電氣類外文翻譯--基于繼電保護(hù)的電力系統(tǒng)監(jiān)控設(shè)備

1、<p>　　Power System Monitoring and Control Facilities on Protective Relays </p><p>　　Abstract: It is now possible to consider integrating the functions of the power system protection systems with those

2、of the local and remote data collection and control systems. A structured approach to this integration is necessary. However, if the full benefits are to be realized. A solution which will solve many of the problems prev

3、iously associated with this integration is presented together with an example of how it might in future be applied in a typical substation. </p><p>　　Keywords: Digital communications, Integration </p>

4、<p>　　1. Introduction </p><p>　　The current practice in power system transmission and distribution environments is to separate the functions of the local control, protection and supervisory control and

5、 data acquisition (SCADA) systems. One reason for this has been the technical constraint that has limited the amount of integration which can be reliably achieved. Local control facilities have consisted of hardwired pan

6、els taking up much control room space. </p><p>　　Control logic has been provided by hardwired contacts or programmable logic controllers. Until recently much of the protection equipment has consisted of anal

7、ogue devices, again taking up much space. Most modern protection devices using electronic and microprocessor technologies have so far concentrated on reducing the space taken to implement traditional protection functions

8、. </p><p>　　Generally, SCADA systems have been added more recently and have supplied their own transducers, interface units and wiring. These have grown up in parallel with the local control and protection s

9、ystems despite the fact that this often resulted in much functional duplication. Where information concerning the protection operation has been required by the SCADA system this has been derived in a secondary fashion, f

10、or example, feeding the protection outputs back into SCADA digital input units. </p><p>　　Recent technology advances have led to the realization that this degree of duplication is becoming less and less nece

11、ssary. Given infinite computing power it could be argued that the information necessary to perform protection functions is all available or can be made available on the SCADA network. It is conceivable then that the SCAD

12、A system could perform its own protection algorithms and issue its own trip signals through its control network. In practice reliability requirements and the need </p><p>　　One reason for the failure of syst

13、ems to integrate protection functions within an overall control package is the sheer amount of processing required. Modern digital protection relays use state of the art microprocessors to provide complex protection

14、functions. When many of these are spread around a substation it is clear that the processing power required to absorb their functions at a central point is formidable. On the other hand the analogue and digital transduce

15、rs used by the SCADA syste</p><p>　　The ability of the protection equipment to replace much of the local control and SCADA I/O systems hinges on the ability of the protection equipment to communicate in a st

16、ructured and deterministic way. It is essential that the protection performance is not compromised whilst at the same time the requirements of the local control and the SCADA systems are still met. From the local control

17、 and SCADA point of view the principal requirements are for analogue inputs for measurement and data logging,</p><p>　　2. Protective Relay Communications </p><p>　　2.1 Communications Philosophy

18、</p><p>　　The protective relays' prime function remains the protection of the power system. It is essential therefore that the relays' protection performance is not compromised by the requirements of

19、 data monitoring and control. For this reason it is considered necessary to provide monitoring and control communications separate from any communications requirements of the protection. Thus in a blocking scheme for exa

20、mple, blocking signals would be transmitted over their own protection signaling link e.g. p</p><p>　　Also, there remains those users who do not yet need some or all of the features available .It is important

21、 for these users that the operation of the relay does not depend on the monitoring and control communications link and that the full protection capabilities can still be realized when such links have not been installed.

22、</p><p>　　The full benefits of relay communications will only be achieved if they can be installed at all the relevant points on a utility's power system. This will not happen overnight and it is therefo

23、re very important that any chosen system can be installed on a piecemeal basis across a system as it becomes required. </p><p>　　One of the major factors influencing the take up of relay communications will

24、be the cost to the user. This cost consists not just of the additional cost of the hardware on the relay but also wiring costs, set-up and configuration costs and on-going operational costs. It is important therefore tha

25、t steps are taken to control all of these cost areas. Set against these costs should be the savings on the SCADA system and the operational savings which result from the increase in system data availabl</p><p&

