CHAPTER 3

1. Define the term dynamo.- A generator, especially one for producing direct current.

2. Name the various parts of the dynamo and indicate which parts are stationary and which rotate.

- Two sections of dynamos are the stator which is stationary and rotor, the portion that rotates

3. From what material is each part listed in Question 2 made?

- Stator’s field is built up of customary laminated steel core and winding, while the rotor, is build up of laminated core, and slotted to receive the insulated copper armature winding.

4. What is meant by pole core? pole shoe?

- Pole cores is built of a stack of steel laminations about 0.025 in. thick per lamination, having good magnetic qualities; rivets are driven through holes in the sheets to fasten together a stack of such laminations equal to the axial length of the armature core. Pole shoe permits the flux to spread out over a wider area where the flux enters the armature core.

5. Why are laminations used in constructing the field core?

- Field core is built up of a stack of steel lamination because it has good magnetic qualities.

6. Why are laminations used in constructing the armature core?

-Armature core is built up of a stack of steel lamination because it has good magnetic qualities. It has circular section.

7. Why are pole cores constructed with a shoe?

-Poles cores are constructed with a shoe in order to permit the flux to spread out a wider area where the flux enters the armature core.

8. What two kinds of field winding are used for generators and motors? Describe the construction of each?

The shunt field – a shunt in which there are turns of fine wires.

Compound field – a compound field in which both a shunt and series winding are used.

9. What is the purpose of dipping and baking field coils?

-The purposes of dipping and baking field coils are to add stiffness, mechanical strength, and good insulating properties to the winding.

10. What is the yoke? What purpose does it serve? How it is usually constructed?

-Yoke is the outside frame of a machine; it is usually a circular iron or steel ring of rectangular section, sometimes rounded on the surface for added strength. It is where the field-pole assemblies are bolted.

11. Why is cast steel or rolled steel more desirable than cast iron for the yoke material of dynamos?

-Cast steel is used because this material makes it possible to reduce the weight by as much as 60 percent without any increase in the reluctance of the magnetic circuit.

12. Describe a commutator construction?

-Commutator is built-up of hard drawn copper bars, wedge-shaped in section when viewed on end, and having V-shaped grooves at each end.

13. What purpose does the commutator serve in a generator? In a motor?

-Commutator performed the process of rectifying the alternating current, that is changing the internal alternating current to an external direct current.

14. What is the function of the armature winding in a generator? In a motor?

-Armature winding is virtually the heart of the dynamo, it is where the voltage is generated in the generator or where the torque is developed in the motor.

15. Under what conditions is it necessary to use a brush rigging in which each arm contains several brush holders and brushes?

-In large machines, a brush arm may have several brush holders, into each of which is placed a carbon or copper-graphite brush rides freely, without chattering, on the commutator.

16. What keeps the brushes in good contact with the commutator?

-Each brush is held down firmly on the commutator by a spring that exerts a pressure of about 1 to 2 lb per sq. in.

17. How is the brush surface made to conform with the commutator surface?

-The surface of the brushes in contact with the commutator must be ground or sandpapered smooth so that perfect contact exists between them.

18. What purpose is served by the brush pigtails?

-Each brush arms also contain flexible copper pigtails for good electrical connection between the insulated brush arms and the respective brushes.

19. Which terminal is positive on a generator? On a motor?

-In a generator the positive terminal “feeds” current to the load while in the motor it is the terminal that is connected to the positive bus of the source.

20. Name the two general types of armature winding.

-The two general types of armature winding are the lap and wave.

21. Distinguish between a simplex-lap and a simplex-wave winding with regard to construction; with regard to the number of parallel paths.

-In simplex-lap windings, coil are connected to adjacent commutator segments, while in the simplex-wave windings the coil ends are connected to a commutator segments very nearly, but never exactly, equal to the distance between poles of

the same polarity, that is alternate poles. In simplex-lap winding the currents divide into P parallel paths, where P is the no. of poles, while the no. of parallel in simplex-wave winding is to, regardless the no. of poles.

