Earlier this morning, there was a Transmission-level fault that occurred at approximately 10:07AM. PQ monitors in the city-area captured the following waveforms at the 22kV incomer and at the 400V LT incomer side.
Here, the benefit of monitoring at L-N instead of L-L at 22kV is being showed clearly here. It is evident that there was a single-phase fault (L2) and that it originated upstream at higher voltage levels.
Note. A single-phase fault at 22kV will cause the other two phases to swell (not seen here).
There were reports of voltage dips in other transmission blocks from other PQ monitors. With this kind of magnitude observed here at 22kV, it is very likely that this fault originated in the same transmission block as well.
Update: 230kV cable damage along Keppel Road (South Region).
When a 230kV fault occurs, a quarter of Singapore will feel the worst dip magnitude (the region where the fault occurs), with the other 3 regions observing shallow voltage dips. Below is an example (via a Dranetz HDPQ) in the North region of Singapore during this same incident.