1. Which of the following is minimized by laminating the core of a transformer?
(A) Hysteresis loss(B) Eddy current loss
(C) Heat loss
(D) All of the above.
Ans: (B) Eddy current loss
Explanation:
In a transformer, the eddy current loss is proportional to the square of the diameter of the core.
Larger the diameter, the more the eddy current loss.
Hence the transformer core is laminated so that the net effective diameter of the transformer core reduces and thus eddy current loss can be minimized.
Eddy current loss. Copper loss. Stray loss. By laminating the core of transformer we make the eddy current circulating path narrow, means increasing the resistance of eddy current and proportionately reducing the eddy current.
What is eddy current loss ?
Eddy current loss is conductive I2R loss produced by circulating currents induced in response to AC flux linkage, flowing against the internal resistance of the core.
What is eddy current ?
Eddy currents (also called Foucault's currents) are loops of electrical current induced within conductors by a changing magnetic field in the conductor according to Faraday's law of induction. Eddy currents flow in closed loops within conductors, in planes perpendicular to the magnetic field.
(A) To provide oxygen to the cooling oil
(B) To provide cooling air
(C) To arrest flow of moisture when outside air enters the transformer
(D) To filter the transformer oil.
2. The function of the breather in a transformer is
(A) To provide oxygen to the cooling oil
(B) To provide cooling air
(C) To arrest flow of moisture when outside air enters the transformer
(D) To filter the transformer oil.
Ans:(C) To arrest flow of moisture when outside air enters the transformer
3. Iron loss in a transformer occurs in
(A) core
(B) winding
(C) insulating oil
(D) main body.
Ans: (A) core
Explanation:
Iron loss occurred in core of transformer and copper take place in winding of transformer. Iron loss are divided in two losses 1. eddy current loss and hysterisis loss. these both losses are take place in transformer core.
Open circuit test are used for finding core losses or no load losses and short circuit test are used for finding copper loss in winding.
(A) Hysteresis loss
(B) Eddy current loss
(C) Copper loss
(D) All losses have the same magnitude.
4. Under no load conditions, which of the following loss is negligible?
(A) Hysteresis loss
(B) Eddy current loss
(C) Copper loss
(D) All losses have the same magnitude.
Ans: (C) Copper loss
Explanation:
During no-load conditions, no current flowing through the winding so copper loss is negligible.
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| Some Important Points About core type and shell-type transformer |
5. Open circuit test of a transformer gives
(A) hysteresis loss
(B) eddy current loss
(C) the sum of hysteresis and eddy current loss
(D) copper loss.
Ans: (C) the sum of hysteresis and eddy current loss
Explanation:
Explanation:
Open circuit test are used for finding core losses or no load losses and short circuit test are used for finding copper loss in the winding.
6. Copper loss in a transformer occurs in
(A) core
(B) winding
(C) main body
(A) core
(B) winding
(C) main body
(D) bushings.
Ans: (B) winding
7. Which test on a transfonner provides information about regulation, efficiency and Heating under load conditions?
(A) Open circuit test
(B) Back to back test
(C) Hopkinson test
(D) Short circuit test.
Ans: (B) Back to back test
Explanation:
sumpner's or back to back test on a transfonner provides information about regulation, efficiency and Heating under load conditions
By this test we know about temperature rise in the transformer.
8. For transformer, the condition for maximum efficiency is
(A) hysteresis loss = eddy current loss
(B) core loss = hysteresis loss
(C) copper loss = iron loss
(D) total loss = 2/3 x copper loss.
Ans: (C) copper loss = iron loss
Explanation :
Condition for maximum efficiciency is
copper loss = iron loss
9. Eddy current losses in a transformer core can be reduced by
(A) reducing the thickness of laminations
(B) increasing the thickness of laminations
(C) increasing the airgap in the magnetic circuit
(D) reducing the airgap in the magnetic circuit.
Ans: (A) reducing the thickness of laminations
10. Natural air cooling is generally restricted for transformer upto
(A) 1.5 MVA
(B) 5 MVA
(C) 15 MVA
(D) 20 MVA
Ans: (A) 1.5 MVA
Explanation:
The natural air cooling method is also known as the self-cooled method.
In this method, the heat generated by the transformer is cooled by the circulation of natural air.
This method of cooling is effective for smaller output transformer upto 1.5 MVA.
Beyond that level, natural air cooling is not very effective and the transformer can be heated upto a dangerous level which can cause serious damage to the transformer.
11. The size of the transformer core mainly depends on
(A) Frequency
(B) Area of core
(C) Flux density of core
(D) Both frequency and area of core
Ans:(D) Both frequency and area of core
Explanation:
From emf equation of transformer
E=4.44fNAB
Where
E= Voltage
f= frequency
A= Area of the core
N= number of turns
B =magnetic flux density
In general, we can say
A=E/(4.44fNB)
For the constant value of E,N,B if we increase F, then Area of the core will decreases means the size of the transformer will reduce.
Higher frequency implies faster MMF variations with time hence higher emf inducted on coils, then for same voltage lower core area is needed or lower number of turns, in any case, lower volume.
12. The transformer oil should have __ Volatility and __ Viscosity.
(A) Low & High
(B) High & High
(C) Low & Low
(D) High & Low
Ans:(C) Low & Low
Explanation:
Transformer oil or insulating oil is an oil that is stable at high temperatures and has excellent electrical insulating properties.
Volatility is quantified by the tendency of a substance to vaporize. Volatility is directly related to a substance’s vapor pressure. At a given temperature, a substance with higher vapor pressure vaporizes more readily than a substance with lower vapor pressure.
Therefore the transformer should have low volatility.
Viscosity is a measure of a fluid’s resistance to flow.
Low viscosity substance moves quickly.
Therefore transformer Oil having low viscosity i.e greater fluidity will cool transformers at a much better rate.
13. During the open circuit test of a transformer
(A) Primary is supplied rated voltage
(B) Primary is supplied current at reduce the voltage
(C) Primary is supplied rated KVA
(D) Primary is supplied full load current
Ans: (A) Primary is supplied rated voltage
Explanation:
An open circuit test is performed to determine the iron loss in the transformer.
In this method, the secondary of the transformer is left open-circuited.
A wattmeter is connected to the primary.
An ammeter is connected in series with the primary winding. A voltmeter is optional since the applied voltage is the same as the voltmeter reading.
Rated voltage is applied at primary.
