电气工程与其自动化专业英语.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与无源低通滤波器。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(由于比较大的电压与电流,以及缺乏容易获得电源),过滤器在配电网络(由于大电压与电流),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与家酿啤酒电路(低成本与简单性)。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与电容相比,与电感是贵的。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与可预测性的过滤器,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与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)。与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与注入噪声。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 combine not only the electrical but all monitoring techniques into a complete solution.3.5电机故障的根源启动故障序列与状态监测到如果有辱人格的过程是缓慢的。这样的根本原因是:设计或制造缺陷,不适当的环境条件,超载,超速行驶,疲劳,过度振动。失效模式完成降解过程开始的根源。这种失效模式:核心绝缘失败,定子绕组故障,其失败,转子与定子的机械完整性的失败一个有效的状态监测策略必须专注于根源与失败模式显示缓慢的序列。旋转电机,故障轴承相关的主要根源,紧随其后的是绕组与转子相关原因。对小型感应电机,因为使用的低电压下,定子绕组很少受断层影响。同时,由于崎岖的鼠笼式的设计,很少有笼的缺点。导致故障的主要因素在这种情况下是轴承维护不当。对于大型高压电机,由于介质压力与增加振动,定子绕组故障的比例大于的小机器。也。轴承很大,这使得他们更不受磨损。为了找出可能的机器故障给出一个定性的参数的数量测量电动机的状态,可以被监控。Fig.3.14所示,这些参数包括:电动机温度、磨损的部件,机械振动水平,定子电流谐波组件、转子轴磁通或电压与电流。定子绕组绝缘状态。温度监测技术旨在确保电动机的不同组件的温度不超过规定的限制标准。磨损监测技术的目标是确保这些参数的值的电阻隔离材料的定子绕组或某些运动部件的尺寸是坐落在可接受的操作限制规定的操作标准。机械振动监测技术水平的目标是确保电机的励磁的支持结构,由气隙电磁场与扭矩频谱。在自然与其他频段,不超过规定的水平操作标准。电通量、电流与放电监测技术的目标是预测可能的故障通过分析供应系统电流与电压的频率谱。模糊逻辑的方法可能是一个完整的故障监控系统解决方案的关键。这种方法可能所有监测技术不仅电气合并到一个完整的解决方案。