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The efficiency of two identical transformers under load conditions can be determined by?

1 Answer

The efficiency of two identical transformers under load conditions can be determined by back-to-back test.

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Answer : An ideal transformer will have maximum efficiency at a load such that copper loss equal to iron loss.

Description : For a transformer, operating at constant load current, maximum efficiency will occur at?

Answer : For a transformer, operating at constant load current, maximum efficiency will occur at unity power factor.

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

Answer : A transformer operates 24 hours day at full -load. It's full -load efficiency is : equal all day efficiency 

Answer : Generators for peak load plants are usually designed for maximum efficiency at 50 to 75 percent full load.

Description : The secondary of a current transformer is always short-circuited under operating conditions because it?

Answer : The secondary of a current transformer is always short-circuited under operating conditions because it avoids core saturation and high voltage induction.

Answer : In a D.C. shunt motor, under the conditions of maximum power, the current in the armature will be more than full-load current.

Answer : Distribution transformers are generally designed for maximum efficiency around 50% load.

Answer : Power transformers are generally designed to have maximum efficiency around near full-load.

Description : The efficiency of a transformer, under heavy loads, is comparatively low because?

Answer : The efficiency of a transformer, under heavy loads, is comparatively low because copper loss becomes high in proportion to the output.

Answer : The direction of rotation of an hysteresis motor is determined by position of shaded pole with respect to main pole.

Description : Three identical resistors connected in star consume 5000 W. If the resistors are connected in delta across the same supply, the power consumed will be

Answer : Three identical resistors connected in star consume 5000 W. If the resistors are connected in delta across the same supply, the power consumed will be 15000 W

Description : If the percentage impedances of the two transformers working in parallel are different, then?

Answer : If the percentage impedances of the two transformers working in parallel are different, then parallel operation will still be possible, but the power factors at which the two transformers operate will be different from the power factor of the common load.

Description : Two transformers are connected in parallel. These transformers do not have equal percentage impedance. This is likely to result in?

Answer : Two transformers are connected in parallel. These transformers do not have equal percentage impedance. This is likely to result in loading of the transformers not in proportion to their kVA ratings.

Answer : Natural oil cooling is used for transformers up to a rating of 3000 kVA.

Answer : Short circuit test on transformers is conducted to determine copper losses.

Answer : Necessary conditions required to be satisfied in order to ensure successful parallel operation of single phase transformers:  1. Only transformers having the same phase displacement between primary and secondary ... . 7. The phase sequence must be followed strictly on HV and LV side connection.

Answer : Natural air cooling is generally restricted for transformers up to 1.5 MVA .

Description : Losses which occur in rotating electric machines and do not occur in transformers are?

Answer : Friction losses windage losses 

Description : The efficiencies of transformers compared with that of electric motors of the same power are?

Answer : Transformers have high efficiency than the same ratted motors

Description : Explain the concept of initial and final conditions in switching for L and C.

Answer : i) Inductor: The current through an inductor cannot change instantly. If the inductor current is zero just before switching, then whatever may be the applied voltage, just after switching the inductor ... open-circuit.  The initial and final conditions are summarized in following table:

Description : Two transformers with identical voltage ratings are working in parallel to supply common load. The percentage impedance of one transformer is higher compared to that of other. The load sharing ... respective impedance (4) Depend on the resistance to leakage reactance ratio of each transformer

Answer : Two transformers with identical voltage ratings are working in parallel to supply common load. The percentage impedance of one transformer is higher compared to that of other. The load sharing between the two transformer will: Be inversely proportional of their respective impedance

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%.

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

Description : The maximum load that a power transformer can carry is limited by its?

Answer : The maximum load that a power transformer can carry is limited by its voltage ratio.

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

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

Description : Two transformers A and B having equal outputs and voltage ratios but unequal percentage impedances of 4 and 2 are operating in parallel. The transformer A will be overloaded by 

Answer : Two transformers A and B having equal outputs and voltage ratios but unequal percentage impedances of 4 and 2 are operating in parallel. The transformer A will be overloaded by 33%

Description : State any two conditions for parallel operation of 3-phase transformer.