22. In general, what is a frog-leg winding?

-Frog leg winding is a combination of a multiplex-wave and a simplex-lap winding. It has a unique features retaining the advantages of both types without their inherit disadvantages.

23. What is the important requirement with regard to the coil span of all types of armature winding? –

-The distance of two sides of a coil must be equal (or very nearly so) to the distance between two adjacent poles. The coils span must be 180 electrical degrees, or approximately so.

24. Explain what would happen if the coil span were 360 electrical degrees in a generator; in a motor.

- If the coil ends are connected to segments exactly 360 electrical degrees apart, every group of P/2 coils would constitute a complete reentrancy because there are 360 electrical degrees in every pair of poles (P/2).

25. State the formula to determine the coil span Ys for an armature winding.

Ans. Ys = (s/p)-k

Where: Ys – coil pitch, in slots

s - total number of armature slots

p - number of poles

k - any part of s/p that subtracted to make Ys an integer

26. What is the commutator pitch in a simplex-lap winding? A duplex-lap winding? A multiplex-lap winding?

-The ends of the coils of simplex-lap winding are connected to adjacent commutator segments. They are all connected together in succession at successive commutator segments. Duplex-lap is when the ends of the first lap coil are joined to segments 1 and 3 instead of 1 and 2, the succeeding coils will be joined to segments 2 and 4, 3 and 5, 4 and

27. What is meant by the term reentrancy?

-Reentrancy is used to designate this important fact where the winding is the said to close upon itself or reenter.

28. Under what condition is the reentrancy of a duplex-lap winding single? Double?

-If the commutator has an even number of segments, the odd-numbered segments will join together one half of all the coils, while the even-numbered segments will join together the other half of all the coils. Such a winding is double reentrant. On the other hand, a duplex-lap winding on armature having odd number segments

will be singly reentrant.

29. Under what condition is the reentrancy of a triple-lap winding single? Triple?

-Triplex-lap winding would have the first coil ends connected to segments 1 and 5 and reentrancy would depend only upon the relation between the number of 7 commutator segments and the plex.

30. What is the purpose of multiplex-lap winding?

31. State the general rule for determining the reentrancy of a multiplex-lap winding.

-The degree of reentrancy of lap windings is equal to the highest common factor between the number of commutator segment and the “plex” of the winding.

32. What general rule can be used to determine the number of parallel paths in a multiplex-lap winding?

- Commutator pitch (Yc) multiplied by the no. of poles (P) determines the no. of parallel paths.

33. To what values of machine ratings are multiplex-lap windings restricted?

-Multiplex-lap windings are generally restricted to low-voltage high-=current machines because, practically speaking, it is desirable to limit the current pr path to values no greater than about 250 to 300 amp.

34. Why must the ends of wave coils are never be connected to the commutator exactly 360 electrical degrees apart?

-For if the ends of the coil is connected to the commutator exactly 360 degrees apart it will cause a complete closure, which violates the first property of the commutator that the entire winding must be trace from segment to segment, and from coil side to coil side. For tracing winding once around the commutator the last coil end should arrive one segment behind or one segment ahead to the starting segment.

35. State the general rule for determining the commutator pitch in a simplex-lap winding.

-In a simplex-lap winding the commutator pitch is always equal to one.

36. Explain why only two brush sets need be used in a machine in which the armature is awave wound.

The use of two sets of brushes is often very convenient, particularly in installation in which brushes cannot be replaced without difficulty. Furthermore, in wave-wound machine equipped with as many brush sets as poles, if one or more of the brush sets develop poor contact with the commutator, satisfactory operations still possible.

37. How are the conductors in each path of a lap winding distributed around the armature?

-The conductors in each of the P paths of a lap winding are distributed under two poles, a north and a south pole.

38. How are the conductors in each path of a wave winding distributed around the armature winding?

-The conductors in each of the two paths of a wave winding are distributed under all the poles.

39. Under what conditions is it desirable to use two brush sets in machines having wave-wound armatures?

-In a multi-polar machine two sets of brushes where used with convenience particularly in installation in which brushes cannot be replaced without difficulty.

