A mixed‐mode KHN‐biquad using DVCC and grounded passive elements suitable for direct cascading

In this paper a mixed‐mode (input and output signals can be current or voltage) Kerwin–Huelsman–Newcomb (KHN) biquad with low/high input impedance and high/low output impedance depending on the type of the corresponding signal (current/voltage) is presented. The circuit is constructed using three differential voltage current conveyors (DVCCs), two grounded capacitors and three grounded resistors. The circuit simultaneously provides bandpass (BP), highpass (HP) and lowpass (LP) responses when the output is current and notch, BP and LP responses when the output is voltage. The notch and allpass responses can be obtained by connecting appropriate output currents directly without using additional active elements. Because of the low input and high output impedance of the circuit for current signals and the high input and low output impedance for voltage signals, it can be used in cascade for realizing higher‐order filters. SPICE simulation results are given to verify the theoretical analysis. Copyright © 2008 John Wiley & Sons, Ltd.     

A simple derivation of the spectral transformations for IIR filters

A simple method is given for deriving the spectral transformations for infinite-impulse response (IIR) filters, which can be used to transform a prototype low-pass (LP) digital filter to another LP, high-pass (HP), bandpass (BP), or band-stop (BS) digital filter with prescribed passband edge(s) and the same tolerances as those of the prototype. The method is based on a combination of bilinear transformation with the analog frequency transformation and is simpler-conceptually, as well as from the calculation point of view-than the conventional method based on all-pass transformation functions.     

小波分析在大型同步发电机微机继电保护中的应用研究

构造了基于小波变换的高通和带通宵虑皮器并应用于发电机定子不对称故障保护和相接地保护。基于ＥＭＴＰ和动模录波数据的仿真结果,表明小波变换方法可以有效地改善保护的灵敏性、选择性和速动性。     

Low‐power,low‐noise,active‐RC band‐pass filters using a ‘lossy’ LP–BP transformation

A new and straightforward design procedure for simple canonical topologies of allpole, active‐RC, low‐selectivity band‐pass (BP) filters, with low sensitivity to component tolerances is presented. The procedure is primarily intended for discrete‐component, low‐power filter applications using just one amplifier for relatively high‐order filters. The design procedure starts out with an ‘optimized’ low‐pass (LP) prototype filter, yielding an ‘optimized’ BP filter, whereby the wealth of ‘optimized’ single‐amplifier LP filter designs can be exploited. Using a so‐called ‘lossy’ LP–BP transformation, closed‐form design equations for the design of second‐ to eighth‐order, single‐amplifier BP filters are presented. The low sensitivity, low power consumption, and low noise features of the resulting circuits, as well as the influence of the finite gain‐bandwidth product and component spread, are demonstrated for the case of a fourth‐order filter example. The optimized single‐opamp fourth‐order filter is compared with other designs, such as the cascade of optimized Biquads. Using PSpice with a TL081 opamp model, the filter performance is simulated and the results compared and verified with measurements of a discrete‐component breadboard filter using 1% resistors, 1% capacitors, and a TL081 opamp. Copyright © 2011 John Wiley & Sons, Ltd.     

A DC stabilized log‐domain nth‐order multifunction filter based on the decomposition of nth‐order HP filter function to FLF topology

The design of high‐order log‐domain filters can be easily accomplished by transposing already known linear‐domain G_m‐C filter topologies to their counterparts in the log‐domain through the employment of a set of complementary operators. To achieve the G_m‐C filter topologies, the multiple feedback approach is widely used due to its accrued advantages. In this paper a synthesis approach for the development of an nth‐order multifunction log‐domain filter comprising lowpass (LP), highpass (HP) and bandpass (BP) filter functions is proposed. The approach is based on the decomposition of nth‐order HP filter function to follow‐the‐leader‐feedback (FLF) topology. The design is simple and simultaneously achieves nearly all of the chief advantages. The design offers superior performance factors vis‐à‐vis the ones recently reported. To verify the high‐order behavior of the topology, a 5th‐order multifunction filter was designed and the achieved simulated results verify the theory. Copyright © 2008 John Wiley & Sons, Ltd.     

