中文2455字
关于标准或非标准冲击波对电力变压器的影响的
研究
Kaveri Bhuyan, Member, IEEE, and Saibal Chatterjee, Member, IEEE
摘要
这篇论文诣在反映电力变压器的过电压性能的观察结果。这个冲击试验模拟了在电力变压器实际运行时存在的一个现象，即一个变压器承受由于雷电或其他干扰作用于联接线上时所产生的入射过电压。一个模拟的非线性变压器模型将帮助我们分析变压器在不同种冲击波形下的过电压效应，并且将通过MATLAB SIMULINK进行仿真。对于一定范围内的实用波形（标准或非标准）和不同的线圈链接方式，对于代表了实际电场下的过电压波形的非标准雷电冲击电压波形和标准雷电波形的比较就可以实现。对于变压器承受标准或非标准冲击波形时的表现将体现在本论文中。对地最大电压和随着试验进行所出现的，针对0%线圈分接和10%线圈分接的贯穿线圈的过电压也将分别被记录和分析。
关键词——建模；电力设备；标准和非标准冲击波；变压器线圈
I 绪论
检查电力变压器的正常与否对供电的可靠性至关重要。冲击试验是一种有效的控制工具，它在电力变压器上执行，用以评估它们绝缘的完全性[1]。变压器绝缘在很大程度上视瞬时电压和线圈上的压力而决定[2]。带有长波和大数量级的不同的冲击电压可能是因为操作失误，雷电过电压或实验室的冲击电压试验所造成的[3]。假设进行雷电冲击电压试验，1.2/50μs的标准雷电过电压波形常被用于变压器试验[4]。当变压器用标准波形的过电压试验时，由于部分线圈的共振，实际上线圈的绝缘承受的是（单向或双向震动的）非标准波。同样，在实践中电力系统的所有组成部分都要承受由雷电或操作引起的不同种波形的瞬时过电压的危险。因此，在非标准冲击波下估算绝缘体的绝缘强度是十分必要的[4]。
电力系统50%以上的故障是由于线圈的绝缘故障引起的[4]。为了设计绝缘结构，了解贯穿于绝缘结构的电压变化和针对特定电压波形的绝缘强度情况是十分必要的[2]。SIMULINK模块基于3MVA, 33/11 kV的三相变压器的参数而建立[2]。80个主线圈和8个额外线圈被用作装配线圈[5]。对于中性点接地的变压器线圈在标准冲击电压波(1.2/50μs)下、在3μs, 8μs 和15μs 下的截波下以及在非标准冲击波下的性能研究已经完成。暂态研究的基础就是标准和非标准冲击波下变压器线圈的暂态响应。
II研究框架
在研究中，线圈受不同种冲击波作用，并且随着测定时间进行线圈的对地电压和随着测定时间进行线圈之间的电压将以线圈的不同部分为观察对象通过SIMULINK模块测定。SIMULINK模块的响应对于抽头线圈是在低阻抗的特定参照下研究的,即分别针对抽头线圈全开放（0%抽头）和抽头线圈处于实际情况下（10%抽头）两种情况在冲击电压波下进行试验。特性曲线表现了在全波下、3 μs, 8 μs 和15 μs,三种截波和阻尼振荡波下0%抽头和10%抽头两种线圈的对地电位的最大值和随着测定时间进行的线圈间电压的最大值。
在图1的（A）和（B）中,特性曲线表明了0%抽头线圈的对地电压的最大值和随着测定时间进行的，线圈间电压分别在实际的全波、3 μs, 8 μs 和15 μs截波、脉冲波、双脉冲波形和阻尼振荡波下的波形的不同。
针对线圈的过电压响应的对比性研究已经完成，观察结果被记录在表I 中。
图1 0%抽头时线圈的对地电压最大值的变化情况
表1: 0%抽头时线圈的对地电压最大值
在图2的（A）和（B）中,特性曲线表明了10%抽头线圈的对地电压的最大值和随着测定时间进行的，线圈间电压分别在全波、3 μs, 8 μs 和15 μs 截波、脉冲波、双脉冲波形和阻尼振荡波下的波形的不同。
针对10% 抽头线圈的过电压响应的对地电压的最大值的对比性研究已经完成，它是在实际的全波、3 μs, 8 μs和15 μs截波、脉冲波、双脉冲波形和阻尼振荡情况下研究的。观察结果被记录在表II中。
图2 10%抽头时线圈的对地电压最大值的变化情况
表2 10%抽头时线圈的对地电压最大值的变化情况
在图3的(A) 、(B)中,特性曲线表明了0% 抽头时的线圈间电压最大值的集中不同情况和随着时间进行，线圈间分别在实际的全波、3 μs, 8 μs and 15 μs截波、脉冲波、双脉冲波形和阻尼振荡情况下的电位波形。
针对0%抽头线圈的过电压响应的线圈间最大值的对比性研究已经完成，它是在全波、3 μs, 8 μs和15 μs截波、脉冲波、双脉冲波形和阻尼振荡情况
下研究的。观察结果被记录在表III中。
图3 0%抽头时线圈梯度电压最大值的变化情况
表3 0%抽头时线圈梯度电压的最大值
在图4的(A)、(B)和(C)中,特性曲线表明了10%抽头的线圈间电压最大值的几种不同的情况和分别在实际的全波、3 μs, 8 μs和15 μs截波、脉冲波、双脉冲波形和阻尼振荡波形下的电位分布。针对线圈的过电压响应的对比性研究已经完成，观察结果被记录在表IV中。
图4: 10%抽头时线圈梯度电压最大值的变化情况
表4：10%抽头时线圈梯度电压的最大值
III．推断
1.在截波下线圈的对地电压的最大值经过观察出现在中部段位置，无论是0%抽头或10%抽头的情况。
2.在非标准冲击波下可能的线圈之间的电压的最大值经过观察出现在线圈末端，无论是0%抽头或10%抽头的情况。
IV实验结果的分析
一定范围内的实际波（无论标准或非标准）和不同的线圈连接方式，以及不同的绝缘特点。其在非标准雷电冲击电压波下的波形，代表了电场中实际遭遇过电压时的电位波形，并且可以定量地研究其在标准雷电冲击波下的波形[6]。在此需要提出，标准波形下的主绝缘和
非标准波形下的副绝缘值得特别注意。全波因为其相对较长的持续性而引发了主要的振动，并且在线圈间和线圈与地之间产生了较高的电压。截波因为其较大的振幅而在线圈中部和尾部产生了较高的电压。0%抽头的情况比10%抽头的情况包含更高的电压。
V.结论
暂态研究的基础就是由于标准或非标准的冲击波对变压器线圈产生的暂态响应的研究。为了合理地设计线圈的绝缘结构，设计者需要了解每一个变化过程，至少是线圈的每一部分的暂态电压变化过程，或者是线圈每一部分与其相邻线圈线圈部分之间的暂态电压变化过程。为了确保变压器正常运行时的电压值在耐雷电冲击电压之下，对比标准和非标准雷电波下绝缘特性的不同是十分必要的[6]。
这项研究在未来将被延伸到在其它非标准雷电冲击波下绝缘特性的研究中，例如衰减波形和递增振荡波形。基于这些大量研究的必要性，相关测试标准应该相应的改变。电力变压器在纳秒级的波前时间内的波过程应该在更深远的研究中实施。基于这些大量的研究，对于制造另一种波形而不是标准波形的需要和愿望在冲击试验中应该被确定并且相应的调整和发展。
Study of Effects of Standard and Non-Standard Impulse Waves On Power
Transformer
Abstract