If the applied voltage is normal voltage then normal flux will be set up. Since iron loss is a function of applied voltage, the normal iron loss will occur. Hence the iron loss is maximum at rated voltage. This maximum iron loss is measured using the wattmeter.
14. Which type of winding is used in a 3-phase shell type transformer?
Rectangular Type
Cylindrical Type
Sandwich Type
Circular type
Ans:Sandwich Type
Explanation:
Sandwich Type Winding
LV winding is placed close to the core which is at ground potential.
HV section lies between two LV sections.
Sandwich winding provide control over the short circuit impedance of the transformer.
In sandwich coils, leakage can be controlled easily by bringing HV and LV coils close on the same magnetic axis.
Reactance can be reduced by increasing the number of sandwich coil hence mutual flux is increased.
15. A transformer has negative voltage regulation when its load power factor is
(A) Lagging
(B) Leading
(C) Unity
(D) Any of the above
Answer: (B) Leading
Explanation:
For leading power factor load, the secondary voltage increases slightly with an increase in the load current. Thus for leading power factor loads, the regulation is negative (raise in voltage as load current increases)
When load is of the capacitive type, V2 > E2 & hence, regulation becomes negative.
16. The main purpose of performing short circuit test in a transformer is to measure its
(A) Copper loss
(B) Core loss
(C) Insulation Resistance
(D) Total loss
Answer:(A) Copper loss
Explanation:
Short circuit test is conducted to find the copper loss.
It is calculated under the assumption that core loss is neglected.
When SC test is conducted on the LV side it would require a larger voltage to get the rated current.
Hence core loss cannot be neglected in this case and wattmeter doesn’t give the copper loss alone.
Therefore to get accurate results that test is done on the HV side.
17. The short circuit test in a transformer is performed on
(A) Low voltage side
(B) High voltage side
(C) Either 1 & 2
(D) Both 1 & 2
Answer: (B) High voltage side
Explanation:
Short circuit test is conducted to find the copper loss.
It is calculated under the assumption that core loss is neglected.
When SC test is conducted on the LV side it would require a larger voltage to get the rated current.
Hence core loss cannot be neglected in this case and wattmeter doesn’t give the copper loss alone.
Therefore to get accurate results that test is done on the HV side.
18. Flash point of transformer insulating oil should be more than
(A) 100°
(B) >140°
(C) 75°
(D) Below 75°
Answer:(B) >140°
Explanation: Transformer oil or insulating oil is an oil that is stable at high temperatures and has excellent electrical insulating properties.
As per standard rules, the flash point of transformer oil should be greater than or equal to 140 degrees.
10. In a transformer, the magnetic coupling between the primary and secondary circuit can be increased by
(A) increasing the number of turns
(B) using soft material for windings
(C) using the magnetic core of low reluctance
(D) using transformer oil of better quality.
Ans: (C) using the magnetic core of low reluctance
19. If flux density in the core of a transformer is increased
(A) frequency on secondary winding will change
(B) wave shape on secondary side will be distorted
(C) size of the transfomer can be reduced
(D) eddy current losses will reduce.
Ans: (C) size of the transformer can be reduced
Explanation:
Flux density and frequency is inversely proportional to the size of the transformer. KVA is directly proportional to the size of the transformer
20. Which loss in a transformer varies significantly with load?
(A) Hysteresis loss
(B) Eddy current loss
(C) Copper loss
(D) Core loss.
Ans: (C) Copper loss
Explanation:
copper loss is directly proportional to the load current. so if load current increase then the copper loss also increases.
Copper loss is due to ohmic resistance of the transformer windings.
The copper loss for the primary winding is I12 × R1 and for secondary winding is I22 × R2.
Where I1 and I2 are current in primary and secondary winding respectively.
R1 and R2 are the resistances of primary and secondary winding respectively.
It is clear that Cu loss is proportional to the square of the current, and current depends on the load. Hence copper loss in the transformer varies with the load.
21. Voltage remaining constant, if the frequency is increased then
(A) eddy current losses will decrease
(B) hysteresis losses will decrease
(C) eddy Current losses will remain unchanged
(D) Hysteresis losses remain unchanged.
Ans: (C) eddy Current losses will remain unchanged
Explanation:
If the frequency is increased, while V remains constant, Bm will decrease; however, ƒ Bm remains constant. Thus, eddy current loss Pe remains unchanged. Hence, as frequency increases.
22. The power factor in a transformer
(A) is always unity
(B) is always leading
(C) is always lagging
(D) depends on the power factor of the load.
Ans: (D) depends on the power factor of the load.
23. At no load the current taken by a transformer
(A) lags behind the applied voltage by 75°
(B) lags behind the applied voltage by 50°
(C) leads the applied voltage by 50°
(D) leads the applied voltage by 80°.
Ans: (A) lags behind the applied voltage by 75°
Explanation:
Ideally, a transformer draws the magnetizing current, lags primary applied voltage by 90°. But the transformer also has core loss current component which will be in phase with applied voltage. And no load current is nothing but the vector summation of these two currents. Hence, the no load current will not lag behind applied voltage by exactly 90° but it lags somewhat less than 90°. It is in practice generally about 75°.
24. The efficiency of a transformer does not depend on
(A) current
(B) load
(C) power factor
(D) all of the above.
Ans: (C) power factor
25. Which of the following transformer will be smallest in size ?
(A) 10 kVA, 50 Hz
(B) 10 kVA, 60 Hz
(C) 10 kVA, 100 Hz
(D) 10 kVA, 200 Hz.
Ans: (D) 10 kVA, 200 Hz.
Explanation:
The transformers which handle high power have their size more or less proportional to the frequency as the power lost in iron increases with the frequency and therefore the Xmer gets heated up more rapidly. Therefore for its efficient cooling the surface area has to be increased which demands for larger Xmers.
26. A short circuit test on a transformer gives
(A) copper losses at full load
(B) copper losses at half load
(C) iron losses at any load
(D) sum of iron losses and copper losses.
Ans: (A) copper losses at full load
Explanation:
Short circuit test is used to determine the copper losses taking place in the transformer under operation, while open circuit test gives us the value of core losses taking place in the transformer.
27. Leakage fluxes in a transformer may be minimized by
(A) sectionalizing and interleaving the primary and secondary windings
(B) constantly cooling the core
(C) under rating the transformer
(D) reducing the reluctance of the iron corc to the minimum.
Ans: (A) sectionalizing and interleaving the primary and secondary windings
Explanation:
Flux leakage in a transformer can be minimized by winding the primary and secondary coils one over the other.Core of the transformer is made of soft iron.
