1. The basic construction of
Dc Motor The basic structure of
DC Motor is the same as that of AC motor, it is also composed of motor stator and motor rotor. Figure 1 shows the construction of a DC motor.
Figure 1 DC motor construction
1-cooling fan; 2-motor shaft; 3-armature; 4-main magnetic pole; 5-motor carbon brush; 6-motor rotor; 7-patch plate 8-group outlet box; 9-bearing end cover
1. motor stator
The key of the stator of DC motor is composed of main pole, commutation pole, brush equipment, motor shaft and bearing end cover.
1) Main pole
The main magnetic pole is used to cause the main electromagnetic field in the DC motor operation. It is composed of two parts: the core and the excitation winding which is sheathed on the core, as shown in Figure 2. The core part of the winding lock sleeve is called the pole body, and the wider part near the armature (motor rotor) is called the pole shoe. Most of the main poles of DC motors do not need electromagnets, but the excitation winding creates electromagnetic fields according to DC power supply. If the direction of excitation current is changed, the direction of main magnetic field will also be changed. The pole shoe can fix the real excitation winding, and can also be of the magnetoelectric type with smaller magnetic density, and make the electromagnetic field more symmetrical and effective in the magnetic density. Although the electromagnetic field caused by DC power does not cause the loss, the electromagnetic field on the surface of the pole changes during the armature fitness, so eddy current loss is needed on the core. In order to reduce the iron loss better, the main pole core is made of 1-1.5mm thick low magnetic thick steel plate stamping die. The key to the iron chip is air oxide film insulation. The excitation winding is made of the inductor of the copper core coil of the insulation layer. It is divided into two categories. One is called shunt winding, which has more turns and smaller cable diameter; the other is called series excitation winding, which has fewer turns and thick cable diameter. The excitation electromagnetic coils on each main pole form the excitation winding according to serial connection, which can ensure the same excitation current on each pole. The direction of current in the main pole electromagnetic coil is reversed when connected in series to ensure that the polarities of the poles are sorted by N and s replacement. All the main poles are fixed on the motor shaft with anchor bolts.
Figure 2 main pole of DC motor
(a) The core of the main pole transformer made of thin steel sheet; (b) the main pole and the excitation winding are fixed on the motor shaft together
1-pole shoe; 2-motor shaft; 3-excitation winding
2) Commutation pole
The commutation pole is basically the same as the main pole structure, and it is also composed of two parts: the core and the excitation winding which is sheathed on the core, as shown in Fig. 3. But in volume, it is smaller than the main magnetic field. Its key function is to deal with the problem of phase change caused by DC motor operation, so it is called commutation pole. The core of the commutation pole is usually made of a whole carbon steel plate. The commutation pole excitation winding is usually made of flat copper core winding with large cross section. It is used in series with armature winding to improve the commutation problem.
Figure 3 commutation pole of DC motor
(a) the construction of the commutation pole; (b) the order in which the pole is placed
1-motor shaft; 2-core; 3-excitation winding
3) Brush equipment
The brush equipment is composed of brush, brush grip, brush rod, brush rod base, braid, spring yellow structure, etc., as shown in Figure 4.
Brush is a conductive block made of high-purity graphite, which is placed in the brush holder and pressed on the surface of the motor rotor with certain working pressure with elastic yellow. The braid introduces the current and leads it out of the brush. The brush holder is installed on the brush rod arm. According to the size of the electric flow, one or a group of related brushes are provided on each brush rod arm. The current on the same rotary brush rod is gathered into one piece and connected with the external circuit through the patch panel. The working pressure of spring yellow can be adjusted to ensure the brush and the motor rotor surface good touch. Brush and brush grip should be well matched to avoid too tight or too loose. Generally, several groups of brushes are the same as the number of main poles, and the distribution of brush groups to the surface of motor rotor should be uniform. Each brush group is installed on a seat ring of an adjustable part through the brush rod arm, as shown in Figure 4 (a). When rotating the seat ring, the relative position of brush rod on the motor rotor can be adjusted. The seat trap is located in the prominent position on the bearing end cover or rolling bearing cover, and is tightened by tightening screws.
