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Suzhou Shouxin Motor Co., Ltd. tells you how to answer 14 frequently asked questions from customers

Views: 179     Author: Site Editor     Publish Time: 2022-08-05      Origin: Site

苏州首信电机有限公司公司告诉您如何回答14个客户常问的问题

在接触很多购买电机的客户之后,向技术收集了一些平时客户询问的问题以及相关的回答。或许您在使用电机或者更换电机的时候也会遇到这样的困惑。在购买电机的时候有几个关键词,普通电机、铝壳电机、变频电机、三相异步电机、立式安装、卧式安装、电机功率、电压、直流电机、交流电机等购买时需要了解的。

 

1.为什么漏电断路器在使用变频器时易跳闸呢?

这是因为变频器的输出波形含有高次谐波,而电机及变频器与电机间的电缆会产生泄漏电流,该泄漏电流比工频驱动电机时大了许多,所以产生该现象。

变频器操作输出侧的漏电流大约为工频操作时的3倍多,外加电动机等漏电流,选择漏电保护器的动作电流应该大于工频时漏电流的10倍。

 

2.我要做电机变频调速实验,普通电机可以实现变频调速吗?还是必须买变频电机?

要做电机变频调速实验用普通的交流电机就行。

直流电机也可以实现变频,例如现在的直流变频空调:其把工频交流电转换为直流电源,并送至功率模块,模块受微电脑送来的控制信号控制,和交流变频所不同的是模块输出受控的直流电源送至压缩机的直流电机,控制压缩机的排量,从而实现“变频调速”。

 

3.什么样的电机是交流变频电机?

简单点说就是交流电机的控制中使用了变频技术。交流变频电机实际上是一种靠调节交流电频率来调速的电机,调整交流电频率要靠变频器,电机本身不会变频,在很多要求不高的场合就是拿普通电机加变频器调速当交流变频电机使用。

 

4.变频器单相220v能变出三相380v吗?

是不可以。变频器本身是不能升压的,更不能从单相220v变出三相380v。从理论上这是可行的,用变压器将单相220V升高为380V,然后单相380V转换为三相380V。

 

5大功率电机拖动的皮带都有一个减速机与电机相连,减速机在这里的作用?

减速机的用途可简略归纳一下:

降速同时提高输出扭矩,扭矩输出比例按电机输出乘减速笔,但要注意不能超出减速箱额定扭矩。

减速同时降低了负载的惯量,惯量的减少为减速比的平方。大家可以看一下一般电机都有一个惯量数据。

6.解答一下电机起动时转速慢的原因?

如果仅仅是起动时转速慢,起动后正常。可能是起动电容不匹配、或者是电机设计本来就是这样的(根据场所设计)、还有可能就是负载阻力过大等因素造成的起动时间过长。

如果起动后转速还慢,可能是问题可能是电压不足、电容不匹配、转动阻力大等。

 

7.绕线型异步电机转子集电环的电刷怎样选择?

主要根据电刷的工作条件是否满足电流密度(A/cm2)和集电环园周边缘的线速度(m/s)来确定。确定公式:

①电刷载流量(A)=电刷电流密度(A/cm2)×电刷宽度L(cm)×电刷厚度b(cm)≥电机转子额定电流(A);

②集电环园周边缘的线速度(m/s)=电动机额定转速(r/m)/60(s)×集电环周长(m)≤电刷适用的规定范围(m/s)。

 

其常用电刷有不墨电刷、电化石墨电刷和金属石墨电刷三种。使用中应注意经常检查电刷活动情况、电刷压力和磨损程度。电刷在刷握中要能上下自由活动,无卡阻。卡刷时把电刷两侧面在砂布上磨平即可。电刷的压力要根据电刷的品种和型号进行合适的调整。目前附在刷握上的电刷压紧弹簧多属拉伸压缩弹簧,其压力随着电刷的磨损逐渐减小,故在电机运行过程中,其电刷压力应随时调整。

 

8.60HZ的电机放在50HZ的电源上用,需要注意什么?

这是由于电机的电流频率低于设计频率,要使其转动中产生的空载反电动势减小、空载电流增大,对电机造成损坏,因此就要求其空载电压降低了。

在变频调速技术中,电动机的频率和定子电压是同时改变的。即是频率下降,电压也要同时下降,电动机才不会过流,才会得到理想的运行效果。

 

9.变频器输出端为什么要加输出电抗器,它作用是什么?