40. Under what conditions is it desirable to use as many brush sets as poles in machines having wave-wound armatures?

-When a machine is equipped with many brush sets as poles it is still possible to have satisfactory operation beside when more of the brush develops poor contact with the commutator.

41. What are multiplex-wave windings?

-It is a type of armature winding with more than two even parallel paths.

42. Under what circumstances would it be desirable to use multiplex-wave windings?

-In such situation where current rating is too high, specifically above 600 amps, it is necessary to use armature winding having more than parallel path (Multiplex- wave winding).

43. Why is it possible to have circulating currents in lap-wound armatures?

-The circulating currents can flow in lap-wound armature only because the conductors of each path are not distributed completely around the circumference, as in wave-windings, but occupy position under one pair of poles at a time.

44. Why is it impossible to have circulating currents flowing in wave-wound armatures?

-The circulating currents cannot flow in the wave-wound armatures, it can only flow in lap-wound armatures because the conductors of each path are not distributed completely around the circumference but occupy positions under one pair of poles at a time.

45. State the rule for determining the commutator pitch in a multiplex-wave winding.

-In general, a multiplex-wave winding requires Yc to be chosen that after the winding is tracedoncearound the commutator, the last coil end arrives m segments behind or ahead the startingpoint.

46. In tracing a simplex-wave winding once around the commutator, at what segment should one arrive with respect to the starting point?

-In a simplex-wave winding, the last coil end arrives one segment behind or one segment ahead the starting point.

47. Answer Question 46 for a duplex-wave winding; a triplex-wave winding; a multiplex- wave winding?

-In a duplex-wave winding, the last coil end arrives two segments behind or ahead of the starting point.

In a triplex-wave winding, the last coil end arrives three segments behind or ahead the starin point.

In a multiplex-wave winding, the last coil end arrives m segments behind or ahead the starting point.

48. Why it is usually more satisfactory to construct armature that have more commutator segments than slots?

- It is more satisfactory to design the armatures with more commutator segments than slots for the following reason:

a.) As the number of commutator segments is increased, the voltage between those that are adjacent to each other decreases and the number of turns of wire in the coil or coils connected to the adjacent segment also decreases. The result is that there is less sparking at the commutator because of the improved commutation.

b.) As the number of slots is reduced, the armature core teeth become mechanically stronger, so that, from the standpoint of handling in manufacture, there is less damage to laminations and coils.

c.) Assuming that a comparatively large number of segments has been selected so that good commutation will result, the choice of an armature core with one-half, one-third, one-fourth, etc., as many slots means that fewer coils will have to be constructed; this reduces the cost manufacture.

49. Are pitch calculations Ys and Yc affected when an armature has more segments than slots?

-The pitch calculations for Ys and Yc are made exactly the same way, regardless of whether the number of slots and segments are the same or not.

50. What is meant by a double-element coil? A triple-element coil? When are they necessary?

-DOUBLE-ELEMENT COIL - when an armature has twice as many commutator segments as slots, each of the completely formed coils is a sort of double-element coil, in the sense that it serves double capacity.

- This is necessary because each slot must hold as many wires as are ordinarily held by two slots when the number of slots equals the number of segments.

TRIPLE-ELEMENT COIL - when the armature has three (3) times as many segments as the slots.

51. Under what condition is it desirable to wind an armature before the commutator is pressed on the shaft?

-The winding must be completed first before the commutator is pressed on the shaft. These practices make sit possible to insert the coils in the slots more easily because there is ordinarily very little space between the core and the commutator

52. What is meant by a “dead” or “dummy” element?

-It is the unconnected element of the winding.

53. When does an armature winding have a “dummy” element?

-When the arrangement states, “the number of segment is one less than 2, 3, 4, etc., times the number of slots” is followed then the dummy element will exist.

54. What purpose is served by a “dummy” element?

-The purpose served by a dummy element is to keep the revolving structure balanced mechanically.

