Chapter--7-Power-System-Protections-section-7-1-In.ppt

单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,Chapter 7,Power System Protections,Section 1 Introduction,Text,New Words and Expressions,Exercises,End,Resume,Section 1 Introduction,The steady-state operation of a power system is frequently disturbed by various faults on electrical equipment.To maintain the proper operation of the power system,an effective,efficient and reliable protection scheme is required.Power system components are designed to operate under normal operating conditions.However,if due to any reason,say a fault,there is an abnormality,it is necessary that there should be a device which senses these abnormal conditions and if so,the element or component where such an abnormality has taken,Section 1 Introduction,place is removed,i.e.deleted from the rest of the system as soon as possible.This is necessary because the power system component can never be designed to withstand the worst possible conditions due to the fact that this will make the whole system highly uneconomical.And therefore,if such an abnormality takes place in any element or component of the power system network,it is desirable that the affected element/component is removed from the rest of the system reliably and quickly in order to restore power in the remaining,Section 1 Introduction,element.This is why the protective relay must be reliable,maintainable and fast in operation.,In early days,there used to be electromechanical relay of induction disk-type.However,very soon the disk was replaced by inverted cup,i.e.hollow cylinder and the new relay obtained was known as an induction cup or induction cylinder relay.This relay,which is still in use,possesses several important features such as higher speed,higher torque for a given power input and more uniform torque.,Section 1 Introduction,However,with the advent of electronic tubes,electronic relays having distinct features were developed during 1940s.With the discovery of solid state components during 1950s,static relays with numerous advantages were developed.The use of digital computers for protective relaying purposes has been engaging the attention of research and practicing engineers since late 1960s and 1980s.Now,the microprocessor/mini computer-based relaying scheme,because of its numerous advantages such as self-checking feature,Section 1 Introduction,and flexibility,has been widely used in power systems all over the world.,The overall system protection is divided into following sections:(i)Generator protection,(ii)Transformer protection,(iii)Bus protection,(iv)Feeder protection,(v)Transmission line protection.,Section 1 Introduction,（1）Since faults on a well designed and healthy system are normally rare,the relays are called upon to operate only occasionally.This means that the relaying scheme is normally idle and must operate whenever fault occurs.In other words,it must be reliable.,（2）Since the reliability partly depends upon the maintenance,the relay must be easily maintainable.,Section 1 Introduction,（3）The maloperation of the relay can be in two ways.One is the failure to operate in case a fault occurs and second is the relay operation when there is no fault.As a matter of fact,relay must operate if there is a fault and must not operate if there is no fault.,（4）Relaying scheme must be sensitive enough to distinguish between normal and the faulty system.,Section 1 Introduction,（6）Phase sequence relays such as(i)negative sequence relays and,(ii)zero sequence relays,（7）Differential relays and percentage differential relays,（8）Distance relays such as(i)plane impedance relays,(ii)angle impedance relays,i.e.Ohm or reactance relays,(iii)angle admittance relays,i.e.Mho relays and,(iv)offset and restricted relays,（9）Pilot relays such as(i)wire pilot relays,(ii)carrier channel pilot relays,(iii)microwave pilot relays.,New Words and Expressions,power system protection,电力系统保护，电力系统继电保护,abnormality,n.异常，反常，不正常,sense,v.检测，读出，断定；感觉，感受，感到,relay,n.继电器，中继器；v.中继，转播，用继电器控制,circuit breaker,断路器,trip coil,跳闸线圈，脱扣线圈,electromechanical relay,电磁继电器,New Words and Expressions,solid state,固态,static relay,静态继电器，无触点继电器,self-checking,自检，自校,maloperation,n.误操作，误动作，维护不当,energize,v.激励，激磁，驱动，通以电流,overcurrent relay,过电流继电器,undervoltage relay,低电压继电器，欠压继电器,underfrequency relay,低周继电器，低频继电器,New Words and Expressions,plane impedance relay,平面阻抗继电器,angle impedance relay,角度阻抗继电器,angle admittance relay,角度导纳继电器,Mho relay,姆欧继电器，电导继电器,offset relay,偏置继电器,restricted relay,制约式继电器,pilot relay,控制继电器，辅助继电器,wire pilot relay,有线控制继电器,New Words and Expressions,carrier channel pilot relay,载波控制继电器,microwave pilot relay,微波控制继电器,transductor relay,饱和电抗型继电器,rectifier bridge relay,整流桥型继电器,electronic relay,电子继电器,Return,Resume,简历是个人经历的文字记载。撰写个人简历是为了一定的目的，向特定的读者或机构介绍个人的有关情况，如申请攻读学位或求职等均须递交申请信、推荐信和简历。,简历写作要求做到实事求是，简明扼要，语言正确，格式规范。简历的内容和篇幅因人、因事及个人资历而异，一个较为完整的简历大体包括：个人情况，教育状况，工作经历，著作和论文出版与发表情况，所参加的学术团体，推荐人等项目。作者可根据实际需要取舍或增添，有重点地突出有关的内容。,Resume,1.个人情况（Personal）,个人情况通常包括姓名、性别、出身年月、出生日期、国籍、婚姻状态、配偶资料、健康状况、常驻地址、通信地址、电话及电子信箱等内容。有时还需写明个人身高、体重以及爱好等。,2.教育状况（Education）,教育状况主要写明何地何校毕业、何时何处被授予何种学位。若为获得学位，最好注明所学主要科目。根据需要，还应当写明自己的外语程度。编写顺序一般最高学历或最近学历先写，时间安排成倒叙的顺序。,Resume,3.工作经历（Experience）,工作经历可写成Experience，还可视具体情况写成working Experience，Research Experience，Teaching Experience，Professional Experience，Employment等。工作经历一般应包括工作单位、工作时间、工作内容、工作成效以及担任的职务等。叙述的顺序也可按由近及远的倒序方法。,Exercises,I.Choose the best answer into the blank,1.The protective relay disconnects faulted elements in a power system by,.,A.determining its location B.acting as a brain,C.tripping the proper circuit breakers D.sensing the fault,2.When the trip coil of a circuit breaker is excited by a protective relay,the circuit breaker is,.,A.switched on B.switched off,C.connected to a fault elementD.turned on,Exercises,I.Choose the best answer into the blank,3.Any protection scheme consists basically of,.,A.two elementsB.three elements,C.four elementsD.five elements,4.The,of a protective relay is that it must operate correctly if there is a fault and must not operate if there is no fault.,A.sensitivityB.selectivity,C.rapidityD.reliability,Exercises,I.Choose the best answer into the blank,5.The protective scheme that senses zero sequence current and operates as necessary is called as,.,A.overcurrent protection,B.zero sequence protection,C.negative sequence protection,D.directional protection,Exercises,III.Translate the following into Chinese,The relays used for power system protection are usually divided into two groups:(i)primary relays,(ii)backup relays,according to their roles in the overall system protection.,The primary relays are the first line of defense.They sense the fault and,if it exists,send the signal to the proper circuit breaker by closing its trip coil and hence clear the fault.The fault may not be cleared if the relay maloperation or the circuit breaker fails to operate.The causes of failure in the circuit breaker,Exercises,III.Translate the following into Chinese,are either failure of supply to its trip coil or a struck mechanical lever.The failures in protective relay are because of wrong setting of the relay,bad contacts or open circuit in the relay coil.In such cases,the backup relays are used as the second line of defense.They have longer operating time even though they sense the fault along with the primary relays.Relay operating time is defined as the time interval between sensing of fault by the relay and sending the trip signal to the proper circuit breaker.,Chapter 7,Section 1,End,