DC generator[1]Yesmechanical energyEquipment converted into DC power.It is mainly used asDC motor, electrolysis, electroplating, electro smelting, charging and alternatorexcitationEtcDC motor。Although where DC power is needed, power rectification elements are also used toalternating currentbecomeDCHowever, from the point of view of ease of use, reliability of operation and some working performance, the DC motor is not compatible withalternatorcomparison.The potential waveform of the DC generator is good and the electromagnetic interference is small. However, due to the existence of the commutator, its manufacturing and maintenance are complex and its price is high.
Chinese name
DC generator
Foreign name
dynamo, DC Generator
Type
Power generation equipment
Excitation mode
Separate excitation, series excitation, parallel excitation and compound excitation
In 1832, Pixie made a permanent magnet hand driven DC generator, which was the first reported DC generator in the world[3]。
In 1838, Lenz put forward the reversible principle that motor can be used as both generator and motor.
In 1845, Wheatstone made the first DC generator excited by electromagnet (previously used permanent magnet)[4]。
In 1851, Sinstein proposed to replace permanent magnet with energized coil as the excitation of motor.
From 1852 to 1856, the Anglo French Alliance Company was established and made into an electromagnetic DC generator driven by a steam engine. The generator entered the industrial and commercial application fields for the first time.
In 1860, Basinot applied the principle of motor reversibility to make the first DC motor that can be used as both a generator and a motor[1]。
In 1866, W. Siemens proposed the principle of self excitation of DC motor by using motor remanence, and made a self excited DC generator (Dy. namo).
In 1873, Fontaine used the electricity generated by the DC generator to run the DC motor at the Vienna World Expo, which solved the power supply problem of the DC motor that had puzzled for many years (before that, the DC motor used batteries as the power supply), and promoted the application of the DC motor.
DC motor germination and development period (1821-1895)
From the birth of the first DC motor in 1821 to the DC generator in Adams Power Station in Niagara Falls in 1895Hydro generatorThe failure in international bidding is the budding development period of DC motor.During this period, the incandescent lamp independently invented by Edison and Swan (J.W_Swan, 1828-1914) (Figure 8.1) around 1880 greatly promoted the application of DC and stimulated the development of DC generators.Since then, DC motors have been singing all the way to dominate the world.However, in 1895, the failure of the DC generator bid in Niagara Falls Adam s Power Station quickly curbed the soaring momentum of DC motors and the situation of DC motors dominating the world.During the period from 1821 to 1895, the theory of DC motor became increasingly perfect and mature;Continuously improve the structure and move towards unity;In terms of products, from small to large, from laboratory to practical application.
working principle
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Use the motor to drive the armature to make it rotate at a constant speed in the counterclockwise directionturn, coil edge a b and c d respectively cutmagnetic forceLine, induction generationemf。
The working principle of the DC generator is toarmatureThe alternating electromotive force generated by induction in the coil is matched by the commutatorbrushThe commutation effect of is such that it becomes a DC electromotive force when it is led out from the brush end because the electromotive force led out by brush A through the commutation plate is always the electromotive force in the coil side cutting the N-pole magnetic force line.Therefore, brush A always has a positive polarity. In the same way, brush B always has a negative polarity.Therefore, the brush end can draw pulsating electromotive force with constant direction but varying magnitude[2]。
DC generator
Conclusion:IntracoilInduced electromotive forceIt is an alternating electromotive force, while the electromotive force at brush A and B is a DC electromotive force.WhenalternatorWhen the armature ofCutting magnetic induction line movement。When the coil is turned to the position shown in Figure 1.1. B, useRight-handed ruleIt can be judged that the direction of induced electromotive force generated by conductor in section ab is b → a;If the direction of the induced electromotive force generated by the conductor of the cd section is d → c, the brush A in contact with the slide 1 is the positive pole, and the brush B in contact with the slide 2 is the negative pole.When the coil turns to the neutral plane (the plane perpendicular to the magnetic induction line), the induced electromotive force gradually decreases from the maximum value to zero.When the coil turns over the neutral plane, the direction of the induced electromotive force generated by the conductor in section ab is from a to b;The direction of induced electromotive force of conductor in cd section is c → d.At this time, brush A is changed to contact with the slider 2 of the commutator, and brush B is in contact with the slider 1.With the coil inmagnetic fieldWith continuous rotation in, the induced electromotive force between commutator slides 1 and 2 is an alternating electromotive force whose size and direction change with time, but brushes A and B alternately contact commutator slides 1 and 2 that rotate with the coil at the same time, so a pulsating DC electromotive force is generated between brushes A and B, and the output from A and B is DC.
