From a value perspective, it makes sense to balance strength of the structures with the total number of structures themselves. These can be from 50 to 100 feet tall or more (the world’s tallest is over 1200 feet tall in China) and as a result of that increased height can get expensive to produce. Working from the bottom up, the first piece of equipment is the pole or tower that the circuits will be attached to. To get all that power moving around without causing major problems takes some special equipment, though. This is necessary for moving power from a 4 gigawatt-capable nuclear plant, for example, tens or hundreds of miles to a population center. For the transmission lines, though, which handle bulk power, the voltages can be as high as 500 kV and still carry thousands of amps of current. In any other world, these would be considered extremely high voltage. If you’ve noticed, so far I’ve referred to 10 kV as “low voltage” and 30 kV as “lower voltage”, each of which are well out of the reach of most engineers or hobbyists to handle safely. This is where the voltages start to get a little bit out of hand. For a given amount of energy, a higher voltage will lower the current, which reduces the amount of current in the wires, reduces the amount of heat the wires generate, and reduces the amount of resistive losses. At the plant, however, electricity is generated at low voltage (on the order of 10 kV) and is sent through the GSUs in order to increase the voltage. From there the power flows out to other substations which can either step the voltage up even further for long-distance transmission, or step the voltage down for distribution to homes and businesses. Each conventional power plant has at least one substation with specialized transformers called generator step-ups (GSU). Part of the reason for this relative simplicity of the transmission lines is that their only purpose is to connect electrical substations with other substations and provide bulk power transportation. Transmission lines will almost never have anything attached to the conductors themselves, although sometimes unrelated equipment are attached to the structures like cell towers. A distribution line may have fuses, transformers, voltage regulators, capacitors, reclosers, or any number of other devices attached to the power lines themselves. Transmission structures also do not have any equipment on them that attaches to the power lines. While a typical residential service may only include a single phase, the electric grid itself is a three-phase system and the transmission lines are meticulously balanced so that an equal amount of current flows on each of the three phases. ![]() Transmission lines are always built with sets of three conductors with an optional small wire or two at the top of the structure to serve as lightning protection. These can be easily distinguished from distribution by their larger size, but there are a few other indicators that you are looking at a transmission line rather than a distribution line. ![]() The other side of this division are the much larger, higher-voltage lines known as transmission lines. This illustrates the area and equipment which are protected from lightning strikes by the ground wire which is only designed to carry energy in the case of a fault like a lightning strike. ![]() A simple sketch of a transmission line, with three phases per circuit and a single ground wire at the top. The number of energy-carrying wires on them is three or fewer (per circuit, some distribution poles carry more than one three-phase circuit) and they tend to hold other equipment on them as well, such as transformers, fuses, switches, and even telephone and cable lines. These are known as distribution lines, and can be buried underground in newer neighborhoods or are strung on smaller poles around 40 feet in height. One group consists of smaller, lower-voltage lines (under 30 kV in most situations) which deliver power to homes and businesses. There are typically two types of power lines that make up the grid, which can be divided based on their function. The Difference Between Transmission Lines and Distribution Lines Of course, we shouldn’t leave out the most obvious part of the grid: the wires that actually form the grid itself. 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. ![]() 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. The power grid is a complicated beast, regardless of where you live.
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