电气工程专业英文论文

电气工程专业英文论文

用于分布式在线UPS中的并联逆变器的一种无线控制器
A Wireless Controller for Parallel Inverters in Distributed Online UPS Systems
Josep M. Guerrero', Luis Garcia de Vicufia", Jose Matas'*, Jaume Miret", and Miguel Castilla"
. Departament #Enginyeria de Sistemes, Automatica i Informhtica Industrial. Universitat Polithica de Catalunya
C. Comte d'Urgell, 187.08036 -Barcelona. Spain. Email: .. Departament #Enginyeria Electrbnica. Universitat Polit6cnica de Catalunya
AV. Victor BaLguer s/n. 08800I - Vilanova i la Geltrh. Spain
Absiract - In this paper, a novel controller for parallelconnected
online-UPS inverters without control wire
interconnections is presented. The wireless control technique is
based on the well-known droop method, which consists in
introducing P-oand Q-V schemes into the inverters, in order to
share properly the power drawn to the loads. The droop method
has been widely used in applications of load sharing between
different parallel-connected inverters. However, this method
has several drawbacks that limited its application, such as a
trade-off between output-voltage regulation and power sharing
accuracy, slow transient response, and frequency and phase
deviation. This last disadvantage makes impracticable the
method in online-UPS systems, since in this case every module
must be in phase with the utility ac mains. To overcome these
limitations, we propose a novel control scheme, endowing to the
paralleled-UPS system a proper transient response, strictly
frequency and phase synchronization with the ac mains, and
excellent power sharing. Simulation and experimental results
are reported confirming the validity of the proposed approach.
1. INTRODUCTION
The parallel operation of distributed Uninterruptible Power
Supplies (UPS) is presented as a suitable solution to supply
critical and sensitive loads, when high reliability and power
availability are required. In the last years, many control
schemes for parallel-connected inverters has been raised,
which are derived from parallel-schemes of dc-dc converters
[I], such as the master-slave control [2], or the democratic
control [3]. In contrast, novel control schemes have been
appeared recently, such as the chain-structure control [4], or
the distributed control [ 5 ] . However, all these schemes need
control interconnections between modules and, hence, the
reliability of the system is reduced since they can be a source
of noise and failures. Moreover, these communication wires
limited the physical situation ofthe modules [6].
In this sense, several control techniques has been proposed
without control interconnections, such as the droop method.
In this method, the control loop achieves good power sharing
making tight adjustments over the output voltage frequency
and amplitude of the inverter, with the objective to
compensate the active and reactive power unbalances [7].
This concept is derived from the power system theory, in
which the frequency of a generator drops when the power
drawn to the utility line increases [8].
0-7803-7906-3/03/$17.00 02003 IEEE. 1637
However, this control approach has an inherent trade-off
between voltage regulation and power sharing. In addition,
this method exhibits slow dynamic-response, since it requires
low-pass filters to calculate the average value of the active
and reactive power. Hence, the stability and the dynamics of
the whole system are hardly influenced by the characteristics
of these filters and by the value of the droop coefficients,
which are bounded by the maximum allowed deviations of
the output voltage amplitude and frequency.
Besides, when active power increases, the droop
characteristic causes a frequency deviation from the nominal
value and, consequently, it results in a variable phase
difference between the mains and the inverter output voltage.
This fact can be a problem when the bypass switch must
connect the utility line directly to the critical bus in stead of
its phase difference. In [9], two possibilities are presented in
order to achieve phase synchronization for parallel lineinteractive
UPS systems. The first one is to locate a particular
module near the bypass switch, which must to synchronize
the output voltage to the mains while supporting overload
condition before switch on. The second possibility is to wait
for the instant when phase matching is produced to connect
the bypass.
However, the mentioned two folds cannot be applied to a
parallel online-UPS system, since maximum transfer time
ought to be less than a % of line period, and all the modules
must be always synchronized with the mains when it is
present. Hence, the modules should be prepared to transfer
directly the energy from the mains to the critical bus in case
of overload or failure [lo].
In our previous works [11][12], we proposed different
control schemes to overcome several limitations of the
conventional droop method. However, these controllers by
themselves are inappropriate to apply to a parallel online-
UPS system. In this paper, a novel wireless control scheme is
proposed to parallel different online UPS modules with high
performance and restricted requirements. The controller
provides: 1) proper transient response; 2) power sharing
accuracy; 3) stable frequency operation; and 4) good phase
matching between the output-voltage and the utility line.
Thus, this new approach is especially suitable for paralleled-
UPS systems with true redundancy, high reliability and
power availability. Simulation and experimental results are
reported, confirming the validity of this control scheme.
Fig. 1. Equivalenl cimuif ofan invener connecled 10 a bus
t"
Fig. 2. P-odraop function.
11. REVlEW OF THE CONVENTIONAL DROOP METHOD
Fig. 1 shows the equivalent circuit of an inverter connected
to a common bus through coupled impedance. When this
impedance is inductive, the active and reactive powers drawn
to the load can be expressed as
EVcosQ - V2 Q=
where Xis the output reactance of an inverter; Q is the phase
angle between the output voltage of the inverter and the
voltage of the common bus; E and V are the amplitude of the
output voltage of the inverter and the bus voltage,
respectively.
From the above equations it can be derived that the active
power P is predominately dependent on the power angle Q,
while the reactive power Q mostly depends on the outputvoltage
amplitude. Consequently, most of wireless-control of
paralleled-inverters uses the conventional droop method,
which introduces the following droops in the amplitude E
and the frequency U of the inverter output voltage
u = w -mP (3)
E = E ' - n Q , (4)
being W* and E' the output voltage frequency and amplitude
at no load, respectively; m and n are the droop coefficients
for the frequency and amplitude, respectively.
Furthermore, a coupled inductance is needed between the
inverter output and the critical bus that fixes the output
impedance, in order to ensure a proper power flow. However,
it is bulky and increase:; the size and the cost of the UPS
modules. In addition, tho output voltage is highly distorted
when supplying nonlinezr loads since the output impedance
is a pure inductance.
It is well known that if droop coefficients are increased,
then good power sharing is achieved at the expense of
degrading the voltage regulation (see Fig. 2).
The inherent trade-off of this scheme restricts the
mentioned coefficients, which can be a serious limitation in
terms of transient response, power sharing accuracy, and
system stability.
On the other hand, lo carry out the droop functions,
expressed by (3) and (4), it is necessary to calculate the
average value over one line-cycle of the output active and
reactive instantaneous power. This can be implemented by
means of low pass filters with a smaller bandwidth than that
of the closed-loop inverter. Consequently, the power
calculation filters and droop coefficients determine, to a large
extent, the dynamics and the stability of the paralleledinverter
system [ 131.
In conclusion, the droop method has several intrinsic
problems to be applied 1.0 a wireless paralleled-system of
online UPS, which can he summed-up as follows:
Static trade-off between the output-voltage regulation
(frequency and amplitude) and the power-sharing
accuracy (active an4d reactive).
2) Limited transient response. The system dynamics
depends on the power-calculation filter characteristics,
the droop coefficients, and the output impedances.
Lost of ac mains synchronization. The frequency and
phase deviations, due to the frequency droop, make
impracticable this method to a parallel-connected
online UPS system, in which every UPS should be
continuously synchronized to the public ac supply.
1)
3)
111. PROPOSED CONTROL FOR PARALLEL ONLINE UPS
INVERTERS
In this work, we will try to overcome the above limitations
and to synthesize a novel control strategy without