28. Essential condition for the parallel operation of transformer is the
(A) they must have equal kVA ratings
(B) their voltage ratings must be in proportion to the load shared
(C) they must operate at the same frequency
(D) their ratio of transformation must be in proportion to the load shared.
Ans: B) their voltage ratings must be in proportion to the load shared
Explanation:
1.Same voltage ratio and turns ratio (both primary and secondary voltage rating is same)
2. Same percentage impedance and X/R ratio.
3.Identical position of tap changer
4.Same KVA ratings
5.Same phase angle shift (vector group are same)
6.Same frequency rating
7.Same polarity
8.Same phase sequence.
29. Which of the following transformers will be largest in size?
(A) 1 kVA, 25 Hz
(B) 1 kVA, 50 Hz
(C) 1kVA, 60 Hz
(D) 1KVA, 100 Hz.
Ans:(A) 1 kVA, 25 Hz
Explanation:
The transformers which handle high power have their size more or less proportional to the frequency as the power lost in iron increases with the frequency and therefore the Xmer gets heated up more rapidly. Therefore for its efficient cooling the surface area has to be increased which demands for larger Xmers.
30. A step-up transformer increases
(A) power
(B) power factor
(C) voltage
(D) frequency
Ans: (C) voltage
Explanation:
Step transformer increase voltage and reduce the current
Step down transformer decrease the voltage and increase the current.
In step up transformer, The number of turns on the secondary of the transformer is greater than that of the primary.
the primary winding of the step-up transformer is made up of thick insulated copper wire because the high magnitude current flows through it and secondary winding made from thin copper wire beacuse low magnitude current flowing through it.
In step Down transformer, The number of turns on the primary of the transformer is greater than the turn on the secondary of the transformer.
The primary winding of the step-down transformer is made up of thin insulated copper wire because the low magnitude current flows through it and secondary winding made from thick copper wire because high magnitude current flowing through it.
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31. In a step-down transformer
(A) secondary turns are less than primary turns
(B) Secondary power is less than primary power
(C) phase shift is always 180
(D) secondary current is always more than primary current.
Ans: (A) secondary turns are less than primary turns
Explanation:
In step Down transformer, The number of turns on the primary of the transformer is greater than the turn on the secondary of the transformer.
The primary winding of the step-down transformer is made up of thin insulated copper wire because the low magnitude current flows through it and secondary winding made from thick copper wire beacuse high magnitude current flowing through it.
32. Power transformers are usually designed to have maximum efficiency
(A) near full load
(B) at 75% of full load
(C) at 50% of full load
(D) between 50% and 75% of full load.
Ans:(A) near full load
Explanation:
Similar to normal transformers power transformers are also designed to get maximum efficiency at load which is near to the full load of a transformer specified. Only in the case distribution transformer maximum efficiency is achieved at 50-60% of full load.
33. Distribution transformers are usually designed to have maximum efficiency
(A) near full load
(B) near 75% of full load
(C) near 50% of full load
(D) near no load.
Ans: (C) near 50% of full load
34. Iron losses of a transformer can be approximately calculated if
(A) the gauge of sheet used in core is known
(B) the material of core and yoke is known
(C) the weight of core and yoke is known
(D) the shape of core and yoke is known.
Ans: (C) the weight of core and yoke is known
35. In high-frequency transformers,
(A) carbon cores are used
(B) wooden cores are used
(C) ferrite cores are used
(D) aluminum cores are used.
Ans:(C) ferrite cores are used
Explanation:
Ferrite core power transformers are widely used in switched-mode power supplies (SMPSs). The powder core enables high-frequency operation, and hence much smaller size-to-power ratio than laminated-iron transformers.
36. In a transformer it is difficult to measure the efficiency by output-input measurement methods because
(A) the output is sinusoidal and hence cannot be measured
(B) losses are abnormally high
(C) the efficiency of a transformer is usually high and hence accurate measurement will be necessary.
(D) output is out of phase with respect input.
Ans: (C) the efficiency of a transformer is usually high and hence accurate measurement will be necessary.
37. The transformer laminations are insulated from each other by
(A) Mica strip
(B) Paper
(C) Thin coating of Varnish
(D) Any of the above
Ans: (C) Thin coating of Varnish
Explanation: The purpose of providing a coating of varnish in windings are
To keep moisture out of the windings to preserve insulation.
To protect the windings from humming or vibrating when magnetized.
To increase the electrical insulation and dielectric strength.
Provide heat dissipation from coil.
38. Two transformers are connected in parallel. These transformers have different percentage impedance. It is likely to result in
(A) Loading in the transformer is not proportional to their KVA rating.
(B) Short circuit in secondary
(C) Higher copper loss
(D) Power factor of one of the transformer is leading while that of the other is lagging.
Ans: (A) Loading in the transformer is not proportional to their KVA rating.
Explanation:
If percentage impedance is unequal means one of the transformers has high impedance as compared to other transformers.
In this case, the transformer having high impedance will have a smaller amount of current flowing through the windings.
While Low impedance transformer offers a large amount of current to flow in the windings.
Therefore high percentage information will be lightly loaded while subjected to heavy load.
Whereas low percentage impedance will be overloaded for the same load.
39. Which of the following is the main advantage of autotransformer over a two winding transformer?
(A) Reduces hysteresis losses
(B) Reduce eddy current losses
(C) Copper losses are negligible
(D) Saving of copper material
Ans: (D) Saving of copper material
Explanation: An autotransformer is built with only a single conductor, which serves both as the primary and secondary coil. Thus, it saves the cost of extra wire for the secondary winding.
40. Which winding of the transformer has less cross-section area?
Primary winding
Secondary Winding
High Voltage Winding
Low Voltage Winding
Ans: High Voltage Winding
Explanation:
We know that current density is defined as the ratio of current to the perpendicular cross-section area through which current is crossing.
Value of current density of HV winding is more in comparison to LV winding because of better cooling of HV winding
Since HV winding is placed far from the core in Comparison to LV winding which is placed near to the core.
Current density is inversely proportional to the area of the core so the thin wire is used for HV winding.
Therefore HV winding has Low cross-sectional area.
41. The core used in the high-frequency transformer is usually
(A) Copper Core
(B) Iron Core
(C) Mild Steel Core
(D) Air core
Ans: (D) Air core
Explanation:
An air-core transformer is designed to be used at a high frequency, used in radio circuits.
