Can Transformers be Reconnected as Autotransformers to Increase Their KVA Rating?

Can Transformers be Reconnected as Autotransformers to Increase Their KVA Rating?
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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 nameplate KVA as an insulating transformer. Examples of autotransformer applications are changing 600 volts to 480 volts in either single phase or three phase; changing 480 volts to 240 volts single three phase or vice versa; or the developing of a fourth vire (neutral) from a 480 volt three phase three wire system or obtaining 277 volts single phase. This voltage is normally used for operating fluorescent lamps or similar devices requiring 277 volts
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Related questions

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

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

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

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

why transformers are rated in kVA ?

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.

[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 transformers is leading while that of the other lagging C. Transformers having higher copper losses will have negligible core losses D. Loading of the transformers not in proportion to their kVA ratings.

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

55 When a 400Hz transformer is operated at 50Hz its KVA rating is A. Reduced to 1/8 B. Increased 8 times C. Unaffected D. Increased 64 times 56

Description : 55 When a 400Hz transformer is operated at 50Hz its KVA rating is A. Reduced to 1/8 B. Increased 8 times C. Unaffected D. Increased 64 times

Last Answer : A. Reduced to 1/8

54] 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

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

Why Transformer rating is given in kVA?

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.

Define kVA rating of transformer.

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

The kVA rating of Three-phase transformer with Voltage = 200V and Current = 100A will be :

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

why transformer rating is measured in 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.

Which of the listed transformer uses a single winding to produce voltage transformation? A. Stepup transformers B. Stepdown transformers C. Autotransformers D. Isolation transformers

Description : Which of the listed transformer uses a single winding to produce voltage transformation? A. Stepup transformers B. Stepdown transformers C. Autotransformers D. Isolation transformers

Last Answer : Answer: C

Power transformers have rating (a) equal to 50 kVA (6) equal to 100 kVA (c) above 200 kVA (d) none of the above

Description : Power transformers have rating (a) equal to 50 kVA (6) equal to 100 kVA (c) above 200 kVA (d) none of the above

Last Answer : (c) above 200 kVA

A 400V/100 V, 10 KVA two-winding transformer is reconnected as an auto-transformer across a suitable

Description : A 400V/100 V, 10 KVA two-winding transformer is reconnected as an auto-transformer across a suitable voltage source. The maximum rating of such an arrangement could be  A) 50 KVA B) 15 KVA C) 12.5 KVA D) 8.75 KVA

Last Answer : A 400V/100 V, 10 KVA two-winding transformer is reconnected as an auto-transformer across a suitable voltage source. The maximum rating of such an arrangement could be 50 KVA

Why Silica gel is used in transformers?

Description : Why Silica gel is used in transformers?

Last Answer : Silica Gel is used to remove the moisture in the air entering in to the transformer. During the breathing of the transformer air enters in to the transformer. This air makes contact with the hot ... Silica gel crystals will be in blue color initially and after absorbing moisture it turns to pink.

What are the conditions for parallel operation of two transformers ?

Description : What are the conditions for parallel operation of two transformers ?

Last Answer : Transformers which are to be operated parallel should have to satisfy the following conditions: Polarities of both the transformers should be same else lead to short circuit Voltage rating of ... Phase displacement of transformers should be same Phase sequence of two transformers should be same

What is the significance of vector grouping in Power Transformers?

Description : What is the significance of vector grouping in Power Transformers?

Last Answer : Answer:Every power transformer has a vector group listed by its manufacturer. Fundamentally it tells you the information about how the windings are connected (delta or wye) and the phace difference betweent ... Delta primary, Wye Secondry and the current is at 11 o clock reffered to the voltage.

How is magnetic leakage reduced to a minimum in commercial transformers?

Description : How is magnetic leakage reduced to a minimum in commercial transformers?

Last Answer : By interleaving the primary and secondary windings.

What are the conditions for parallel operation of two transformers ?

Description : What are the conditions for parallel operation of two transformers ?

Last Answer : Transformers which are to be operated parallel should have to satisfy the following conditions: Polarities of both the transformers should be same else lead to short circuit Voltage rating of ... Phase displacement of transformers should be same Phase sequence of two transformers should be same

What is BIL and How Does it Apply to our Transformers ?