变频器输出端增加输出电抗器,是为了增加变频器到电动机的导线距离,输出电抗器可以有效抑制变频器的IGBT开关时产生的瞬间高电压,减少此电压对电缆绝缘和电机的不良影响。

电抗器的主要作用:是用以限制电机连接电缆的容性充电电流及使电机绕组上的电压上升率限制在540V/μs以内,它还用于钝化变频器输出电压(开关频率)的陡度,减少逆变器中的功率元件(如IGBT)的扰动和冲击。

 

10.交流伺服电机可以用变频器控制吗?

由于变频器和伺服在性能和功能上的不同,应用也不大相同,所以是不可以的。

在速度控制和力矩控制的场合要求不是很高的一般用变频器,也有在上位加位置反馈信号构成闭环用变频进行位置控制的,精度和响应都不高。现有些变频也接受脉冲序列信号控制速度的,但好象不能直接控制位置。

在有严格位置控制要求的场合中只能用伺服来实现,还有就是伺服的响应速度远远大于变频,有些对速度的精度和响应要求高的场合也用伺服控制,能用变频控制的运动的场合几乎都能用伺服取代。

 

关键是两点:一是价格伺服远远高于变频,二是功率的原因:变频最大的能做到几百KW,甚至更高,伺服最大就几十KW。伺服的基本概念是准确、精确、快速定位。变频是伺服控制的一个必须的内部环节,伺服驱动器中同样存在变频(要进行无级调速)。

 

11.调速电机能频繁起动吗?

调速电动机能频繁启动,我们公司做调试用的电机都是调速电机,经常这样频繁启动,也没出现过怎么问题。不过能尽量减少频繁启动当然是最好了。不管怎么电机频繁启动次数多,对电机都会有损害。

 

12.怎么才能知道电机是星型/三角接法?

星形接法是三相绕组一端相连,另一端分别接三相电源,形状像字母“Y”;三角接法是三相绕组首尾相连,形成一个“△”形,三角形的顶端再接三相电源。

它们的相电压不同,一般星形接法的电机额定电压是220V,三角接法的额定电压是380V。接法在接线盒的盖板内外侧一般都会有标明,不同的接法对应不同的电源电压。

 

13.电机的极数对其选用有何影响?

电机目前有2/4/6/8级电机,特殊用途的电机级数可能更高。电机的极对数越多,电机的转速就越低,但它的扭距就越大;在选用电机时,您要考虑负载需要多大的起动扭距,比如象带负载起动的就比空载起动的需要扭距就大,如果是大功率大负载起动,还要考虑降压启动(或星三角启动);至于在决定了电机极对数后和负载的转速匹配问题,则可考虑用不同直径的皮带轮来传动或用变速齿轮(齿轮箱)来匹配。如果由于决定了电机极对数后经过皮带或齿轮传动后达不到负载的功率要求,那就要考虑电机的使用功率问题了。

 

14.什么是串激电机,具体原理是什么?

串激(串励)电机就是定子绕组和转子绕组串联的。

工作原理:在交流电源供电时,产生旋转力矩的原理,仍可以用直流电动机的运转原理来解释。当导体中通有电流时,在导体的周围产生磁场,其磁力线的方向取决于电流方向。将通电的导体放入磁场中,这磁场与通电导体所产生的磁场相互作用,将使此导体受到一个作用力F,并因此而产生运动,导体会从磁力线密的地方向磁力线稀的方向移动,当将由两个互相相对的导体组成的线圈放入磁场时,线圈的两个边也受到了作用力,此二力的方向相反,产生力矩。当线圈在磁场中转动时,相应的二个线圈边,从一个磁极下转到另一个磁极下时,此时由于磁场极性有了改变,将使导体受到的作用力的方向改变,也使转矩的方向改变,从而使线圈向反方向转动,于是线圈只能绕中心轴来回摆动。

 


Suzhou Shouxin Motor Co., Ltd. tells you how to answer 14 frequently asked questions from customers

After contacting many customers who purchased motors, I collected some questions and related answers from customers. Maybe you will also encounter such confusion when using the motor or replacing the motor. There are several key words when buying a motor, common motor, aluminum shell motor, variable frequency motor, three-phase asynchronous motor, vertical installation, horizontal installation, motor power, voltage, DC motor, AC motor, etc. What you need to know when purchasing .