The currents are usually small but the voltages can vary.
They can be used to change voltages, match one stage to other, for matching antennas to the radio circuit.
They have many uses within a radio.
42. Open circuit test on a transformer yields
(A) core losses
(B) copper losses
(C) sum of core and copper losses
(D) leakage of reactance.
Ans:(A) core losses
43. The leakage flux in a transformer depends upon
(A) load current
(B) load current and voltage
(C) load current, voltage and frequency
(D) load current, voltage frequency and power factor.
Ans: (A) load current
Explanation:
In a Transformer, Core flux is the difference of primary flux and Secondary flux which are opposite to each other in direction.
So, some of the primary flux passes through the core and remaining becomes leakage flux (Because Secondary flux forces it to get out of the core).
The same is the case with Secondary flux. Now, flux is directly proportional to Voltage and Current.
When Current increases due to increased load (and voltage remains the same).Then both primary and secondary flux increase. Because both of them increases, so their difference remains the same. And all remaining flux is forced out. Hence leakage flux increases with current, but Core flux remains constant.
44. Which of the following is not a routine test on transformers?
(A) Polarity test
(B) Radio interference test
(C) Core insulation voltage test
(D) Impedance test
Ans:(B) Radio interference test
45. A transformer will have the highest efficiency near
(A) 25% of rated load
(B) 50% of rated load
(C) 75% of rated load
(D) 93% of rated load.
Ans:(D) 93% of rated load.
Explanation:
Transformer have higher efficiency near full load.
46. A 1 KVA transformer, at full load, will have
(A) copper losses greater than iron losses
(B) iron losses greater than copper loses
(C) windage losses more than iron losses
(D) windage losses less than copper losses.
Ans: (A) copper losses greater than iron losses
47. In a transformer if peak voltage is fed to the primary
(A) the iron losses will be less
(B) the iron losses will be more
(C) the copper losses will be less
(C) the windage losses will be more.
Ans:(A) the iron losses will be less
Explanation:
if primary is fed with max input then useful flux will be more and losses will reduce
48. The phase difference between the primary and secondary voltage of a transformer is
(A) 0
(B) 90°
(C) 180°
(D) Between 30' and 60°
Ans:(C) 180°
49. In a transformer, the copper loss at half load as compared to that at full load will be
(A) 4 times
(B) 2 times
(C) Half
(D) One-fourth.
Ans:(D) One-fourth.
Explanation:
The copper losses of the transformer at X times the full load is proportional to X^2 times the losses at full load.
50. Harmonics in transformer result in
(A) Increase core losses
(B) Increases I2R Losses
(C) Interference with communication circuits
(D) All of the above
Ans: (D) All of the above
Explanation: We know that
Inductive reactance XL = ωL = 2πfL.
So as the frequency changes it also changes XL ( Inductive Reactance).
And I= V/XL
So if XL changes current also gets affected.
Whenever high current flows and if the frequency is higher than normal than the transformer gets Overheated.
Therefore Eddy’s current and Hysteresis Loss will increase in the transformer.
51. Oil is provided in an oil-filled transformer for
(A) Lubrication
(B) Insulation
(C) cooling
(D) both cooling and insulation
Ans: (D) both cooling and insulation
Explanation: There are two main functions of the transformer oil
Coolant: The copper coil in transformer carries a very high current and soon becomes hot. So transformer oil reduces the temperature of the transformer hence prevent burning of coil.
Insulator: Transformer oil has a great dielectric strength so it can withstand with a quite high voltage, so is used as a insulator in the transformer.
52. Iron loss in a transformer can be determined by
(A) Open circuit test
(B) Short Circuit test
(C) Both 1 & 2
(D) None of the above
Ans: (A) Open circuit test
Explanation: Open circuit test is also called a no-load test.
It is used to determine the no-load losses (core loses in a transformer
Since the no-load current is low therefore the copper loss is neglected in this case.
53. Which of the following is not a part of transformer?
(A) Conservator
(B) breather
(C) Exciter
(D) Buchholz relay
Ans: (C) Exciter
Explanation: Exciter is generally used for starting of motor. Since the transformer is a static device and there is no moving part as in the motor.
54. The path of the magnetic flux in transformer should have
(A) low reluctance
(B) low resistance
(C) high reluctance
(D) high resistance.
Ans: (A) low reluctance
Explanation:
1. If there is a low resistance, then there will be a smoother flow of magnetic flux through the core material.
2. Easily magnetized materials have low resistance and high permeability, whereas non-magnetic materials have high reticence and low permeability.
3. The formula of reluctance is r = l/μA. The higher the value of μ, the more will be the flux flows and the lower the flux, the lesser will be the reluctance value.
Magnetic reluctance, or magnetic resistance, is a concept used in the analysis of magnetic circuits. It is analogous to resistance in an electrical circuit, but rather than dissipating electric energy it stores magnetic energy.
Low the reluctance, less the opposition to flux therefore more flux can pass through the transformer core.
55. The desirable properties of transformer core material are
(A) low permeability and low hysteresis loss
(B) high permeability and high hysteresis loss
(C) high permeability and low hysteresis loss
(D) low permeability and high hysteresis loss.
Ans: (C) high permeability and low hysteresis loss
Explanation:
Desirable properties of the material for transformer core:1. Low hysteresis loss
2. Low reluctance
3. High permeability
4. Adequate mechanical strength
56. Which of the following test is performed to determine the (A) leakage reactance
(B) Short circuit test
(C) Open circuit test
(D) Both Open circuit and short circuit test
(E) Test by an Impedance bridge
Ans: (B) Short circuit test
Explanation:
Short circuit or Impedance test
Short circuit test or Impedance test is performed to determine
⇒Copper loss at full load
⇒Equivalent impedance (Zo1 or Zo2)
⇒Leakage reactance (Xo1 or Xo2)
In this test low voltage winding is short-circuited by a thick conductor.
Short circuit test is performed on HV side of the transformer.
Low voltage (5 to 10%) is applied to the primary and slowly increase till full load current are flowing both in primary and secondary.
The ammeter reading gives full load current IL.
Since applied voltage is small so flux (Φ) is also small therefore core loss is small hence core loss can be neglected.
57. During SC test the Power Input to a transformer comprises predominately
(A) Core loss
(B) Copper loss
(C) Hysteresis loss
(D) Eddy current loss
Ans: (B) Copper loss
Explanation:
Low voltage (5 to 10%) is applied to the primary and slowly increase till full load current are flowing both in primary and secondary.