Answer : Conditions for Parallel operation of 3 phase transformer 1) Voltage ratings of both the transformers must be identical. 2) Percentage or p.u. impedance should be equal in magnitude. 3) X/R ratio ... between primary & secondary voltages must be same. 6) Phase sequence on both sides must be same.

Description : In a transmission line if booster transformers are to be used, preferred location will be  (A) At the receiving end (B) At the sending end (C) At the intermediate point (D) Anywhere in the line 

Answer : In a transmission line if booster transformers are to be used, preferred location will be At the intermediate point

Description : For high efficiency of transfer of power, internal resistance of the source should be?

Answer : For high efficiency of transfer of power, internal resistance of the source should be less than the load resistance.

Answer : Transformer efficiency is maximum when copper losses are equal to iron losses.

Answer : In an actual transformer the iron loss remains practically constant from no load to full load because core flux remains practically constant.

Description : Negative voltage regulation is indicative that the load is?

Answer : Negative voltage regulation is indicative that the load is capacitive.

Description : In a given transformer for a given applied voltage, losses which remain constant irrespective of load changes are?

Answer : In a given transformer for a given applied voltage, losses which remain constant irrespective of load changes are hysteresis and eddy current losses.

Description : Minimum voltage regulation occurs when the power factor of the load is?

Answer : Minimum voltage regulation occurs when the power factor of the load is leading.

Description : In a step-down transformer, there is a change of 15 A in the load current. This results in change of supply current of?

Answer : In a step-down transformer, there is a change of 15 A in the load current. This results in change of supply current of less than 15A.

Description : The maximum constant load torque under which a synchronous motor will pull into synchronism at rated rotor supply voltage and frequency is known as?

Answer : The maximum constant load torque under which a synchronous motor will pull into synchronism at rated rotor supply voltage and frequency is known as pull-in torque.

Answer : The area under a load curve gives energy consumed.

Description : Classify the transformers based on the construction, frequency and power.

Answer : Classification of Transformer Based On: i) Construction: Shell type, Core type, Berry type ii) Change in voltage level: Step-Up, Step-Down, iii) Number of phases: Single phase, Three phase iv) ... Control vi) Cooling: Self-cooled, Air-cooled, Forced-air cooled, Oil-cooled, Forced-oil cooled. 

Description : Which of the following connection of transformers will give highest value of secondary voltage ? (A) Delta primary delta secondary (B) Delta primary star secondary (C) Star primary star secondary (D) Star primary delta secondary

Answer : Which of the following connection of transformers will give highest value of secondary voltage ? (A) Delta primary delta secondary (B) Delta primary star secondary (C) Star primary star secondary (D) Star primary delta secondary

Description : Core type transformers are popular in___________.  (A) High voltage applications (B) Low voltage applications (C) All of the above (D) None of the above

Answer : Core type transformers are popular in High voltage applications

Description : The friction losses in Real Transformers are :  (A) 0% (B) 5% (C) 25% (D) 50%

Answer : A

Description : An additional condition for parallel operation of three-phase transformers over single-phase transformers is that

Answer : An additional condition for parallel operation of three-phase transformers over single-phase transformers is that the transformers should belong to the same vector group

Description : Which of the following is the advantage of using CRGO steel in transformers? A) High magnetic flux density B) Low permeability C) Both A and B D) None of these

Answer : It definitely High Magnetic Flux Density since a crgo steel has always a more around 3% of silicon proportion among the remaining ferrite which make cold rolled grain oriented steel having high flux magnetic ... for more about the crgo core you can learn here https://nicoreindia.com/crgo-core/

Answer : Instrument transformers are potential transformers, current transformers.

Description : What is the back EMF in Transformers?

Answer : Current transformers (CT) : Current transformer (CT) actually step down the high current to low current for the operation of relays. Current transformer is use for measurement of ... use for relay. This is about potential transformer.

Description : Why do transformers make noise?

Answer : Transformers make noise based on it out put if an transformer outputs is 400v maximum than a 398v be apply to that transformer it also make a noise because of that 

Answer : The power factor of a single phase load can be calculated if the instruments available are three ammeters or three voltmeters.

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