电气工程及其自动化专业英语.doc

Electronic filters are electronic circuits which perform signal processing functions, specifically to remove unwanted frequency components from the signal, to enhance wanted ones, or both. Electronic filters can be passive or active. A passive filter is a kind of electronic filter that is made only from passive elements - in contrast to an active filter, it does not require an external power source (beyond the signal). most filters are linear. in most cases, passive filters are composed of just the four basic elements - resistors, capacitors, inductors, and transformers. More complex passive filters may nonlinear elements, or more complex linear elements, such as transmission lines.Television signal splitter consisting of a passive high-pass filter and a passive low-pass filter. The antenna is connected to the screw terminals to the left of center.A passive filter has several advantages over an active filter:Guaranteed stability . Scale better to large signals (tens of amperes, hundreds of volts), where active devices are often impractical No power supply needed Often less expensive in discrete designs (unless large coils are required) For linear filters, potentially greater linearity depending on components requiredThey are commonly used in speaker crossover design (due to the moderately large voltages and currents, and the lack of easy access to a power supply), filters in power distribution networks (due to the large voltages and currents), power supply bypassing (due to low cost, and in some cases, power requirements), as well as a variety of discrete and home brew circuits (for low-cost and simplicity). Passive filters are uncommon in monolithic integrated circuit design, where active devices are inexpensive compared to resistors and capacitors, and inductors are prohibitively expensive. Passive filters are still found, however, in hybrid integrated circuits. Indeed, it may be the desire to incorporate a passive filter that leads the designer to use the hybrid format.An active filter is a type of analog electronic filter that uses active components such as an amplifier. Amplifiers included in a filter design can be used to improve the performance and predictability of a filter, while avoiding the need for inductors (which are typically expensive compared to other components). An amplifier prevents the load impedance of the following stage from affecting the characteristics of the filter. An active filter can have complex poles and zeros without using a bulky or expensive inductor. The shape of the response, the Q (quality factor). and the tuned frequency can often be set with inexpensive variable resistors. In some active filter circuits, one parameter can be adjusted without affecting the others. Using active elements has some limitations. Basic filter design equations neglect the finite bandwidth of amplifiers. Available active devices have limited bandwidth, so they are often impractical at high frequencies. Amplifiers consume power and inject noise into a system. Certain circuit topologies may be impractical if no DC path is provided for bias current to the amplifier elements. Power handling capability is limited by the amplifier stages. Active filters can implement the same transfer functions as passive filters.2.4电子过滤器是电子电路执行信号处理功能,专门删除不需要的频率成分的信号,以提高想要的,或两者兼而有之。电子过滤器可以被动或主动。无源滤波器是一种电子过滤器,只从被动的元素在一个有源滤波器相比,它不需要外部电源(以外的信号)。大多数过滤器是线性的。在大多数情况下,被动的过滤器是由四个基本元素电阻、电容器、电感器、变压器。更复杂的被动过滤器可能非线性元素,或更复杂的线性元素,如输电线路。电视信号分配器组成的无源高通滤波器和无源低通滤波器。螺旋天线连接到终端的中心。在一个有源滤波器无源滤波器有几个优点:保证稳定性。规模更大的信号(几十安培,数百伏),在活跃的设备通常是不切实际的不需要电源经常在离散的设计更便宜(除非大线圈是必需的)线性过滤器,潜在的更大的线性取决于所需的组件它们通常用于扬声器分频设计(由于比较大的电压和电流,以及缺乏容易获得电源),过滤器在配电网络(由于大电压和电流),电源绕过(由于低成本,在某些情况下,电力需求),以及各种各样的离散和家酿啤酒电路(低成本和简单性)。被动过滤器是罕见的在单片集成电路设计中,活跃的设备在哪里便宜的电阻和电容相比,和电感是贵的。被动的过滤器还发现,然而,在混合集成电路。事实上,它可能是希望把一个无源滤波器,设计师使用混合格式。一个有源滤波器是一种模拟电子滤波器,使用一个放大器等活性成分。放大器包含在一个过滤器设计可以用于提高性能和可预测性的过滤器,同时避免需要电感(通常是昂贵的比其他组件)。一个放大器可以防止以下阶段的负载阻抗影响过滤器的特点。一个有源滤波器可以有复杂的极点和零点不使用笨重的或昂贵的电感器。响应的形状,Q(质量因素)。和廉价的调谐频率通常可以设置可变电阻。在一些有源滤波器电路,一个参数可以调整而不影响他人。使用活动元素有一定的局限性。基本滤波器设计方程忽略了有限带宽的放大器。活跃的设备有有限的带宽,所以他们在高频率通常是不切实际的。放大器系统消耗功率和注入噪声。某些电路拓扑可能是不切实际的如果没有提供直流路径为偏置电流放大器的元素。放大器功率处理能力是有限的。有源滤波器可以实现相同的传输函数作为被动的过滤器。The root causes of electrical machines failures initiate the failure sequence and are detectable by condition monitoring if the degrading process is slow. Such root causes are: - defective design or manufacture, - improper ambient conditions, - overload, - over-speed, - fatigue, - excessive vibration. The failure modes accomplish the degrading process started by the root causes. Such failure modes are: -core insulation failure,-stator winding failure, -bearing failure,-rotor and stator mechanical integrity failure An effective condition monitoring strategy must concentrate on root causes and failure modes that show a slow failure sequence. For rotating electrical machines, the primary root causes for failures are bearing related, followed closely by winding and rotor related causes. For small induction electrical machines, because of the low voltages used, the stator windings are rarely affected by faults. Also, thanks to the rugged design of the squirrel cage, there are few cage faults. The main factor that causes faults in this case is the improper bearings maintenance. For large, high-voltage electrical machines, because of the dielectric stress and increased vibration, the percentage of stator windings faults is larger than in the case of small machines. Also. the bearings are large, which makes them more impervious to wear and tear. In order to identify possible machine faults a number of parameters that give a qualitative measure of the motor condition, can be monitored. As shown in Fig.3.14, such parameters are: motor temperature, wear of components, mechanical vibrations levels, stator current harmonic components, rotor shaft flux or voltage and current. stator winding insulation condition. Temperature monitoring techniques aim to ensure that the temperature of the different components of the motor does not exceed the limits prescribed by the standards. Wear monitoring techniques aim to ensure that the values of such parameters like the electric resistance of the isolation material of the stator winding or the dimensions of certain moving parts are situated within acceptable operating limits as stated by the operating standards. Mechanical vibrations levels monitoring techniques aim to ensure that the excitation of the support structure of the electrical machine, by the air gap electromagnetic field and torque spectrum. at natural and other frequencies, does not exceed the levels prescribed by the operating standards. Electrical flux, current and discharge monitoring techniques aim to predict possible faults by analyzing the frequency spectra of the supply system current and voltage. A fuzzy logic approach may be the key solution for a complete fault monitoring system. Such a method may comb