Explanation of DC generator principle
Explanation of DC generator principle[6]
Explanation of DC generator principle[6]
Explanation of DC generator principle[6]
Explanation of DC generator principle[6]
Explanation of DC generator principle[6]
Explanation of DC generator principle[6]
Explanation of DC generator principle[6]
Explanation of DC generator principle[6]
difference
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DC generator andDC motorThere is no difference in structure.But the DC generator is driven by other machines to make its conductor coil rotate in the magnetic fieldCutting magnetic induction line, generate induced electromotive forcemechanical energybecomeelectric energy。The DC generator consists of a stationary part and a rotating part.The stationary part is called the stator, which includes the casing andmagnetic poleOf course, magnetic poles are used to generate magnetic fields;The rotating part is called rotor, also called armature[2]。The armature iron core iscylinderShaped, made of silicon steel sheets, with grooves punched on the surface and placed in the groovesArmature winding。Commutator isDC motorThe commutator is the two arc-shaped conductive slides 1 and 2 connected with two ends a and d of the coil abed, and these two arc-shaped conductive slides are insulated from each other.As the coil rotates.Two stationary brushes A and B are pressed tightly on the commutator slide and connected withExternal circuitAre connected.In order to reduce the pulsation of the DC output from the DC generator, the armature winding is not singlecoilIt is composed of many coils, which are evenly distributed in the slot of the armature iron core, and the end point of the coil is connected to the corresponding slide of the commutator.The commutator is actually composed of many arc-shaped conductive slides, which are insulated from each other by mica sheets.The more the number of coils and commutator slides, the smaller the DC pulsation generated, which of course also brings difficulties in manufacturing.The magnitude of the induced electromotive force generated by the DC generator and the magnitude of the stator magnetic fieldMagnetic inductionIt is proportional to the rotating speed of the armature.The rated output voltage of small and medium-sized DC generators is not high, which is 115 V, 230 V and 460 V.Large DC generator outputRated voltageAt about 800 volts, the DC generator with higher output voltage belongs to the range of high-voltage special units, which is less used.
structure
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Rotating motorThe structural form must meetelectromagnetismThe rotating motor must have two parts: static and rotating[5]。
Consists of armature core, armature winding, commutator, shaft and fan
Static part
1. The main magnetic pole is a kind of electricitymagnetSchematic diagram of main magnetic pole and reversing pole of iron core made by laminating 1-1.5mm thick steel plates[2]
2. Commutating pole (also called additional pole or interpole)
Function -- improve commutation
The commutating pole is installed between two main magnetic poles and is also composed of iron core and winding
The iron core is generally processed from a whole piece of steel or steel plate;Commutating pole winding in series with armature winding
3. The frame is usually welded by cast iron or thick iron plate, which has two functions:
Fix the main magnetic pole, reversing pole and end cover
The main circuit part of a DC motor is used to generate electromotive force through current and induction to realize electromechanical energy conversioncoilComposition, components and embedding method (Figure 1.1.16)
An important part of DC motor, which is used to convert the DC current passing through the brush into the alternating current in the winding or the alternating electromotive force in the winding into the DC electromotive force at the brush end
Excitation mode
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According to different excitation modes, DC generators can be divided into
Separately excited DC generator
Armature and excitation winding are powered by two independent DC power supplies.[2]
selfshunt excitation DC generator
After the armature and excitation winding are connected in parallel, they are powered by an independent DC power supply.
Series excited DC generator
The armature and excitation winding are connected in series and powered by an independent DC power supply
Compound excited DC generator
The compound excitation motor has two windings, a shunt excitation winding and a series excitation winding. The shunt excitation winding is connected in parallel with the armature, and is connected in series with the series excitation winding and powered by an independent DC power supply.
The main excitation modes of DC generator are separately excited, shunt excited and compound excited.
Weak current cause
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If the DC generator used for automobiles and tractors does not generate electricity or the power generation is weak, the following reasons can be found according to the situation[2]：
(1)driveThe belt is too loose or the belt slips due to oil contamination, resulting in the generator not reaching the specified speed.
(2) The generator rotates in the wrong direction.
(3)CommutatorOil contamination on the surface affects the current output.
(4) Commutator desoldering causes armature coil open circuit.The soldered off wire ends often occur on the most severely burned rectifying pieces.
(5) The commutator is severely ablated, and black spots appear, affecting the current output.
(6)Brush wearToo much, or brush springelastic forceReduce the contact between the brush and the commutatorpressurereduce.Affects current output.
DC generator
(7) The insulation of the magnetic field coil is affected with moisture, and the insulation fails, resulting in short circuit to ground or open circuit of the coil.(8) The armature coil is damped, causing a short circuit in the wiring.
(9) The insulation of armature or field terminal is damaged, and it is grounded to the generator housing.
(10)Brush holderGround with the generator housing.
(11) The terminal is rusted.
(12) Wiring error, the insulating brush is not connected to the armature terminal+, but the grounding brush is connected to it.
(13) Generatormagnetic fieldResidual magnetism disappears.The battery can be connected to both ends of the excitation coil.Re magnetize with 1~4 A current, but the power on time should be as short as possible.
