变电站与电力系统继电保护.doc

中文3826字附录1：外文资料翻译A1.1 Substation and Power System ProtectionWith the development of undertaking of the electric wire netting , the pattern of national network has already taken shape basically. Scientific and technological level raise, electric environmental protection can strengthen, make scientific and technological competence and advanced international standards, Chinese of power industry close day by day. Electric management level and service level are being improved constantly, strategic planning management of electric power development, production operate manage , electric market administration and electric information management level , high-quality service level ,etc. general to raise enterprise.The purpose of a substation is to transform the characteristics of the electrical energy supplied to some form suitable for use, as for example, a conversion from alternation current to direct current for the use of city railway service, or a change from one voltage to another, or one frequency to another. Their functions include:Tap.TO be economical, transmission of larger amounts of power over long distances must be done at voltages above 110,000 volts. Substations for supplying small amounts of power from such high-voltage lines are not satisfactory from the standpoint of operation and are also uneconomical. It is, therefore, common practice to install a few substations at advantageous points along the high-tension lines and step down the high-transmission voltage to a lower secondary-transmission voltage from which numerous small loads may be supplied.Distribution.Any substation that is used to transform electrical energy to a potential that is low enough for general distribution and utilization is a distributing substation. Such a substation will generally receive its energy over a few comparatively high-tension lines and distribute it over a large number of low-voltage lines.Industrial.When fairly large blocks of power are required by industrial plants, it often becomes necessary and advisable to install an individual substation to supply such a load directly from the main high-voltage line or secondary line of lower voltage. Its simplest form would comprise only switching equipment, there being no voltage transformation. In most cases a voltage transformation is probably needed; hence transformer equipment is included.Sectionalizing.In very long high-voltage large capacity lines, particularly when several circuits are run in parallel, it is often necessary to split the lines into sections, in order that proper protection to the line and service can be obtained. Such a substation is , therefore, helpful in sectionalizing damaged sections of a line, providing continuity of service. Such a substation will generally comprise only switching equipment. In long lines it may also serve to supply power-factor-correcting equipment.Transmission-line Supply.It is becoming more and more common to install the high-tension equipment of a power plant outdoors, the installation becoming nothing more than a step-up substation receiving its power at generator voltage, then stepping up its voltage and finally sending it out over high-voltage transmission lines. Such a substation is nothing more than an outdoor distributing substation turned around, the voltage being stepped up instead of stepped down.Power-factor Correction.The voltage at the end of long lines tends to increase as the load supplied is decreased, while on the other hand it tends to decrease as the load is increased. Owing to the inductance and capacity effects, this variation in voltage is accompanied by a wide variation in power factor of a line, it is necessary to use synchronous condensers at the end of the line. To supply such a machine the transmission-line voltage must be stepped down, hence a power-factor-correcting substation will include switching equipment, transformers, and all equipment necessary for the operation of synchronous condensers.Railway.Substations supplying railways may be generally classified under two heads, namely, as alternating current and as direct current. In the cases of alternating-current substations the problem is generally one of voltage transformation and of supplying single-phase power to the trains. It is, however, possible to supply single-phase to three-phase inside the locomotive by the use of a phase converter. In the case of direct-current railways, the substations are generally supplied whit three-phase power and converted to direct current by means of rotary converters, motor-generator sets, or rectifiers.Direct current for Light and Power.There are still a few sections in some of out large cities, which are supplied with direct-current three-wire systems. Such a supply is invariably obtained from synchronous converters. There are also certain types of motor loads in industrial plants, which require direct current.Because many