26、gt;　　2.2 Communications Topology </p><p>　　It is possible to connect the SCADA system and the protective relays using a number of different communications topologies. The choice of topology is important as i

27、t has a direct bearing on the communications efficiency of the system. </p><p>　　Figure 1: Simple Protection/SCADA Topology </p><p>　　A simple form of connection is to connect each relay separat

28、ely to remote terminal units (RTU's) fitted with digital communications facilities. These RTU's in turn connect to the SCADA network -see Figure 1. These RTU's act as network switches, the main SCADA system b

29、eing responsible for the actual polling of information. In this topology the protective relays have effectively become intelligent transducers. There is a saving for the SCADA system in terms of the transducers that have

30、 been replac</p><p>　　Figure 2: Use of Multidrop Connections </p><p>　　An improved communications topology is illustrated in Figure 2. Several relays are connected to a single RTU on a single co

31、mmunications spur. This relies on the protective relays being fitted with a communications link capable of multidrop connection. In this scheme the RTU is now responsible for the polling of all units attached. In this wa

32、y information can be pre-processed and overall data rates can be reduced. This requires a more complex RTU, however a single RTU can handle more relays so fe</p><p>　　Figure 3: Use of Substation Central Comp

33、uter</p><p>　　A more sophisticated topology is shown in Figure 3. This topology utilizes an IBM PC compatible computer as a substation computer. Where reliability is thought to be a problem, a second slave c

34、omputer is added in parallel with the first. The substation computer replaces the RTU’s described above and gives a number of advantages to the user. Firstly there is now a local control point within the substation in ad

35、dition to the remote control facilities of the SCADA network. This can take the form of</p><p>　　Separate communications spurs are likely to be taken to each substation section, each capable of supporting32

36、relays. Up to eight spurs can be provided by a single PC giving a theoretical capacity of 256 relays. On such a system it is still possible for a modern PC to poll and extract data from each relay at a rate greater than

37、once a second.</p><p>　　In the unlikely event that this number of relays is insufficient further substation computers may be added. These may be independently connected into the SCADA system. Alternatively,

38、an optional additional level of substation computer with the same control facilities, may be added, as in Figure 4. Note now that each substation computer may be physically remote. It is also worth noting that this final

39、 topology has in effect become a mini SCADA system in its own right. For many smaller utilities t</p><p>　　Figure 4: Multi Level Topology </p><p>　　2.3 Communications Hardware </p><p&

40、gt;　　Hardware for digital communications can take many forms, most of which are not suitable for use in power system environments. The first choice to be made is between parallel and serial systems. Parallel systems invo

41、lve the transmission of several bits of information concurrently over several separate wires (typically eight or sixteen). Such systems offer faster data transfer rates than serial systems but involve far higher wiring c

42、osts. For this reason they are not suitable as a universal soluti</p><p>　　Serial communications involve the transmission of streams of data one bit at a time over a single pair of wires. Clearly wiring cost

43、s are reduced at the expense of overall data transmission rates which are proportionally lower. For monitoring and control applications the slower data rates remain acceptable and serial type communications are used almo

44、st exclusively. </p><p>　　The communications hardware most commonly used by protective relays at present conforms to the EIA’s RS232 standard. This takes the form of the familiar 25 or 9 way 'D' conn

45、ector. This has usually been used to connect the relay to a personal computer (sometimes indirectly, via a modem) allowing the relay to be setup and allowing post fault information to be extracted. RS232 connections are

46、convenient because of their almost universal availability. </p><p>　　RS232 connections do have a number of limitations which make them less suitable in monitoring and control applications. The most serious o

47、f these is that RS232 is designed for point to point systems. A single device can only communicate with one other device over a given link.If communications with more devices are required, as they are for data monitoring

48、 and control within substations, separate links must be provided. Alternatively, multiplexers or code switches could be added though this woul</p><p>　　RS232 also imposes a limit on the physical length of th

49、e communications link of just over 15, and a maximum data rate of 19.2kbaud. This can also be overcome but again requires additional equipment. Finally RS232 does not offer any significant level of isolation. Optically i