communication wires that could be appropriate to highperformance
paralleled industrial UPS. The objective is to
connect online UPS inverters in parallel without using
control interconnections. This kind of systems, also named
inverter-preferred, should be continuously synchronized to
the utility line. When an overload or an inverter failure
occurs, a static bypass switch may connect the input line to
the load, bypassing the inve:rter [14][15].
Fig. 3 shows the general diagram of a distributed online
UPS system. This system consists of two buses: the utility
bus, which is connected lo the public ac mains; and the
secure bus, connected to the distributed critical loads. The
interface between these buses is based on a number of online
UPS modules connected in parallel, which provides
continuously power to the: loads [16]. The UPS modules
include a rectifier, a set of batteries, an inverter, and a static
bypass switch.
1
1638
Q ac mains
utility bus
I I I
j distributed loads !
Fig. 3. Online distributed UPS system.
syposr /
I 4
(4
Fig. 4. Operation modes of an online UPS.
(a) Normal operation. (b) Bypass operation. (c) Mains failure
The main operation modes of a distributed online UPS
1) Normal operation: The power flows to the load, from
the utility through the distributed UPS units.
2) Mains failure: When the public ac mains fails, the
UPS inverters supply the power to the loads, from the
batteries, without disruption.
Bypass operation: When an overload situation occurs,
the bypass switch must connect the critical bus
directly to the ac mains, in order to guarantee the
continuous supply of the loads, avoiding the damage
of the UPS modules.
For this reason, the output-voltage waveform should be
synchronized to the mains, when this last is present.
system are listed below (see Fig. 5):
3)
Nevertheless, as we state before, the conventional droop
method can not satisfy the need for synchronization with the
utility, due to the frequency variation of the inverters, which
provokes a phase deviation.
To obtain the required performance, we present a transient
P-w droop without frequency-deviation in steady-state,
proposed previously by OUT in [ 111
w=o -mP (5)
where is the active power signal without the dccomponent,
which is done by
. -
I t -1s
P= p ,
( s + t - ' ) ( s + o , )
being zthe time constant of the transient droop action.
The transient droop function ensures a stable frequency
regulation under steady-state conditions, and 'at the same
time, achieves active power balance by adjusting the
frequency of the modules during a load transient. Besides, to
adjust the phase of the modules we propose an additional
synchronizing loop, yielding
o=w'-m%k,A$, (7)
where A$ is the phase difference between the inverter and the
mains; and k, is the proportional constant of the frequency
adjust. The steady-state frequency reference w* can be
obtained by measuring the utility line frequency.
The second term of the previous equality trends to zero in
steady state, leading to
w = w' - k4($ -@'), (8)
being $and $* the phase angles of the output voltage inverter
and the utility mains, respectively.
Taking into account that w = d $ / d t , we can obtain the
next differential equation, which is stable fork, positive
d$ *
dt dt
- + km$ = - + k,$' . (9)
Thus, when phase difference increases, frequency will
decrease slightly and, hence, all :he UPS modules will be
synchronized with the utility, while sharing the power drawn
to the loads.
IV. CONTROLLIEMRP LEMENTATION
Fig. 5 depicts the block diagram of the proposed
controller. The average active power P , without the dc
component, can be obtained by means of multiplying the
output voltage by the output current, and filtering the product
........................................................................................
io
",.
L
Sj'nchronirorion loop
.......................................................................................
Fig. 5. Block diagram of the proposed controller.
using a band-pass filter. In a similar way, the average
reactive power is obtained, hut in this case the output-voltage
must be delayed 90 degrees, and using a low-pass filter.
In order to adjust the output voltage frequency, equation
(7) is implemented, which corresponds to the frequency
mains drooped by two transient-terms: the transient active
power signal term; and the phase difference term, which
is added in order to synchronize the output voltage with the
ac mains, in a phase-locked loop (PLL) fashion. The outputvoltage
amplitude is regulated by using the conventional
droop method (4).
Finally, the physical coupled inductance can be avoided by
using a virtual inductor [17]. This concept consists in
emulated an inductance behavior, by drooping the output
voltage proportionally to the time derivative of the output
current. However, when supplying nonlinear loads, the highorder
current-harmonics can increase too much the outputvoltage
THD. This can be easily solved by using a high-pass
filter instead of a pure-derivative term of the output current,
which is useful to share linear and nonlinear loads [I 1][12].
Furthermore, the proper design of this output inductance can
reduce, to a large extent, the unbalance line-impedance
impact over the power sharing accuracy.
v. SIMULATION AND EXPERIMENTARELS ULTS
The proposed control scheme, (4) and (7), was simulated
with the parameters listed in Table 1 and the scheme shown
in Fig. 6, for a two paralleled inverters system. The
coefficients m, n, T, and kv were chosen to ensure stability,
proper transient response and good phase matching. Fig. 7
shows the waveforms of the frequency, circulating currents,
phase difference between the modules and the utility line,
and the evolution of the active and reactive powers. Note the
excellent synchronization between the modules and the
ACmiiinr 4 j. ...L...I.P...S...1... ..........................B...u...n...r.r..r..e..s... ................................... i
Fig. 6. Parallel operation oftwa online UPS modules,
mains, and, at the same time, the good power sharing
obtained. This characteristik let us to apply the controller to
the online UPS paralleled systems.
Two I-kVA UPS modules were built and tested in order to
show the validity of the proposed approach. Each UPS
inverter consisted of a single-phase IGBT full-bridge with a
switching frequency of 20 kHz and an LC output filter, with
the following parameters: 1. = 1 mH, C = 20 WF, Vi" = 400V,
v, = 220 V, I50 Hz. The controllers of these inverters were
based on three loops: an inner current-loop, an outer PI
controller that ensures voltage regulation, and the loadsharing
controller, based on (4) and (7). The last controller
was implemented by means of a TMS320LF2407A, fixedpoint
40 MHz digital sigrial processor (DSP) from Texas
Instruments (see Fig. 8), using the parameters listed in Table
I. The DSP-controller also includes a PLL block in order to
synchronize the inverter with the common bus. When this
occurs, the static bypass switch is tumed on, and the droopbased
control is initiated.
1640
big 7 Wa\cfc)rms for r, ;mnectcd in parallel. rpchrontred io Ihc ac mdnl.
(a) Frequencics ufhoth UPS (b) Clrculattng currcni among modulcs. (CJ Phmc d!Nercn;: betucen ihc UPS a#>dth e ai mum
(d) Ikiril uf the phze diNmncc (e) md (0 Activc and rcactlw pouerr "I ooih UPS
Note that the iimc-acs arc deliheratcly JiNercni due in thc disiinct timuion*uni) ofthe \ inrblrr
1641
TABLEI.
PARAMETEROSF THE PARALLELESDYS TEM.
Filter Order I I
Filter Cut-off Frequency I 0, I 10 I rags
Fig. 8 shows the output-current transient response of the
UPS inverters. First, the two UPS are operating in parallel
without load. Notice that a small reactive current is circling
between the modules, due to the measurement mismatches.
Then, a nonlinear load, with a crest factor of 3, is connected
suddenly. This result shows the good dynamics and loadsharing
of the paralleled system when sharing a nonlinear
load.
Fig. 8. Output current for the two paralleled UPS, during the connection of B
common nonlinear load with a crest factor of 3. (Axis-x: 20 mddiv. Axis-y:
5 Mdiv.).
VI. CONCLUSIONS
In this paper, a novel load-sharing controller for parallelconnected
online UPS systems, was proposed. The controller
is based on the droop method, which avoids the use of
control interconnections. In a sharp contrast with the
conventional droop method, the controller presented is able
to keep the output-voltage frequency and phase strictly
synchronized with the utility ac mains, while maintaining
good load sharing for linear and nonlinear loads. This fact let
us to extend the droop method to paralleled online UPS.
On the other hand, the proposed controller emulates a
special kind of impedance, avoiding the use of a physical
coupled inductance. Th.e results reported here show the
effectiveness of the proposed approach.