This paper aims to highlight the observations made on surge performance of a power transformer. The impulse test on power transformers simulates the conditions that exist in service when a transformer is subjected to an incoming high voltage surge due to lightning or other disturbances on the associated transmission line. A simulated non-linear transformer model helps to analyze the surge response under varying impulse waveforms accurately and so surge modeling of the transformer using MATLAB SIMULINK has been done. For a range of applied waves(both standard and non-standard) and different winding connections, comparison of the insulation characteristics under non-standard lightning impulse voltage waveforms which represent actual surge waveforms encountered in the field and the characteristics under the standard lightning impulse waveform quantitatively can be made. An investigation on the transformer behavior when subjected to standard and non standard impulse waves is done in this paper. The maximum voltage to ground and maximum voltage across the coils along with the time of their occurrences against different coils for 0% tapping and 10%tapping respectively is recorded and analyzed. Index Terms-- Modeling, Power Equipments, Standard and Non standard impulse waves, Transformer winding.
I. INTRODUCTION
Monitoring the health of power transformer is important for the reliability of electrical power supply. Impulse tests are an efficient quality control tool, performed on power transformers to assess their insulation integ rity [1]. Transformer insulation is determined to a great extent by the transient voltages and stresses which appear in the transformer winding [2]. Varying impulse voltages with long wave shape and large magnitude may be due to switching fault, lightning surge or by commercial impulse voltage test in the laboratory [3]. In case of lightning impulse voltage test, standard waves shape of 1.2/50 μs is used to test the transformer [4]. When the transformer is tested with standard wave shape, due to part winding resonance, the winding insulation is stressed with (unidirectional and bidirectional oscillatory) nonstandard waves. Also in
practice all the components in a power system are stressed with transient over voltages of a wide variety of wave shapes caused by lightning as well as switching. Hence, it is necessary to estimate the dielectric strength of the insulation under these non standard impulse wave shapes [4].
More than 50% of the failures in power transformers are due to insulation failure in windings [4]. To design the insulation it is necessary to know the voltage appearing across the insulation (as a function of time) and the strength of insulation against the particular voltage wave [2]. A SIMULINK model is constructed on the basis of the design data of a practical 3 MVA, 33/11 kV three phase transformer [2]. The main winding constitutes of 80 coils and 8 extra coils are used as tap coils [5]. The study of the behavior of the transformer winding with one grounded end is done when stressed by standard impulse voltage wave (1.2/50 μs),chopped impulse waves chopped at 3 μs, 8 μs and 15 μs and
non-standard impulse waves. The basis of the transient studies is calculation of transient responses due to application of standard and non standard impulse wave to the transformer winding.