350 MW汽轮机高旁保护导致推力瓦损坏的原因分析

针对某电厂350 MW汽轮机推力瓦在高压旁路保护动作后损坏事故,根据机组运行参数与操作记录,从运行操作、轴向推力产生原理、自动调节失控原因、高低旁保护逻辑合理性等方面进行了详细推理和分析,找出了推力瓦损坏的原因,是高旁保护动作后低旁不动作使中压缸做功大幅增加而产生的不平衡轴向推力增加。根据分析结果,采取了相应防范措施,避免了本机组再次出现此类事故。所作分析和措施对其他机组也具有一定的借鉴意义。     

超临界汽轮机高中压缸联合启动

针对超临界汽轮机高中压缸联合启动过程中出现的问题,介绍了其联合启动过程和高低压旁路的控制方式,分析了高中压调节汽门的开度匹配、热态启动下再热蒸汽压力、高排通风阀与逆止阀的开关和旁路的投入与切除对机组运行的影响,并给出了相应的解决措施。     

1000MW汽轮机缸效率能耗敏度分析

以东汽1 000 MW汽轮机为研究对象,采用汽轮机组定功率变工况计算方法,对汽轮机各汽缸效率在THA、70%THA、50%THA、40%THA滑压工况进行敏度分析,得到相应工况下各汽缸效率变化对汽轮机热耗率和机组发、供电煤耗率的影响规律。分析表明,缸效率的能耗敏度随缸效率变化基本呈线性关系;低压缸效率的能耗敏度最大,高压缸效率次之,中压缸效率较小;随机组负荷降低,高压缸效率的能耗敏度增加,中、低压缸效率的能耗敏度变化较小。在THA工况下低压缸效率下降1%,供电煤耗敏度绝对值增加1.246g/(kW h),相对值升高0.433%;高压缸效率下降1%,供电煤耗敏度的绝对值增加0.44g/(kW h),相对值升高0.154%;中压缸效率下降1%,供电煤耗敏度的绝对值增加0.352g/(kW h),相对值升高0.122%。分析结果可对同类型机组进行节能诊断,进而指导机组的优化运行。     

大容量汽轮机双压凝汽器抽空气系统连接方式分析

分析了汽轮机双压凝汽器抽空气系统连接方式,由于高压侧和低压侧存在压力差,高压侧和低压侧抽空气系统的连接方式需引起高度重视,以发挥双压凝汽器的技术优势.从设备投资、经济效益、运行调整等方面,分析了3种凝汽器抽空气系统连接方式的特点,并且提出了凝汽器抽空气系统连接最佳方式,为设备制造和设计部门及运行机组提供参考和借鉴.     

超临界600MW机组双背压凝汽器抽空气管路的改进

某电厂超临界600MW机组基建投产以来,高、低压凝汽器压差一直较小,分析判断认为其根源是凝汽器抽空气管路设计配置不合理,导致低压凝汽器空气抽出受阻,从而出现传热恶化的现象。通过调整节流孔板孔径等措施,恢复了凝汽器的双背压设计功能,提高了机组运行效率。     

某电厂汽机DEH控制系统故障原因的探讨

某电厂150MW机组调试启动过程中,汽机DEH系统多次出现故障,表现为:抗燃油系统压力频繁波动,高、中压调门上下摆动,高压主汽门和低压调门有时也摆动,机组负荷出现大幅度晃动现象,严重时导致机组跳闸或甩负荷;低压调门还常发生卡涩,单阀切顺序阀运行时负荷出现波动。结合现场处理情况,对故障原因展开理论分析。     

汽轮机汽封改造的节能效果分析

介绍通流部分综合升级改造的330 MW汽轮机汽封改造方案,分析所采用蜂窝汽封、刷式汽封、接触式汽封等新型汽封的工作原理、优点和在汽轮机轴系、通流部分中适用的部位。刷式汽封在汽轮机上的应用比较广泛,高、中、低压缸各部位均适合;接触式汽封主要应用于轴端密封;蜂窝汽封用在低压缸末级、次末级叶顶部位及高、中压缸轴端。330 MW汽轮机高、中、低压缸轴端采用3种汽封相结合的方案改造后,轴封漏汽量明显减小。汽轮机高、中压后轴封漏汽量、经过轴加的凝水温升都有明显的降低;高、中压缸间平衡盘汽封漏汽量占主蒸汽流量的份额为1.02%,小于THA工况设计数据1.503%,汽封改造的节能效果显著。     

1000MW汽轮机轴承振动大的原因分析及处理

潮州发电公司1 000 MW汽轮机自投产以来,轴承振幅一直超标,对机组的安全经济运行造成严重威胁;主要体现在两方面:一是启机过程中高中压缸轴承振动偏大,二是低负荷工况下低压缸轴承振幅与真空度成正比变化。其原因是启动过程中高中压缸膨胀不畅、低压缸柔性设计,汽轮机动静碰磨造成的。利用机组大修机会,拆出高压下缸,用大梁抬起中压下缸调端,对轴承箱重新研磨台板接触面、更换滑块及滑销、制作注油通道以及重新调整汽缸猫爪负荷分配;同时对低压外缸的变形量进行有限元分析,加固低压外缸并改造低压汽封,汽轮机轴承振动大的问题已得到成功解决。     