The ammeter reading gives full load current IL.
Since applied voltage is small so flux (Φ) is also small therefore core loss is small hence core loss can be neglected.
58. The maximum load that a power transformer can carry is limited by its
(A) Voltage ratio
(B) Temperature Rise
(C) Cooper Loss
(D) Dielectric strength of coil
Ans:(A) Voltage ratio
Explanation:
The amount of power a transformer can transfer depends primarily on the magnetic properties and the volume of its core.
This power is frequency-dependent and it scales essentially with P ∝ V ∝ F.
For a given core size and core material (which also depends on the application), the number of turns then determines the inductance and the capacitance of the primary and secondary coils.
In power applications, the number of turns in a winding is usually chosen in such a way that the magnetic flux density in the core at the rated voltage is of the same order of magnitude as the saturation flux density of the core material.
Decreasing the number of turns would lead to saturation of the transformer core, losses would rapidly increase, and finally, the transformer would stop operating as a transformer altogether.
When increasing the number of turns you will not fully utilize the core anymore (or, alternatively, you can make the core slimmer), but at the same time, you need more conductor material for the winding (remember that the thickness of the wire was determined by the current rating!). So in effect, the transformer will become more bulky and expensive.
Smaller turn number means larger core but smaller winding volume, larger turn number means smaller core but larger winding volume.
59. A shell-type transformer has
(A) High eddy current losses
(B) Reduce magnetic leakage
(C) Low hysteresis losses
(D) All of the above
Ans: (B) Reduce magnetic leakage
Explanation:
In shell-type transformer both the primary and secondary coils are turned in the same core, i.e in the middle leg.
Shell type transformer has a double magnetic circuit and three limbs.
At first, either the primary or the secondary winding are wound around the middle leg, and then above it the other one is wound. In this case, there is least possible leakage.
When the primary side is excited, it would produce the flux that must cut the secondary coil.
Here at the time of production of flux it simultaneously cuts the secondary coil with the least amount of leakage and produces the necessary output voltage.
60. A transformer can have zero voltage regulation closer to zero
(A) On full load
(B) On overload
(C) On leading power factor
(D) On zero power factor
Ans:(C) On leading power factor
Explanation:
Voltage regulation is defined as the ratio of the difference between no-load voltage and full load voltage to no-load voltage. Voltage regulation depends on the nature of the load.
For lagging and unity power factor V2 > E2.
where,
V2 = Secondary terminal voltage on given load.
E2 = Secondary terminal voltage on no load.
As the load increase, it tends to become capacitive and V2 start increasing.
Now at a certain point of leading power factor, V2 = E2, and regulation become zero.
In leading, the power factor condition load is just able to supply the reactive power for the active power flow.
61.Core losses in a transformer
(A) vary from 1% to 3% between no load and full load
(B) vary from 10% to 50% between no load and full load
(C) decrease as the load on transformer increases
(D) depend only on the supply voltage.
Ans: (A) varies from 1% to 3% between no load and full load
62. The function of transformer oil in a transformer is
(A) to provide insulation and cooling
(B) to provided protection against lightning
(C) to provide protection against short-circuiting
(D) to lubricate the moving parts.
Ans:(A) to provide insulation and cooling
Explanation:
Function of transformer oil :
1. The construction of the transformer should be such that the heat generated at the core and at the windings should be removed efficiently.
2. Moreover, in order to avoid the insulation deterioration, the moisture should not be allowed to creep into the insulation
3. Both these objectives can be achieved by immersing the built up transformer in a closed tank filled with noninflammable insulting oil called transformer oil.
4. In order to increase the cooling surface exposed to ambient, tubes or fins are provided on the
outside of tank walls.
63. Buchholz relay is used on
(A) Air-cooled transformers
(B) Oil cooled transformers
(C) Welding transformers
(D) Fumace transformers
Ans:(B) Oil cooled transformers
64. Buchholz relay is generally not provided on transformers below
(A) 1 kVA
(B) 5 KVA
(C) 50 KVA
D) 500 KVA
Ans: (D)500 KVA
65. Operating time of the Buchholz relay is of the order of
(A) 0.1 microsecond
(B) 0.1 milli second
(C) 0.1 second
(D) 1 second.
Ans:(C) 0.1 second
66. In a distribution transformer, normally
(A) core losses are equal to copper losses
(B) core losses are more than copper losses
(C) core losses are less than copper losses
(D) core losses are half of the copper losses.
Ans:(C) core losses are less than copper losses
67. The secondary winding of which of the following transformers is always kept closed?
(A) Current transformer
(B) Voltage transformer
(C) Power transformer
(D) Step down transformer
Answer.(A) Current transformer
Explanation. If the current transformer secondary is not shorted when unused and kept open then it can develop a very high voltage across secondary which may damage transformer insulation.
68. If the supply frequency of a transformer increases, the secondary output voltage of the transformer
(A) Increase
(B) Decrease
(C) Remain the same
(D) Any of the above
Answer.(C) Remain the same
Explanation: The transformer is a static device that changes Voltage from one side of its coil to the other at a constant frequency.
Frequency does not change because of the working principle of the transformer-based on Mutual induction which happens without any change in frequency.
69. Power transformers are designed to have maximum efficiency at
(A) Full load
(B) 50% load
(C) 80% load
(D) no load
Answer.(A) Full load
Explanation: Power transformers are used for transmission as a step-up device hence they are not directly connected to consumers therefore, load fluctuation is very less. So the power transformer can operate on full load.
70. A Buchholz relay will operate in a transformer whenever there is
(A) large internal fault
(B) saturation of magnetic circuit
(C) over load
(D) any of the above.
71. Which of the following protection is normally not provided on small distribution transformers ?
(A) Over current protection
(B) Buchholz relay
(C) Over fluxing protection
(D) All of the above.
Ans:(B) Buchholz relay
72. In a transformer
(A) open circuit and short circuit tests are conducted on low voltage side
(B) open circuit and short circuit tests are conducted on high voltage side
(C) open circuit test is conducted on high voltage side and short circuit test on low voltage side
(D) open circuit test is conducted on low voltage side and short circuit test on high voltage side.
Ans:(D) open circuit test is conducted on low voltage side and short circuit test on high voltage side.