帮忙翻译电气工程及自动化的英语论文，只有一小段

以下翻译杜绝机译，请放心采用。
In this winding system, we use Mitsubishi A series PLC as master station PLC because it has the characteristic of quick response and great ability of information processing. 在这一卷绕系统中，我们采用了三菱的A系列PLC（可编程控制器）作为主站控制器，因为它具有迅速响应的特性和巨大的信息处理能力。It is used to control the behaviors of the total winding system together with FX series PLCs of winding and unwinding system. 它被用来控制整个卷绕系统以及卷绕和退绕系统FX系列PLC的性状。The operating actions of the system and the sequence of these actions were edited beforehand into the control program by the designer. 系统的动作行为和这些动作的顺序被设计人员事先编辑进控制程序中。The control program sets a series of operations of the winding system, which tells the PLCs how to control a system. 此控制程序设定卷绕系统的一系列运作，他告诉PLC如何来控制系统。The current states of all sensors or actuators are saved as an array of input, output or flag signals in the PLC memory. 所有传感器或执行器的现行状态都被作为输入、输出或旗号信号的阵列，在PLC存储器保存下来。Therefore, the PLC program is the basis of monitoring in a PLC controlled manufacturing system.因此，PLC程序在一个由PLC控制的制造系统中是监控的基础。 The programming method used is the ladder diagram method. 所采用的编程方法是梯形图法。The PLC system provides a design environment in the form of software tools running on a host computer terminal which allows ladder diagrams to be developed, verified, tested, and diagnosed. PLC系统提供了一个软件工具形式的设计环境，这些软件工具在可以开发、验证、测试、并诊断梯形图的主机终端上运行。First, the high-level program is written in diagrams. 首先，在梯形图中写下高层次的程序。Then, the ladder diagram is converted into binary instruction codes so that they can be stored in random-access memory (RAM) or erasable programmable read-only memory (EPROM). 然后梯形图就被转换成二进制指令码，所以它们就可被储存在随机存取存储器（RAM）或可擦除可编程序只读存储器（EPROM）中。Each successive instruction is decoded and executed by the CPU. 每一个相继的指令由CPU（中央处理器）解码和执行。Thefimctionof the CPU is to control the operation of memory and I/O devices and to process data according to the program. CPU的功能是控制存储器和输入/输出器件的工作，并根据程序处理数据。Each input and output connection point on a PLC has an address used to identify the I/O bit. 在一个PLC上的每一个输入和输出连接点都有一个地址，用来识别该输入/输出位。The method for the direct representation of data associated with the inputs, outputs, and memory is based on the fact that the PLC memory is organized into three regions: input
image memory, output image memory, and internal memory[4]. 这种用于直接表示与输入、输出和存储器相关的数据的方法是基于以下事实，即PLC存储器被组织进了三个区域：输入图像存储器、输出图像存储器和内部存储器【4】

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　　1主题内容与适用范围

　　1.1本导则适用于电压等级在35~220kV的国产油浸电力变压器、6kV及以上厂用变压器和同类设备，如消弧线圈、调压变压器、静补装置变压器、并(串)联电抗器等。

　　对国并进口的油浸电力变压器及同类设备可参照本导则并按制造厂的规定执行。

　　1.2本导则适用于变压器标准项目大、小修和临时检修。不包括更换绕组和铁芯等非标准项目的检修。

　　1.3变压器及同类设备需贯彻以预防为主，计划检修和诊断检修相结合的方针，做到应修必修、修必修好、讲究实效。

　　1.4有载分接开关检修，按部颁DL/T574-95《有载分接开关运行维修导则》执行。

　　1.5各网、省局可根据本导则要求，结合本地区具体情况作补充规定。

　　2引用标准

　　GB1094.1~1094.5-85电力变压器

　　GB6451.1~6451.5-86油浸式电力变压器技术参数和要求

　　GB7251-87变压器油中溶解气体分析和判断导则

　　GBJ148-90电气装置安装工程电力变压器、油浸电抗器、互感器施工及验收规范

　　GB7665-87变压器油

　　DL/T572-95电力变压器运行规程

　　DL/T574-95有载分接开关运行维修导则

　　3检修周期及检修项目

　　3.1检修周期

　　3.1.1大修周期

　　3.1.1.1一般在投入运行后的5年内和以后每间隔10年大修一次。

　　3.1.1.2箱沿焊接的全密封变压器或制造厂另有规定者，若经过试验与检查并结合运行情况，判定有内部故障或本体严重渗漏油时，才进行大修。

　　3.1.1.3在电力系统中运行的主变压器当承受出口短路后，经综合诊断分析，可考虑提前大修。

　　3.1.1.4运行中的变压器，当发现异常状碚或经试验判明有内部故障时，应提前进行大修；运行正常的变压器经综合诊断分析良好，总工程师批准，可适当延长大修周期。中华人民共和国电力工业部1995-06-29发布1995-11-01实施

