电动机的接地保护时如何实现的？

直流电机的基本工作原理

Dc excitation of the magnetic circuit in the electrical equipment, except for the application of dc motor magnets (dc contactor relays, etc), the most important is used in dc motor In the factory, synchronous generator excitation machine, battery charger, etc, are dc generators, Boiler feed motor is the prime mover In addition, in many industries, such as large rolling equipment, large precision machine tool, mine hoist, streetcars, cable equipment, strict linear consistent place, usually adopts dc motivation to work as a prime mover, drag the machinery Dc generator is usually a dc power supply output power; to load, Dc motor is a prime mover drive to work, all production machines load energy output In the control system, dc motor and other USES, such as tachogenerators, servo motor, etc Although dc motor generator and the use of different, but they are basically the same structure, using electric and magnetic energy to realize the interaction with the power switch

The biggest weakness of dc motor are the current problems, non-ferrous metal, high cost and the maintenance and operation Therefore, the motor industry is trying to improve the control performance of ac motor, and instead of dc motor However, in recent years in using thyristor rectifier instead of dc generators, has made great progress Including dc motor rotate motor, everything is all according to the fact that we know of the two basic principles A: is the conductor cuts flux produces induction emf, Another: the conductor in electric magnetic field in the role Therefore, from the structure, including any motor magnetic circuit of the part and From the above principles, any motor embodies electric and magnetic interaction, electricity and magnetism are the two contradictions in the unity of opposites In this chapter we discussed in dc motor, the structure and working principle of dc motor is discussed "magnetic" and "electricity" interact each other, and embodies both restricts the relationship between physical phenomena and armature emf, electromagnetic torque, electromagnetic power, the armature reaction, etc)

一、 直流发电机的基本工作原理

Dc motor generator and has the same structure, just dc generator engine (usually by ac motor rotate and drag) Visible, it is the mechanical energy into electrical equipment Dc motor are in the dc power supply, drag on various working machinery (machine, pump, electric cable, equipment, etc), and it is the job of the mechanical energy into electrical equipment However, the current SCR rectifier devices have been replaced dc generators, in order to enable us to a better understanding of dc motor, it is necessary to also tells the dc generators

We first to observe how dc generators

As shown in figure 1, brush A, B separately with two and A half circle, then contact between two brush A and B is the direct current output We'll look at the poles movement in between the coil Figure 1 (a) can see, when the coil ab edge in N a range according to counterclockwise, right, then DingZe application generator generated from the point of the emf B, Then the CD edge is winding in S very range according to counterclockwise, according to the hand movement DingZe can judge, generators, CD sides of the induced emf direction from d pointing to c From the perspective of coil, induction emf is d - c - b - a Therefore, and the connected a copper wire brush is in January and are potentials, Instead of coil and d connected the two and copper brush B is in negative potential If connected, current/from A load of the brush, brush with coil flows along B closed Current

When the coil ab edge to S very range, CD edge is transferred to N a range (figure 1, b), with the right to know, when DingZe judgment of coil CD side direction of emf from c to d, and turn into S very ab side within the scope of the emf, which direction is there a to b Due to the brush in space is motionless, therefore, and the copper wire d connected with brush A contact, 2 it is still the potential And the copper wire connected a 1 and brush contact, its potential B is still negative Through/when the current is still A load flow from the brush, brush with coil together constitute B closed current pathways However, should pay attention to when the current in a coil has been reversed

Therefore, when the coil constantly rotating, although two brush contact with the coil of change, but the edge, brush A is always are potential, brush B is always A negative potential Therefore, there are two brush with the direction of the emf is constant, the load is constant direction of voltage and current That is, while the induction emf in coil abcd alternating direction, but always with A brush in N A range of coil edge contact, brush B always and in S very within the scope of the coil edge contact, their polarity unchanged Hence, the alternating current copper wire brush after rectifying and pass, become the dc / These two semicircular copper is called commutation, they together called commutator

