Natural ester dielectric fluids are being used as alternatives for mineral insulating oils in oil-filled power apparatuses. Although partial discharges (PDs) are recognised as one of the main causes of degradation of dielectrics used in power equipment, their characteristic voltages appear to be temperature-dependent. In this contribution, the pre-breakdown and breakdown behaviour of two natural ester fluids, extracted from canola oil (NE1) and soybean oil (NE2) is reported. To assess the effectiveness of the temperature dependence, −5, 0, and + 20°C have been identified as test temperatures. It was found that the different pre-breakdown and breakdown characteristic voltages increase with increasing temperature for both types of esters. The delay time is always longer for canola oil when compared to soybean oil regardless of the test temperature. The analysis of the average propagation velocity of NE1 and NE2 indicates that PDs propagate faster in NE2 than in NE1. The field strength at the tip of the needle electrode during the inception of the streamers leading to breakdown indicates that streamers in both oils are propagating in the slow mode. It is found that the temperature has a significant influence on the PDs ’ parameters for both fluids.

中文翻译：

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AC应力下天然酯的预分解和分解现象的温度依赖性

天然酯介电液已被用作油浸式电力设备中矿物绝缘油的替代品。尽管局部放电（PDs）被认为是电力设备中电介质退化的主要原因之一，但其特征电压似乎与温度有关。在此贡献中，报道了从菜籽油（NE1）和大豆油（NE2）中提取的两种天然酯油的分解前和分解行为。为了评估温度依赖性的有效性，已将-5、0和+ 20°C确定为测试温度。已经发现，对于两种类型的酯，不同的预击穿和击穿特性电压随着温度的升高而增加。无论测试温度如何，低芥酸菜子油的延迟时间总是比大豆油长。对NE1和NE2的平均传播速度的分析表明，PD在NE2中的传播比NE1中的传播更快。在出现拖缆导致击穿的过程中，针状电极尖端的场强表明，两种油中的拖缆都以慢速模式传播。发现温度对PD有显着影响 ' 两种流体的参数。