55. Under what conditions do circulating currents flow in lap-wound armature?

-In a large lap-wound machines, troubled is frequently encountered when air gaps between stationary poles and rotating armature are not the same. These conditions cause the generated voltages in the various parallel paths to differ widely, and as a result, large circulating currents flow in the armature.

56. Why are circulating currents detrimental to good operation?

-These circulating currents tend to heat armature above the temperature caused by the normal load current and caused an undue amount of sparking at the brushes. These sparking should be avoided because it causes undue burning wear of the commutator, and if carried too far, may result in flashover from positive to negative brushes and condition representing a short circuit across the supply lines. Also small differences in air gaps under the various poles are lack of similarity in the flux distribution of the poles can produce inequalities such that, in time, it may appear as bearing wear.

57. What is an equalizer connection?

-Equalizer connection is constructed with low resistance copper wires that connected together in the point of the armature winding which should , under ideal conditions, be at exactly the same potential at all times but which, because of mechanical and electrical difference, are not.

58. What two important functions are served by equalizer connections in lap-wound armatures?

-. they relieve the brushes of the circulating current load by causing the latter to be bypassed.

-they create a magnetic affect that actually reduces the flux under poles those poles where there is too much magnetism and increases the flux under those poles where there is little magnetism.

59. State the general rule for determining the number of equalizer connection to be used in an armature that is to be equalized 100 per cent.

-To achieve 100 percent equalization all coils must be properly connected.

60. Exactly why does frog-leg winding eliminate the necessity for using equalizer connections?” Explain carefully.

-Any wave element and the succeeding lap element connected on the commutator exactly 2 pole pitches apart eliminate the use of equalizer. These elements together have the important characteristic properties that is possessed by an equalizer.

61. Is it possible to place a lap winding on top of a properly designed wave winding and have this combination of windings perform as satisfac0tory as a frog-leg winding? Explain.

- No, because they are non-potential-generating wires and carry equalizing currents only.

62. What is the origin of the term frog-leg winding?

- The term frog-leg is used to indicate the similarity between this type of coil and the legs of the frog.

63. If the lap section of a frog-leg winding is always simplex, what must be the multiplicity of the wave section?

-If the lap section of a frog-leg winding is always simplex the multiplicity of the wave section or “plex” is equal to P/2.

64. How many parallel paths are there in a P-pole frog leg winding?

-For frog-leg winding have as many circuit in parallel as duplex-lap winding because the simplex-lap portion supplies P circuits and the multiplex-wave section also provides P circuits, the total being 2xP paths in parallel.

CHAPTER 4

1. Name the three general of d-c generator.

- Shunt , Series and compound.

2. How does the construction of the fields differ in the three types of generator?

-: If the excitation is produce by a field winding that is connected to full, or nearly full, line voltage, the machine is a shunt generator.

- If the excitation originated in a field winding connected in series with the armature, so that the flux depends upon the current delivered to the load, the machine is a series generator.

If the excitation is produced by two field windings, one connected to the field, or nearly full, line voltage and the other excited by the line or armature current, a comparatively large current, the machine is compound generator.

3. What current does the series fields carry in the long-shunt compound generator? The short-shunt compound generator ?

-: Comparatively large current.

4. In a compound generator, why is the series-field coil wound over the shunt coil?

-: Because the compound generator acting together with the fairly constant shunt excitation

5. What voltage is developed by a series generator at no load? Why?

- The terminal voltage is very low at light load because the excitation is low under this connection.

6. What voltage is developed by a shunt or compound generator with the shunt field open? Why?

-: The speed of generation and the flux.

7. Distinguish between a separately excited and a self- excited shunt generator.

-: A self- excited is a short shunt connection while separately excited is a long-shunt connection.

8. Upon what two factors does the no load voltage of a shunt generator depend?

- The speed of rotation and the flux.

9. How is the field of a shunt generator usually controlled?

- when a generator is in operations, whether or not it is delivering a load current, the shunt field is always excited

10. Why is it not desirable to operate a generator, why is the flux created by a shunt field not directly proportional to the field current?

