一种改进的备自投逻辑

以110 kV及以下变电所常见的分段备自投和进线备自投为例,结合现场工程实际,分析了许继公司分段备投装置WBT-821A的备自投动作逻辑缺陷,分别从软件设计和屏柜设计方面提出了改进方法;详细分析了四方公司的进线备投装置CSC-246的特殊闭锁问题,指出了使用中应注意的问题.     

一种改进的备自投逻辑

以110 kV及以下电压等级变电所常见的分段备用电源自投装置和进线备用电源自投装置为例,结合现场工程实际,剖析了某公司分段备投装置WBT-821A的备自投装置动作逻辑缺陷,即：其“加速备投”开入如果使用不当可能造成备投误动或者无故延长负荷停电时间。为此,分别从软件设计上提出增设控制字和从屏柜设计方面提出备投开入采用“TWJ”的改进方法,另外,详细分析了某公司的进线备投装置CSC-246 的特殊闭锁问题,指出了在实际工程实践中应注意的问题,对工程实践具有重要指导意义。     

两种备自投装置的逻辑分析与改进

以110kV及以下变电所常见的分段备自投逻辑和进线备自投逻辑为例,结合现场工程实际,分析了许继公司的分段备自投装置WBT-821A的备自投动作逻辑缺陷,分别从软件设计方面和屏柜设计方面提出了改进方法,详细分析了四方公司的进线备投装置CSC-246在主变动作后的特殊逻辑闭锁问题,指出了在使用中应注意的问题。     

备自投逻辑方案的分析与改进

备自投装置是供配电环节中重要的二次设备。对一起备自投误动事故进行了分析,找出了备自投充放电和闭锁备自投逻辑的纰漏。并提出了三种解决方案。最终用最优方案更改了二次接线。完善了备自投逻辑,提高了电力系统供电的可靠性。     

一起“备自投”误动事故的分析和对策

通过一起备用电源自投装置误动事故原因的分析,介绍了＂备自投＂装置的动作逻辑,提出防范措施,供电网继保运行人员参考。     

110kV备自投装置误动原因分析

分析某110kV变电站备自投装置误动原因,指出这是由于自投装置没有判断出110kV母线无压是因二次空开跳闸引起的,且装置本身采样精度低.并提出优化备自投逻辑、提变装置采样精度的解决方案.     

一种防止母联备自投动作造成过负荷的闭锁逻辑

为避免高峰负荷时母联备自投动作可能造成变压器严重过载,提出一种计算变压器各侧开关电流之和的闭锁逻辑:开关电流之和大于备用变压器额定电流一定倍数时,对备自投装置实施闭锁。分析了此闭锁逻辑在110kV变电站不同变压器容量配置,不同一次接线方式等情况下的实际运用,针对CT变比不同的情况,提出了将采集电流在备自投逻辑中折算为一次电流进行相加或者引入CT变比调整系数两种解决方案,并对闭锁电流值的整定给出建议值。此闭锁逻辑对负荷进行了定量处理,且易于在各厂家、各型号备自投装置中实现,具有一定的实用价值。     

对微机型备自投装置动作逻辑的改进

微机型备自投装置实际使用时,经常发生装置原有的动作逻辑不能满足现场需要,必须根据运行需要专门开发动作逻辑的情况,而且装置的自适应功能普遍有待于进一步完善。这些情况,增加了设备运行、检修、管理的负担,也为电网运行造成了一定的安全隐患。通过对各种主接线形式下的备自投装置动作特点进行分析,提出了与接线形式和运行方式无关的动作流程,并以此为基础,改进了装置的动作逻辑。经现场测试,改进后的动作逻辑简单可靠,能够满足各种不同接线方式的运行要求,具有较强的自适应功能。     

一次备自投装置误动原因分析及防范措施

电源备自投装置做为提高供电可靠性的保证措施,由于第一代微机保护装置程序不完善,闭锁逻辑不完善,导致在变电站检修中备自投装置误动。分析了备自投装置动作逻辑,误动原因,并对该备投装置现场进行实际试验,确定该备投装置存在程序缺陷,针对该类型缺陷提出了防范该类型微机备投装置误动的措施。     

备自投装置充放电逻辑分析

充放电逻辑对备自投的正确动作具有十分重要的意义,它关系着电网能否安全有效地运行。结合实际经验,对充放电逻辑在进线备自投中的作用以及运行人员、设计人员、定值整定人员、保护人员在实际运用中应注意的问题做一个分析与总结。     

An improved charge-sharing elimination pseudo-domino logic

In low-power digital circuit, the deviation of node voltage from nominal value due to charge-sharing leads to erroneous output. This problem is more prominent in domino logic when the device is scaled down. The scaling of the device involves scaling of threshold voltage, resulting in high leakage, less robustness and degradation in noise margin. The paper proposes an improved domino approach in terms of reduced leakage, low power dissipation and better noise margin. The stacking effect and pseudo buffer are used in precharge phase to control the gate-to-source voltage of pull-down network for less power consumption and increase in performance in terms of speed of operation. A modified keeper is introduced to reduce the charge-sharing problem. The proposed domino approach is tested against area overhead, ageing and process, voltage and temperature variation. The circuit is simulated using Cadence Virtuoso Spectre for 90 nm technology. The results obtained from the simulation represent the usefulness of the proposed circuit in terms of power dissipation, stability due to temperature variation, leakage due to temperature variation and delay. The result also shows that the circuit is less prone to charge redistribution problem that exist in domino circuit.     