Figure 4-4 brush construction
(a) the construction of brush equipment; (b) the brush is placed in the brush holder
1-brush holder; 2-spring yellow pin; 3-brush rod; 4-brush; 5-brush grip; 6-brush braid; 7-pressing finger; 8-elastic yellow tissue
4) Bearing end cover and motor shaft
The bearing end cover and motor shaft are made of steel casting or thick steel plate. The motor shaft is not only a part of the equivalent circuit of DC motor, but also a support frame for fixed fixed DC motor. The main magnetic pole and the commutation pole are fixed on the inner cavity of the motor shaft, and each side of the motor shaft has a bearing end cover. The management center of the bearing end cover is equipped with rolling bearing, and roller bearing is used for large and medium sized DC motor. Because the rolling bearing of large and medium-sized DC motor is not strong enough, it has independent bearing with seat.
2. motor rotor (armature)
The key of the rotor of DC motor is composed of armature core, armature winding, motor rotor, transmission shaft, etc. Motor rotor is the nerve center of heat transfer in mechanical and electrical engineering, so it is also called armature.
1) Armature core
Armature core is generally made of 0.35-0.5mm insulation layer ferrite core lamination, mainly to reduce the core consumption better, which is different from the composition of the main pole of motor stator, as shown in Fig. 5 It is shown that the ferrite core is punched with slots, which is used to place armature winding. The ferrite core of a large volume DC motor also has radial vent, which is used to generate radial natural ventilation channel. The key effect of armature core is to produce equivalent circuit.
Figure 5 cross section of armature core, core punch and armature slot of DC motor
1-armature core overall; 2-motor rotor; 3-armature winding components; 4-armature core punch; 5-armature slot cross section
2) Armature winding
The armature winding is mainly composed of the inductor of the copper core coil with insulating layer, and it is received on the commutation according to the law. Its key effect is to complete the transformation of kinetic energy.
3) Motor rotor
The structure of the motor rotor is a barrel which is folded by many metal plates (changing photos) with dovetail shape, as shown in Figure 6. The mica insulation layer of 0.6-mm is used in the photo room. Two v-rings are firmly clamped on both sides of the drum, and V-shaped mica insulation ring is padded between the V-ring and the photo changing drum. Each change photo has a small groove on it to facilitate the welding of the winding of the transformer ground wire. The small volume DC motor should be made of plastic motor rotor, which has simple processing technology and low raw materials. The rotor of motor is the key construction of DC motor. It is also called motor commutator to change the direction of current in armature winding when DC motor is running.
Figure 6 structure of motor rotor
1-piece biotite; 2-jam nut; 3-v-ring; 4-sleeve specification; 5-photo change; 6-mica insulation
3. magnetic density
Magnetic density is the gap between the main pole and armature of DC motor. The magnetic density of small and medium sized DC motor is about 1-3mm, and that of large and medium DC motor is about 10-12mm. Although magnetic density is small, it is harmful to the characteristics of DC motor.
2. Factory nameplate of DC motor
A factory nameplate is nailed on the motor shaft of each DC motor, which indicates the various technical data information of the proper application of the DC motor. The main parameters include the data information of the model and specification and rating of the DC motor.
DC motor
Model and specification z-72 excitation and parallel excitation
Output power: 55kW; excitation working voltage: 380V
Working voltage: 380V excitation flux: 2.06a
Current volume 116a budget quota continuous
Speed ratio: 1500r/min, temperature rise: 80 ℃
Factory nameplate of DC motor
1. model and specification of DC motor
The key of DC motor model and specification is composed of commodity number, design scheme number, specification and model number.
2. rating data information
(1) Maximum power PN
For motors, it refers to the mechanical power output on the shaft under the rated standard; for the generator set, it refers to the rated power output at the occurrence end of the armature under the rated value standard.
(2) Rated current UN
For motor, it refers to the working voltage of switching power supply under rated value standard; for generator set, it refers to DC voltage when the maximum power is output at rated voltage.