- as the speed is gradually lowered without changing the field excitation lower readings of Eg and revolution per minute are recorded

11. In normal operation of a shunt generator, why is the flux created by a shunt field not directly proportional to the field current?

- because magnetic saturation sets in after the field current is increase beyond a certain value.

12. What is meant by the saturation curve? What test must be performed to determine data for its construction?

-: a magnetization curve, data is plotted.

13. What is the relation between no load volts and field current below the knee of the magnetization curve? Why?

- The field current is gradually increased then, as the iron saturates with increasing value of flux, the generated voltage does not increase as rapidly as the field current.

14. What does the saturation curve emphasize?

Answer: The generated voltage is directly proportional to the flux.

15. How does the no load voltage of a shunt generator vary with changes in speed if the field current is kept constant?

- if the field is kept constant while the speed decrease, the voltage will rise and fall, in direct proportion to the changed speed, because the generated voltage will depend on the speed of rotation and the flux or the field current.

16. What is meant by the building up of a self excited shunt generator?

- It means that several important conditions have been fulfilled.

17. What condition must be fulfilled before a self excited shunt generator will build up?

- the value of the voltage to which a given generator will build up will determined by other factors.

18. What determines the voltage to which a self excited generator will build up?

- Rise from its residual value (total voltage) to its normal operating value.

19. What simple test can be performed to show that a self excited shunt generator will not build up because the field is reverse?

- flashing the field

20. If a self excited shunt generator does build up, will it do so if the field is reverse? If the armature leads are reversed? If the direction of the rotation is reversed? If the residual field is reversed? Give reason for your answer.

- if a self excited shunt generator builds up and the residual field is weakened, the generator will build down, not up. However if the field is strengthened because the field winding is properly connected to the positive and negative brushes, the generated voltage will rise, which in return will cause an increase in field current, in flux and a still larger generated voltage.

21. What is meant by flashing the field? When must this be done?

-: since a self excited shunt generator cannot build up unless it is given an initial boost or push by a residual voltage, it should be clear that a new machine or one that has loss its residual flux because of a long period of idleness must be separately excited to create a necessary magnetism. This practice is generally referred to as flashing the field. This is usually done while the armature is at rest by connecting the shunt field to a separate dc source such as battery for a few seconds.

22. What causes the voltage of a separately excited shunt generator to drop when it is loaded?

-in a separately excited shunt generator, the armature is always develop a voltage as soon as the field is connected to its separate source supply; the points made concerning build up do not apply to separately excited generators. This the reason why voltage drops when it is loaded.

23. What causes the voltage of a self excited shunt generator to drop when it is loaded?

- the voltage of a self excited tends to drop when it is loaded because a no load voltage builds up to the required voltage which is ready to supply power to a number of electrical loads up to its rated capacity.

24. Why it is important to keep the armature resistance of a generator as low as possible? In designing the winding, how could this be accomplished?

- because the generated voltage with depends upon the flux is always greater than the terminal or load voltage by exactly the amount of the voltage dropin the armature circuit.

25. What is meant by voltage regulation of a shunt generator?

- A voltage regulator is an electrical regulator designed to automatically maintain a constant voltage level. A voltage regulator is an example of a negative feedback control loop. It may use an electromechanical mechanism, or electronic components. Depending on the design, it may be used to regulate one or more AC or DC voltages.

26. Assuming a certain regulation for a self excited shunt generator, would this value be increased or decreased if the same machine were operated as a separately excited shunt generator? Give reasons for your answers.

- When a self-excited shunt generator is operated at a speed approximating the name-plate value with the field switch open, the armature will generate a residual voltage.

27. How is the terminal voltage of a shunt generator usually controlled?

- It is possible to prevent the terminal voltage V from changing as the load changes by merely adjusting the field rheostat as the voltage changes in accordance with the load.

28. What is the principle operation of the Tirrill regulator?

-: Tirrill regulator formerly used almost exclusively for such service but now superseded by other types that are quicker acting and more reliable.

29. What type of voltage regulator is generally used at a present for d-c generators?

-: Diactor (direct acting) unit

30. Explain why the regulation of a self excited shunt regulator can be improved by operating the machine at lower speed. Why is the lower speed practically inadvisable?