Description : What is BIL and How Does it Apply to our Transformers ?

Last Answer : ANSWER: BIL is an abbreviation for Basic Impulse Level. Impulse tests are dielectric tests that consist of the applica¬tion of a high frequency steep wave front voltage between windings ... breakdowns when his system is properly protected with lightning arrestors or similar surge protection devices.

What is Meant by "Impedance" in Transformers?

Description : What is Meant by "Impedance" in Transformers?

Last Answer : ANSWER: Impedance is the current limiting characteristic of a transformer and is expressed in percentage.

Can 60 Hz Transformers be Used at Higher Frequencies?

Description : Can 60 Hz Transformers be Used at Higher Frequencies?

Last Answer : A: Transformers can be used at fre¬quencies above 50 Hz up through 400 Hz with no limitations provided nameplate voltages are not exceeded. However, 50 Hz transformers will have less voltage ... Where better regulation and smaller physical size are required, contact us for special 400 Hz designs.

What are the Conditions for parallel operation of transformers?

Description : What are the Conditions for parallel operation of transformers?

Last Answer : A. a) Same voltage ratio of transformer: If two transformers of different voltage ratio, are connected in parallel with same primary supply voltage, there will be a difference in secondary voltages. If ... not in same phase sequence, during the cycle, each pair of phases will be short circuited.

What are the advantages of parallel operation of transformers?

Description : What are the advantages of parallel operation of transformers?

Last Answer : A. 1) To maximize electrical power system efficiency: Generally electrical power transformer gives the maximum efficiency at full load. If we run numbers of transformers in parallel, we can switch ... running in parallel can be removed from system to balance the capital investment and its return.

Can the transformers be used at higher frequencies than rated frequency?

Description : Can the transformers be used at higher frequencies than rated frequency?

Last Answer : A. Yes. Transformers can be used at higher frequencies than rated frequency. However as the frequency increases voltage regulation decreases.

What is meant by “impedance” in transformers? Why is it important?

Description : What is meant by “impedance” in transformers? Why is it important?

Last Answer : A. Impedance is the current limiting characteristic of a transformer and is expressed in percentage. It is used for determining the interrupting capacity of a circuit breaker or fuse employed to protect the primary of a transformer

Can Single Phase Transformers be used for Three Phase applications?

Description : Can Single Phase Transformers be used for Three Phase applications?

Last Answer : A. Yes. Three phase transformers are sometimes not readily available whereas single phase transformers can generally be found in stock. Three single phase transformers can be used in delta connected primary and ... K VA single phase transformers can be used to accommodate a 30 KVA three phase load.

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

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

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

What is the significance of vector grouping in Power Transformers?

Description : What is the significance of vector grouping in Power Transformers?

Last Answer : A. Every power transformer has a vector group listed by its manufacturer. Fundamentally it tells you the information about how the windings are connected (delta or wye) and the phase difference between the ... Delta primary, Wye Secondary and the current is at 11 o clock referred to the voltage.

What are the types of cooling systems it transformers?

Description : What are the types of cooling systems it transformers?

Last Answer : A. 1. ONAN (oil natural, air natural) 2. ONAF (oil natural, air forced) 3. OFAF (oil forced, air forced) 4. ODWF (oil direct, water forced) 5. OFAN (oil forced, air forced)

Why Delta Star Transformers are used for Lighting Loads?

Description : Why Delta Star Transformers are used for Lighting Loads?

Last Answer : A. For lighting loads, neutral conductor is must and hence the secondary must be star winding.This lighting load is always unbalanced in all three phases. To minimize the current unbalance in the primary we use delta winding in the primary. So delta / star transformer is used for lighting loads.

How do you classify transformers based on construction?

Description : How do you classify transformers based on construction?

Last Answer : A. Based on construction transformers are of two types. They are distinguished from each other based on merely the manner by which primary and secondary windings are placed around the core. ... surrounds considerable part of windings. Another recent development is wound core type or spiral core.

Why do transformers hum?

Description : Why do transformers hum?

Last Answer : Transformer noise is caused by a phenomenon which causes a piece of magnetic sheet steel to extend itself when magnetized. When the magnetization is taken away, it goes back to its original condition ... core. The degree of flux determines the amount of magnetostriction and hence, the noise level.

