requirements.

D. Primary Resistor or Reactor Starting

This method uses either a series resistor or reactor bank to be placed in the circuit with the motor. Resistor starting is more frequently used for smaller motors.

When the motor is started, the resistor bank limits the flow of inrush current and provides for a voltage drop at the motor terminals. The resistors can be selected to provide voltage reductions up to 50%. As the motor comes up to speed, it develops a counter EMF (electro-magnetic field) that opposes the voltage applied to the motor. This further limits the inrush currents. As the inrush current diminishes, so does t>e voltage drop across the resistor bank allowing the torque generated by the motor to increase.At a predetermined time a device will short across the resistors and open the starting contactor effectively removing the resistor bank from the circuit. This provides for a closed transition and eliminates the concerns due to switching transients.

Reactors will tend to oppose any sudden changes in current and therefore act to limit the current during starting. They will remain shorted after starting and provide a closed transition to line voltage. E .Star delta Starting

This approach started with the induction motor, the structure of each phase of the terminal are placed in the motor terminal box. This allows the motor star connection in the initial startup, and then re-connected into a triangle run. The initial start time when the voltage is reduced to the original star connection, the starting current and starting torque by 2 / 3. Depending on the application, the motor switch to the triangle in the rotational speed of between 50% and the maximum speed. Must be noted that the same problems, including the previously mentioned switch method, if the open circuit method, the transition may be a transient problem. This method is often used in less than 600V motor, the rated voltage 2.3kV and higher are not suitable for star delta motor start method.

Ⅳ. INCREMENT TYPE

The first starting types that we have discussed have deal with the way the energy is applied to the motor. The next type deals with different ways the motor can be physically changed to deal with starting issues. Part Winding

With this method the stator of the motor is designed in such a way that it is made up

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of two separate windings. The most common method is known as the half winding method. As the name suggests, the stator is made up of two identical balanced windings. A special starter is configured so that full voltage can be applied to one half of the winding, and then after a short delay, to the second half. This method can reduce the starting current by 50 to 60%, but also the starting torque. One drawback to this method is that the motor heating on the first step of the operation is greater than that normally encountered on across-the-line start. Therefore the elapsed time on the first step of the part winding start should be minimized. This method also increases the magnetic noise of the motor during the first step.

Ⅴ.Conclusion

There are many ways asynchronous motor starting, according to the constraints of power systems, equipment costs, load the boot device to select the best method. From the device point of view, was the first full-pressure launch the cheapest way, but it may increase the cost efficiency in the use of, or the power supply system in the region can not meet their needs. Effective way to alleviate the buck starts the power supply system, but at the expense of the cost of starting torque.

These methods may also lead to increased motor sizes have led to produce the required load torque. Inverter can be eliminated by the above two shortcomings, but requires an additional increase in equipment costs. Understand the limitations of the application, and drives the starting torque and speed, allowing you for your application to determine the best overall configuration.

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A.2：译文

感应电动机启动的方法

摘 要

许多方法可用于启动大型交流感应电动机。选择如全电压，通过自耦变压器或Y形三角电压降低，软起动器，或可调速驱动器的使用都可以有潜在的优势和权衡。降压起动可以降低起动转矩，防止损坏负载。此外，校正电容器可用于降低功率因数，但必须注意正确的尺寸。错误的电容器的使用可能会导致重大损失。选择适当的启动方法，电机将包括为保证电机的设计提供了所需的性能的同时，最大限度地降低其成本的初始荷载的动力系统分析。本文将最常用的起动方法和推荐的应用研究。 作者关键字：电动机起动 降压启动 自耦变压器 星三角起动 功率因数校正

1. 简介

有起动异步电动机的几种常见方法：全电压，降低电压，Y形三角洲，和部分绕组类型。低电压型可包括固态启动器，变频驱动器，和自耦变压器。这些，连同全电压，或直接起动，当电动机的应用场合被确定后可以给购买者大量类型的变化。每种方法都有其自身的好处，以及性能的权衡。合理的选择包括对电力系统透彻的研究，负载的加速以及设备的全部成本。

为了使负载能够很好的加速，电动机必须产生比负载需求更大的转矩。一般来说，在机械特性曲线上集中有三点。第一点是堵转转矩(LRT)，使电机由静止到旋转的最小转矩。第二点是最小启动转矩，使电机由静止加速到出现制动转矩是的最小转矩。最后一点是临界转矩，就是电机能产生的最大转矩。如果任何一段虚线在负载曲线以下，则电机就不能启动。如图1所示。电机的加速时间是由负载的惯性以及电机的机械特性曲线和负载的特性曲线之间的差额决定的。总的来说，电机的加速时间越长，则电机转子铜条、端环、定子绕组产生的热量也就越多。这些热量会给这些部件带来额外的压力甚至还会影响到电机的使用寿命。

2. 全电压

全电压起动方法，也被称为直接起动，是采用最简单的方法，具有最低的设备成本，是最可靠的。该方法利用一个控制器闭合电流接触器给电动机输入全压。这种方

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法将使电机产生最高的起动转矩和提供最短的加速时间。

由于用此方法起动电机会使启动电流达到电机额定电流的六到七倍，因此方法也是给供电系统带来最大的压力大的方法。如果供电系统比较薄弱，大功率电机的突然启动不仅会使电动机的电压瞬间下降，而且会使给电机供电的整个母线端电压下降。电压下降会使此电动机的启动转矩和工作在同一母线上的电动机的转矩下降。异步电动机的转矩大约和输入电压的平方成比例变化。因此，由于电压的大幅下降，工作在此供电系统的电动机可能停车。另外许多控制系统监控器工作在低电下，第二个全压起动时电压问题会使正在运行的电机离线。同时，母线电压变化，直接启动的另一个问题驱动设备突然被加载。由于瞬时转矩可以超过转子制动转矩的600%，这个冲击负荷会增加设备的磨损，如果负载不能承受由电机起动产生的力矩，甚至会造成灾难性故障。

2.1 电容器和启动

异步电动机功率因数通常很低，因此在开始有很大的感性无功。如图2所示。在启动时通过给电机增加电容器可以降低对系统的这种影响。电机需要大量的无功电流滞后于输入电压90度。这个无功功率不产生任何输出，但是这是电机运行所必需的。输入电压产生无功功率和这个无功功率组成的可用无功功率功率表测量。电容器担任提供一个超前90度的电流。由电容器产生的超前电流取消了电机需要的滞后电流，降低了从供电系统输入的感性无功功率。

避免过电压和电机损坏应小心谨愤确保电容器被切除当电机达到额定转速时，否则由于功率损失，电动机利用由电容器提供的磁化电流将不会进入发电模式，这将在下一段和附录中详述。

2.2 功率因数校正

电容器还可以留下永久连接到提高全负荷功率因数，当以这种方式使用它们被称为功率因数校正电容器。电容器不应容量大于电动机的励磁电流，除非当功率降低时他们可以和电机分离。

另外的电容器将改变有效开路时间常数的电机，时间常数表明剩余电压在电机额定电压衰减到36.8%的功率损失后所需的时间。没有电容的典型值是两到三秒。

由于电容器和电动机的前端相连，电容器可以在电动机的电源已断开，继续提供磁化电流。这是一个较长的时间常数为系统显示。如果电机是驱动大惯性负载，电机可以改变与励磁发电机行动。从电容器和轴驱动的负载电流。这可能会导致在电机端子实际上在上升至近50%，在某些情况下，额定电压在电压。如果重新连接电源之前，

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