一种改进的纵联零序方向保护方案

相较于单回线,同塔双回和多回输电线路发生故障时零序特征更为复杂多变,导致传统的纵联零序方向保护误动或拒动频发。首先从灵敏度、弱电强磁和跨线故障三个方面分析了传统纵联零序方向保护的性能,指出其中存在的问题。然后,提出了一套新型的纵联零序方向保护方案:通过零序方向电压补偿算法提升零序方向元件在高阻故障下的灵敏度,通过零序综合方向元件消除零序互感的影响,构造了跨线故障识别逻辑。最后,通过三个现场实例分析,验证了该算法的有效性。     

An improved full-bridge zero-voltage switching PWM converter usinga two-inductor rectifier

An improved full-bridge ZVS PWM power convertor using a two-inductor rectifier DC/DC power converter is presented in this paper. For this improved topology, the main devices are switched under zero-voltage (ZVS) conditions using the energy stored in the secondary filter inductors. In addition, it utilizes the low leakage inductance of a coaxial winding transformer to reset the currents in the rectifier diodes and eliminate the secondary voltage spike. The two-inductor rectifier has only one diode conduction drop in addition to frequency doubling in the output capacitor. The secondary filter size in the proposed topology is rather small. The advantages of the new topology include a wide load range with ZVS, no lost duty cycle due to diode recovery, no secondary voltage spikes, in addition to high power density and high efficiency     

一种改进型馈线自愈控制方案及实现

对主干线的分布式和集中型自愈控制方案,分别介绍了其处理逻辑流程,总结了各自的优点、缺点。针对主干线分布式和集中型自愈控制方案的优缺点,考虑IEC61850在自愈控制方案中的应用,提出了一种改进型自愈控制方案。该方案对于故障诊断、定位和隔离采用和分布式自愈控制相同的逻辑流程,对存在多恢复方案的故障下游失电负荷的供电恢复采用执行故障处理预案的方式。故障处理预案在主站事先定义好,并通过IEC61850通信规约下发到相应的智能配网终端,由智能配网终端在故障恢复时判断当前电网状态后执行相应的故障处理预案,实现故障下游负荷的供电恢复。该改进型自愈控制方案集中了分布式和集中型自愈控制方案的优点,同时避免了其缺点和不足之处。理论分析和工程应用表明,提出的改进型自愈控制方案具有较强的工程实用性。     

An adaptive switching scheme for uncertain discrete time‐delay systems

In this paper, an adaptive switching control algorithm is proposed for the stabilization of uncertain discrete‐time systems with time‐varying delay. It is assumed that the time delay is unknown and time varying, nonetheless bounded with a known bound. It is supposed that the system is highly uncertain, and that a set of controllers are designed (off‐line) to stabilize the system in the whole uncertain parameter space; subsequently, a switching scheme is developed to stabilize the uncertain time‐delay system. A thorough stability analysis for the uncertain time‐delay system under the mentioned control scheme is provided. Furthermore, an upper bound on the allowable rate of change of the system parameters and delay is obtained. Simulation results are presented to show the efficacy of the proposed switching scheme. Copyright © 2008 John Wiley & Sons, Ltd.     

An improved control scheme based in droop characteristic for microgrid converters

In the present work, an improved version of the conventional-droop control for microgrid converter is presented. The modifications added to the control are based on a feed-forward current control that allows the converter to work in several modes, both when it is grid connected or in island. The use of this control represents the main contribution of this paper, permitting the inverter to work as a grid supporting source or ancillary services provider when it works grid connected. In this mode the converter varies the injected active and reactive power with the variation of voltage module and frequency using the same main control loop as when it is working in island mode.     

An improved control scheme for a series-capacitive reactancecompensator based on a voltage-source inverter

Power utilities have traditionally used series capacitors to increase the power transfer capability of transmission lines, but their widespread use has been limited by concerns for the harmful effects of series resonances. An advanced, controllable series VAr compensator has the potential to avoid such problems and, therefore, allow more efficient use of existing transmission plant. This paper describes a modified control scheme for an advanced series VAr compensator based on a single voltage source inverter. Practical results from a working prototype demonstrate the ability of the compensator to provide a rapidly controllable magnitude of compensation     

Fuzzy logic switching of thyristor controlled braking resistorconsidering coordination with SVC

This paper presents a new switching control scheme for braking resistors (BR) using fuzzy logic to enhance overall stability of electric power systems. In addition, the coordination with an SVC is also considered to achieve a wider stable region. The braking resistor is set on one of the generator busbars, where the real power output from the generator is measured to determine the firing-angle of the thyristor switch. The switching control scheme is simple so as not to require heavy computation on the microcomputer based switching controller. An SVC is set on one of the busbars in the system. The switching of the SVC uses a similar fuzzy logic control scheme to the one for the BR. Simulation results show the effectiveness of the proposed fuzzy logic switching control scheme     

一种适用于光伏场站送出线的自适应距离保护改进方案

由于光伏场站的弱馈性,当送出线路发生经过渡电阻短路时,传统距离保护可能无法正确动作。而自适应距离保护方案在一定程度上解决了区内故障保护拒动的问题,但存在区外故障误动的可能。首先分析了区外故障时自适应距离保护误动的原因,进而提出了一种自适应距离保护的改进方案。在现有自适应距离保护的动作特性基础上,引入线路的短路阻抗,根据区内、外故障下线路短路阻抗的大小差异,构成保护的辅助判据,以甄别可能引起现有自适应距离保护误判的区外故障。该方法仅依靠光伏侧电气量近似求取线路短路阻抗值,与现有自适应距离保护相互配合实现区内、外故障正确判别。最后通过PSCAD仿真验证了改进方案的有效性。