Renewable energy has long been touted as a major requirement in the fight to stave off the world’s growing climate emergency. Governments have been slow to act, but prices continue to come down and the case for renewables grows stronger by the day.
However, renewables have always struggled around the issue of availability. Solar power only works when the sun is shining, and wind generators only when the wind is blowing. The obvious solution is to create some kind of large, grid-connected battery to store excess energy in off-peak periods, and use it to prop up the grid when renewable outputs are low. These days, that’s actually a viable idea, as South Australia proved in 2017.
Without warning on an early August evening a significant proportion of the electricity grid in the UK went dark. It was still daylight so the disruption caused was not as large as it might have been, but it does highlight how we take a stable power grid for granted.
The story is a fascinating one of a 76-second chain of unexpected shutdown events in which individual systems reacted according to their programming, resulted in a partial grid load shedding — what we might refer to as a shutdown. [Mitch O’Neill] has provided an analysis of the official report which translates the timeline into easily accessible text.
It started with a lightning strike on a segment of the high-voltage National Grid, which triggered a transient surge and a consequent disconnect of about 500MW of small-scale generation such as solar farms. This in turn led to a large offshore wind farm deloading itself, and then a steam turbine at Little Barford power station. The grid responded by bringing emergency capacity online, presumably including the Dinorwig pumped-storage plant we visited back in 2017.
Perhaps the most interesting part followed is that the steam turbine was part of a combined cycle plant, processing the heat from a pair of gas turbine generators. As it came offline it caused the two gas turbines feeding it to experience high steam pressure, meaning that they too had to come offline. The grid had no further spare capacity at this point, and as its frequency dropped below a trigger point of 48.8 Hz an automatic deloading began, in effect a controlled shutdown of part of the grid to reduce load.
A massive power outage in South America last month left most of Argentina, Uruguay, and Paraguay in the dark and may also have impacted small portions of Chile and Brazil. It’s estimated that 48 million people were affected and as of this writing there has still been no official explanation of how a blackout of this magnitude occurred.
While blackouts of some form or another are virtually guaranteed on any power grid, whether it’s from weather events, accidental damage to power lines and equipment, lightning, or equipment malfunctioning, every grid will eventually see small outages from time to time. The scope of this one, however, was much larger than it should have been, but isn’t completely out of the realm of possibility for systems that are this complex.
Initial reports on June 17th cite vague, nondescript possible causes but seem to focus on transmission lines connecting population centers with the hydroelectric power plant at Yacyretá Dam on the border of Argentina and Paraguay, as well as some ongoing issues with the power grid itself. Problems with the transmission line system caused this power generation facility to become separated from the rest of the grid, which seems to have cascaded to a massive power failure. One positive note was that the power was restored in less than a day, suggesting at least that the cause of the blackout was not physical damage to the grid. (Presumably major physical damage would take longer to repair.) Officials also downplayed the possibility of cyber attack, which is in line with the short length of time that the blackout lasted as well, although not completely out of the realm of possibility.
This incident is exceptionally interesting from a technical point-of-view as well. Once we rule out physical damage and cyber attack, what remains is a complete failure of the grid’s largely automatic protective system. This automation can be a force for good, where grid outages can be restored quickly in most cases, but it can also be a weakness when the automation is poorly understood, implemented, or maintained. A closer look at some protective devices and strategies is warranted, and will give us greater insight into this problem and grid issues in general. Join me after the break for a look at some of the grid equipment that is involved in this system.
The power grid is a complicated beast, regardless of where you live. Power plants have to send energy to all of their clients at a constant frequency and voltage (regardless of the demand at any one time), and to do that they need a wide array of equipment. From transformers and voltage regulators to line reactors and capacitors, breakers and fuses, and solid-state and specialized mechanical relays, almost every branch of engineering can be found in the power grid. Of course, we shouldn’t leave out the most obvious part of the grid: the wires that actually form the grid itself.
You might be reading this six minutes early. Assuming that the Hackaday editors have done their job, this article should have appeared in your feed right on the half-hour. We have a set schedule to keep you supplied with the tastiest of hardware hacks and news. For some of you though perhaps there has been a treat, you’ve seen it and all the other stories six minutes early.
Think for a minute of a modern car on a hot day. When you turn on the air conditioning you will hear a slight dip in the engine revs as it accommodates the extra load. So it is with an alternating current power grid; a simple example is a power station supplying a city. In periods such as cold nights when the demands of the city go up, the result would be that the power station needs to work harder to satisfy it, and until that happens there would be a slight dip in its line frequency. Power grids compensate for this by increasing and decreasing the available generating capacity in real time, maintaining a mean frequency such that the “grid time” of a clock controlled by it matches an atomic clock as closely as possible over time.
It is at this point we leave the realm of electrical engineering and enter that of international politics, normally something far removed from Hackaday’s remit. It is fair to say that the history between Serbia and Kosovo is extremely delicate, and to understand some of the context of this story you should read about the war at the end of the 1990s. After the conflict the Serbian-majority region of what is now Kosovo refused to pay the Kosovan utility for its electricity, eventually leading to the Kosovans refusing to pay for that region’s share of the power received by Kosovo from Serbia. The resulting imbalance between demand and supply was enough to drag the supply frequency down across the whole continent, and though a short-term agreement has been reached the problem still remains on the grid.
Clocks and Mains Frequency
So if you are a continental European and you find yourself six minutes behind your British or American friends, don’t worry. We know that among our readers are people with significant experience in the power generation world, perhaps some of you would like to use your six minutes to give us a bit of insight in the comments. Meanwhile here at Hackaday we maintain an interest in the mechanics of power distribution even if some might say that it is Not A Hack. We’ve taken a look at utility poles, and examined how power grids are synchronised.
As for those slow clocks, the use of mains frequency to keep accurate time is quite brilliant and has been used reliably for decades. Tightly regulating grid frequency means that any clock plugged into an outlet can have the same dead-on accuracy for the cost of a few diodes. These clocks count the zero crossing of the alternating current. There may be moment to moment drifts but the power utility injects or removes cycles over the long term so the sum of crossings is dead on over the course of the day. It’s an interesting phenomenon to experiment with and that’s why we see it in microcontroller projects from time to time.
The electrical grid transmits power over wires to our houses, and our Bryan Cockfield has covered it very well in his Electrical Grid Demystified series, but what part does the earth ground play? It’s commonly known to be used for safety, but did you know that in some cases it’s also used for power transmission?
Typical House Grounding System
A pretty typical diagram for the grounding system for a house is shown here, along with a few of the current carrying conductors commonly called live and neutral. On the far left is the transformer outside the house and on the far right is an appliance that’s plugged in. In between them is a breaker panel and a wall socket of the style found in North America. The green dashed line shows the normal path for current to flow.
Notice the grounding electrodes for making an electrical connection with the earth ground. To use the US National Electrical Code (NEC) as an example, article 250.52 lists eight types of grounding electrodes. One very good type is an electrode encased in concrete since concrete continues to draw moisture from the ground and makes good physical contact due to its weight. Another is a grounding rod or pipe at least eight feet long and inserted deep enough into the ground. By deep enough, we mean to include factors such as the fact that the frost line doesn’t count as a good ground since it has a high resistance. You have to be careful of using metal water pipes that seemingly go into the ground, as sections of these are often replaced with non-metallic pipes during regular maintenance.
Notice also in the diagram that there are places where the various metal cases are connected to the grounding system. This is called bonding.
Now, how does all this system grounding help us? Let’s start with handling a fault.