cities have experience rapid growth, their substations have often reached the limits of their capacity. As a result, downtown distribution systems are often overworked and many need a major, overhaul, overhaul, or expansion. However, space is scarce. Downtown business owners do not want “ugly” new substation marring the areas appearance, but nor do businesses and residents grid the prospect of grid disturbances.One example of a system capable of integrating equipment monitoring with substation automation is the GE Harris integrated Substation Control System (ISCS). The system can integrate data from both substation system and equipment online monitoring devices into a common data base. The data can then be processed by an expert system into information on the status and health of monitored equipment using self-diagnostic programs. This information is then sent to a CMMS for automatic generation and tracking of maintenance work orders leads directly to the significant efficiencies found with condition-based maintenance programs.ABB Power and its industry partners have combined to develop the ABB Power System software. The system contains a diagnostic and maintenance system that reports necessary maintenance before failure. It allows utilities and industrial customers to easily expand from a single computer to a full system, without re-engineering.the directional protection basisEarly attempts to improve power-service reliability to loads remote from generation led to the dual-line concept. Of course, it is possible to build two lines to a load, and switch the load to whichever line remains energized after a disturbance. But better service continuity will be available if both lines normally feed the load and only the faulted line is tripped when disturbances occur. Fig.14-1 shows a single-generator, two-line, single-load system with breakers properly arranged to supply the load when one line is faulted. For the arrangement to be effective it is necessary to have the proper relay application. Otherwise, the expensive power equipment will not be able to perform as planned. Consider the application of instantaneous and/or time delay relays on the four breakers. Obviously the type of the relay cannot coordinate for all line faults. For example, a fault on the line terminals of breaker D. D tripping should be faster than B, however, the condition reverses and B should be faster than D. It is evident that the relay protection engineer must find some characteristic other than time delay if relay coordination is to be achieved.The magnitude of the fault current through breakers B and D is the same, regardless of the location of the fault on the line terminal of breaker B or D. Therefore relay coordination must be based on characteristics other than a time delay that starts from the time of the fault. Observe that the direction of current flowing through either breaker B or D is a function of which line the fault is on. Thus for a fault on the line between A and B, the current flows out of the load bus through breaker B toward the fault. At breaker D the current flows toward the load bus through breaker D. In this case breaker B should trip, but breaker D should not trip. This can be accomplished by installing directional relays on breakers B and D that are connected in such a way that they will trip only when current flows through them in a direction away from the load bus.Relay coordination for the system shown in Fig.14-1 can now be achieved by their - salvations of directional over current time delay relays on breakers B and D. Breakers A and C can have no directional over current time delay relays. They may also now have instantaneous relays applied. The relays would be set as follows: The directional relays could be set with no intentional time delay. They will have inherent time delay. The time delay over current relays on breakers A and C would have current settings that would permit them to supply backup protection for faults on the load bus and for load equipment faults. The instantaneous elements on breakers A and C would have current settings that would not permit them to detect faults on the load bus. Thus the lines between the generator and the load would have high-speed protection over a considerable portion of their length. It should be observed that faults on the line terminals of breakers A and C can collapse the generator voltage. The instantaneous relays on breakers A and C cannot clear the circuit instantaneously, because it takes time for power equipment to operate. During this period there will be little or no current flow through breakers B and D. Therefore, B or D cannot operate for this fault condition until the appropriate breaker at the generating station has operated. This is known as sequential tripping. Usually, it is acceptable under such conditions.Direction of current flow on an a. c. system is determined by comparing