II. THE FRAME WORK OF INVESTIGATION During the investigation, the winding is excited with different impulse waves and the potential to ground along with time of occurrence for the coils and potential across the coils with time of occurrence is observed at different parts of the winding for the Simulink based model. The response of the Simulink based model is studied with low resistance with special reference to the tap windings during open end condition (0% tappings) and when the tap windings are in series with the actual winding (10% tappings) against impulse voltage waves. The characteristic curve showing the variation of maximum voltage to ground and their time of occurrence along the winding and variation of maximum voltage across the coils and their time of occurrence along the winding with applied full voltage, chopped impulses at 3 μs, 8 μs and 15 μs, pulsed wave and two impulse waveforms varying in time to chop with damping oscillations are drawn for both 0% tapping and 10% tapping.
In Fig. 1, (A) and (B), the characteristic curve shows the variation of maximum voltage to ground and their time of occurrence along the winding with applied full voltage,chopped impulses at 3 μs, 8 μs and 15 μs, pulsed wave and two impulse waveforms varying in time to chop with damping oscillations for 0% tapping.
A comparative study has been done on the surge response of the coils and the observations are tabulated in Table I.
In Fig. 2, (A) and (B), the characteristic curve shows the variation of
maximum voltage to ground and their time of occurrence along the winding with applied full voltage,chopped impulses at 3 μs, 8 μs and 15 μs, pulsed wave
and two impulse waveforms varying in time to chop with damping oscillations for 10% tapping.
A comparative study has also been done on the response of the coils to applied full voltage, chopped impulses at 3 μs, 8 μs and 15 μs, pulsed wave and two impulse waveforms varying in time to chop with damping oscillations for maximum potential to ground with time of occurrence and 10% tapping. The observations are tabulated in Table II.
In Fig. 3, (A) and (B), the characteristic curve shows the variation of maximum voltage across the coils and their time of occurrence along the winding with applied full voltage, chopped impulses at 3 μs, 8 μs and 15 μs, pulsed wave and two impulse waveforms varying in time to chop with damping oscillations for 0% tapping.
A comparative study has been done on the response of the coils to applied full voltage, chopped impulses at 3 μs, 8 μs and 15 μs, pulsed wave and two impulse waveforms varying in time to chop with damping oscillations for maximum potential across the coils with time of occurrence and 0% tapping. The observations are tabulated in Table III.
In Fig. 4 (A), (B) and (C), the characteristic curve shows the variation of maximum voltage across the coils and their time of occurrence along the
winding with applied full voltage, chopped impulses at 3 μs, 8 μs and 15 μs, pulsed wave and two impulse waveforms varying in time to chop with damping oscillations for 10% tapping.
A comparative study has been done on the response of the coils to applied full voltage, chopped impulses at 3 μs, 8 μs and 15 μs, pulsed wave and two impulse waveforms varying in time to chop with damping oscillations for maximum potential across the coils with time of occurrence and 10% tapping. The observations are tabulated in Table IV.
III. INFERENCES
1. The maximum potential to ground is observed along the mid winding coils sections with both 0% and 10% tappings and with chopped impulse waves.
2. The maximum potential across the coils is observed in the end coil winding sections with both 0% and 10% tappings and with Non-standard impulses.
IV. ANALYSIS OF THE OBSERVATION
For a range of applied waves (both standard and nonstandard) and different winding connections, comparison of the insulation characteristics under
non-standard lightning impulse voltage waveforms which represent actual surge waveforms encountered in the field and the characteristics under the standard lightning impulse waveform quantitatively can be made [6]. It may be mentioned here that for the major insulation the effects of Standard wave shapes and for the minor insulation the effects of the Non standard wave shapes gets special attention. The full wave because of its relatively long duration causes major oscillations and develops high voltages across the windings and between the winding and ground. The chopped waves because of its greater amplitude
produce higher voltages at the middle end of the windings. The 0% tappings condition maintains a higher voltage profile than in the 10% tapping conditions.
V. CONCLUSION
The basis of this transient study is investigation of transient responses due to application of standard and non standard impulse wave to the transformer winding. To design correctly the winding insulation, a designer needs to know the transient voltage difference across each turn or at least each section of the winding, and also between each point on one winding and the closest point on the adjacent winding. To ensure the possibility of lowering down the Lightning impulse withstand (LIW) voltage, it is necessary to compare the insulation characteristic of standard and non standard lightning waveforms [6].
This work will be extended further in the future with the study of insulation characteristics under the other non standard lighting impulse waveforms, the damped waveform (C waveform) [7] and rising oscillation waveform (D waveform)[7]. Based on these extensive studies necessary changes in the reference impulse testing standards may be incorporated. Further study on the behavior of Power transformer under transients with front times in the nanosecond regime may be done. The need and desirability of introducing another waveform(s) other than the standard waveform(s) for impulse testing can be identified and justified based on this extensive study.
various M.Tech. thesis.