变压器的局域监督保护系统

变压器的局域监督保护系统

在供电方面，将变压器直接地接到高压输电线是一种比较实际和相对经济的方式。断路器用在输电线上是毋庸置疑的，特别在更高的电压等级。 空气断路器取代了普通的断路器。排除配电装置的故障，检查和排除变压器故障后，拉开接地开关，合上断路器。采用本地区域的监督保护(LASP)系统。 LASP系统在电力系统中从集成设备到继电设备收集不同地区的电流和电压数据。 异步传递模式(ATM)是定向连接的， 分组交换的网络模型在LASP系统和设备之间。依据规程和指南对构架进行建设与下一级变电站网络结构相匹配。环境为电力系统的保护装置开放新的远景。

1. 介绍

架设输电线为了连接负荷， 或通过变压器加强基层的低压网络。 虽然，这种电力系统配置是低廉的， 它提出保护工程的一些特别问题。 当电源后的分接头有多端线路时或电力变压器有多于二个终端， 安全系统设计要求仔细考虑。怎样将变压器与变电站或系统连接是一个问题。 直接连接一次绕组开关检修变压器故障是可行的。有许多配电装置的变量。 断路器通过电流互感器检测故障、确定保护范围、然后清除故障。 因此，装设这么多的线路断路器是毋庸置疑的， 特别在更高的电压[3]。

空气断路器普遍取代线路断路器。变压器和传输线邻近的空气断路器使得电力系统配置逐步扩大化和复杂化。 这导致一个困难的情况，尤其是没有接地开关的情况下 继电器设计要协调继电器顺序和空气断路器的运行。本文为这种难题提出一种解答方案。 它运用本地区域的监督保护(LASP)系统收集本区域的电压和电流数据然后共享数据在继电器中。继电器和主继电器之间信息交换，然后做出可靠和有选择性的决定。 前面提出的LASP系统在运行时间、线路选择、空气断路器装置、空气断路器的死区上要比常规系统更好。 本文提出一种解决方案，假设数字式监督保护的分接头高速通信。 保护区域必须覆盖整条线路包括分接头和运行中的变压器高、低压绕组。 建立LASP系统网络结构的描述。

2. 在变压器分接头安装CBs的可行性

将变压器直接接到高压输电线为一个独立的工业负荷提供电能是一种实用和相对经济的方式。断路器通过电流互感器检测故障、确定保护范围、然后清除故障。 

低压(LV)母线连接更多的设备。分接头馈电给负荷。 如果LV母线被网络化，就会在低压母线侧提供了一些避免错误的方法。目的是防止被保护线路出现故障而提供的后备保护[4]。 它假设，不同的电流保护系统仅在主要变电所监控电流。分接头、变压器、线路上的电流都不作用于继电器。

3. 人机对话和运行理念

在变电所任何部分发生故障以后，故障部分在没有修好之前通过自动开关装置被隔离。自动开关期间， 变电站正常部分也有可能退出运行。正常部分在手动开关期间恢复运行的可能性很大。 使用空气断路器在自动和手工开关期间能使站与站之间进行很好的配合。在自动和手动开关状态期间被作为一个单一故障状态。在手动开关初期该馈线不再向外界供电，它被认为是在故障时间持续范围内，因为自动开关状态期间与手工开关状态期间比较是非常短的。这种方法在没有空气断路器的变电站是差强人意的。安装有空气断路器的变电站将错误状态分成两部分，为了使变电站输出损耗的情况下正确记录空气断路器运行效果[5]。

4. 在变压器分接头使用MOAB的问题

断路器的用途是毋庸置疑的， 特别在更高的电压[3,4]。为了清除变压器保护区域内故障必须切断较远线路的断路器和打开变压器的空气断路器。教员线路的线路断路器可重新闭合，重新投入运行。在远方终端的继电器必须投入监视，而不是远离变压器和变压器分接头，来避免被从系统中切出。高压侧的断路器作用于低压侧发生的故障。这就产生了问题，远方的继电装置在当变压器保护范围内发生高阻抗故障时不会动作。一个作用远方终端跳闸的共同做法是在变压器处安装一个单相接地开关。这是一种带弹簧操动式的开关，远方继电器监视和动作，各自的CBs被打开，它能动作于在变压器保护范围内的线路到地面的所有故障。