Why we need isolation transformers in power circuit ? why cant we use breakers to isolate?

Description : Why we need isolation transformers in power circuit ? why cant we use breakers to isolate?

Last Answer : In Isolation transformer is used, if there is change in parameter values of any side, the other side parameters will remain unchanged.

Is it Possible to Change Three Phase to Two Phase or Vice-Versa with Standard Transformers?

Description : Is it Possible to Change Three Phase to Two Phase or Vice-Versa with Standard Transformers?

Last Answer : Yes. This is a very practical application for standard single phase off-the-shelf transformers. Some typical voltage combinations are as follows: 480 volts three phase to 240 volts two phase, or 240 volts ... 240 volts three phase to 240 volts two phase. Please refer to us for an exact schematic.

Can 60 Hz transformers be operated at 50 Hz?

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.

Can Transformers be Operated at Voltages other than Nameplate Voltages?

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.

What is the Difference Between "Insulating", "Isolating", and "Shielded Winding" Transformers?

Description : What is the Difference Between "Insulating", "Isolating", and "Shielded Winding" Transformers?

Last 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 winding transformer, ... are connected to each other electrically, are not of the insulating or isolating variety.

List some methods of cooling of transformers.

Description : List some methods of cooling of transformers.

Last Answer : A:Air natural, Air blast, Oil Natural, Oil natural air forced, Oil natural water forced, Oil forced, Oil forced air natural, Oil forced air natural, Oil forced water forced.

In transformers, why the low voltage winding is placed near the core?

Description : In transformers, why the low voltage winding is placed near the core?

Last Answer : The winding & Core are both made of metals and so an insulation have to be placed in between them, the thickness of insulation depends on the voltage rating of the winding. In order to reduce the insulation requirement the low voltage winding place near the core.

Mention the properties of oil used in transformers.

Description : Mention the properties of oil used in transformers.

Last Answer : The following are the desirable properties of transformer oil: -->It should be free from moisture --> It should have high dielectric strength --> It should have thermally stability and higher thermal conductivity -->It should be contaminated by temperature rise.

Why are breathers used in transformers ?

Description : Why are breathers used in transformers ?

Last Answer : Breathers are used to entrap the atmospheric moisture and thereby not allowing it to pass on to the transformer oil. Also to permit the oil inside the tank to expand and contract as its temperature increases and decreases. Also to avoid sledging of oil i.e. decomposition of oil.

Why the range of efficiency in transformers higher than those of other electrical machines?

Description : Why the range of efficiency in transformers higher than those of other electrical machines?

Last Answer : Transformers operate at higher efficiency when compared to other electrical machines.This is due to the absence of mechanical losses which is due to the absence of moving parts

What is the range of efficiency of transformers?

Description : What is the range of efficiency of transformers?

Last Answer : A:The efficiency of the transformer will be in the range of 94% to 99%. Among the available electrical machines the transformer has the highest efficiency

What is yoke section of transformers?

Description : What is yoke section of transformers?

Last Answer : The sections of the core which connect the limbs are called yoke. The yoke is used to provide a closed path for the flux.

What are isolation transformers?

Description : What are isolation transformers?

Last Answer : In this type of transformer the primary and secondary are same. When it is required to isolate the primary and secondary circuits these type of transformers are used. It protects the circuits connected in secondary side when major fault occurs in primary side.

What are step down transformers?

Description : What are step down transformers?

Last Answer : They step up voltage from higher value to lower value.

What are step up transformers?

Description : What are step up transformers?

Last Answer : They step up voltage from lower value to higher value.

What are the advantages of shell type transformer over core type transformers?

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.

What are the various types of Transformers?

Description : What are the various types of Transformers?

Last Answer : Based on supply 1.Single phase transformer 2.Three phase transformer Based on winding 1.Auto transformer (single winding) 2.Two winding transformer 3. Three winding transformer 4. Six ... transformer Based on function 1. Step up transformer 2.Step down transformer 3.Isolation transformer

Can DC be applied to transformers ?

Description : Can DC be applied to transformers ?

Last Answer : No i) Transformer works on Faraday's law of Electromagnetic Induction for which current in coil must change. If DC is applied current will not change and transformer will not work. ii) Practically ... is zero. Therefore impedance is low. Thus winding draws more current which may damage the winding.