汽轮机中间分隔轴封漏汽对热耗率影响的分析与计算

利用小偏差理论,分析了汽轮机定主蒸汽流量时,中间分隔轴封漏汽量变化对汽轮机各缸做功量、过再热吸热量以及热耗率的影响。结果表明,当中间分隔轴封漏汽量变化时,汽轮机高压缸做功量与再热吸热量变化较大,中低压缸做功量变化较小。同时,对某台超临界660 MW机组进行了变工况计算。结果显示,当中间分隔轴封漏汽量增加时,汽轮机各段做功量、再热吸热量及热耗率近似线性变化,各部分的变化情况与理论分析结果一致,漏汽主要是通过影响高压缸做功和再热吸热量来改变热耗率,但由于低压缸做功量占汽轮机总功量的比例较大,其变化对热耗率的影响也不可忽视。     

莱芜发电厂 125 MW 机组运行经济性分析

依据２号机修前考核试验结果以及１号、２号、３号机历史试验数据,对三台机组的热耗、高、中、低压缸效率进行了定性和定量的分析,找出了三台机组热耗较高、高、低压缸效率低、中压缸效率高于设计值的原因。     

妈湾电厂2号汽轮机热力系统综合改造

通过分析妈湾电厂2号汽轮机达不到设计出力、热耗高存在的问题，主要对汽轮机疏水系统和给水加热系统进行了优化，减少了工质泄漏，提高回热效率，改善凝汽器真空，从而提高汽轮机高中低压缸的效率。     

华能汕头发电厂1号机组振动故障的分析及处理

华能汕头发电厂１号蒸汽轮机组在大修后启动及运行过程中发生了大轴振动大的故障。通过剖析机组的结构,分析引起振动的各种影响因素,得出：低压缸排汽温度高是引起启动过程振动大的直接原因,冷凝器循环水入口压力大是引起运行过程振动大的原因。提出的故障处理方法是：以稍开低压旁路及给低压旁路喷水,并启动第２台主抽汽器来解决启动过程出现的振动故障;采取调节冷凝器海水回水阀,使入口两侧压力小于或等于０．１０ＭＰａ来解     

超超临界汽轮机固粒侵蚀和汽流激振分析

超超临界汽轮机的开发设计有很多特殊要求,需解决许多技术问题,其中通流部件的防固粒侵蚀、防止高压转子汽流激振、汽轮机选材问题、转子冷却结构问题、低压进汽容积流量小问题,是关系到超超临界汽轮机组能否安全、稳定、经济运行的关键,为此,重点探讨如何防止通流部件的固粒侵蚀(SPE)和高压转子汽流激振问题。     

新一代高效电站加热器

本文针对电站加热器采用碳钢传热管材和光管的传热管形，使用寿命短，传热效率低；与主机使用寿命长和热效率不断提高的发展不相匹配和不相适应的现实，通过借鉴国外经验，提出了采用不锈钢的传热管材，且又为降低成本对不同的加热器采用不同品种的不锈钢管材的有缝焊接管，其使用寿命达到与主机的寿命３０年左右相当。在传热管的管形方面提出了采用波纹管，对电站的各种汽、水型的加热器，其传热效果可提高一倍以上。依据这个技术理论，开发了电站的新一代高效加热器，包括高、低压的给水加热器，热网加热器等间壁式的加热器和混合式的膜式除氧加热器     

Design of IIR linear‐phase nonuniform‐division filter banks with signed powers‐of‐two coefficients

This paper deals with the minimax design of two‐channel linear‐phase (LP) nonuniform‐division filter (NDF) banks using infinite impulse response (IIR) digital all‐pass filters (DAFs) with signed powers‐of‐two (SPT) coefficients. Based on the theory of two‐channel NDF banks using two IIR DAFs, the design problem is appropriately formulated to result in an appropriate Chebyshev approximation for the desired phase responses of the IIR DAFs. Through a frequency sampling and iterative approximation method, the optimization problem for finding the SPT coefficients for the IIR DAFs can be solved by utilizing a weighted least‐squares approach in conjunction with a coordinate rotational digital computer (CORDIC) algorithm. The resulting two‐channel SPT coefficient NDF banks can possess approximately LP response without magnitude distortion. Several simulation examples are presented for illustration and comparison. Copyright © 2008 John Wiley & Sons, Ltd.