50、solated RS232 ports can be created but these are expensive. </p><p>　　A more suitable communications standard is RS485. This allows for a multidrop system with up to 32 nodes on a single spur, sufficient to

51、connect at least a single bay of relays. RS485 specifies a maximum transmission distance of 1200 metres and a maximum data rate over this distance of l00kbaud, significantly further and faster than RS232. It uses a balan

52、ced driver and differential signaling which is less susceptible to interference than the unbalanced driver referenced to ground as used in RS23</p><p>　　RS485 requires a single shielded twisted pair cable wh

53、ich is low cost and easy to terminate. Within the electrical industry in general this has typically been terminated in either 25 or 9 way 'D' connectors similar to those used by RS232. In a substation environment

54、 these connectors are not really suitable and a pair of conventional terminals is preferred. </p><p>　　The use of optical fibres to connect directly between relays remains expensive for most users, especiall

55、y at distribution voltage levels. Fibres are however suitable for connecting the local network of relays to remote master stations where distances exceed 1200 metres or where the risk of interference is high. In such cas

56、es modems are used to interface a group of relays to an optical fibre. As with electrical based communications, a number of different solutions are available. For distances of </p><p>　　Serial data communica

57、tions may be classified as either asynchronous or synchronous. RS232 communications ports on protectivc relays are invariably asynchronous. In asynchronous systems timing or synchronization information is transmitted tog

58、ether with each character. In synchronous systems either a separate clock is transmitted or the receiver derives the clock information from the data itself. Synchronous systems are more complex than asynchronous systems

59、but roughly 20% more efficient. More im</p><p>　　In summary, of the common communications interfaces, multidrop synchronous RS485 transmission using some form of FM encoding is currently the most suitable fo

60、r use in power system data measurement and control applications. This can provide fast economic communications with electrical interference immunity sufficient for power system environments. </p><p>　　2.4 Co

61、mmunications Language </p><p>　　Successful digital communications depends not just on compatible communications hardware but also on the communications language and protocol that are used. Traditionally rela

62、y manufacturers (in common with those in other fields) have developed their own languages. This has been less important in the past when there has been no need to integrate the relays into control systems. When the relay

63、s have been integrated a bespoke solution has been necessary with custom programming for each different r</p><p>　　Until now no language suitable for use by all protective relays has been proposed. The major

64、 drawback with most languages is that they assume the master station must have an intimate knowledge of the relay. If a particular piece of data has been required it has been asked for using its memory location in the re

65、lay or some device specific code. This address must be explicitly coded into the master station software. Moreover the relay has typically responded with raw unformatted data. The master s</p><p>　　The langu

66、age presented here overcomes these problems. It is suitable for use by all relays and other I/O devices and it does not require the master station to have an intimate knowledge of each relay type. The language is designe

67、d around a database stored in each individual relay. The relay uses this database to store all data and settings. The contents of the database are then made accessible over the communications link. The structure of the d

68、atabase is very similar to that of a spreadsheet, c</p><p>　　Figure 5: Database Layout & Cell Types </p><p>　　The database consists of three different types of cell, each one being a superse

69、t of the previous. see Figure 5 above. The three cell types are Heading Cells; Value Cells and Setting/Control Cells. Heading Cells contain a simple piece of text. These are used throughout the database as placemarkers t

70、o split the database into different areas. The most common Heading Cells are the database column heading cells. Value Cells contain a piece of text to describe their contents and a value which may be </p><p>

71、;　　to be converted. Typical Value Cells are measured values such as phase currents, device information such as model number, waveform records, etc. Setting/Control Cells are similar to Value Cells but their contents can

72、be changed. These cells additionally contain information about the minimum and maximum values for the cell and the valid steps. Typical Setting Control Cells are relay protection settings such as current thresholds, syst

73、em control cells such as circuit breaker control. etc. </p><p>　　Individual cells are grouped together into columns of related information. The cell in the first row of each column is a heading cell which de

