What specific impact does high harmonic content in the substation power supply have on transformer DGA results, and how does it differentiate from fault-related gas generation?

High harmonic content in a substation power supply significantly impacts transformer Dissolved Gas Analysis (DGA) results by increasing the rate of oil and paper insulation degradation, leading to the generation of specific gases. Harmonics are voltage or current waveforms with frequencies that are integer multiples of the fundamental frequency (e.g., 60 Hz). These non-sinusoidal waveforms cause increased eddy current and hysteresis losses in the transformer core and windings. These additional losses manifest as heat, accelerating the breakdown of the insulating materials. Specifically, harmonics lead to elevated levels of ethylene (C2H4) and carbon monoxide (CO) in the oil. Ethylene is typically generated from the thermal decomposition of oil, while carbon monoxide is primarily produced from the breakdown of paper insulation. Differentiating between harmonic-induced gas generation and fault-related gas generation requires careful analysis of the gas ratios. Faults such as arcing or severe overheating produce a different gas profile. Arcing produces high levels of acetylene (C2H2), which is usually absent or present only in trace amounts under harmonic-related stress. Overheating (hot spots) will produce ethylene, but at a much higher rate and in greater concentration compared to harmonic-related degradation. Also, the presence of hydrogen (H2) and methane (CH4) in significant quantities typically indicates a fault condition rather than harmonic stress. Furthermore, the total combustible gas (TCG) level will rise more rapidly in the presence of a fault. Examining the historical trends of gas concentrations is also critical. Harmonic-related degradation will typically show a slow, steady increase in ethylene and carbon monoxide, while a fault will cause a rapid and often exponential increase in one or more key gases. Therefore, while harmonics increase certain gases in DGA, the specific ratios and trends, especially the presence of acetylene, hydrogen and methane, and rapid TCG rise, are vital for differentiating them from actual transformer faults.