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.
I found myself staring up at the sky on the night of March 13, 1989, with my girlfriend and her parents in the backyard of their house. The sky was on fire, almost literally. Red and pink sheets of plasma streamed out in a circle from directly overhead, with blue-white streaks like xenon flashes occasionally strobing across the sky. We could actually hear a sizzling, crackling sound around us. The four of us stood there, awestruck by the aurora borealis we were lucky enough to witness.
At the same time, lights were winking out a couple of hundred miles north in Québec province. The same solar storm that was mesmerizing me was causing fits for Hydro-Québec, the provincial power authority, tripping circuit breakers and wreaking havoc. This certainly wasn’t the first time the Sun threw a fit and broke systems on Earth, but it was pretty dramatic, and there are some lessons to be learned from it and other solar outbursts.
January, for many of us in the Northern Hemisphere, can be a depressing month. It’s cold or wet depending where you live, the days are still a bit short, and the summer still seems an awfully long way away. You console yourself by booking a ticket to a hacker camp, but the seven months or so you’ll have to wait seems interminable.
If you want an interesting project to look forward to, take a look at [Benadski]’s idea for a decentralised low voltage local DC power grid for the upcoming SHA 2017 hacker camp in the Netherlands. The idea is to create a network that is both safe and open for hacking, allowing those with an interest in personal power generation to both have an available low-voltage power source and share their surplus power with other attendees.
The voltage is quoted as being 42V DC +/- 15%, which keeps it safely under the 50V limit set by the European Low Voltage Directive. Individuals can request a single 4A connection to the system, and villages can have a pair of 16A connections, which should supply enough for most needs. Users will need to provide their own inverters to connect their 5V or 12V appliances, fortunately a market served by numerous modules from your favourite Far Eastern sales portal.
This project will never be the solution to all power distribution needs, but to be fair that is probably not the intention. It does however provide a platform for experimentation, collaboration, and data gathering for those interested in the field, and since it is intended to make an appearance at future hacker camps there should be the opportunity for all that built up expertise to make it better over time.
Our society needs energy, and lots of it. If you’re reading this then the odds are astronomically good that you’re on a computer somewhere using energy, with the power cord plugged into the mysterious “black box” that is the electrical grid. The same is true if you’re reading this on a laptop or phone, which was charged from said black box even though it may not be connected at this moment. No matter where you are, you’re connected to some sort of energy source almost all the time. For almost every one of us, we have power lines leading up to our homes, which presumably connect to a power plant somewhere. This network of power lines, substations, even more power lines, and power plants is colloquially known as the electrical grid which we will be exploring in a series of articles.
While the electrical grid is a little over a century old, humanity has been using various energy sources since the agricultural revolution at least. While it started with animal fat for candles, wind for milling grain, and forests for building civilizations, it moved on to coal and steam during the industrial revolution and has ended up in a huge interconnected network of power lines connected to nuclear, natural gas, coal, solar, and wind sites around the world. Regardless of the energy source, though, there’s one reason that we settled on using electricity as the medium for transporting energy: it’s the easiest way we’ve found to move it from place to place.
If it hasn’t been made readily apparent to you by now, power grids are astonishing marvels of technology and quite possibly one of the greatest engineering feats of history. Learning how these systems work is easy in theory, but in practice you will be shot if you try to screw around with at a power station. [Tim] and [Marissa] figured there must be an easier way to learn about power grids so they made their own. It’s small, but it still has everything you’d find in high voltage power lines, minus a hundred kilovolts or so.
This mockup of a power grid simulates a power plant by taking a normal DC motor and connecting that to an alternator and transformer. This is two of the simulated generation points, with the third AC/AC power supply serving as a reference generator for synchronizing phase and frequency. It’s only 12V at 60Hz, but it gets the job done.
A power grid isn’t power plants – there’s also transmission line theory. For this, [Tim] and [Marissa] have a few boards packed with inductors to simulate power lines. There are boards for simulated loads, and synchronization systems built on the MSP430.
In the video below, [Marissa] goes over all the ins and out of the system. It’s very well made and excellent for teaching something that can’t be demonstrated without a practical example.