1、英文原文UNDERSTANDING MICROPROCESSOR-BASED TECHNOLOGY APPLIED TO RELAYING1.INTRODUCTION1.1Brief History of Microprocessor-based RelaysDifferent tehonlogies have been used in the past to implement protection functions that properly detect disturbances in power systems and initiate the disconnection of th
2、e faulted components.Originally,electromechanical relays were used to protect power systems.Most relays used either electromagnetic attraction or electromagnetic induction principle for their operation.Plunger type relays formed instantaneous units for detecting overcurrent or over-voltage condition
3、s.balanced-beam relays provided differential protection,distance protection as well as low burden overcurrent units.These relays operated when the magnitude of an operating signal was larger than the magnitude of the restraining signal.These relays were classified as amplitude comparators.Single inp
4、ut induction type relays provided operations with time delays. Two-input inductiontype relays provided directional protection. Two- and three-input induction type relays alsoprovided distance protection. The operation of these relays depended on the phase displacement between the applied electrical
5、inputs. These relays were classified as phase comparators.When solid-state technology was introduced, amplitude and phase comparison wereimplemented using discrete components including vacuum tubes. In early 1960s, advances inthe integration of electronic circuits made this technology suitable for u
6、se in relays. The major advantage of these relays was that no moving parts were needed for performing their intended functions. The operating speeds of these relays were also more than the speed of their electromechanical counterparts and, their reset times were less than the reset times of their el
7、ectromechanical counterparts. In addition to these benefits, the solid-state relays could be set more precisely and needed less maintenance.Solid-state relays appeared to be the technology poised to replace the electromechanical counterparts in late 1960s when researchers ventured into the use of co
8、mputers for power system protection. Their attempts and the advances in the Very Large Scale Integrated (VLSI) technology and software techniques in the 1970s led to the development of microprocessorbased relays that were first offered as commercial devices in 1979. Early designs used the fundamenta
9、l approaches that were previously used in the electromechanical and solid-state relays.Multifunction relays were introduced in the market in the late 1980s.These devices reduced the product and installation costs drastically.This trend has continued until now and has convertefd microprocessor relays
10、 to powerful tools in the midern substations.1.2 Benefits of Microprocessor-based Relays.While the basic protection priciples have remained essedtially unchanged throughout the evolution of the microprocessor-based relays,the adoption of this technology has provided many benefits,and a few shortcomi
11、ngs,compared to the previous tehnologies.The benefits and shortcomings are discussed in this section.The emphasis is on compatringn the microprocessor technology with the electromechanical technology.Comparison with the solid-state technology is also included as required.1.2.1Multiple functionsMicro
12、processor relays provide many functions that were not available in electromechanical or solid-state designs.these features include multiple setting groups,programmable logic,adaptibelogic,self-monitoring,self-testing,sequence-of-events recording,oscillography,and ability to communicate with other re
13、lays and control computers.1.2.2CostThe cost per function of microprocessor-based relays is lower compared to the cost of their electromechanical and solid-state counterparts.The reduction in cost is due to the lower cost of components,production equipment and production techniques.because microproc
14、essor-based relay designs incorporate commercially available electronic components,their product life is limited by the prodct life of the components.Manufactuers control,it has proven to be a significant problem with the solid-state as well as the microprocessor-based relays.1.2.3 Custom logic sche
15、mesA major feature of microprocessor-based relays that was not available in previous technologies is the ability to allow users to develop their own logic schemes,including dynamic changes in that logic.this benefit,however,comes at a cost because this capability increases the complexity of the syst
16、em.1.2.4Sequense of events and oscilographyReporting features,including sequence of events recording and oscillography are a natural by-product of microprocessor-based protection systems.These features make it possible to better analyze the performance of relays as well as system disturbances at minimal additional costs.1.2.5Self-monitoring and slef-testingAnother advantage of microprocessor-based relays is their ability to perform self-monitor