在跳闸时间的MOABs和开关之间的协调是非常复杂的。常规系统为操作MOABs使用一份有差别的保护方式和单相接地开关来增加励磁的顺序和对终端的CBs去励磁。

5. 技术作用的概念

在分接头处使用常规地单独继电器不能提供故障的准确信息。 CBs多次重合闸这种常规保护方式被电力系统广泛且长期采用。分接头故障和高阻抗故障对于电力系统是一个严重的问题。由于上述原因， 安装了LASP系统。LASP系统从变压器保护范围内的分接头处、母线处的所有点采集电流数据。 数据由联合设备(IE)传送继电设备(RE)。 这种保护安装在每个传输线的终端分接头处。 主机依据传输来的数据利用异步传递模式(ATM)功能在继电器中共享数据，与此同时作用于远方终端处的跳闸和部件决定。 IEs在数据分享和交换信息以后可以通入闭锁MOAB开关和作用于与之相关的断路器跳闸。

6. 系统性能

 在常规系统发生在分接头处的故障对于电力系统是一个严重的问题。这个区域被认为是MOAB的动作死区。 在分接头处的MOABs与CBs远程终端相关，他们在没有被损坏前会连续地运作。LASP系统可能成功地判别这种根据同一点处的电压监视和在分接头处电流求和的故障。这将导致开关的闭锁。 而且， 数据共享和各处的信息收集有助于LASP系统发布一个合适的和有选择性的决定。以一个有足够高的阻抗的高阻抗故障没有被常规保护探知 [6] 。应用基尔霍夫定律原理制造的电流差动继电器，这个保护元件被引入到LASP系统。继电器根据开关点CT 二次侧的总电流动作。 使用数据分享和信息交换的LASP系统可以容易地识别这样问题。

7. LASP系统布局

继电器与主继电器之间的信息交流连接良好。LASP系统与同级系统资源共享。 这就意味着充分的真正的连接。 这就提供了在RE和HR 中进行数据共享和信息交换的优势。 LASP系统有许多组分包括硬件和软件。 计划包括数据交换保护系统、 LASP和地方保护、 控制和监督。

在LASP系统中， 出口设备是我们所共知的ATM。 ATM在保护装置和LASP系统之间提供通信和信息传递。有一个变压器、两回线和母线组成的LASP系统模型， ATM网络传送2.488 Mbps数据为取样频率5.760赫兹或更高[7,8]。 ATM是可能传送数据的宽频元件继电技术。 它运作在断路数据元件，数据包具有一定的长度。 ATM使用的是53个字节大小的元件。 这些元件包括应用数据48个字节， 并且5个字节控制信息在集箱。 ATM装置为实用LASP系统提供传输速度高达155 Mbps。在虚拟路径标识符(VPI)和虚拟通道标识符(VCI)领域输入元件的连接信息。 因为开关元件是向前发展的，VPI和VCI也在不断的更新。 48个字节有效负荷包括地址， 电流， 电压， 状态等信息。然而， 在一个共同的设备集线器上聚集多个链接。 这使LASP系统扩大， 即可保护当地，又可延长距离。

LASP系统需要的软件元件包括：

. 定义了两个或多个设备的沟通协议。

. 引导各自设备功能的硬件及软件， 例如NIC。

. 通信软件。

8. 结论

因为超高压断路器很昂贵，所以在变电站设计经中常常被省去。选择变压器，直接从空气开关连接到超高压母线上。LASP系统允许许多继电器和主继电器互相联络，来处理传统保护和控制系统之间的问题。在上，LASP系统动作时间的选择性和可靠性要比传统系统高。 LASP系统引入了地方保护和控制系统。在线路上装设空气断路器和LASP系统是更加可靠和安全的。在动作时间上预计是传统保护时间的25%。断路器不断的重合闸，直到线路和变压器恢复运行，远程终端跳闸也存在于LASP系统。 而且，存在问题的区域，例如死区和高阻抗被成功地解决。 设计的系统结构使用的出口设备，例如ATM传输网络和数据集成和RE。继电器中电压和电流全部的数据收集和数据共享程序，改进了识别和控制电力系统中的故障事件的最终决策。 LASP系统通过有效的数据和信息通信来满足新的要求。作者现在修建一个实验性LASP系统研究以上提出的系统。