二、 直流电动机的基本工作原理

If the dc motor rotor not drag it, and engine the brush of A and B in the dc power supply voltage U (as figure2shows), then what will happen From the chart, brush A, B is A potential negative potential, is extremely in N within the scope of the current in the conductor ab from A to B, S A range of conductor of electricity from CD to d c As I have said before, conductor in electric magnetic field in the role to ab and CD, therefore, two conductors are electromagnetic Fde role According to the current in the conductor of magnetic field and the direction, DingZe left by motor, the direction of force is ab edge to edge, and CD is right Because of the magnetic field is uniform, conductor and the same current flows, so, ab edge and CD edge of the same size So, the coil is received by the electromagnetic force and counterclockwise rotation When the coil to neutral plane, magnetic coil of current equal to zero, electromagnetic force equal to zero, but because the inertia effect, coil continue rotating After half turn coil, although in the position with CD ab switched to S, ab edge extremely range, CD edge to N a range, but, owing to the effect of directional and brush, turn to next CD edge N pole in the current direction also changed from d to c, in the very next ab edge "S the current flow from b vitamin Therefore, the direction of electromagnetic Fdc will remain unchanged, coil still force by turning counterclockwise Visible, respectively in N, S a range of the current in the conductor is changeless, direction, two side of coil is changeless, such force direction, coil can according to the direction of stress on rotating, through the gear transmission belt agencies or other work, mechanical

From the above analysis, we can see, to make the coil according to certain direction, the key problem is when the conductor from a pole limits to another opposite poles range (namely conductor through neutral conductor), after the current direction will also change Commutator and brush is the device to finish the task In dc generator, the commutator and brush the task was to coil of alternating current to direct current to the output, While in dc motor, then use commutator and brush the input of ac motor into coils Visible, commutator and dc motor brush is indispensable key components

Of course, in actual motor, also not only a coil, but there are many a coil of core firmly embedded in the rotor slot, when the conductor in electric fields, by force and in turn, just because of the rotor This is the basic principle of dc motor

Dc motor generator and compare the working principle, they could see the input and output of different forms of energy As has been said before, dc generator engine drive, by the input, output is mechanical energy is, Dc motor is determined by the input dc power supply, power, the output is is energy

Hope can help you

电动机（Motor）是把电能转换成机械能的一种设备。

它是利用通电线圈（也就是定子绕组）产生旋转磁场并作用于转子（如鼠笼式闭合铝框）形成磁电动力旋转扭矩。各种电动机中应用最广的是交流异步电动机（又称感应电动机）。它使用方便、运行可靠、价格低廉、结构牢固，但功率因数较低，调速也较困难。大容量低转速的动力机常用同步电动。

同步电动机不但功率因数高，而且其转速与负载大小无关，只决定于电网频率。工作较稳定。在要求宽范围调速的场合多用直流电动机。但它有换向器，结构复杂，价格昂贵，维护困难，不适于恶劣环境。20世纪70年代以后，随着电力电子技术的发展，交流电动机的调速技术渐趋成熟，设备价格日益降低，已开始得到应用。

扩展资料：

组成部分：

这个部件由一个内齿圈和一个与之相配的齿轮或转子组成。内齿圈与壳体固定能接在一起，从油口进入的油推动转子绕一个中心点公转。这种缓慢旋转的转子通过花键轴驱动输出成为摆线液压电动机。这种最初的摆线电动机问世后，经过几十年演化，另一种概念的电动机也开始形成。

这种电动机在内置的齿圈中安装了滚子，具有滚子的电动机能提供较高的启动与运行扭矩，滚子减少了摩擦，因而提高了效率，即使在很低的转速下输出轴也能产生稳定的输出。通过改变输入输出流量的方向使电动机迅速换向，并在两个方向产生等价值的扭矩。各系列的电动机都有各种排量的选者，以满足各种速度和扭矩的要求。

参考资料来源： 百度百科-电动机 （电力学术语）

参考资料来源： 百度百科-马达 （发动机）

图：保护接地是将电气设备金属外壳通过接地装置与大地紧密连接；保护接零是将电气设备金属外壳与电网的零线紧密连接。保护接地的作用是当发生故障时，降低故障设备外壳的对地电压和跨步电压，减轻人身触电的危险。：保护接地适用于三相三线制电网。  通常还会和漏电保护器一起使用，这样接地之后会跳闸 设备将停止供电。理论如下：正常情况下各相电流相量和为零，因此各相电流在零序电流互感器铁芯中感应的磁通相量和也等于零。此时零序电流互感器的二次侧绕组无信号输出。开关不会动作，电源正常向负载供电。当发生故障时，由于主回路中各相电流相量和不为零，故在零序电流互感器的环形铁芯中产生磁通。而在零序电流互感器二次侧绕组产生感应电压。当故障电流达到预定值时，二次侧绕组的感应电压使脱扣器线圈励磁，主开关跳闸，切断供电回路，消除触电危险和故障。

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