Some excitement today, we had a power failure today where the lights didn't completely go out. Line voltage ended up varying from 20V to 50V and at a peak of 70V. Normal is 120V here in the USA. Seems lightning hit the distribution lines, and took out only two of the three phases. And I was on one of the impacted phases. Houses get only 1 phase, 240V centertapped to ground (earth).. Seems I was seeing power leakage through power customers that get fed all 3 phases, and have loads connecting from one phase to another (208V). That would work its way back through their pole pig transformers back to the distribution lines and then to my pole pig. 3 phase customer loads ended up in series with my loads.

I shut down my air conditioners and fridge, as compressors really don't like under voltages. Computer power supplies don't much like it either.

Later, once Pubic Service fixed it, saw a picture on FB of line crews in bucket trucks attending to the lines. And saw that 2 of the 3 phases were broken.

We had a 15 second brownout two weeks ago on the Lower North Shore in Sydney. About a dozen power supplies required replacement at work as a result. The cause was an ibis (a big ugly bird) getting too close to the primary side of a substation transformer down the road from where I work. Apparently, only the bird's beak remained and a few feathers. He won't get too close again, but the transformer is a write-off.

To add to the fun, some LED bulbs could operate up to half their usual brightness during this event. Others didn't light at all. Incandescents showed most directly the voltage variations. PC power supplies didn't operate at all.

Once had a situation at work where we lost one phase due to an HRC fuse failure on the incoming and the service guys couldn't find the fuses (ended up being on a wall behind discarded office furniture wrongly piled up in the plant room on the 13th floor). A number of three phase motors in the air conditioning plant and other areas didn't survive being run on two phases.

Any balanced load installed in the last twenty years should be connected through a phase failure relay. If one leg breaks, the relay will drop out and protect the load.

The bigger problem is when one loses the neutral on a three phase installation. As I found out when I used to work at Royal Ryde Rehab Hospital, when that happens the voltages across each pair of phases constantly fluctuates as things go 'pop' one by one and it is surge and spike city until everything no longer works.

I was lucky that I was close by the affected switchboard when that happened and was able to open it and throw the main switch. It's a classic case of why submains cables should not be buried in concrete slabs, especially since the slab scanning technology that we find routine today did not exist back then.

Any balanced load installed in the last twenty years should be connected through a phase failure relay.

Yep, and that would have saved us a lot of grief, but the incident I referred to was in the early 1980s, and the building itself was constructed in the 1970s.

The electrician couldn't find any reason for the fuse failure other than fatigue.

It is strange that only one fuse blows though it is possible. Even though they should be, one 20A fuse isn't always the same as another 20A fuse and when the normal load on a fuse is near its capacity, they do run very hot. By the time a load is about 3/4 of the fuse's rating the wire inside the cartridge is usually glowing.

That scenario of the LED's & fans running here is common. MOV's are set in pairs, such that with a decent surge, they do the RCD (GFCI) tripping.

I would have thought that where there was a phase fail risk there would be something as simple as having a relay on two phases: And supplied by the third, such that when any relay coils de-energised this on the two, opened the contactor, or whatever, latching coil circuit and that caused the power to be cut off on all phases.

I did have a contactor set up like that on the fridges. As soon as the voltage fell to a point it opened & cut the fridge power.

A picture of the power company repair crews fixing the problem. One line is continuous, the two others of the 3 phases are broken. Looks like they put insulation covers (like a sock) over the broken wire ends. I suppose so a crew member doesn't get zapped if he happens to back into one of these ends with his back. They use big barrel shaped crimps to join the wires. I don't know if they do that live, I doubt it as when they start inserting the wires into the barrel it would make and break contact and arc a lot. I think they ask someone at the power substation to kill the entire circuit while they do that. .

Hey Wa2ise, as soon as I saw the socks over the broken ends and the cable guy ready to join the ends, I thought of the Doc Emmett joining the ends of the cables in "Back to the Future"!!!!
Now THAT would have been a great picture!
In that line of cars on the right, was there a De Lorean???

Fred.

Just to the right of the notice board, what's the grey box with what looks like a flag pole on it?

The flag pole is in the garden. The box out the front looks like it is independent of the pole and it looks like the traffic signal controller.

When I put my reading glasses on, I see that it is indeed in the garden.

There's a "pole pig" in the background (cylindrical with top hv-insulator "snout")

The ubiquitous pole pig. Let's wire one up backwards and see what happens:

https://www.youtube.com/watch?v=uUc4i4IWhxc