　　3.1.2小修周期

　　3.1.2.1一般每年1次；

　　3.1.2.2安装在2~3级污秽地区的变压器，其小修周期应在现场规程中予以规定。

　　3.1.3附属装置的检修周期

　　3.1.3.1保护装置和测温装置的校验，应根据有关规程的规定进行。

　　3.1.3.2变压器油泵(以下简称油泵)的解体检修：2级泵1~2年进行一次，4级泵2~3年进行一次。

　　3.1.3.3变压器风扇(以下简称风扇)的解体检修，1~2年进行一次。

　　3.1.3.4净油器中吸附剂的更换，应根据油质化验结果而定；吸湿器中的吸附剂视失 程度随时更换。

　　3.1.3.5自动装置及控制回路的检验，一般每年进行一次。

　　3.1.3.6水冷却器的检修，1~2年进行一次。

　　3.1.3.7套管的检修随本体进行，套管的更换应根据试验结果确定。

　　3.2检修项目

　　3.2.1大修项目

　　3.2.1.1吊开钟罩检修器身，或吊出器身检修；

　　3.2.1.2绕组、引线及磁(电)屏蔽装置的检修；

　　3.2.1.3铁芯、铁芯紧固件(穿心螺杆、夹件、拉带、绑带等)、压钉、压板及接地片的检修；

　　3.2.1.4油箱及附件的检修，季括套管、吸湿器等；

　　3.2.1.5冷却器、油泵、水泵、风扇、阀门及管道等附属设备的检朔；

　　3.2.1.6安全保护装置的检修；

　　3.2.1.7油保护装置的检修；

　　3.2.1.8测温装置的校验；

　　3.2.1.9操作控制箱的检修和试验；

　　3.2.1.10无盛磁分接开关和有载分接开关的检修；

　　3.2.1.11全部密封胶垫的更和组件试漏；

　　3.2.1.12必要时对器身绝缘进行干燥处理；

　　3.2.1.13变压器油的处理或换油；

　　3.2.1.14清扫油箱并进行喷涂油漆；

　　3.2.1.15大修的试验和试运行。

　　3.2.2小修项目

　　3.2.2.1处理已发现的缺陷；

　　3.2.2.2放出储油柜积污器中的污油；

　　3.2.2.3检修油位计，调整油位；

　　3.2.2.4检朔冷却装置：季括油泵、风扇、油流继电器、差压继电器等，必要时吹扫冷却器管束；

　　3.2.2.5检修安全保持记装置：包括储油柜、压力释放阀(安全气道)、气体继电器、速动油压继电器等；

　　3.2.2.6检修油保护装置；

　　3.2.2.7检修测温装置：包括压力式温度计、电阻温度计(绕组温度计)、棒形温度计等；

　　3.2.2.8检修调压装置、测量装置及控制箱，并进行调试；

　　3.2.2.9检查接地系统；

　　3.2.2.10检修全部阀门和塞子，检查全部密封状态，处理渗漏油；

　　3.2.2.11清扫油箱和附件，必要时进行补漆；

　　3.2.2.12清扫并绝缘和检查导电接头(包括套管将军帽)；

　　3.2.2.13按有关规程规定进行测量和试验。

　　3.2.3临时检修项目

　　可视具体情况确定。

　　3.2.4对于老、旧变压器的大修，建议可参照下列项目进行改进

　　3.2.4.1油箱机械强度的加强；

　　3.2.4.2器身内部接地装置改为引并接地；

　　3.2.4.3安全气道改为压力释放阀；

　　3.2.4.4高速油泵改为低速油泵；

　　3.2.4.5油位计的改进；

　　3.2.4.6储油柜加装密封装置；

　　3.2.4.7气体继电器加装波纹管接头。

　　4检修前的准备工作

　　4.1查阅档案了解变压器的运行状况

　　4.1.1运行中所发现的缺陷和异常(事故)情况，出口短路的次数和情况；

　　4.1.2负载、温度和附属装置的运行情况；

　　4.1.3查阅上次大修总结报告和技术档案；

　　4.1.4查阅试验记录(包括油的化验和色谱分析)，了解绝缘状况；

　　4.1.5检查渗漏油部位并作出标记；

　　4.1.6进行大修前的试验，确定附加检修项目。

　　4.2编制大修工程技术、组织措施计划

　　其主要内容如下：

　　4.2.1人员组织及分工；

　　4.2.2施工项目及进度表；

　　4.2.3特殊项目的施工方案；

　　4.2.4确保施工安全、质量的技术措施和现场防火措施；

　　4.2.5主要施工工具、设备明细表，主要材料明细表；

　　4.2.6绘制必要的施工图。

　　4.3施工场地要求

　　4.3.1变压器的检修工作，如条件许可，应尽量安排在发电厂或变电所的检修间内进行；

　　4.3.2施工现场无检修间时，亦可在现场进行变压器的检修工作，但需作好防雨、防潮、防尘和消防措施，同时应注意与带电设备保持安全距离，准备充足的施工电源及照明，安排好储油容量、大型机具、拆卸附件的放置地点和消防器材的合理布置等。

　　5变压器的解体检修与组装

　　5.1解体检修

　　5.1.1办理工作票、停电，拆除变压器的外部电气连接引线和二次接线，进行检修前的检查和试验。

　　5.1.2部分排油后拆卸套管、升高座、储油柜、冷却器、气体继电器、净油器、压力释放阀(或安全气道)、联管、温度计等附属装置，并分别进行校验和检修，在储油柜放油时应检查油位计指示是否正确。

