltage regulation refers to the percentage change in secondary voltage when load is changed from no-load to full-load with primary voltage ... 4% voltage regulation, which is less as compared to 6% of transformer B, it is better.

Answer : Transformer breaths in when load on it decreases.

Answer : When a given transformer is run at its rated voltage but reduced frequency, its core flux density is increased.

Description : When secondary of a current transformer is open-circuited its iron core will be?

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 : Why should Dry-Type Transformers never be overloaded?

Answer : Overloading of a transformer results in excessive temperature. This excessive temperature causes overheating which will result in rapid deterioration of the insulation and cause complete failure of the transformer coils.

Description : Can Transformers develop Three Phase power from a Single Phase source?

Answer : No. Phase converters or phase shifting devices such as reactors and capacitors are required to convert single phase power to three phase. 

Description : Can transformers be used in parallel?

Answer : Single phase transformers can be used in parallel only when their impedances and voltages are equal. If unequal voltages are used, a circulating current exists in the closed network between ... listed above, plus the angular displacement and phasing between the two transformers must be identical.

Description : Can transformers be operated at voltages other than nameplate voltages?

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 : What is the difference between “Insulating,” “Isolating,” and “Shielded Winding” transformers?

Answer : Insulating and isolating transformers are identical. These terms are used to describe the isolation of the primary and secondary windings, or insulation between the two. A shielded transformer is ... secondary are connected to each other electrically, are not of the insulating or isolating variety.

Description : If an unsymmetrical line to ground fault occurs at the secondary terminals of a delta/star, ungrounded transformer, then  (A) zero sequence currents are present on both sides of the transformer  (B) ... side  (D) zero sequence currents are present on the primary side but not on the secondary side

Answer : If an unsymmetrical line to ground fault occurs at the secondary terminals of a delta/star, ungrounded transformer, then zero sequence currents are absent on both sides of the transformer 

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

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 : Explain the effect of Harmonics on the Transformer.

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 : List two special feature of welding transformer.

Answer : Special features of welding transformer: i) It is a step down transformer that reduces the source voltage to a voltage desired according to the demands of the welding process. ii) Having large primary turns and less ... V ii) Secondary voltage - 40 to 60 V iii) Secondary current - 200 to 600 A

Description : State two applications of isolation transformer

Answer : Applications of isolation transformer: i) Isolates the load equipment from supply ground: ii) Reduction of voltage spikes iii) It acts as a decoupling device. iv) Protects loads from harmonic distortion.

Description : State why a transformer always have an efficiency of more than 90%.

Answer : As transformer is static device with no moving parts, the losses due to friction & windage are completely absent. Hence transformer has efficiency of more than 90%.

Description : Equivalent circuit of transformer

Answer : Equivalent Circuit Diagram of Transformer Referred to Primary: V1 -Primary Input voltage I1 - Input Current I0- Exciting current/ No load current Im- Magnetizing component ... equivalent of secondary terminal voltage ZL- Load impedance ZL ′- Primary equivalent of load impedance

Description : Single phase transformer

Answer : Single phase Transformer Transformer

Description : What is the use of transformer?

Answer : The use of transformer  is to do lower or raise  the voltage or currents in an electrical  circuit.  That's quite so simple. 

Description : Write about transformer on DC.

Answer : Transformer on DC : Transformer cannot work on DC. Transformer works on electromagnetic induction principle. Electromagnetic induction principle means when flux linking with coil changes and EMF induced in it ... winding insulation will burn.

Description : Even at no-load, a transformer draws current from the mains. Why?

Description : State any four characteristics of core type transformer.

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 : Explain construction and working of single phase Auto transformer.

Answer : Construction of single phase auto transformer: (i) It has only one winding wound on a laminated circular magnetic core. (ii) The core is made of silicon steel stampings. (iii) The two terminals of the ... help of handle. 5) The same transformer can be used as step-up or step down auto-transformer

Answer : No-load current in a transformer lags behind the voltage by about 75°.

Answer : The purpose of providing an iron core in a transformer is to decrease the reluctance of the magnetic path.

Answer : In the transformer low voltage winding has got more cross-sectional area.

Answer : A transformer cannot raise or lower the voltage of a D.C. supply because Faraday's laws of electromagnetic induction are not valid since the rate of change of flux is zero.

Answer : Primary winding of a transformer could either be a low voltage or high voltage winding.

Answer : High voltage winding in a transformer has more number of turns.

Answer : The efficiency of a power transformer is of the order of 98 percent.

Answer : The no load current in a transformer lags behind the applied voltage by an angle of about 75°.

Answer : In a transformer, routine efficiency depends upon load current and power factor of load.

Answer : The maximum efficiency of a distribution transformer is at 50% full load.

Answer : No-load current of a transformer has small magnitude and low power factor.

Answer : Spacers are provided between adjacent coils to provide free passage to the cooling oil.

Answer : Greater the secondary leakage flux less will be the secondary induced e.m.f.

Answer : The purpose of providing iron core in a step-up transformer is to decrease the magnitude of magnetizing current.

Answer : The power transformer is a constant main flux device.

Answer : In a transformer, the tappings are generally provided on low voltage side.

Answer : The use of higher flux density in the transformer design reduces weight per kVA.

Answer : The chemical used in breather for transformer should have the quality of cleansing the transformer oil.

Answer : The chemical used in breather is silica gel.

Answer : An ideal transformer has infinite values of primary and secondary inductances. The statement is false.

Answer : The transformer ratings are usually expressed in terms of kVA.

Answer : Material used for construction of transformer core is usually silicon steel.

Answer : The thickness of laminations used in a transformer is usually 0.4 mm to 0.5 mm.

Answer : conservator or a reservoir tank for insulating oil in transformer which used for balanced the onload oil level with help of oil level indicator which mount on middle part of reservoir tank.

Answer : A transformer oil must be free from moisture.

Answer : Gas is usually not liberated due to dissociation of transformer oil unless the oil temperature exceeds 150°C.

Answer : The main reason for generation of harmonics in a transformer could be saturation of core.

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