The electric field uniformity imposes a significant effect on the breakdown mechanisms of dielectric liquids. In general, breakdown is dominated by streamer initiation under uniform field, while it is dominated …
Effect of Electric Field Uniformity on Breakdown Mechanisms of Dielectric Liquids under Lightning Impulse Read MoreIn this paper, a reduced computational fluid dynamics (CFD) model is proposed for determining the total heat dissipation and the oil temperature distribution of transformer radiators in oil natural air …
A Reduced Radiator Model for Simplification of ONAN Transformer CFD Simulation Read MoreFrequency Response Analysis (FRA) is regarded as the most effective technique for detecting mechanical faults in transformer windings. However, the main challenge in applying the FRA technique lies in the …
Using Lumped Element Equivalent Network Model to Derive Analytical Equations for Interpretation of Transformer Frequency Responses Read MoreAgeing of paper insulation is a key parameter which determines the end of life for transformers. Much research has been conducted in trying to establish where the end of life …
Influence of Paper Ageing on Transformer Failure Read More电力变压器中防止气泡形成的温度限值分析 引言 在液浸式电力变压器中，匝间纸绝缘作为绕组内部的关键结构，其绝缘状态对设备的安全运行至关重要。 在设备运行过程中，固体绝缘的温度会因变压器损耗而上升。 对于高温运行的变压器， 水蒸气会逐步积累，从而在固体液体绝缘边界处形成气泡并析出。这些气泡可导致变压器设备绝缘水平下降，甚至造成绝缘击穿。 鉴于此，变压器必须有效减少气泡的形成。研究结果表明，多种方法可用于防止气泡的形成，其中最有效的方法是限制变压器热点温度，使其低于允许值。但是这也提出一个新问题，热点温度的限值是多少？ 变压器运行温度限值 目前普遍使用的温度限值来自IEC 60076-7:2018 标准。标准中指出，为避免气泡产生，140℃被认为是变压器最高运行温度。相关标准原文为: “此外，仍需注意当热点温度超过140℃时，气泡可能形成并导致变压器的绝缘强度下降。” 标准中同样对温度限值提出了额外的警告，即140℃仅适用于水分含量为2%的变压器。当水分含量增加时，此温度限值将会降低。但140℃与水分含量2%的适用性仍需进一步研究。 发展历史 在确定温度限值“140℃”的适用性前，仍需理解其依据与来源。 在早期的研究中，Kaufmann率先在二十世纪七十年代后期与八十年代初期开始研究气泡。此后，Heinrichs试图通过一个小规模的系统研究干燥的油纸绝缘的气泡生成。他建议温度限值为140℃。本文作者认为这是140℃首次出现在研究文献之中。毫无疑问，这个温度限值经受了时间的考验。 Oommen与Lindgren于2001年重新开始了对气泡的研究。他们的研究成果成为了标准IEEE C57.91与IEC 60076-14中讨论内容的基础。Oommen与Lindgren基于一系列涵盖了纸中水分，油气含量和系统压力等关键参数的试验，建立了一个用于计算气泡起始温度（BIT）的公式。对于绝缘纸中水分含量为2％的脱气系统，该公式计算的气泡起始温度为142.9°C。该工作同样也吸引了其他研究人员对该研究方向的兴趣，有关该研究方向的发展时间线如图1所示。 Fig. 1. BIT研究的发展时间线 更新公式 标准中描述的用于计算气泡形成的公式如式（1）所示（适用于脱气系统）。经过Du等人的研究，该公式被修正为如式（2）所示。 (1) (2) 经对比发现两个公式存在误差。当纸中水分含量为2%时，温度差值超过8K。修正后的模型认为140℃作为运行温度限值不足以防止气泡生成。 尽管修正后公式被用于计算气泡起始温度，但式（2）来自于水分析出曲线，所以该式仅用于计算水分从绝缘纸中析出所需的温度。实际上，气泡的形成需要额外的能量输入，这意味着气泡起始温度可以有所提高。 现有实验结果 多个研究团队已经进行了相关研究以进一步理解牛皮纸矿物油系统中的气泡形成过程，其研究结果如表1所示。从表中可以看出，当绝缘系统中绝缘纸的水分含量为2%时，大部分实验结果中的气泡起始温度超过140℃。当绝缘纸水分含量为1%时，其气泡起始温度显著高于水分含量为2%时的结果，表明气泡起始温度随着绝缘纸水分含量下降而上升。图2描述了气泡起始温度随绝缘纸水分含量（0.5%-7%）的变化情况。 …
电力变压器中防止气泡形成的温度限值分析 Read MoreIntroduction Power transformer insulation serves a vital purpose of providing dielectric protection to the transformer. Solid insulation is wrapped around the winding conductors, usually in thin layers. During service, winding …
Analysing the Power Transformer Temperature Limitation for Avoidance of Bubble Formation Read MoreManaging a large fleet of ageing assets has become a technical challenge faced by many electricity utilities in developed countries. Asset managers are increasingly interested in techniques that can …
Effect of Oil Regeneration on Improving Paper Conditions in a Distribution Transformer Read MoreA considerable amount of power transformers in operation do not own Original Equipment Manufacturer (OEM) technical support. It is desirable and feasible to obtain the related design information by interpreting …
Classification of Transformer Windings Types Using Frequency Response Analysis by Machine Learning Method Read MoreIntroduction The failure of transformers can result in safety issues and economic losses. Although FRA is widely used to detect mechanical winding deformation, the success of this technique lies in …
Interpreting First Anti-Resonance of FRA Responses through Low Frequency Transformer Modelling Read MoreThe prebreakdown and breakdown phenomenon in liquids is termed as ‘Streamer’. To better understand the mechanism of liquid breakdown, we need to have deep insights into the streamer process, which …
Magic to visualise the invisible: a comparison on the optical methods to visualise streamers in insulating liquids Read More