1. Why is the leakage circuit breaker easy to trip when using the inverter?

This is because the output waveform of the inverter contains high-order harmonics, and the motor and the cable between the inverter and the motor will generate leakage current, which is much larger than that when the motor is driven by power frequency, so this phenomenon occurs.


The leakage current on the output side of the inverter operation is about three times that of the power frequency operation. In addition to the leakage current of the motor, the operating current of the leakage protector should be greater than 10 times the leakage current at the power frequency.



2. I want to do a motor frequency conversion speed regulation experiment. Can ordinary motors realize frequency conversion speed regulation? Or do I have to buy an inverter motor?

To do the motor frequency conversion speed regulation experiment, use an ordinary AC motor.

The DC motor can also realize frequency conversion, such as the current DC frequency conversion air conditioner: it converts the power frequency AC power into DC power supply and sends it to the power module. The module is controlled by the control signal sent by the microcomputer. The controlled DC power is sent to the DC motor of the compressor to control the displacement of the compressor, so as to realize "frequency conversion speed regulation".



3. What kind of motor is an AC variable frequency motor?

To put it simply, frequency conversion technology is used in the control of AC motors. AC variable frequency motor is actually a motor that adjusts the speed of the AC frequency. The frequency of the AC frequency needs to be adjusted by the inverter, and the motor itself will not change the frequency. Inverter motor use.


 

4. Can the inverter single-phase 220v change into three-phase 380v?

is not possible. The inverter itself cannot boost, let alone change from single-phase 220v to three-phase 380v. This is theoretically possible, using a transformer to step up the single-phase 220V to 380V, and then convert the single-phase 380V to three-phase 380V.



5 The belt driven by the high-power motor has a reducer connected to the motor. What is the role of the reducer here?

The purpose of the reducer can be briefly summarized:

Decelerate the speed and increase the output torque at the same time. The torque output ratio is multiplied by the motor output by the speed reducer, but be careful not to exceed the rated torque of the speed reducer.


Deceleration reduces the inertia of the load at the same time, and the reduction of inertia is the square of the reduction ratio. You can look at the general motor has an inertia data.

6. Answer the reasons for the slow speed of the motor when starting?

If only the speed is slow when starting, it is normal after starting. It may be that the starting capacitor does not match, or the motor design is like this (according to the site design), or the starting time is too long due to factors such as excessive load resistance.


If the speed is still slow after starting, the problem may be insufficient voltage, mismatched capacitors, large rotation resistance, etc.

 


7. How to choose the brushes of the rotor collector ring of the wound asynchronous motor?

It is mainly determined according to whether the working conditions of the brush meet the current density (A/cm2) and the linear velocity (m/s) of the peripheral edge of the collector ring. Determine the formula:


①Brush current carrying capacity (A) = brush current density (A/cm2) × brush width L (cm) × brush thickness b (cm) ≥ motor rotor rated current (A);


②Linear speed of the peripheral edge of the collector ring (m/s) = rated speed of the motor (r/m)/60 (s) × the circumference of the collector ring (m) ≤ the specified range for brushes (m/s) .


The commonly used brushes are non-ink brushes, electrochemical graphite brushes and metal graphite brushes. In use, attention should be paid to frequently check the brush activity, brush pressure and degree of wear. The brush should be able to move up and down freely in the brush holder without jamming. When the brush is stuck, smooth both sides of the brush on the emery cloth. The pressure of the brush should be adjusted appropriately according to the type and model of the brush. At present, most of the brush compression springs attached to the brush holder are tension and compression springs, and their pressure gradually decreases with the wear of the brush. Therefore, during the operation of the motor, the brush pressure should be adjusted at any time.


 

8. The 60HZ motor is used on the 50HZ power supply. What should I pay attention to?

This is because the current frequency of the motor is lower than the design frequency. To reduce the no-load back EMF generated during the rotation and increase the no-load current, which will cause damage to the motor, the no-load voltage is required to be reduced.


In the variable frequency speed regulation technology, the frequency of the motor and the voltage of the stator are changed at the same time. That is, when the frequency drops, the voltage also drops at the same time, so that the motor will not be over-current, and the ideal operating effect will be obtained.