　　5.1.3排出全部油并进行处理。

　　5.1.4拆除无励磁分接开关操作杆；各类有载分接开关的拆卸方法参见《有载分接开关运行维修导则》；拆卸中腰法兰或大盖宫接螺栓后吊钟罩(或器身)。

　　5.1.5检查器身状况，进行各部件的紧固并测试绝缘。

　　5.1.6更换密封胶垫、检修全部阀门，清洗、检修铁芯、绕组及油箱。

　　5.2组装

　　5.2.1装回钟罩(或器身)紧固螺栓后按规定注油。

　　5.2.2适量排油后安装套管，并装好内部引线，进行二次注油。

　　5.2.3安装冷却器等附属装置。

　　5.2.4整体密封试验。

　　5.2.5注油至规定定的油位线。

　　5.2.6大修后进行电气和油的试验。

　　5.3解体检修和组装时的注意事项。

　　5.3.1拆卸的螺栓等零件应清洗干净分类妥善保管，如有损坏应检修或更换。

　　5.3.2拆卸时，首先拆小型仪表和套管，后拆大型组件，组装时顺序相反。

　　5.3.3冷却器、压力释放阀(或安全气道)、净油器及储油柜等中件拆下后，应用盖板密封、对带有电流互感器的升高座应注入合格的变压器油(或采取其它防潮密封施)。

　　5.3.4套管、油位计、温度计等易损部件拆下后应妥善保管，防止损坏和受潮；电容式套管应垂直放置。

　　5.3.5组装后要检查冷却器、净油器和气体继电器阀门，按照规定开启或关闭。

　　5.3.6对套管升高座、上部管道孔盖、冷却器和净油器等上部的放气孔应进行多次排气，直至排尽为止，并重新密封好擦净油迹。

　　5.3.7拆卸无盛磁分接开关操作杆时，应记录分接开关的位置，并作好标记；拆卸有载分接开关时，分接头应置于中间位置(或按制造厂的规定执行)。

　　5.3.8组装后的变压器各零部件应完整无损。

　　5.3.9认真做好现场记录工作。

　　5.4检修中的起重和搬运

　　5.4.1起重工作及注意事项

　　5.4.1.1起重 荼应分工明确，专人指挥，并有统一信号；

　　5.4.1.2根据变压器钟罩(或器身)的重要选择起重工具，包括起重机、钢丝绳、吊环、U型挂环、千斤顶、枕木等；

　　5.4.1.3起重前应先拆除影响起重工作的各种连接；

　　5.4.1.4如系吊器身，应先紧固器身有关螺栓；

　　5.4.1.5起吊变压器整体或钟罩(器身)时，钢丝绳应分别挂在专用起吊装置上，遇棱角处应放置衬垫；起吊100mm左右时应停留检查悬挂及捆绑情况，确认可靠后再继续起吊；

　　5.4.1.6起吊时钢丝绳的夹角不应大于60°，否则应采用专用吊具或调整钢丝绳套；

　　5.4.1.7起吊或落回钟罩(或器身)时，四角应系缆绳，由专人扶持，使其保持平稳；

　　5.4.1.8起吊或降落速度应均匀，掌握好重心，防止倾斜；

　　5.4.1.9起吊或落回钟罩(或器身)时，应使高、低压侧引线，分接开关支架与箱壁间保持一定的间隙，防止碰伤器身；

　　5.4.1.10当钟罩(或器身)因受条件限制，起吊后不能移动而需在空中停留时，应采取支撑等防止坠落措施；

　　5.4.1.11吊装套管时，其斜度应与套管升高座的斜度基本一致，并用缆绳绑扎好，防止倾倒损坏瓷件；

　　5.4.1.12采用汽车吊起重时，应检查支撑稳定性，注意起重臂伸张的角度、回转范围与临近带电设备的安全距离，并设专人监护。

　　5.4.2搬运工作及注意事项

　　5.4.2.1了解道路及沿途路基、桥梁、涵洞、地道等的结构及承重载荷情况，必要时予以加固，通过重要的铁路道口，应事先与当地铁路部门取得联系。

　　5.4.2.2了解沿途架空电力线路、通信线路和其它障碍物的高度，排除空中障碍，确保安全通过。

　　5.4.2.3变压器在厂(所)内搬运或较长距离搬运时，均应绑轧固定牢固，防止冲击震动、倾斜及碰坏零件；搬运倾斜角在长轴方向上不大于15°，在短轴方向上不大于10°；如用专用托板(木排)牵引搬运时，牵引速度不大于100m/h，如用变压器主体滚轮搬运时，牵引速度不大于200m/h(或按制造厂说明书的规定)。

　　5.4.2.4利用千斤顶升(或降)变压器时，应顶在油箱指定部位，以防变形；千斤顶应垂直放置；在千斤顶的顶部与油箱接触处应垫以木板防止滑倒。

　　5.4.2.5在使用千斤顶升(或降)变压器时，应随升(或降)随垫木方和木板，防止千斤顶失灵突然降落倾倒；如在变压器两侧使用千斤顶时，不能两侧同时升(或降)，应分别轮流工作，注意变压器两侧高度差不能太大，以防止变压器倾斜；荷重下的千斤顶不得长期负重，并应自始至终有专人照料。

　　5.4.2.6变压器利用滚杠搬运时，牵引的着力点应放在变压器的重心以下，变压器底部应放置专用托板。为增加搬运时的稳固性，专用托板的长度应超过变压器的长度，两端应制成楔形，以便于放置滚框；运搬大型变压器时，专用托板的下中应加设钢带保护，以增强其坚固性。

　　5.4.2.7采用专用托板、滚框搬运、装卸变压器时，通道要填平，枕木要交错放置；为便于滚杠的滚动，枕木的搭接处应沿变压器的前进方向，由一个接头稍高的枕木过渡到稍低的枕木上，变压器拐弯时，要利用滚框调整角度，防止滚杠弹出伤人。

　　5.4.2.8为保持枕木的平整，枕木的底部可适当加垫厚薄不同的木板。

　　5.4.2.9采用滑全国纪录组牵引变压器时，工作人员和需站在适当位置，防止钢丝绳松扣或拉断伤人。

　　5.4.2.10变压器在搬运和装卸前，应核对高、低压侧方向，避免安装就位时调换方向。

　　5.4.2.11充氮搬运的变压器，应装有压力监视表计和补氮瓶，确保变压器在搬运途中始终保持正压，氮气压力应保持0.01~0.03MPa，露点应在-35℃以下，并派专人监护押运，氮气纯度要求不低于99.99%。

　　(2005-06-25)

　　整体组装

　　6.2.1整体组装前的准备工作和要求

　　6.2.1.1组装前应彻底清理冷却器(散热器)，储油柜，压力释放阀(安全气道)，油管，升高座，套管及所有组、部件。用合格的变压器油冲洗与油直接接触的组、部件。

　　6.2.1.2所附属的油、水管路必须进行彻底的清理，管内不得有焊渣等杂物，并作好检查记录。

　　6.2.1.3油管路内不许加装金属网，以避免金属网冲入油箱内，一般采用尼龙网。

　　6.2.1.4安装上节油箱前，必须将油箱内部、器身和箱底内的异物、污物清理干净。

　　6.2.1.5有安装标志的零、部件，如气体继电器、分接开关、高压、中压套管或高座及压力释放阀(或安全气道)升高座等与油箱的相对位置和角度需按照安装标志组装。

　　6.2.1.6准备好全套密封胶垫和密封胶。

　　6.2.1.7准备好合格的变压器油。

　　6.2.1.8将注油设备、抽真空设备及管路清扫干净；新使用的油管亦应先冲洗干净，以去除油管内的脱模剂。

　　6.2.2组装

　　6.2.2.1装回钟罩(或器身)；

　　6.2.2.2安装组件时，应按制造厂的“发装使用说明书”规定进行；

　　6.2.2.3油箱顶部若有定位件，应按并形尺寸图及技术要求进行定位和密封；

　　6.2.2.4制造时无升高坡度的变压器，在基础上应使储油柜的气体继电器侧具有规定的升高坡度；

　　6.2.2.5变压器引线的根部不得受拉、扭及弯曲；

　　6.2.2.6对于高压引线，所包扎的绝缘锥部分必须进入套管的均压球内，防止扭曲；

　　6.2.2.7在装套管前必须检查无盛磁分接开关连杆是否已插入分接开关的拨叉内，调整至所需的分接位置上；

　　6.2.2.8各温度计座内应注以变压器油；

　　6.2.2.9按照变压器外形尺寸图(装配图)组装已拆卸的各组、部件，其中储油柜、吸湿器和压力释放阀(安全气道)可暂不装，联结法兰用盖板密封好；安装要求和注意事项按各组部件“安装使用说明书”进行。

