Transformer monitoring is the use of sensors to watch a power transformer's oil, gases and heat for the early signs of a fault, before the transformer fails. A transformer is a large machine that changes voltage on the power grid. Replacing one can take many months, so a utility wants a warning well before it breaks.
The oil inside the transformer carries the early evidence. The oil cools the windings and insulates them. When the insulation or the oil overheats or sparks inside the tank, it breaks down and releases small amounts of gases, which dissolve in the oil. Different faults release different gases. Hydrogen appears with many kinds of fault. Acetylene points to an electric arc, and ethylene points to severe overheating. A dissolved-gas sensor measures these gases. Other sensors measure the oil temperature, the winding temperature, the moisture in the oil and the load on the transformer.
The readings are sent to asset performance management software. It compares each reading with safe limits and with the transformer's own past readings. A slow rise in one gas over weeks is a warning even if the value is still below the limit. This is the idea of predictive maintenance: repair when the data says it is needed, not on a fixed calendar and not after a breakdown. The readings are a kind of time series data, which means numbers with a timestamp.
Say a different transformer shows acetylene on its gas sensor, where there was none last month. Acetylene is the sign of arcing inside the tank, and arcing can grow quickly. The software raises an urgent alert the same day. The maintenance team reduces the load on the transformer and takes it out of service for inspection. Without the alert, it could have failed in a heat wave, when demand is highest and a replacement is not available for months.
Newer sensors do part of the analysis themselves. A sensor now carries enough computing power to process its own reading, so it reports only what matters instead of sending every number onwards. Transformer monitoring sits inside the larger job of looking after power transformers and switchgear.