74、scribes the contents of the column. This organization is invariant across all relays. Thus the contents of any relay can be read in the same way. First the column headings are extracted and presented to the user as a men

75、u. From this menu the user selects a particular column. The text and values for each cell in the selected column are then extracted and ag</p><p>　　In practice it is found that all relay types contain a cert

76、ain amount of common information. This includes the relay type, model number and serial number, its location, communications address, etc. This information is generally required by the master station when the relay is fi

77、rst connected. A special command could be provided to extract this data, however a better solution is to group all the data together in a single reserved column. The format of the column is fixed but the data can now be

78、e</p><p>　　The method of access described can be implemented in a way that is simple, intuitive and requires no reference manual for the user to access a particular piece of data. Moreover the method is cons

79、istent across any number of relays and need not be updated if further relays are added to the system. </p><p>　　From a master station point of view the commands required to access the database are few. The m

80、ost common are: </p><p>　　Get Column Headings </p><p>　　Get Column Text </p><p>　　Get Column Values </p><p>　　Get Cell Text </p><p>　　Get Cell Data </p&

81、gt;<p>　　Get Cell Limits </p><p>　　Preload New Setting </p><p>　　Execute Setting </p><p>　　Abort Setting </p><p>　　From these simple commands more complex sequen

82、ces may be built up as required. </p><p>　　2.5 Time Alignment and Sequence of Event </p><p>　　Recording </p><p>　　One of the important functions of existing SCADA systems is sequenc

83、e of event recording. This gives the system engineer valuable insight into the order in which events on the system occur.The typical accuracy of older systems is ±10ms. This function is currently carried out by the

84、RTU's of the SCADA system which monitor system events using digital inputs. These events are generally time tagged using a system synchronizing pulse distributed around the substation. Often of more importance than t

85、he</p><p>　　The new generations of protective relays now include their own sequence of event recording facilities. Moreover these facilities can be extended using spare relay input channels and separate I/O

86、modules to cover events not specifically related to the protection. In order to achieve this a new method of time synchronization has been devized which removes the need for separate clock synchronization wiring. Rather

87、than trying to synchronize the clocks within each individual relay, the relay clocks </p><p>　　Clearly when these event records are transmitted to the substation computer, events from different relays will b

88、e out of step. This problem is solved by also transmitting the current value of the relay's clock. This is compared with the substation computer's clock and the difference used to calculate the actual time of the

89、 event. </p><p>　　3. Conclusions </p><p>　　Initially, as digital technology was introduced to protective relays, the aim was to mimic the operation of the original electromechanical devices. Mor

90、e recently, as digital technology has advanced, protection performance and the operator interface have been improved. The latest generation of microprocessor based relays will in future offer facilities far in excess of

91、their predecessors. In particular it will be possible to integrate the protection systems with both the local and remote control </p><p>　　If the full advantages of this integration are to be achieved a stru

92、ctured approach is required so that a system wide solution may be derived. A hierarchical system has been presented with the remote control system connected to the substation network via a substation computer. The substa

93、tion computer is additionally capable of replacing much of the local control system. </p><p>　　For such a system to be widely adopted at distribution as well as transmission levels it is important that the s

94、et-up costs associated with the system are reduced. This is achieved by using a low cost communications network and a language which supports a distributed database of device information, that is device specific informat

95、ion is stored within individual relays and not hard coded into master stations. </p><p>　　The information available across the entire power system includes per phase instrumentation values, alarms, equipment

96、 status, sequence of event records, plant status data and disturbance waveform records. </p><p>　　All this is available locally at the substation and remotely without placing additional processing burden on

97、the SCADA system. </p><p>　　譯文題目：黑體，小三；間距：同原文題目</p><p>　　譯文正文：宋體，小四；間距同原文正文</p><p>　　頁眉頁腳：原文頁眉處寫：外文翻譯（原文），宋體，五號。譯文頁眉處寫：外文翻譯（譯文），宋體，五號。原文譯文的頁腳統(tǒng)一編頁碼（不要單獨編頁碼）。</p><p>　　基于