　　6.3排油和注油

　　6.3.1排油和注油的一般规定

　　6.3.1.1检查清扫油罐、油桶、管路、滤油机、油泵等，应保持清洁干燥，无灰尘杂质和水分。

　　6.3.1.2排油时，必须将变压器和油罐的放气孔打开，放气孔宜接入干燥空气装置，以防潮气侵入。

　　6.3.1.3储油柜内油不需放出时，可将储油柜下面的阀门关闭。将油箱内的变压器油全部放出。

　　6.3.1.4有载调压变压器的有载分接开关油室内的油应分开抽出。

　　6.3.1.5强油水冷变压器，在注油前应将水冷却器上的差压继电器和净油器管路上的塞子关闭。

　　6.3.1.6可利用本体箱盖阀门或气体继电器联管处阀让安装抽空管，有载分接开关与本体应安连通管，以便与本体等压，同时抽空注油，注油后应予拆除恢复正常。

　　6.3.1.7向变压器油箱内注油时，应经压力式滤油机(220kV变压器宜用真空滤油机)。
　　图1真空注油连接示意图

　　1-油罐；2，4，9，10-阀门；3-压力滤油机或真空滤油机；5-变压器；6-真空计；7-逆止阀；8-真空泵

　　6.3.2真空注油

　　220kV变压器必须进行真空注油，其它奕坟器有条件时也应采用直空注油，真空注油应遵守制造厂规定，或按下述方法进行，其连接图见图1。

　　通过试抽真空检查油箱的强度，一般局部弹性变形不应超过箱壁厚度的2倍，并检查真空系统的严密性。

　　操作方法：

　　6.3.2.1以均匀的速度抽真空，达到指定真空度并保持2h后，开始向变压器油箱内注油(一般抽空时间=1/3~1/2暴露空气时间)，注油温度宜略高于器身温度；

　　6.3.2.2以3~5t/h的速度将油注入变压器距箱顶约200mm时停止，并继续抽夫空保持4h以上；

　　6.3.2.3变压器补油：变压器经真空注油后补油时，需经储油柜注油管注入，严禁以下部油门注入，注油时应使油流缓慢注入变压器至规定的油面为止，再静止12h。

　　6.3.3胶囊式储油柜的补油

　　6.3.3.1进行胶囊排气：打开储油柜上部排气孔，由注油管将油注满储油柜，直至排气孔出油，再关闭注油管和排气孔；

　　6.3.3.2从变压器下部油门排油，此时空气经吸湿器自然进入储油柜胶囊内部，至油位计指示正常油位为止。

　　6.3.4隔膜式储油柜的补油

　　6.3.4.1注油前应首先将磁力油位计调整至零位，然后打开隔膜上的放气塞，将隔膜内的气体排除再关闭放气塞；

　　6.3.4.2由注油管向隔膜内注油达到比指定油位稍高，再次打开放气塞充分排除隔膜内的气体，直到向外溢油为止，经反复调整达到指定油位；

　　6.3.4.3发现储油柜下部集气盒油标指示有空气时，应用排气阀进行排气；

　　6.3.4.4正常油位低时的补油，利用集气盒下部的注油管接至滤油机，向储油柜内注油，注油过中发现集气盒中有空气时应停止注油，打开排气管的阀门向外排气，如此反复进行，直至储油柜油位达到要求为止。

　　6.3.5油位计带有小胶带时储油柜的注油

　　6.3.5.1变压器大修后储油柜未加油前，先对油位计加油，此时需将油表呼吸塞及小胶囊室的塞子打开，用漏斗从油表呼吸塞座处徐徐加油，同时用手按动小胶带，以便将囊中空气全部排出；

　　6.3.5.2打开油表放油螺栓，放出油表内多余油量(看到油有内油位即可)，然后关上小胶囊室的塞子，注意油表呼吸塞不必拧得太紧，以保证油表内空气自由呼吸。

　　6.4整体密封试验

　　变压器安装完毕后，应进行整体密封性能的检查，具体规定如下：

　　6.4.1静油柱压力法：220kV变压器油柱高度3m，加压时间24h；35~110kV变压器油柱高度2m，加压时间24h；油柱高度从拱顶(或箱盖)算起。

　　6.4.2充油加压法：加油压0.035MPa时间12h，应无渗漏和损伤。

　　6.5变压器油处理

　　6.5.1一般要求

　　6.5.1.1大修后注入变压器内的变压器油，其质量应符合GB7665-87规定；

　　6.5.1.2注油后，应从变压器底部放油阀(塞)采取油样进行化验与色谱分析；

　　6.5.1.3根据地区最低温度，可以选用不同牌号的变压器油；

　　6.5.1.4注入套管内的变压器油亦应符合GB7665-87规定；

　　6.5.1.5补充不同牌号的变压器油时，应先做混油试验，合格后方可使用。

　　6.5.2压力滤油

　　6.5.2.1采用压力式滤油机过滤油中的水分和杂质；为提高滤油速度和质量，可将油加温至50~60℃。

　　6.5.2.2滤油机使用前应先检查电源情况，滤油机及滤网是否清洁，极板内是否装有经干燥的滤油纸，转动方向是否正确，外壳有无接地，压力表指示是否正确。

　　6.5.2.3启动员滤油机应先开出油阀门，后开进油阀门，停止时操作顺序相反；当装有加热器时，应先启动滤油机，当油流通过后，再投入加热器，停止时操作顺序相反。 滤油机压力一般为0.25~0.4MPa，最大不超过0.5MPa

电气工程及其自动化英文论文一篇 内容不限 题目要翻译好

电气工程：
1
Electrical Engineering

My decision to pursue graduate study in the United States is underscored by my desire to be a part of the graduate program at your institution. Purdue University offers the flexibility needed for such a vast and rapidly changing field. The research facilities and the faculty at the university are par excellent.

Communications is an industry that has changed our lives. In a very short period it has changed the way we have looked at things since centuries. It is one industry that is going to shape our future for centuries to come. Hence my desire to do masters in electrical engineering with communications as my major.