Local area supervisory protection

system transformer taps

Connecting a transformer directly to the high voltage transmission line is a practical and relatively inexpensive way of providing service. The use of many circuit breakers is usually not justified, particularly at higher voltages. Motor operated air break switches (MOABs) instead of circuit breakers are used. To cope with the difficulty of switching arrangements, detection and clearing of transformer faults excluding the ground switch for MOABs operation, local area supervisory protection (LASP) system is proposed. LASP System collects current and voltage data from different locations on the power system through integrated equipment (IE) to relay equipment (RE). Asynchronous transfer mode (ATM) is a connection-oriented, packet-switched networking model between the LASP system and the equipment. Some attention is given to the architecture of a solution and some guidelines as to how this structure might be built to match with the next generation substation network architecture are also provided. The environment opens up new vistas for protection applications in the power systems.

1. Introduction

Transmission lines may be tapped to provide intermediate connections to loads, or to reinforce the underlying lower voltage network through a transformer. Although, the resulting power system configuration is inexpensive, it does pose some special problems for the protection engineer. When the multiterminal lines have sources of generation behind the tap points, or if there are power transformers at more than two terminals, the protection system design requires careful thought. It is very often a question of how the transformer is integrated into the station or system. The detection and clearing of transformer faults are intimately connected to the primary switching that is available. There are many variations of such switching arrangements. Breakers are used both as locations for the CTs to detect a fault and define the zone of protection and as the way of clearing the fault. The use of so many CBs is usually not justified, particularly at the higher voltage [3].

Motor operated air break switches (MOABs) instead of CBs are commonly used. The recent enlargement and increased complexity of power system configuration has led to adjacent arrangements of MOABs with transformers and power transmission lines. This causes a difficult situation when relay engineers coordinate operation of relay sequence and MOABs especially, in the absence of ground switches. This paper presents a solution for such difficulty. It utilizes a local area supervisory protection (LASP) system that collects voltage and current data and then shared data among relays. Information is exchanged between relays and the host relay (HR) makes the final reliable and selective decision. The proposed LASP system can operate better than conventional systems with respect to operation time, line selectivity, MOABs arrangements, and dead zone area between MOABs. This paper presents a solution that assumes high-speed communication from the taps facilitating digital supervisory protection. The protection zone must cover the entire line including：taps and operation of the high and low voltage winding of the transformer. A description of the network architecture for building the LASP system

  2. Availability of installing CBs at transformer tap

Connecting a transformer directly to the high voltage transmission line is a practical and relatively inexpensive way of providing service to an isolated industrial load. On low voltage transmission system, circuit breakers are used both as locations for the CTs to detect a fault and define the zone of protection and as the way of clearing the fault.

The low voltage (LV) bus bars may be interconnected although in most applications, the tap feeds a load. Note that if the LV bus bars are networked, some means of isolating a fault on the LV side must be provided so as to prevent back feed for a fault on the protected lines [4]. It is assumed that the current differential protection system monitors the currents only in the main substations. Currents at the taps, either transformers or lines, are not available to the relays.

3. Scenario and operation concept

Following a fault on any component in a station, the faulted component will be isolated through automatic switching operation before being repaired. Some healthy components also may be taken out of service during the automatic switching period. The maximum possible number of healthy components will be restored to service during the manual switching period. The number of station outlets during the automatic and manual switching periods could be compounded for stations with MOABs. The automatic and manual switching states are combined into a single state labelled as fault. The outlets not in service at the beginning of the manual switching state are considered to be out for the total duration of the faulty state because the automatic switching state duration is very short as compared with the manual switching state duration. This approach is adequate for stations without MOABs. For station with MOABs a need exists to split the faulty state into two, to properly capture the effects of MOAB operation on station outlet outage [5].

