非标准雷电冲击电压下油纸绝缘击穿特性

Oil-paper Insulation Breakdown Characteristics Under Non-standard Lightning Impulse Voltages

变压器实际遭受的雷电冲击电压的波前时间及持续时间变化范围很大,传播过程中的折反射还会造成雷电波的波形振荡。雷电侵入变压器绕组后会引起内部谐振,在匝间和饼间形成较高电位梯度,从而导致匝间和饼间的击穿事故。因此设计了油-隔板和匝间绝缘模型,研究了冲击电压波前时间、振荡频率对绝缘模型击穿特性的影响。结果表明：2种绝缘模型击穿电压均随波前时间的降低而增加,波前时间0.25μs陡前沿冲击电压下的U50%比标准雷电冲击下提高了10%～17%;对于匝间绝缘模型,其放电时延受绝缘层厚度和波前时间的影响显著,并且放电时延对波前时间的敏感度随着纸层层数的增加而升高;匝间绝缘模型能够耐受幅值比标准雷电冲击电压幅值更高的振荡雷电冲击电压,模型的U50%击穿电压随振荡频率增大而增大,振荡频率335 kHz时的U50%是标准雷电下的1.25倍;此外,当匝间绝缘模型中绝缘纸总厚度保持恒定时,绝缘纸层数的增加提高了绝缘模型的击穿强度。

The non-standard lightning impulse voltages have variable front times, duration and possible high-frequency components superimposed in the waveform due to the reflection in the substation and other factors. These surges propa- gating into transformer windings may cause resonance and excite high potential gradient, and consequently leads to the breakdown of the windings＇ insulation. Hence, we investigated the impact of lightning impulse＇s front time and oscillation frequency on the breakdown characteristics using two electrode models to simulate the typical insulation configuration of windings in oil-immersed transformers. The experimental results indicate that the breakdown voltage increases with the decrease of front time, for example, the Us0o/～ under 0.25 Ixs steep front impulse voltage is 10%-17% higher than that un- der standard lightning impulse. For tnm-to-turn insulation, its time lag is greatly influenced by the thickness of insulation layer and front time, while this time lag gets more sensitive to the front time with the increase of the number of insulation layers. The tnrn-to-turn insulation can withstand much more severe oscillation lightning impulse in comparison to stan- dard lightning impulse, and its U50o/o increases with the oscillation frequency, from instance the U50～ under an oscillation lightning impulse of 335 kHz is 25% higher than that under standard lightning impulse. Furthermore, while the total insu- lation paper thickness of turn-to-turn remains the same, increasing the layer number will raise the breakdown voltage of insulation.