The rated current of DC motor is generally not high, and the rated current of DC motor is 110, 220, 440, 630, 800, 1000V, etc.; the rated current of DC motor is 48, 72, 115, 230, 460, 630, 1000V and other classes.
(3) Rated voltage in
For generating units, it refers to the output current when the rating is included; for motors, it refers to the input current when the rating is included. Therefore, for the generator set, the rated current
The multiplication of UN and rated voltage in refers to the rated power of its output; for motors, the rated current
The multiplication of UN and rated voltage in refers to the input rating of UN.
(4) Rated speed ratio NN
It refers to the speed ratio of motor rotor under the rated value standard, and the enterprise is r/min.
(5) Excitation method refers to the relationship between the motor rotor switch power supply and armature switch power supply
(6) Excitation working voltage (UF) refers to the DC voltage of the rotor winding of the motor. The size of the system is related to the excitation method.
(7) Excitation current is the current of stator winding of motor which is needed for the main flux caused by motor.
Besides the above rating data information, there are budget quota and heating up.
3. Excitation method of DC motor
The method of obtaining current quantity of excitation winding (stator winding) of DC motor is called excitation method. Excitation method is very harmful to the operation characteristics of DC motor, and DC motor is often classified according to different excitation methods. The following are various excitation methods.
1. He Li style
There is no electrical connection between the excitation winding and armature winding of the Shunt DC motor, that is, the two power circuits are separated from each other. They apply their own switch power supply system when the motor is running.
2. self encouragement
The excitation winding and armature winding of self encouraging DC motor are connected in a certain way. In DC motor, the excitation current is provided by the generator unit itself; in DC motor, the excitation winding and armature winding are supplied by copper switch power supply system. According to the different interface modes between excitation winding and armature winding, self encouraging type can be divided into three types: parallel excitation, series excitation and compound excitation.
1) Shunt type
For parallel excited DC motor, the excitation winding is connected with armature winding in series, and the working voltage on the shunt winding is the DC voltage of armature winding. Therefore, the size of the flux is related to the armature working voltage. The excitation current of medium and
Small Dc Motor is only 2% ~ 3% of rated current under all normal conditions, and 5% ~ 10% for medium and small DC motor. In order to create the induced EMF, the number of coil turns of excitation winding is more and the cable diameter is smaller. Therefore, the winding turns are many, and the transmission line is fine.
2) Series excitation type
The connection method of series excitation DC motor is connected with armature winding in series. The excitation current on the series excitation winding is the armature current. Therefore, the characteristics of series excitation winding are the small number of coil turns and the thick transmission line.
4. Maintenance cycle time and new project specification
1. The maintenance cycle time of DC motor should be the same as that of large furnace and overhaul cycle.
2. The newly installed motor shall be inspected and maintained before the capital is put into operation. If the event cannot be completed, it shall be maintained once after one year of operation.
3. Before maintenance, the motor must be disintegrated, and all-round inspection and cleaning shall be carried out to eliminate the shortcomings of the motor and carry out timely experiments.
4. The following new items for maintenance are specified:
(1) Clean the ash, remove the coupling wheel, and measure the magnetic density of the motor rotor.
(2) Dismantling and pulling out motor rotor
(3) Maintenance of motor stator
(4) maintenance of motor rotor
(5) check and clean the rolling bearing, and replace the rolling bearing if necessary
(6) check the motor commutator and brush equipment.
(7) . check and clean natural ventilation and refrigeration equipment.
(8) Check the standard parts.
5. : the normal overhaul of DC motor does not need to remove the outer cover on both sides. Only when the rolling bearing must be removed and the defects such as the top electromagnetic coil and cooling fan must be removed, the end cover of one end or two end bearing can be opened.
6. : overhaul shall be based on the technical condition of motor, the advantages and disadvantages of rolling bearing and lubricating grease, the insulation level and operation status of electromagnetic coil. However, it is necessary to check the insulation and damage condition of each part in detail, and carry out cleaning. The new overhaul items in the specification are as follows:
1) Regular inspection and cleaning of motor outside
2) check the rolling bearing and change oil according to the condition if necessary