Structure of large generator
In fact, the rotor is not a permanent magnet (ordinary magnet). In order to obtain it more easily and control the magnetic field strength, the rotor actually uses electromagnets.
largealternatorAll three phasesalternatorIn order to improve the power generation capacity, the output voltage of the generator is usually about several thousand volts. In this way, according to P=UI, the current can be reduced to reduce the wire loss.
The stator has three windings, which are placed at an angle of 120 degrees respectively, so that one of the two endpoints of the three windings is tied together, which is the neutral line (zero line), while the line at the other endpoint of the other three windings is the phase line (live line)
And the rotor is usually 2-6 pole rotor. Since the number of poles of the rotor directly determines the frequency of power generation, the power supply in China is 50HZ, that is, 50 magnetic induction lines are cut every second, or 3000 magnetic induction lines are cut every minute.At this time, if the single pole (rotor with only one electromagnet) rotates, it needs 3000 revolutions. If the two pole rotor is used, it only needs 1500 revolutions.Six poles only need 500 revolutions (the formula is 3000 revolutions/minute ÷ number of poles=speed)
And in fact, each of these poles is a winding. They send a small part of the electricity generated by the stator to the rotor for excitation after rectification through carbon brush and receiving ring (not commutator, but a ring, which can let electricity flow into the rotor without affecting the rotor operation).As long as the excitation current is controlled, the magnetic field strength can be controlled, and the generation voltage and current can be controlled.
Even if there is no current flowing through the coil, the generator rotor also has a small amount of residual magnetism (residual magnetism, that is, a small amount of magnetization of steel). Then as long as it is running, the stator can slowly build up the voltage even if it emits a small amount of electricity, and then build up the current to run. If the new unit or a small amount of residual magnetism is gone, it can be connected to an external power supply for excitation,After the voltage is established, it will be switched to self excitation.
This is how large generators generate electricity.
Generators in the laboratory usually use permanent magnets (i.e. ordinary magnets) as the stator to make the rotor run. The wires in the rotor cut the magnetic induction line to generate electricity. The generated electricity passes through the receiving ring (generators use the receiving ring, and each winding has two rings. Usually, the laboratory has only one winding, so as to achieve power generation). Of course, there are also two windings,In order to get DC, a commutator is needed.Otherwise, if the receiving ring is used directly, the electricity generated is AC power.
Obviously, the efficiency of large units must be higher than that of the laboratory.
Schematic diagram of DC generator
In a very simple way, if the receiving ring is used to output electric energy, the equipment will be heavily loaded and the voltage and current may be unstable due to poor contact. At the same time, the spark generated is also a loss. The reason why there is spark is that the electric energy is lost through heat
Application principle
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alternatorIt is usually composed of stator, rotor, end cover, brush, base and bearing.
The stator is composed of the base, stator core, wire wrapped winding and other structural parts that fix these parts[2]。
The rotor is composed of rotor iron core, rotor magnetic pole (with magnetic choke and magnetic pole winding), slip ring, (also called copper ring and collector ring), fan, shaft and other components.
The stator and rotor of the generator are connected and assembled through the bearing, base and end cover to enable the rotor to rotate in the stator. A certain excitation current is passed through the slip ring to make the rotor become a rotating magnetic field. The stator coil moves to cut the magnetic line of force, thus generating induced potential. The current is generated when it is led out through the terminal and connected to the circuit.
In terms of physical structure, the stator and rotor of the generator are completely independent and non-interference with each other in addition to being driven by a driving force;
The stator of the generator is the active power source, which generates induced electromotive force and current. Under the drive of the prime mover, it outputs the active power of alternating current. The size of the active power is determined by the prime mover (oil volume, air volume, air volume, water volume, etc.).
The rotor of the generator is a reactive power source, and the windings introduce DC from the outside to establish a magnetic field. Under the drive of the prime mover, the reactive power of AC is transmitted outward. The reactive power is determined by the DC input from the outside (most of which are generated by the spontaneous AC rectification of the generator).
Circuit schematic diagram of throttle
From the electromagnetic principle, the rotor and stator are closely connected. The active and reactive power of the generator are output by the stator. The torque of the rotor determines the size of the active power, and the DC current of the rotor coil determines the size of the reactive power.
Purchasing method
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Load analysis
Many factors affect the selectionGenerator SetAmong them, the characteristics of system power load is an important factor.The user is selecting oneDiesel generator setThe following points must be carefully considered before:
a. Is it used as a common generator set or a standby generator set[2]。
b. Consider the increased power consumption of the system in the future.
c. The allowable voltage drop of the system.
d. Motor starting condition.
2. Unit power calibration
Generally, the diesel generator set supplied to users is a common one, which can supply power to the load at rated power for 12 consecutive hours (including the ability to run at 110% rated power for 1 hour).When the mains power failure is not frequent and the power supply time is not long, users can use the generator set whose power is calibrated as a standby unit.It shall not operate at 80% of the maximum power for more than 200 hours per year, and shall not operate at 100% of the maximum power for more than 25 hours per year.