 

9. Why should an output reactor be added to the output end of the inverter, and what is its function?

An output reactor is added at the output end of the inverter to increase the wire distance from the inverter to the motor. The output reactor can effectively suppress the instantaneous high voltage generated when the inverter's IGBT switches on and off, and reduce the adverse effects of this voltage on cable insulation and motor.


The main function of the reactor is to limit the capacitive charging current of the motor connection cable and limit the voltage rise rate on the motor winding to within 540V/μs, and it is also used to passivate the output voltage (switching frequency) of the inverter. to reduce the disturbance and impact of power components (such as IGBTs) in the inverter.



10. Can AC servo motors be controlled by inverters?

Because the performance and function of the inverter and the servo are different, and the applications are not quite the same, it is not possible.


In the occasions of speed control and torque control, the general-purpose inverters are not very demanding, and there are also inverters that add position feedback signals to the upper position to form a closed-loop frequency conversion for position control, and the accuracy and response are not high. Now some frequency converters also accept the pulse train signal to control the speed, but it seems that they cannot directly control the position.


In the occasions with strict position control requirements, it can only be realized by servo, and the response speed of servo is much higher than that of frequency conversion. In almost all cases, it can be replaced by servo.


The key is two points: one is that the price of servo is much higher than that of frequency conversion, and the other is the reason for power: the largest frequency conversion can achieve hundreds of KW, or even higher, and the largest servo is tens of KW. The basic concept of servo is accurate, precise and fast positioning. Frequency conversion is a necessary internal link of servo control, and there is also frequency conversion in servo drives (stepless speed regulation is required).



11. Can the speed regulating motor be started frequently?

The speed-regulated motor can be started frequently. The motors used for debugging in our company are all speed-regulated motors, which are often started frequently without any problems. However, it is of course best to minimize frequent startups. No matter how many times the motor is started frequently, it will damage the motor.



12. How can I know if the motor is star/delta connection?

The star connection method is that one end of the three-phase windings is connected, and the other end is connected to the three-phase power supply, which is shaped like the letter "Y"; the delta connection method is that the three-phase windings are connected end to end to form a "△" shape, and the top of the triangle is connected to the three-phase power supply.


Their phase voltages are different. Generally, the rated voltage of the star-connected motor is 220V, and the rated voltage of the delta-connected method is 380V. The connection method is generally marked on the inside and outside of the cover plate of the junction box, and different connection methods correspond to different power supply voltages.


 

13. How does the number of poles of the motor affect its selection?

Motors currently have 2/4/6/8 grade motors, and the number of motor grades for special purposes may be higher. The more pole pairs of the motor, the lower the speed of the motor, but the greater its torque; when choosing a motor, you should consider how much starting torque the load needs, such as starting with a load than no-load The torque required for starting is large. If it is a high-power and large-load starting, the step-down starting (or star-delta starting) should also be considered; as for the matching of the speed of the motor and the load after the number of pole pairs of the motor is determined, it can be considered different. Diameter pulley to drive or match with variable speed gear (gear box). If the power requirement of the load cannot be met after the belt or gear drive is determined after the number of pole pairs of the motor is determined, then the use power of the motor must be considered.



14. What is a series motor and what is the specific principle?

A series-excited (series-excited) motor is a series of stator windings and rotor windings.


Working principle: When the AC power supply is supplied, the principle of generating rotational torque can still be explained by the operation principle of the DC motor. When a current flows through a conductor, a magnetic field is generated around the conductor, and the direction of the magnetic field lines depends on the direction of the current. Put the energized conductor into a magnetic field, and the magnetic field interacts with the magnetic field generated by the energized conductor, which will cause the conductor to be subjected to a force F, and thus cause movement. , when a coil composed of two conductors facing each other is placed in a magnetic field, the two sides of the coil are also subjected to a force, and the two forces are in opposite directions, resulting in a torque. When the coil rotates in the magnetic field, when the corresponding two coil sides turn from one magnetic pole to the other, the direction of the acting force on the conductor will change due to the change of the magnetic field polarity, which also makes the The direction of the torque changes, causing the coil to turn in the opposite direction, so the coil can only swing back and forth around the central axis.