73. For a transformer, operating at constant load current, maximum efficiency will occur at
(A) Zero power factor
(B) Unity power factor unity
(C) 0.8 leading power factor
(D) 0.8 lagging power factor
Ans:(B) Unity power factor unity
Explanation:
Maximum efficiency for a transformer will be achieved at full load. While in the case of power factor also every device is set to get maximum efficiency at unity power factor. Thus, one will have maximum efficiency if load is nearly equal to full load and at unity power factor
74. The function of a breather in a transformer is
(A) to provide protection against overcurrents
(B) to suppress harmonics
(C) to arrest the flow of moisture from atmospheric air
(D) to control the level of oil in the tank.
Ans: (C) to arrest the flow of moisture from atmospheric air
Explnationation:
Transformer Breather Helps to Prevent Atmospheric Moisture and Reduce Maintenance Costs. During the breathing cycle of a transformer, it is crucial to prevent atmospheric moisture from entering the transformer, which can contaminate the oil
75. A good voltage regulation of a transformer means
(A) difference between primary and secondary voltage is least
(B) difference between primary and secondary voltage is maximum
(C) output voltage fluctuation with power factor is the least
(D) output voltage fluctuation from no load to full load is least.
Ans:(D) output voltage fluctuation from no load to full load is least.
Explanation:
Voltage regulation is the measure of how well a power transformer can maintain constant secondary voltage given a constant primary voltage and wide variance in load current. The lower the percentage (closer to zero), the more stable the secondary voltage and the better the regulation it will provide.
76. A transformer can have zero voltage regulation at
(A) zero power factor
(B) lagging power factor
(C) leading power factor
(D) unity power factor.
Ans:(C) leading power factor
Explanation:
When the leading load is connected to the transformer difference of Rcosφ and Xsinφ is multiplied with the current, thus we may get -ve, zero voltage regulations at this condition.
77. The colour of dry silica gel is
(A) pale yellow
(B) pale pink
(C) pale green
(D) blue
Ans:(D) blue
Explanation:
Ready to use silica gel is blue in colour. When the silica gel has soaked up a lot of moisture, the silica gel turns to pink. Once the silica gel turns pink it cannot adsorb any more moisture. It needs to be regenerated.
78. The colour of moist silica gel is
(A) red
(B) Pink
(C) blue
(D) yellow.
Ans: (B) Pink
Explanation:
Ready to use silica gel is blue in colour. When the silica gel has soaked up a lot of moisture, the silica gel turns to pink. Once the silica gel turns pink it cannot adsorb any more moisture. It needs to be regenerated.
79. The noise of the transformer mainly due to
(A) Cooling fan
(B) magnetostriction in an iron core
(C) Mechanical vibration
(D) All of the above
Ans: (B) magnetostriction in iron core
Explanation:
Most transformers use laminated iron cores. The lamination may not all be tightly “glued” together so that one or more may be free to slightly move or vibrate in response to the force of the ac magnetic field. In other cases, the core material, ferrite or lamination, may exhibit a slight “magnetostrictive” effect.
80. In a transformer the primary flux is ___ secondary flux.
(A) Greater than
(B) Smaller than
(C) Either 1 & 2
(D) Equal to
Ans: (D) Equal to
Explanation:
The transformer is said to be a constant main flux device. It is due to the high permeability and greater mutual flux which maintain a constant value.
If you increase the load in the case of a transformer, the secondary will draw more current and hence demagnetizing the core.
If you increase the load in the case of a transformer, the secondary will draw more current and hence demagnetizing the core.
This, in turn, draws more current from the primary to maintain the main flux at a constant value.
Similarly, for reducing the load, the secondary current decreases, and hence the primary current also reduces.
81. What would happen if a transformer is connected to a DC supply?
(A) No effect
(B) Operate with high efficiency
(C) Damage the transformer
(D) Operate with low frequency
Ans: (D) Damage the transformer
Explanation:
A transformer works on the principle of mutual induction, in which you need a varying magnetic field in a winding to induce an EMF in the secondary winding.
In DC generally change in frequency with respect to time is zero.
So a dc source cannot provide varying magnetic field, hence mutual induction is not possible.
Since the primary winding has a low value of winding resistance, the high value of current flowing through it can damage the winding.
82. An autotransformer can be used as
(A) Step up device
(B) Step down device
(C) Both step up and step down
(D) None of the above
Ans: (C) Both step up and step down
Explanation:
Normal transformers have two winding placed on two different sides i.e. primary and secondary.
In Auto Transformer, one single winding is used as primary winding as well as secondary winding i.e primary and secondary shares the common single winding.
The primary is electrically connected to the secondary, as well as magnetically coupled to it. Auto transformers are often used to step up or step down voltages upto 240 V range.
83. The friction loss in a transformer is
(A) 20%
(B) 0%
(C) 50%
(D) more than 50%
Ans: (B) 0%
Explanation:
As we know that transformer is a static device so there is no rotating part hence no friction loss.
84. In an Auto Transformer, The Primary and Secondary are_____Coupled
(A) Electrically only
(B) Magnetically only
(C) Both electrically & magnetically
(D) None of the above
Ans: (C) Both electrically & magnetically
Explanation:
Normal transformers have two winding placed on two different sides i.e. primary and secondary.
In Auto Transformer, one single winding is used as primary winding as well as secondary winding i.e primary and secondary shares the common single winding.
Therefore the primary is electrically connected to the secondary, as well as magnetically coupled to it.
85. The essential condition for parallel operating of two single phase transformer is that they should have same
(A) efficiency
(B) capacity
(C) voltage ratio
(D) polarity.
Ans:(D) polarity.
86. In a transformer the resistance between the primary and secondary must be
(A) Zero
(B) 1 killo ohm
(C) 100 killo ohm
(D) Infinite
Ans:(D) Infinite
Explanation:
In a transformer, the coils are not electrically connected therefore the resistance is ideally infinite. BUT an auto transformer does the same using a single coil as primary with one or more taps for secondary in different parts of the coil. In this case, the resistance will ideally be ZERO, or a short-circuit if you will.
87. The secondary of a current transfomer is always short circuited under operating conditions because
(A) it avoids core saturation and high voltage induction
(B) it avoids high voltage surges
(C) it protects the primary circuit
(D) it is same for operation.
Ans: (A) it avoids core saturation and high voltage induction
88. The main advantage of an auto transformer over a two winding transfomer is that
(A) no cooling is required
(B) hysteresis losses are minimised
(C) eddy current losses are minimised
(D) only one winding is used as a result there is substantial saving in material.