-: The tendency on the part of the shunt generator to lose voltage with increasing values of load maybe minimized by operating the machine at lower speed.

-An objection operation at lower speed however, is that the machine is likely overheat bec. The copper loss in the field is increased and ventilation, that is, cooling is not as good bec. The fanning action of the armature is reduced.

31. Make two simple sketches showing a compound generator connected long shunt and short shunt.

Short-shunt connection Long-shunt connection

32. What are meant by the following terms when applied to compound generator: Cumulative! Over compound, under compound, flat compound, differential-compound?,

- Compound generator is a machine having both shunt and series excitation, the series field is wound directly over the shunt field.

- The action of the series field must oppose, that is, “buck”, the shunt field, the machine is referred to as differential-compounded.

- The shunt and series field coils around of each of the main poles should be so connected that they create flux in the same direction if tendency of the generator to lose voltage is to be counteracted, machine is cumulative-compounded.

- If the terminal voltages at no load and full load are equal, the machine is said to be flat-compound.

- If the full load voltage is higher than the no load value, it is called an over-compound generator.

- If the full load voltage is less than the zero-load voltage, it is referred to as an under-compound machine.

33. How can the degree of compounding be most readily adjusted?

- The degree of compounding is determined primarily by the number of series field turns or, more particularly, by the full load series field ampere turns with respect to the shunt field ampere turns.

34. What is meant to by a diverter? What material is generally used for its construction? Why?

-: Diverter is a low resistance shunt. The material that generally used for its construction is copper because it creates no flux.

35 Why is no flux produced by the diverter?

- The diverter diverts or bypasses, part of the load current through a section of wire that creates no flux.

36. What would be the objection to constructing the diverter of copper?

-: The series field is less effective in creating flux to boost the generated emf to an extent determined by the diverted current.

37. Explain why the terminal voltage of a series generator rises from its residual value at no load to some maximum value as load is applied.

- When a generator has a single field is connected in series with the armature, the load current is simultaneously excitation current.

38. What causes the terminal voltage of a series generator to level off to some maximum value as load is increased and then to decrease rapidly to zero with further application of load.

- A load that are considerably above normal values, the iron portions of the magnetic circuits become highly saturated, under which condition the subtractive effect exceed the slowly rising generated emf; the terminal voltage then begins to drop.

39. Name practical application of the series generator.

- In this country, t is sometimes used in a d-c system for voltage-boosting purposes or to minimize leakage currents in grounded d-c system so that electrolytic ation in underground structures maybe reduced; it is sometimes employed in the thury high voltage d-c systems for the transmission of electrical energy.

40. What is meant for armature reaction?

-: When the armature of the d-c generator carriers a load current, it becomes an electromagnet, apart from the magnetic effect induced in it by the main poles.

41. What is the general direction of the armature reaction flux with respect to the main field flux?

- Armature flux is directed downward through the armature, whereas the main field is from left to right.

42. What two important detrimental effects are produced by armature reaction?

-: Chamfered pole shoes and by employing pole laminations with one pole tip.

43. Explain why armature reaction tends to reduce the total flux in a generator.

-: If the decrease is usually greater than the increase, because of magnetic saturation.

44. Why is necessary to shift the brushes in non Interpol generators when the load changes?

-: The brushes must be shifted back and forth continually as the load changes because the effect of armature reaction depends upon the value of the armature current.

45. In noninterpole generator, how can the main pole tips be constructed to minimize the effect of armature reaction?

-: The rounded surface of the pole shoe is not concentric with the circular armature core; this reduces the effectiveness of the armature magnetomotive force (mmf) at the pole tips and in the commutation zone.

46. In what winding t direction must the brushes be shifted as the load is increased on noninterpole generators?

- The brushes must be shifted back and forth.

47. What are interpoles?

-: Interpoles is used to correct the objectionable commutation effects of the armature reaction.