the current vector with some other reference vector, such as a voltage vector. In the system of Fig. 14-1 the reference voltage vector would be derived from the voltages on the load bus. Direction of current or power flow cannot be determined instantaneously on a. c. systems whose lines and equipment contain reactance. This is apparent from the fact that when voltage exists, the lagging current can be plus or minus or zero, depending on the instant sampled in the voltage cycle. Accordingly, the vector quantities must be sampled over a time period. The time period for reasonably accurate sampling may be from one-half to one cycle. Work is proceeding on shorter sampling periods where predicting circuits are added to the relay to attempt to establish what the vectors will be at some future time. The process is complex, because it must make predictions during the time when electrical transients exist on the system. Usually, the shorter the time allowed for determining direction, the less reliable will be the determination.differential protection Much of the apparatus used on a power system has small physical dimensions when compared to the length of general transmission-line circuits. Therefore, the communications between the apparatus terminals may be made very economically and very reliably by the use of direct wire circuit connections. This permits the application of a simple and usually very effective type of differential protection. In concept, the current entering the apparatus is simply compared against the current leaving the apparatus. If there is difference between the two currents, the apparatus is tripped. If there is no difference in the currents, the apparatus is normal and no tripping occurs. Such schemes can usually be made rather sensitive to internal faults and very insensitive to external faults. Therefore, relay coordination is inherent in the differential relay scheme.The simplest application of differential relaying is shown in Fig. 14-4. Here one simple power conductor is protected by a differential relay. The relay itself usually consists of three coils, one of which is the coil that detects the difference current and initiates circuit tripping. It is called the operating coil and is designated by an O in the figure. The other two coils are restraint coils and are designated by R in the figure. The restraint coils serve a practical purpose. They prevent operation for small differences in the two current transformers that can never be exactly identical, as a result of manufacturing and other differences. Otherwise, the restraint coils serve no theoretical purpose. Fig. 14-4 shows the condition of current flow for an external fault during which the relay should not trip. The current I1 enter and leaves the power circuit without change. The current transformers are assumed to have a 1 : 1 ratio for simplicity, and their secondary windings are connected to circulate the I1 currents through the restraint coils of the differential relay only. If current left or entered the power circuit between the two current transformers (an internal fault), then the currents in the transformers would be different, and the difference current would flow through the operating coil of the relay. 本文译自电力英语阅读A1.2 变电站与电力系统继电保护随着电力电网事业的发展，全国联网的格局已基本形成。科技水平得到提高，电力环境保护得以加强，使中国电力工业的科技水平与世界先进水平日渐接近。电力管理水平和服务水平不断得到提高，电力发展的战略规划管理、生产运行管理、电力市场营销管理以及电力企业信息管理水平、优质服务水平等普遍得到提高。变电站的目的是改变电能特性以满足使用要求。例如，从交流转换为直流为城市铁路供电，或者从一个电压等级转换为另一十电S等级，或者从一个频率转换为另一个频率。变电站的功能包括：分支为了经济性，大容量电力的远距离传输必须在110kV以上的电压下进行。从运行的角度来看，从这样的高压线直接引出向小容量负荷供电的变电站是不能令人满意的，也是不经济的。因此，一个常规办法是：沿着高压线路在适合的地点设置一些变电站，将高传输电压降到一个较低的二级传输电压，从这个电压向小容量负荷供电。 配电任何用于将电能变换为可以直接配电和利用的较低压等级的电能的变电站都是配电变电站。这样的变电站一般将从A条电压相对高的线路接受电能，并向大量较低电压线路配送电能。工业当工厂需要大量电能时，设置一个自己的单独的变电站是有必要的也是明智的，这个变电站直接从主高压线路或较低电压的二级输电线路取得电能。其最简单的形式没有电压的转换，只由开关设备组成。但是，在大多数情况下需要一个电压转换，因此工业变电站应该包括变压器设备。分段在很多高压大容量的长线路中，尤其是几条线路并联运行时，经常需要将线路分段，目的是为了使线路获得适当的保护和维护。这样的变电站有助于隔寓线路中的故障段，保证连续供电。这种变电站通常只由开关设备组成。在长线路中，还可以提供功率因数调整设备。输电线路的电源在发电厂的户外设置高压设备已经变得越来越昔遍，安装的装置只不过是一个升压电站，它以发电机电压接受电能，然后将电压升高，并最终通过高压输电线路将电能送出。这种变电站只不过是将户外配电变电站反过来，电压是被升高而不是降低。功率因数调整随着供电负荷的减小，长线路末端的电压趋向于升高，而随着供电负荷的增大，线路末端的电压趋向于降低。由于电感和电容的影响，这个电压的变化将伴随着线路功率因数而变化，因此有必要在线路末端设置同步调相机。为了向同步调相机供电，就必须将高压输电线路的电压降低，因此，一个功率因数调整变电站将包括开关设备、变压器和所有运行同步调相机所需要的设备。铁路一般地，向铁路供电的变电站分为两类，即交流类和直流类。如果是交流变电站，其问题一般是一个电压转换和向铁路机车负荷单相供电的问题。然而，也有可能在机车内通过相位变换锚由单相电源向三相负荷供电。如果是直流铁路，这种变电站一般由三相电源供电，并通过旋转变流器、电动机发电机组或者整流器等将交流变换为直流。照明和动力用直流现在，仍然有一些在大城市以外的地区采用直流三线系统供电，这种电源总是从同步换流器获得。另外，工厂中还有某些类型的电动机负荷要求采用直流电源，这些一般都是由旋转换流器供电。对于电解工业，低压直流电源绝对是必须的，因此也需要使用电动机发电机组或旋转变记器。由于城市不断发展，许多城市变电站已经达到其负荷极限，所以市区配电系统经常是超负荷运行，许多配电站急需升级、检修或扩建，问题是空间不足。市中心的业主不希望外观“丑陋”的新变电站影响当地的景观，商家和居民也不想将来被星罗棋布的电网所干扰。变电站自动化的新趋势是状态维修。ABB公司与联邦爱迪生公司合作开发了一套贯穿整个系统的规划，一旦联邦爱迪生公司的配电系统发生故障，可使电能流向发生改变。联邦爱迪生公司的项目总裁迈克罗维说：“对这几个变电站的发行包括肥现有的辐射状的馈电系统改成环形母线系统，以增加系统的稳定性。”GE哈里其变电站综合控制系统（ISCS）就是一个将设备监测与变电站自动化相结合的系统。该项系统能够将来自变电站系统和设备在线监控装置的数据进行综合，并输入数据库，然后由一个专家系统利用自我诊断程序进行分析，得出有关被监测设备的运行善的信息