Really not sure what/who this is for. There aren't many 3-phase LV AC + DC use cases apart from industrial load + control. I can't imaging the DC part can be transmitted at a voltage that will make the system efficient while avoiding an expensive step-down conveter.
Readit Newsbill3478 commented on Hybrid AC/DC distribution system with a shared neutral (2020) electrical-engineering-po... · Posted by u/1970-01-01
bill3478 commented on Hybrid AC/DC distribution system with a shared neutral (2020) electrical-engineering-po... · Posted by u/1970-01-01
bill3478 commented on Widespread power outage in Spain and Portugal bbc.com/news/live/c9wpq8x... · Posted by u/lleims
> Many people don't even have cash anymore, either in their wallet or at home.
Even if you have cash many shops would not sell anything in case of a mass outage because registers are just clients which depend on a cloud to register a transaction. Not reliable but cheap when it works.
Many supermarket chains (in the West at least) have satellite links at their major locations because they can't afford to close a store just because the local ISP had an issue.
The real question is how long can some of the smaller banks' datacenters stay up.
bill3478 commented on Widespread power outage in Spain and Portugal bbc.com/news/live/c9wpq8x... · Posted by u/lleims
bringing islands together requires one to synchronize both -- frequency and phase. It is super difficult for large generators and transmission lines. transient heat dissipation can be a real bummer.
They can use GPS to synchronise or back-to-back DC if available.
bill3478 commented on Widespread power outage in Spain and Portugal bbc.com/news/live/c9wpq8x... · Posted by u/lleims
This sounds big enough to require a black start. Unfortunately, those are slow and difficult.
If an entire nation trips offline then every generator station disconnects itself from the grid and the grid itself snaps apart into islands. To bring it back you have to disconnect consumer loads and then re-energize a small set of plants that have dedicated black start capability. Thermal plants require energy to start up and renewables require external sources of inertia for frequency stabilization, so this usually requires turning on a small diesel generator that creates enough power to bootstrap a bigger generator and so on up until there's enough electricity to start the plant itself. With that back online the power from it can be used to re-energize other plants that lack black start capability in a chain until you have a series of isolated islands. Those islands then have to be synchronized and reconnected, whilst simultaneously bringing load online in large blocks.
The whole thing is planned for, but you can't really rehearse for it. During a black start the grid is highly unstable. If something goes wrong then it can trip out again during the restart, sending you back to the beginning. It's especially likely if the original blackout caused undetected equipment damage, or if it was caused by such damage.
In the UK contingency planning assumes a black start could take up to 72 hours, although if things go well it would be faster. It's one reason it's a good idea to always have some cash at home.
Edit: There's a press release about a 2016 black start drill in Spain/Portugal here: https://www.ree.es/en/press-office/press-release/2016/11/spa...
A true black start has several factors (which make it difficult and notable):
1. The grid has to fully collapse with no possibility of being rescued by interconnection
2. As a result, a generation asset has to be started without external power or a grid frequency to synch to
3. An asset capable of this is usually a small one connected to a lower voltage network that has to then backfeed the higher voltage one
4. Due to the difficulty of balancing supply/demand during the process, the frequency can fluctuate violently with a high risk of tripping the system offline again
None of this applies in yesterday's case:
The rest of the European synchronous grid is working just fine.
News reports stated Spain restored power by reconnecting to France and Morocco.
By reestablishing the HV network first, they can directly restart the largest generation asset with normal procedures.
As they bring more and more load or generation online, there's little risk of big frequency fluctuations because the wider grid can absorb that.
bill3478 commented on Tarsnap has given 2^18 dollars to open source daemonology.net/blog/2023... · Posted by u/cperciva
Of the top 10 languages on https://www.tiobe.com/tiobe-index/, only Visual Basic uses ^ as the power operator. Google must really like Visual Basic.
bill3478 commented on Tarsnap has given 2^18 dollars to open source daemonology.net/blog/2023... · Posted by u/cperciva
Is that the power operator or the xor operator?
Every time, without fail, somebody shows a bug about a piece of code that we take for granted (In this case, the String class) the bug is related to concurrent modifications.
Concurrency is so hard that even OpenJDK developers can't prevent these kind of bugs
Is not that OpenJDK developers can't prevent these, but there's a forbidding cost for doing so.
The simplest "safe" way of doing this involves defensively copying the input argument. However, the `compress` function will likely make yet another smaller copy, making the constructor very allocation and CPU intensive.
In fact, due to the fixed array size in Java, all thread-safe implementations must either allocate two arrays to hold the two possible encodings, which guarantees one piece of garbage, or iterating the input array twice.
For such a core class like String, this is probably unacceptable cost. And the constructor is not documented to be thread-safe, so no one should expect it to.
In reality, there are much more impactful data structures to abuse in Java.