[mythtv-users] UPS with mythbuntu

[Simon Hobson]

Mike Perkins <mikep at randomtraveller.org.uk> wrote:

>>> If it's a cable feed (or similar) with decoder etc, then same things applies - if you power your kit off the UPS it will still work if the supplier's end is still running.
>> 
>> And the falling tree that just took out your power line missed the
>> cable running two feet below it...
>> 
> They only do crazy things like that in the US. I couldn't believe the junk I saw strung up on the poles over there.
> 
> In the UK, almost everything is underground except high-voltage distribution lines, usually across rural areas. Some telephone lines are also still on poles, but only one or two from a distribution point to the house roofline.
> 
> Most phone lines are below ground, as are all cable lines.

In rural areas in particular, there are still a *lot* of overhead phone cables strung for miles - but then there won't be Cable TV in these areas.
The point really is, consider all elements. If you have good batteries and a long runtime - then consider what else needs to be running for your recordings to be able to carry on. If you only have a short runtime and will be doing a shutdown "almost as soon as the power goes off" then it probably doesn't matter as you'll lose at least part any recordings in progress anyway*.
From experience - and again it needs adjusting to suit your own situation, I recommend waiting a few minutes before starting a shutdown. A large number of faults are transient - eg birds flying through HV lines and causing a flashover - and breakers may reset automatically or remotely from a control centre. It's annoying if the lights go out, come back on half a minute later, but your systems are already shutting down.

Where I used to work, we were on the end of a rural distribution network of overhead cables (11kV, we had our own substation). I found that power cuts generally fell into one of a small range of lengths :
- A few seconds - can't remember how long, perhaps 30. Consistent with a transient fault and a breaker auto-reclosing.
- A few minutes - long enough for the control centre operator to notice and manually reclose.
- 90 minutes +/- only a few - time for the on-call engineer to visit the substation and manually close the breaker. I believe the target time for response was 90 minutes, black mark for being slow, but due to "frosty relations" at the time between staff and management (organisational changes !) I suspect there was an element of "not going to do it faster or they'll expect that again in future.
- "Hours" - where it's a hard fault and they need the linesmen out to fix it.

The first two of these are worth having runtime to ride through. The latter two are a value judgement - is it important enough to you, do you have enough power events of the type, and do you feel it's worth shelling out on batteries ?


Where I work now, we are close to the 132kV substation. Power cuts are fairly rare, which unfortunately lulls management into a false sense of security - we ran without a working UPS for ages (and had servers with uptimes over a year), and we still don't have much battery capacity now (only enough for very brief outages, and barely enough to shut down some of the servers). 7kW of servers goes very quiet when the lights go out !
Last ones we had were during some "storms" last May - UK readers may recall the west coast of Cumbria had some severe snow and it made the national news because a lot of farmers lost a lot of livestock. The neutral wire on one of the 132kV lines up to Sellafield broke and dropped across the phase lines. It didn't cause a solid faults, our lights were flickering a bit for several minutes - then it all went quiet.


* Except for that small window of opportunity where your program has just ended as the power goes off and it's only the post-roll you lose.