Ans: (D) only one winding is used as a result there is substantial saving in material.
89. Auto transfomer is used
(A) when operator is not available
(B) when copper losses are to reduced
(C) when higher efficiency is desired
(D) when the transformation ratio is small.
Ans: (D) when the transformation ratio is small.
90. The efficiency of two identical transformers under load conditions can be determined by
(A) Short Circuit test
(B) Open Circuit test
(C) No Load test
(D) Back to Back test (Sumpner Test)
Answer: (D) Back to Back test (Sumpner Test)
Explanation:
Back to Back test or Sumpner Test is done to test a transformer efficiency, heating & voltage regulation on full load.
It can be carried only when two identical transformers are available.
The LV side of the two transformers are connected in parallel with each other and the source is connected to the variable supply voltage.
The transformers are kept in this condition for 48 hours and the temperature is noted on an hourly basis and a curve is plot which should become constant after some time also it should be within limit.
91. The transformer ratings are usually expressed in terms of
(A) KW
(B) KVAR
(C) KVA
(D) Volts
Answer: (C) KVA
Explanation:
Why transformer rated in KVA not in KW ?
The rating of any electrical machine shows its ability to carry the mechanical load without showing any signs of overheating.
There are two types of losses in a transformer
⇒Iron Losses
⇒Copper loss
Copper losses ( I²R)depends on Current which passing through transformer winding.
Iron Losses (Core Losses or Insulation Losses) depends on Voltage.
This shows that the transformer is designed for Iron losses-rated voltage and copper losses-rated current.
since power factor is dependent on the load which is not stable.
But KVA tells you the current rating of the transformer, regardless of the power factor of the load.
Hence, total transformer loss depends on volt-ampere (VA) and not on phase angle between voltage and current
That is why the transformer rating can be in kVA, and not in kW.
92. Which winding in a transformer has more number of turns?
(A) Secondary winding
(B) primary winding
(C) High voltage winding
(D) Low voltage winding
Answer:(C) High voltage winding
Explanation:
High voltage winding have more turns but they carry less current then Low voltage winding transformer.
If the input power is given to the HV side, then the voltage is stepped down.
Similarly, if input power is given to LV side – the Voltage is stepped up.
93. In an to transfomer, effective saving on copper and copper losses will occur, when the transformation ratio is
(A) more than 1
(B) nearly equal to 1
(C) less than 1
(D) 0.707.
Ans: (B) nearly equal to 1
94. An auto transformer has
(A) only one winding
(B) two windings of the same gauge of wire
(C) two windings of different materials
(D) more than two windings.
Ans: (A) only one winding
95. Which of the following conditions should be fulfilled for the parallel operation of two transformers?
(A) Percentage impedance should be the same
(B) Polarities of both secondaries should be same
(C) Voltage ratings should be the same
(D) All of the above.
Ans: (D) All of the above.
96. If the transformer core is made of copper
(A) copper losses will be less
(B) eddy current losses will be more
(C) hysteresis losses will be more
(D) none of the above.
Ans: (B) eddy current losses will be more
97. If the ohmic resistance of windings of a transformer is zero then
(A) there will be maximum magnetic leakage
(B) copper loss will be zero
(C) core loss will be more than copper loss
(D) transformation ratio will be infinite.
Ans: (B) copper loss will be zero
98. A transformer transform
(A) Current
(B) Voltage & current
(C) Frequency
(D) Voltage
Answer: (B) Voltage & current
Explanation:
A transformer is a static device that is used to convert the voltage or current to a higher (step-up) or lower (step down) level.
The Distribution Transformer, Auto Transformer, and Tap changing Transformer basically belong to the family of Power Transformer with respective unique features.
In an Instrument Transformer, voltage or current on one side of the transformer, comparatively high (therefore not suitable for direct measurement), is scaled down to voltage or current to levels that is convenient for measurement with suitable instrumentation. Accordingly, the two types of Instrument Transformers are the Current Transformer and the Potential Transformer. Some applications may call for constant current (as in welding) or constant voltage. Such transformers am called Constant Current and Constant Voltage Transformers.
99. The essential condition for parallel operation of two single-phase transformer is that they should have the same
(A) KVA Rating
(B) Turn Ratio
(C) Polarity
(D) Both 2 & 3
Answer: (D) Both 2 & 3
Explanation:
The same turns ratio are required so that the open-circuit secondary voltages of the transformers are closely matched in order to avoid excessive circulating currents when the parallel connections are made.
If the transformers are connected with different polarities then the two emf’s induced in the secondary winding which are in parallel, will produce a short circuit current between both transformers.
100. Three-to-three phase transformer connection possible for parallel operation is
(A) Delta -Y to A-Y
(B) Delta - Delta to Delta-Y
(C) Y -Y to Delta-Y
(D) Delta -Y to Y - Delta.
Ans: (A) Delta -Y to A-Y
101. Three-to-three phase transformer connection not feasible for parallel operation is
(A) Y -Y to Y-Y.
(B) Y -Y to Delta-Delta
(C) Y - Delta to A-Y
(D) Y - Delta to Delta-Y.
Ans: (C) Y - Delta to A-Y
102. When a transformer operates under no load conditions, the current
(A) will lag the applied voltage by 90°
(B) will lag the applied voltage by about 75°
(C) will lead the applied voltage by about 75°
(D) will be in phase with the applied voltage.
Ans:(B) will lag the applied voltage by about 75°
Explanation:
When the transformer is operating at no load, the secondary winding is open-circuited, which means there is no load on the secondary side of the transformer and, therefore, current in the secondary will be zero.
Which of the following condition should be fullfilled for the parallel operation of two Transformers
(A) Ratio of equivalent resistance and equivalent reactance should be the same
(B) Turn ratio should be the same
(C) Purcentage inpedance should be the same
(D) All of the above.
Ans:(D) All of the above.
103. If a transformer core is made of copper and coils are made up of steel wire, then
(A) magnetising current will be reduced
(B) copper losses in the winding will be more
(C) eddy current losses will be less
(D) all of the above.
Ans:(B) copper losses in the winding will be more
104. Which of the following loss in a transformer is zero even at full load?
(A) eddy current loss
(B) hysteresis loss
(C) core loss
(D) friction loss.
Ans: (D) friction loss.
Explanation: Since the transformer is a static device so there is no moving part as a generator or motor therefore, there is no friction loss.