My interest in electronics blossomed during my high school years. It was the time when technology had begun to make an impact on the lives of people in India. Hence engineering with electronics as my major was the first choice for my undergraduate studies. Right since the beginning of my undergraduate study electronics is a subject that has fascinated me with its power of applications. The subjects that I have studied include Linear Electronics, Digital Electronics. These laid the foundation for my courses in Electronic Communication & Communication Systems at a later stage. My undergraduate studies already focus on the communications aspect of electronics. A masters degree in electrical engineering with communications as major field is the next logical step.

For the past four months I have been working as a project trainee at the Indian Institute for Advanced Electronics. I am working on the design and development of a "PC Controlled Digital Serial Data Generator". This short stint has given me invaluable practical experience. It has given me the confidence to pursue a masters degree and also kindled a desire to do research.

During the course of my work at IIAE, I have come across several scientists. Most of them work in different areas of communications. Interactions with them have made me realize the vastness and the scope of communications. My discussions with them convinced me that specializing in communications will suit me very well.

The subject of research which interests me very much is spread spectrum communication systems. Coding theory and combinations is another research subject which arouses my curiosity. The subject Communication Theory which I am studying at present introduces these topics in theory. I am eager to find out more about the applications of coding theory to spread spectrum communication systems.

In addition I have been a student member of the IEEE (Institute of Electrical and Electronics Engineers, Inc.) for the past three years. Through its workshops/seminars and publications like the 'The Spectrum' it has exposed me to a lot of emerging technologies in the field of communications.

It is a strong belief in my family that the American education system has the best to offer in the whole world. This belief arises out of the experience that my parents had when they did their Masters of Science in the University of Pennsylvania during the years 1967-69. If I can get an opportunity to be a part of that intellectually stimulating environment, I am sure my talents will be put to optimal use.

India is a developing country with an enormous potential in the information technology business. To serve the needs of this developing industry and more important its vast population, communications is going to become of utmost importance. Thus conditions here are very conducive to supplement my aspirations when I return after completing my graduate studies.

2
Electrical Engineering

As a graduate student, I will undertake research and coursework in Electrical Engineering to enhance my competencies in this field. I intend to complete my master's degree in order to pursue my doctorate. The research that I am most interested in pursuing at Northeastern University surrounds the optical properties of MEMS devices, and the development of substrate-based fast electro-optical interfaces. My interest in this area stems from my undergraduate study in MEMs development for tri-axial accelerometers.

Engineering has been a key interest of mine since childhood. While still in grade school I enjoyed listening to my father, an electrical engineer, teach me about advances in technology, and was always eager to hear more. I was introduced to my first computer at the age of five, and have loved interacting with them ever since. My decision to study engineering as a career was no surprise to those who knew me.

In college I found that I was always studying something I enjoyed. I believe it is because I enjoy my life and my work that I have been successful. Spending hours in the laboratory is not something that I dread, but instead I take pride in my work and its successful completion. One example of this that is still fresh in my mind is the successful design of a fully functional microprocessor in the Xilinx environment. All told, the project took over 150 hours of each design-team member's time. However, I did not look on it as a drain, but an experience for learning and a focus for my professional and technical development. When we finished the project we felt the sense of worth and pride in completion of a task that was once above our level of knowledge.

Pursuing a graduate degree in the research field I have chosen also feels like a challenge, and I know that study will frustrate me at times. However, I feel that my commitment to learning will not be swayed. I feel confident in my ability to be creative in my perspective, and to persevere. My ultimate goal is to be an innovator in the field I have chosen to study. Professionalism and creativity are my most valued strengths.

At the heart of my interest is the advancement of man in concert with his environment. My personal philosophy of life will matter greatly during my study and after its completion. That is why I devote time to reflection on my goals and their implications. Money has never been a motivator for my work, nor do I think it will be in the future. However, as a professional and a graduate, I realize that my earning potential will be significant. That is why I also commit myself to charity and fairness. In the past I have been a member of the Boy Scouts of America, and have achieved the rank of Eagle Scout. In the course of my experience in that organization, I learned respect and moral value. Now, as a member of the IEEE, I value my professional standing and its commensurate moral implications. Ethics in engineering is as important as technical skill, and as such I intend to uphold my own ethical obligations to the best of my ability.

As a Northeastern University student, I would commit all that I have to offer to my study. I intend to pursue research in MEMS technology. At Rowan University as an undergraduate student I have already conducted some research and development of MEMS sensors for military applications, resulting in publication. An article, written by myself and my project member David Bowen and edited by our advisor Dr. Robert Krchnavek, was published in the NAVSEA Intelligent Ships Symposium Proceedings of 2001. The paper was titled "Designing a 3-Axis, Monolithic, MEMS-Based Accelerometer" and was under review for endorsement by the US Navy's NAVSEA facility in Philadelphia during that year.

Building on my past success in MEMs design, I hope to advance my understanding. Through research at the graduate level, it is my hope to become familiar with, and innovate the design of MEMs Optics in hopes of creating a reliable and practical MEMs Electro-Optical Interface for use in consumer electronics. It is my hope, that through my research, optical waveguides for intradevice communication might be realized.

Finally, my intent to pursue graduate study is laid plain. Study of MEMs optics is my intended focus, and I am committed to my goal. In pursuing a doctoral degree, I have closely analyzed myself to determine the reasons for my previous successes and my goals for the future. I have found that I do and have always enjoyed engineering, and that I have a strong desire to pursue my study further. I am prepared to commit myself to that study, and achieve what I have set out to do.

3
I Wish to Pursue an MS Degree in Electrical Engineering

During my senior year at Purdue University, I made a decision that has impacted the entire course of my education. While my classmates were making definite decisions about their career paths, I chose to implement a five-year plan of development and growth for myself. I designed this plan in order to examine various careers that I thought might interest me, as well as to expand upon my abilities at the time. As I was attaining a BS degree in Electrical Engineering, I decided to focus primarily on fields related to the VLSI (Very Large-Scale Integrated) circuits area. My main goals were either to gain work experience or to further my education by pursuing an MS degree in Electrical Engineering (MSEE). I saw an opportunity to both work and learn through employment at Xilinx Inc. Operating as a product engineer at a successful, high-tech semiconductor company has enabled me to utilize my technical and interpersonal skills in new and challenging ways. The position has also allowed me to interact with a multitude of departments including marketing, integrated circuit (IC) design, software/CAD development, manufacturing, reliability, accounting, and sales. I thus have gained an array of experience that extended beyond the parameters of my own responsibilities. In the workplace, I rely heavily upon the interpersonal techniques I developed as a counselor in a Purdue residence hall, as well as the organizational skills I had acquired through holding various leadership positions in cultural and engineering societies. I have also cultivated an interest in high-technology marketing that has continued to grow throughout my career.

