案件

使用Opt100在线DGA显示器识别热点

连接到底部排水阀的入口和出口油管
Published: 2019年8月15日
Power Generation and Transmission

VAISALA OPT100安装在阿根廷的CTM Salto Grande - 乌拉圭边境,以评估50/50/100 MVA Transformer上的气动问题,以便可以在1年内在不同的操作条件上对其进行研究以确定是否存在相关性。在气体水平和工作条件之间,例如加载和顶部油温度。

问题的背景
CTM Salto Grande installed an OFAF 100 MVA sealed single-phase GSU transformer in 2002 and since commissioning has had issues with suspected overheating. Ethane, and to a lesser degree methane, had appeared and was increasing. Thermal issues are a specific concern for this transformer as its oil contains DBDS, which at high temperatures can lead to the formation of corrosive sulfur. Hardly any hydrogen was found, except for spikes after the addition of Irgamet39 metal passivator to oil, which were assumed to be caused by stray gassing due to the Irgamet39. Nitrogen, but not oxygen, was also present at the same level as in the ambient air.

Project overview
2017年6月,安装了VAISALA OPT100多气体DGA,以实时测量关键故障气体。监视器连接到变压器,同时活着作为水力发电工厂的运行条件,不允许停工。由于Opt100的独特设计,这不是问题,并且安装完成了半天。使用基于集成的浏览器软件和蜂窝调制解调器从OPT100收集信息。

一年来,变压器维护团队分析了DGA数据,并将其与变压器的工作条件进行了比较,以查看两者之间是否存在任何相关性。在此过程中,CTM Salto Grande在此过程中每两到三个星期都采用油样在其实验室进行分析以进行比较。

变压器于2017年10月脱气。在此过程中,Opt100继续进行测量。同时,每两个小时采集实验室样品。在图3中可以看到两组结果的比较(PDF)。

调查结果:负载与气体
图4显示了变压器加载和CO2石油浓度,由Opt100在线监视器和实验室参考衡量,表明CO明显增加2在高负载期间。当负载较低或变化时,CO2remained stable or even decreased. This could indicate that during longer periods of high loading, there is a hotter area inside the transformer causing CO2纸或油的形成。

The decrease in CO2在较低的负载和温度期间,可能是由于CO的交换2随着温度的变化,纸和油之间。从负载数据中看不清,但是当我们包含估计的热点时会变得更加清晰:t热点≈tTop Oil+ H * gR * ipu^2, where gR is the average temperature difference between winding and oil measured at the factory during FAT and H = 2 is the estimated hot spot factor.

尝试使用估计的热点温度尝试了几种数学模型:线性和另一个数学温度,其阈值可用于在CO上作用的热点2concentration, estimated at around +70°C. More work is needed to refine the models. However, it is not a simple correlation, since it is possible that there is a large CO2exchange over time that is not visible in data covering just a few days.

Yet another possible reason for the decreasing CO2可能是由于环境空气和油之间的高部分压力梯度,气体正在从水箱中逃脱,尽管这是密封的变压器。然而,脱气后氮水平相对较快的事实表明,变压器并非完全气体。

其他断层气体,除了c2H6,在试验期间没有与负载显示任何明显的相关性。脱气后的气体水平的增加很可能是由于一部分油中无法脱气的气体所致,例如在纸上浸渍的石油,石油粘在狭窄的空间中。当这种油扩散到处理的油中时,气体水平会增加。

将OPT100与实验室测试进行比较
除响应时间外,在整个时期将监视器读数与实验室DGA结果进行了比较。为简单起见,仅在图8中显示甲烷。蓝线是监视器的测量数据,灰色区域是监视器的准确性规范。实验室引用显示为蓝点。

通过将在线显示器与实验室参考进行比较时,必须考虑样品的质量和实验室程序的不确定性。此外,重要的是要记住,无论实验室还是在线监视器是否都有自己的不确定性。在比较结果并就监视性能得出结论时,应考虑这些。

在这种情况下,由于未知实验室的不确定性,因此根据IEC 60567中发布的平均实验室准确性示例使用了+/- 15%[3]。因此,为了将实验室与在线DGA进行比较,比较趋势比实际测量更重要。如果趋势相似,并且具有不确定性的区域是重叠的,那么您可以得出结论,两种不同的方法是广泛同意的。

总体而言,CTM Salto Grande对读数的相关性非常满意,并正在向其车队中添加其他在线DGA监视器来监视变形金刚的操作。采样和实验室测试将继续进行某些方面,例如Furans和电介质强度,但是变电站维护经理同意“增加在线DGA和水分为我们提供了在CTM Salto Grande实施预测维护计划的关键工具。”

Moisture in oil
The moisture in transformer oil varies as the temperature fluctuates either due to loading, ambient temperature, or both. This effect was seen in this study as shown in Figure 9. The top oil temperature and the moisture in oil (ppm) is shown over a one-year period. It shows how moisture is released from the insulating paper surface into the oil when the temperature increases and then absorbed back into the paper when the temperature decreases.

然而,水解吸比吸收更快,因此,当水分作为ppm绘制在最高油温度下时,可见滞后。这意味着具有不同负载的变压器永远不会达到平衡。

这种现象使定义适当的时间在实验室中进行水分析的合适时机具有挑战性。在相同的温度下,由于磁滞作用,油含量在采样时是否升高或降低。

This is a very important factor to consider when taking an oil sample to determine the moisture in the solid insulation from a transformer with varying load and fluctuating temperature. This is also a key reason Online Moisture measurement is so much more effective in determining long-term moisture trends in the oil/paper. But it also indicates that when sampling oil, in order to be able to make any conclusions on moisture in a transformer, it is crucial to always record the oil temperature as well.

结论
该研究的结果表明,变压器负载与CO之间存在明显的相关性。2. It is not yet clear to the authors whether the decrease in CO2在较低的加载期间是由于CO2exchange between oil and paper or CO2从变压器泄漏出来。需要进一步的分析以更好地识别热点的位置。多亏了Opt100,CTM Salto Grande能够更好地确定变压器中问题的原因,以及需要采取哪些类型的纠正措施来解决它。现在已经启动了其他测试,并且随着OPT100在线安装,气体以及热点形成更严重的故障的风险 - 现在正在监视和更好地控制。

脚注
Asked for feedback on the OPT100, Eduardo Briosso, Asset Maintenance Manager at CTM, wrote that “over two years after installation we have had no problems with the equipment at all – no user intervention and no consumables have ever been needed.”

下面以PDF下载案例,以查看图1-10。

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