48. By what electrical circuit must the intepolewinding be excited? Why?

- Mechanical neutral, the exciting windings for these poles are always permanently connected in series with the armature because interpoles must produce fluxes that directly proportional to the armature current.

49. In what some is interpole effective?

-: In the commutating zone.

50. Dointerpole prevent flux distortion? Explain.

- Yes. Because interpoles produces fluxes that are directly proportional to the armature current.

51. What are compensating windings?

- Are used for the purpose of neutralizing the effect of armature reaction in the zones outside the influence of the interpoles and particularly to maintain a uniform flux distribution under the faces of the main poles.

52. Explain why compensating windings correct flux distortion.

- To neutralize the effect of armature reaction in the zones outside the influence of the interpoles.

53. What current is carried by the compensating winding? Why?

- The total armature current. Because the current per path in the armature winding is equal to the total armature current divided by the number of the armature paths.

54. Why each turn of a compensating winding more effective in producing flux than each turn of the armature winding? What is the relation between them?

- The compensating winding carries the total armature current, it is much more effective in producing flux per turn than is each armature winding turn.

55. What is meant by flashing over?

- It is the effect of the armature reaction is neutralized, regardless of the armature current.

56. What two important functions are performed by the commutator and the brushes in a dc generator?

- First, a possible high current in the coil undergoing short circuit and second, the inductance property of the coil that opposes a reversal of current.

57. What are the three stages in the commutation process?

- (a) before short circuit, when the current is in one direction. (b) the short circuit period, which is the most severe period and (c) after short circuit, when the current begins to flow in the opposite direction.

58. What is meant by reactance voltage? To what property of the armature coil does it owe its existence?

- It oppose the material in a reverse direction and this property gives rise to a voltage as a result of which the smaller machine, the inductance. To the inductance property of the coil.

59. Explain why the brushes must be shifted beyond the magnetic neutral in noninterpole generators if sparkles commutation is to result?

- So that a voltage will be generated in the coil in the direction in which the current is about to flow.

60. When interpoles are used, Why must they be somewhat stronger than would be necessary t neutralize the effect of armature reaction if the sparkles commutation is to result?

- To overcome the armature reaction flux, or why brushes, when shifted, are moved a little beyond the exact magnetic neutral.

61. Why do power plants usually have several generators to provide electrical service?

- Because the several units can then be operated singly or in various parallel combinations, on the basis of the actual load demand.

62. Why is service continuity so important in industrial plants? In the home? On the farm?

- It would be obviously important if a power plant contained a single unit, because a breakdown of the prime mover or the generator would necessitate complete shutdown of the entire station.

63. What important condition must be fulfilled before a shunt generator is connected in parallel with another?

- the external characteristic of the two shunt generator should be similar to each other.

64. Under what condition will two shunt generators operating in parallel divide the total load in exact proportion to the machine ratings?

- if they are similar to each other.

65. Under what condition will two shunt generators operating in parallel divide the total not divide the total load in exact proportion to the machine ratings?

- if the two shunt generator is not similar to each other.

66. Explain carefully the exact procedure for connecting a shunt generator in parallel with others already supplying a load.

- First, connect a larger generator in parallel with the latter after which the smaller machine, when gradually unloaded, is disconnected from the line and second, connect another generator with the other one and have the two machines operate jointly to supply the total load.

67 How should a generator, already in parallel with others and sullying a load, be disconnected from the bus?

-The terminal voltage should not have the same value.

68. Why will two shunt generators operating in parallel always be in stable equilibrium?

-If each one carrying their proper share of the total load.

69. What is equilibrium? When must it be used?

- is a very low-resistance copper wire that joins together identical ends of the serial fields, the other ends of the switch are connected together after the main switches have been closed.

70. Why will two compound generators operating in parallel be in unstable equilibrium when no equalizer is used?

- instability would result if the machines are over compounded.

71. Explain carefully why an equalizer connection makes it possible for two compound generators to operate in parallel in stable equilibrium.

-to over compound generators and not those that have drooping characteristics, such as under compound machines.

72. Make a wiring diagram showing how two long-shunt compound generators must be connected for operation in parallel.