Being able to monitor voltages and currents is essential for many applications, with the national electrical grid being no exception. The obvious complication here is that the voltages and currents are massively higher than for those other applications, making safely monitoring these somewhat of an engineering challenge. The used systems for current monitoring are detailed by [Jordan Taylor], also known as [The Electric Brit], in an explainer of grid-level current transformers (CTs) and associated elements that help to provide galvanic isolation for safe current measurements.

Even if the basic principles remain the same, when you’re dealing with currents of 5 kA and more, the associated clearances and penalties for getting a detail wrong increasingly correspondingly. The CTs help to implement over-current protection (OCP), over-voltage protection (OVP) as well as differential protection, which is useful to detect leakage and shorts, which could also happen inside the CT if the windings become damaged.

Any such failure condition can trigger a circuit breaker to be tripped, or other corrective measures to be taken. Incidentally this also how it can be detected when someone is tapping off power in an illicit manner. As with all transformers they’re never perfect due to issues like core saturation, and thus performing accurate measurements and picking the right type of transformer is an art in itself, as explained in the video.

Ultimately CTs and the associated equipment are what makes an AC power grid responsive to any changes and with it into the reliable foundation of modern-day society.