  4. Problems of using of MOAB at transformer tap

The use of so many circuit breakers is usually not justified, particularly at the higher voltages [3,4]. In order to clear the fault in the transformer zone of protection the remote line breakers must be tripped and the transformer MOAB opened. The remote CBs can re-close, re-energizing the line. The relays at the remote terminal must be set to see into, but not beyond the transformers to avoid tripping sample system with line and tapped transformer. the high side breakers for low side faults. This creates a problem in setting the remote relays since they may not operate for high impedance faults within the transformer zone of protection. A common method of tripping the remote terminals is to provide a single-phase ground switch at the transformer. This is a spring-operated switch that puts a solid line-to-ground fault within the transformer zone of protection which the remote line relays will see and operate, opening their respective CBs.

Coordination between the MOABs and circuit breakers tripping time is very complicated. The conventional system uses a differential protection scheme and the single-phase ground switch for operating the MOABs in addition to a number of sequence operations for energizing and de-energizing the CBs at the terminals.

 5. Function concept of the technique

Using conventional individual relays at the tap point does not give precise information regarding the fault point. Also, longer operating time is taken by the conventional protection scheme in addition to the number of multi-shot re-closing relays applied to the CBs. Fault at the tapped point and high impedance fault are a sever problem for this system. For this reason, a LASP system is installed. To perform LASP system current data must be taken from all the points at the tapped point, bus bar and transformer through the protected area. The data is transmitted by integrated equipment (IE) to relay equipment (RE). This protection scheme has to be installed for every terminal tapped point on the transmission line. Trip or block decision for remote terminals is issued from the host computer based on data sharing among relays using Asynchronous Transfer Mode (ATM) functionality. The IEs have the access to lock out the MOAB switches and trip the associated breakers after data sharing and exchanging the information.

6. System performance

 Fault occurring at the tapped point causes a severe problem for conventional system. This area is considered as a dead zone for MOAB’s operation. The MOABs at the tapped point associated with CBs at the remote terminals are working continually until they are damaged. The LASP system can distinguish successfully such type of faults based on current summing at the tapped point and also on the voltage monitoring at the same point. This will cause locking out decision for the switches. Moreover, the data sharing and information collected everywhere assist the LASP system to issue a proper and selective decision. A high impedance fault is characterized by having impedance sufficiently high such that it is not detected by conventional protection [6]. One of the protection elements involved in LASP system uses the current differential relaying as a basic application of Kirchhoff’s current law. The relay operates on the sum of the currents flowing in CT secondaries from switching points. Using LASP system for data sharing and information exchange can recognize such problems easily.

7. LASP system configuration

The relays communicate among themselves and with the HR as well. The LASP system has peer to peer resource sharing. This is the true meaning of full connectivity. It yields one of the major benefits that is sharing data and exchanging information among the RE and HR. The LASP system consists of many components including both hardware and software. The scheme contains full protection system consisting of data communication system, LASP and local protection, control and supervision.

In the LASP system, the access device is known as ATM. The ATM provides communication and information transfer between protection equipments and LASP system. For a model LASP system of a transformer, two section lines and a bus bar, the ATM network transmits up to 2.488 Mbps of data for a sampling frequency up to 5.760 Hz or higher [7,8]. The ATM is a broad band cell relay technology that can transmit data. It works by breaking data into cells, which are packets of a fixed length. ATM uses cells that are 53 bytes in size. These cells include 48 bytes of application data, and 5 bytes control information in a header. The ATM devices offer transmission speeds up to about 155 Mbps for practical LASP system. Connection information for a cell is encoded in the virtual path identifier (VPI) and virtual channel identifier (VCI) field. As cells are forward from switch to switch, the VPI and VCI filed are updated. The 48 bytes Payload includes the address, current, voltage, status, etc information. However, connection concentrators aggregate multiple links in a common device. This enables the LASP system to be extended, both locally and across geographic distances.

The software components required in a LASP system include.

. Protocols that define and regulate the way two or more devices communicate.

. Hardware-level software that guide the functionality of individual devices, such as NIC.

. Communication software.

8. Conclusions

Since EHV breakers are expensive they are often omitted in station design such as this. As with the tapped transformer, the transformer is tied directly to the EHV bus through MOAB. To cope with difficulty and problem areas of conventional protection and control system, LASP system allows many relays to communicate with each other and with the HR. The LASP system can perform better than conventional system with respect to operation time, section selectivity, and reliability. The LASP system introduces