105. Lamination of the transformer core is made of
(A) Cast Iron
(B) Silicon Steel
(C) Aluminum
(D) Cast Steel
Answer: (B) Silicon Steel
Explanation:
Silicon steels are used for electrical transformer cores and cores of other electrical devices for the following reasons:-
1. Low hysteresis loss.
2. High permeability.
3. Virtually eliminated aging.
4. High resistance.
106. Stones are provided in the substation to
(A) To provide insulation
(B) To avoid Fire accident during leakage of transformer oil
(C) To avoid growing of plants and weed
(D) All of the above
Ans: (D) All of the above
Explanation:
Why stones are provided in substatones ?
Oil leakage takes place during operation or when changing the oil in the transformer. This oil spillage can catch fire is dangerous to the switchyard operation. So Stones is provided to protect from fire when oil spillage takes place.
In plain grounds when grass grows it will form moisture and cause damage to transmission lines and also cause current leakage. Stones eliminate the growth of small weeds and plants or grass inside the Substation.
107. A transformer on no-load is switched on to a source of voltage. It will draw a current
(A) Which is several times the steady-state magnetizing current depending upon the initial state of the residual flux in the transformer core.
(B) Which is several times the steady-state magnetizing current depending upon the initial state of the residual flux in the transformer core.
(C) Which is the same as the steady-state magnetizing current.
(D) Which is twice the steady-state magnetizing current provided the core has no residual flux.
Ans: (A) Which is several times the steady-state magnetizing current depending upon the initial state of the residual flux in the transformer core
Explanation:
Whenever a transformer is on no-load,i.e the secondary winding has no burden(load) connected to it.
The transformer must actually withdraw zero current from the primary side.
But practically even on no-load, a small amount of current is drawn from the primary side, to set up the required magnetic flux in the magnetic core.
At no load, the transformer draws some current (Im) in order to establish the flux in the transformer core which lags the applied voltage by 90° ( since flux is required to create a magnetic pool in order to transfer energy from one port to another) called as magnetizing current.
This magnetizing current (no-load current) is about 3-5% of the full load current and it accounts for the losses in a transformer.
108. Cruciform shape is used in the transformer core to
(A) Reduce core loss
(B) Reduce core reluctance
(C) Reduce winding copper
(D) All of the above
Ans: (D) All of the above
Explanation:
Cruciform core Transformer
Cruciform core design reduces the net area of the core, decrease the I2R looses in the transformer.
The cruciform shape also reduces the mean length of turns thus provide a copper saving of transformer.
109. Which of the following test is performed to determine the (A) leakage reactance
(B) Short circuit test
(C) Open circuit test
(D) Both Open circuit and short circuit test
(E) Test by an Impedance bridge
Ans: (B) Short circuit test
Explanation:
Short circuit or Impedance test
Short circuit test or Impedance test is performed to determine
⇒Copper loss at full load
⇒Equivalent impedance (Zo1 or Zo2)
⇒Leakage reactance (Xo1 or Xo2)
In this test low voltage winding is short-circuited by a thick conductor.
Short circuit test is performed on HV side of the transformer.
Low voltage (5 to 10%) is applied to the primary and slowly increase till full load current are flowing both in primary and secondary.
The ammeter reading gives full load current IL.
Since applied voltage is small so flux (Φ) is also small therefore core loss is small hence core loss can be neglected.
110. During SC test the Power Input to a transformer comprises predominately
(A) Core loss
(B) Copper loss
(C) Hysteresis loss
(D) Eddy current loss
Ans: (B) Copper loss
Explanation:
Low voltage (5 to 10%) is applied to the primary and slowly increase till full load current are flowing both in primary and secondary.
The ammeter reading gives full load current IL.
Since applied voltage is small so flux (Φ) is also small therefore core loss is small hence core loss can be neglected.
111. The maximum load that a power transformer can carry is limited by its
(A) Voltage ratio
(B) Temperature Rise
(C) Cooper Loss
(D) Dielectric strength of coil
Ans:(A) Voltage ratio
Explanation:
The amount of power a transformer can transfer depends primarily on the magnetic properties and the volume of its core.
This power is frequency-dependent and it scales essentially with P ∝ V ∝ F.
For a given core size and core material (which also depends on the application), the number of turns then determines the inductance and the capacitance of the primary and secondary coils.
In power applications, the number of turns in a winding is usually chosen in such a way that the magnetic flux density in the core at the rated voltage is of the same order of magnitude as the saturation flux density of the core material.
Decreasing the number of turns would lead to saturation of the transformer core, losses would rapidly increase, and finally, the transformer would stop operating as a transformer altogether.
When increasing the number of turns you will not fully utilize the core anymore (or, alternatively, you can make the core slimmer), but at the same time, you need more conductor material for the winding (remember that the thickness of the wire was determined by the current rating!). So in effect, the transformer will become more bulky and expensive.
Smaller turn number means larger core but smaller winding volume, larger turn number means smaller core but larger winding volume.
112. A shell-type transformer has
(A) High eddy current losses
(B) Reduce magnetic leakage
(C) Low hysteresis losses
(D) All of the above
Ans: (B) Reduce magnetic leakage
Explanation:
In shell-type transformer both the primary and secondary coils are turned in the same core, i.e in the middle leg.
Shell type transformer has a double magnetic circuit and three limbs.
At first, either the primary or the secondary winding are wound around the middle leg, and then above it the other one is wound. In this case, there is least possible leakage.
When the primary side is excited, it would produce the flux that must cut the secondary coil.
Here at the time of production of flux it simultaneously cuts the secondary coil with the least amount of leakage and produces the necessary output voltage.
113. A transformer can have zero voltage regulation closer to zero
(A) On full load
(B) On overload
(C) On leading power factor
(D) On zero power factor
Ans:(C) On leading power factor
Explanation:
Voltage regulation is defined as the ratio of the difference between no-load voltage and full load voltage to no-load voltage. Voltage regulation depends on the nature of the load.
For lagging and unity power factor V2 > E2.
where,
V2 = Secondary terminal voltage on given load.
E2 = Secondary terminal voltage on no load.
As the load increase, it tends to become capacitive and V2 start increasing.
Now at a certain point of leading power factor, V2 = E2, and regulation become zero.
In leading, the power factor condition load is just able to supply the reactive power for the active power flow.
114. A tap changer is used on a transformer for
(A) Adjustment in primary voltage
(B) Adjustment in secondary voltage
(C) adjustment in both primary and secondary voltage
(D) adjustment in power factor
Ans: (B) Adjustment in secondary voltage
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