My experiences with Xilinx have heightened my hunger for knowledge in the VLSI field. Two months after joining the corporation, I applied to several part-time programs in the vicinity that would allow me to acquire an MSEE degree within two to three years. San Jose State seemed an ideal choice, for its evening MSEE courses would allow me to pursue two independent, full-time positions concurrently. The San Jose program has complimented my Xilinx duties well; both demand large levels of energy and enthusiasm while guiding me to my ultimate goal a high degree of education in VLSI sciences. The resources that I poured into both endeavors have reaped many gains. I have been promoted to a Product-Yield Engineering position within Xilinx's Coarse Grain Static Memory (CGSM) Product Engineering division. My extensive coursework plays a key role in my continued success at Xilinx. Relevant classes in advanced digital and analog VLSI design, as well as sub-micron ULSI technology, have allowed me to understand more completely the workings of Xilinx, a fab-less semiconductor company that also functions as a software and hardware design, testing, and marketing center. The gains in knowledge I have made through the combination of work experience and education have indeed been exponential.

The academic records of my senior year at Purdue, coupled with my MSEE coursework, are ample proof of my dedication to learning. I feel I have overcome through hard work and dedication the brief "dry phase" I underwent at Purdue during the close of my sophomore and the first semester of my junior years. My performance at that time is in no way indicative of my usual achievements; they are instead the result of urgent family difficulties that required much foreign travel and serious attention to resolve. In May, I shall graduate with an MSEE degree from San Jose well ahead of my original estimates. This early graduation with Dean's Honors is the result of my firm belief in the value of diligence, as well as my renewed determination to strive for perfection in both work and school.

I am now embarking on another five-year plan, during which I hope to fulfill several specific career goals. For instance, being part of a very dynamic and results-oriented Yield team at Xilinx calls for continuous development of computational and statistical techniques. The Yield team is divided to focus on specific process/fabrication issues and process (manufacturing) optimization. My own position is an integral part of the optimization group. Speed and cost issues continue to press high technology atmospheres towards optimization, probability and stochastic processes and systems, and rigorous simulations of mathematical models. The MS in EES&OR offered at your university will grant me the statistical knowledge that is crucial for process and production optimization in a fab-less environment. In addition, product engineering requires fundamental research on mathematical models for linear and non-linear programming, as well as the utilization of efficient computer software. I continuously employ the knowledge I gained at Purdue in Operations Research and advanced mathematics courses. Yet despite the value of these classes and my high performance in them, I now require further education to best fulfill my duties. An MS in the EES&OR field, will give me knowledge that is invaluable to a career in product development, project management and strategic planning. The program will allow me to improve decision-making skills in operations, strategy, and policy issues. I will strengthen my theory and application in countless areas:continuous, discrete, numerical optimization; probabilistic and stochastic processes; dynamic systems and simulation; economics, finance, and investment; decision analysis; dynamic programming and planning under uncertainty; operations and service; corporate and individual strategy; and private and public policy , the EES&OR program will not only help me to excel at Xilinx but will also further any future career. My commitment to work and education over the last three years proves that I will pursue this MS with enthusiasm and technical edge that the MS would provide is I will be working while attending Stanford, I shall mingle education with practical application, and bring to the table interesting problems from my experience and past education.

Technical challenges encountered through projects in the EES&OR program will provide motivation and opportunity for methodological data collection, processing and presentation issues presented are integral to my future goals, and the management challenges raised will provide invaluable experience for professional practice. This will in turn build a solid foundation for a life-long career that can overcome any problem in decision-making. In addition, taking courses in economics, finance, and investment analysis will allow much growth of knowledge in investment issues in different industries. The EES&OR program thus appeals not only to my engineering, economics, science and mathematical background, but will compliment my technical abilities with the conceptual frameworks needed to analyze problems in operations, production, strategic planning, and marketing in the realm of emiconductor/IC/engineering systems. I feel that I am prepared to meet the challenges of the curriculum. My coursework in intermediate microeconomics and macroeconomics, international trade, operations research, linear algebra, and probabilistic methods, along with my extensive calculus background, will allow me to function well within the program.

My long-term career goals include a move into marketing and product management. I believe that attaining this MS degree is the cornerstone to achieving my goals. It will give me the academic background necessary to succeed in product development, project management, and strategic planning. It will improve decision-making skills necessary for optimizing performance. The integration of two excellent programs in Economics Systems and Operations Research thus suits my current position and ties in with future goals perfectly by improving decision making in operations, strategy and policy. At present I desire to continue at Xilinx; attending a program that provides the flexibility and convenience of the SITN, is therefore imperative. Hence, being at Stanford as an HCP student alsoattracts me. I believe that Stanford is the best environment for me to achieve my goals while gaining exposure to and experience with a diverse student body and faculty. It is my belief that one continues to learn throughout one's life, and the most effective method of learning is through interaction with rd's diversity offers an environment for learning, both inside and outside the classroom. I hope to share my varied knowledge with my classmates and to take from them a new understanding of topics that are foreign to me. I believe that no other school provides students with the combination of education and environment offered by Stanford. Its outstanding academic reputation, mingled with its diverse environment and thriving Bay Area location, creates an opportunity for growth that is second to none. I have many ambitions for myself as I embark on this stage of my life. I believe that an education from Stanford will provide invaluable experiences and skills that will allow me to become a successful and innovative business leader in the new millennium.

4
Research Department of Biomedical Engineering is designed to research on and solve the bio-electrical and biomagnetic engineering problems in the field of biology and medicine with the aid of engineering principles and methods. Its main task is to explain, from perspective view of engineering, the biological and pathologic processes of the living organisms, especially human beings, and research on and develop the related medical devices and life science devices. Its research directions mainly include the modeling and emulation of the biological system, testing and analysis of biomedical signals, the biomedical imaging and processing , the biological effects of electromagnetic field and the development of artificial organs and medical devices, etc.

Electromagnetic Bioengineering
With the development and integration of electromagnetism, biology and medicine, biological electromagnetism exercises more and more influence on human life and health, environment protection and biological engineering. The research on electromagnetic bioengineering is a new research direction for IEECAS, mainly including research on rules of mutual influence between electromagnetic field and life matter, biological electromagnetic effect and its application in biology, medicine and medical equipment. At present, the research team has set up labs such as biological electromagnetic environment lab, biological electromagnetic signals & electromagnetic property testing lab, electromagnetic biological effect testing lab and biological electromagnetic simulation lab. It is equipped with various electrical and magnetic fields for experiments of biological electromagnetic effects, simulation software and biochemical experiment equipment. With such equipments, it can do biological electromagnetic experiments on live animals and detached live cells, detect, analyze and process the very weak biological electromagnetic signals, analyze and test live organism or detached cell under electromagnetic interaction with biochemical quantitative methods. The recent research work focuses on the effects

方向对不对，不知你要哪种，告诉我，我再接着找多的话email you