Breakdown of gas insulated switchgears due to partial discharges (PD) is a major threat for the safe and reliable operation of power system network. In recent times, PD based diagnostics has been widely adopted by electrical utilities in order to evaluate the health of high voltage insulation system. However, very few reports are only available on the PD characteristics of gas insulated medium voltage (MV) circuit breaker prototypes, in particular with mixture of gases, over a wide range of pressure and voltage stress. Deep analysis of nature of PD signals in mixture of gas insulation and its time–frequency characteristics is important in order to develop efficient online condition monitoring systems for circuit breakers. This paper is aimed at the analysis of PD characteristics of a 22 kV MV circuit breaker prototype filled with SF 6 /N 2 gas mixtures using time–frequency (T-F) mapping and clustering technique. PD tests are carried out at different gas pressures (1–5 bar) and at different gas mixture ratios. Important PD parameters such as PD inception voltage, phase resolved PD (PRPD) pattern and PD repetition rate are evaluated. Clustering analysis of PD signals from the time–frequency mapping is carried out and formation of three different clusters consisting of short, long and repetitive PD pulses is identified. Online real time monitoring of individual cluster density will be helpful to understand the degradation of gas insulation of circuit breakers. Keeping in mind the minimal usage of SF 6 gas, from the results, it is noted that 10% SF 6 gas can be mixed with 90% N 2 at 3 bar pressure to get satisfactory PD performance of a 22 kV medium voltage circuit breaker.

中文翻译：

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SF6/N2混合气体中压断路器局部放电时频图聚类技术分析

由于局部放电 (PD) 引起的气体绝缘开关设备击穿是电力系统网络安全可靠运行的主要威胁。最近，基于 PD 的诊断已被电力公司广泛采用，以评估高压绝缘系统的健康状况。然而，很少有关于气体绝缘中压 (MV) 断路器原型的局部放电特性的报告，特别是在很宽的压力和电压应力范围内的气体混合物。深入分析气体绝缘混合物中局部放电信号的性质及其时频特性对于开发高效的断路器在线状态监测系统非常重要。本文旨在使用时频 (TF) 映射和聚类技术分析充满 SF 6 /N 2 气体混合物的 22 kV 中压断路器原型的局部放电特性。局部放电测试在不同的气体压力（1-5 巴）和不同的气体混合比下进行。评估重要的 PD 参数，例如 PD 起始电压、相位分辨 PD (PRPD) 模式和 PD 重复率。对来自时频映射的 PD 信号进行聚类分析，并确定了由短、长和重复 PD 脉冲组成的三个不同集群的形成。单个集群密度的在线实时监测将有助于了解断路器气体绝缘的退化情况。记住 SF 6 气体的最低使用量，从结果来看，