Not being on standby this week i was called to a complete poweroutage of our local POCO substation in Titirangi at around 15.00 hrs.
Luckily i was not far away and working in an other substation scoping some jobs for the new year.
Could I please investigate what was going on ?
At the same time reports came in that an LV line was melting away about 5 km's away in a side road.
Arriving at the sub, T1 transformer (33kV / 11kV, 10,000 kVA) was out and tripped on master trip.
T2 was not in the sub and was removed for major overhaul in the workshop.
Checking the area around the TX, nothing obvious from damage, no Buch holtz alarm or oil leaks or blown insulators.
Spoke to control room and decided to reliven T1 with T1 incomer out to give a quick soaktest before applying a load.
OCB closed TX humming nicely for about 20 seconds, then whissshh!! , TRIP. (Sounded like a sky rocket).
Some black blobs were visible atop the TX but no smoke.
OK we have a problem here, went through the process off testing, isolating, earthing the TX supply , outgoing and VT.
After i got my access permit i could have a closer look and found the 11 kV junction box vented itself and spilled thick insulating oil through one of the gaskets.