Power-line communication facts for kids
Power-line communication, often called PLC, is a cool way to send information using the same wires that deliver electricity to your home or school! Imagine sending internet signals or control messages through the power outlets.
This technology is used for many things. It can help with home automation, like controlling lights or appliances. It's also used for Internet access, which is sometimes called broadband over power lines (BPL).
Different PLC technologies work with different types of wires. Some work only inside one building. Others can connect different parts of the electrical grid, like the main power lines and the wires inside your house.
It's a bit like wireless communication because both deal with signals in busy environments. One challenge is making sure the signals don't interfere with radio broadcasts.
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How Power-Line Communication Works
Power-line communication systems add a special signal, called a carrier signal, to the electrical wires. Think of it like adding a secret message on top of the regular electricity flow.
The power system was built for electricity at 50 or 60 Hz. This means the wires aren't perfect for carrying the higher frequencies needed for data. Getting these signals to travel far is a big challenge for PLC.
Avoiding Radio Interference
A main concern for PLC is making sure it doesn't mess with radio services. Many countries have rules about signals sent over wires. These rules treat the wires almost like radio transmitters.
This often means that PLC signals must use frequencies below 500 kHz. Or they must use special radio bands that don't need a license.
Data Speed and Distance
The speed of data and how far it can travel vary a lot with different PLC systems.
- Slow and Far: Low-frequency signals (around 100–200 kHz) on big power lines can carry simple voice or control signals. These signals might only be a few hundred bits per second, but they can travel for many miles!
- Fast and Short: Faster systems, like those for a local area network (LAN), can send millions of bits per second. But these usually only work within one building or even just one floor. The good news is they save you from installing new network cables.
Controlling Power with Ripple Control
Ripple control is a way power companies use PLC to manage electricity. They add a special sound-like tone to the AC power line. These tones are usually between 100 and 2400 Hz.
Each area often has its own tone frequency. This stops signals from affecting nearby towns. The power company sends codes by turning the tone on and off slowly.
Special equipment at your home, often part of your electricity meter, receives these codes. It can then turn your appliances on or off. This helps power companies save money and prevent brownouts or rolling blackouts.
PLC for Utilities: Long Distances
Utility companies use special devices called coupling capacitors to connect radio transmitters and receivers to high-voltage power lines. These systems often use frequencies from 24 to 500 kHz. The signals can be quite powerful, up to hundreds of watts.
These signals help control important equipment like switchgear. They also protect transmission lines. For example, if there's a problem on a power line, PLC can help quickly shut it down to prevent damage.
While utilities now use fiber optic cables for most communication, PLC is still useful. It can be a backup system or used in places where installing fiber optics is too hard or expensive.
How it Works for Utilities
The signals are usually sent using amplitude modulation. This means the strength of the signal changes to carry information. A special pilot frequency is sent all the time to check if the system is working.
To keep the signals from going where they shouldn't, wave traps are used. These devices block the high-frequency PLC signals but let the normal power current (50–60 Hz) pass through.
PLC systems are popular with utilities because they can send data over their own power lines. This gives them a lot of control over their communication network.
Automatic Meter Reading
PLC is also used for automatic meter reading (AMR). This means your electricity meter can send readings to the power company automatically. This helps the company get fresh data to better control the power system.
- One-way systems: Meters send readings to a central station. These are simpler and cheaper but harder to change if needed.
- Two-way systems: The central station can send commands to meters, and meters can send back information. This allows for network changes, getting readings, or sending messages.
PLC is an important part of smart grid systems. These grids use technology to make electricity delivery more efficient and reliable.
PLC Inside Your Home
Power-line communication can use your home's electrical wiring for home automation. This lets you control lights and appliances without installing new wires.
Home Control (Narrowband)
Home control devices usually send a signal between 20 and 200 kHz into your home's wiring. This signal carries digital commands. Each device has an address, so you can control them individually.
These devices can plug into outlets or be wired in permanently. Since the signals can sometimes travel to nearby homes, these systems use a "house address" to keep your controls private. X10 is a well-known technology that has been used since the 1970s.
Low-Speed Narrowband
Narrowband PLC has been around for a long time. Early systems in the 1920s used frequencies from 15 to 500 kHz for things like telemetry (sending measurements from far away).
In the 1930s, ripple carrier signaling was used on medium and low voltage power lines. For many years, people looked for a cheap way to send data both ways, like for remote meter reading.
A system called "spread frequency shift keying" (S-FSK) was developed. It's simple and low-cost but sends data very slowly (200 to 1200 bits per second). It's widely used in Italy and parts of the EU.
S-FSK sends short bursts of tones when the AC line voltage is at zero. This helps avoid noise from arcing wires. These systems are usually two-way, allowing meters and central stations to send data and commands.
More recently, there's been a lot of interest in using digital communication to make PLC more reliable and affordable.
Medium-Speed Narrowband
Newer systems use a technology called OFDM (Orthogonal Frequency-Division Multiplexing). This sends data faster without causing radio interference. OFDM uses hundreds of slow data channels and can adapt to noise by turning off channels with interference.
The PoweRline Intelligent Metering Evolution (PRIME) alliance was formed in 2009. Their system uses OFDM and can send data at speeds up to 128.6 kilobits per second. It uses IPv4 for its upper layer.
In 2011, several companies created the G3-PLC Alliance. G3-PLC also uses OFDM and can operate in different frequency bands around the world. It's designed for very strong and secure communication, even across transformers. G3-PLC uses IPv6 and can connect meters, grid devices, and other smart objects.
High-Frequency PLC for Networks
High-frequency PLC uses higher parts of the radio spectrum for communication.
Home Networking (LAN)
PLC can be used in homes to connect computers and other devices that have an Ethernet port. Powerline adapters plug into power outlets and use your home's existing electrical wiring to create an Ethernet connection. This lets devices share data without needing new network cables.
Popular standards for home powerline networking include HD-PLC and HomePlug AV. These were adopted by the IEEE 1901 standard in 2010. Millions of HomePlug devices have been sold worldwide.
Broadband over Power Line (BPL)
Broadband over power lines (BPL) is a system that sends two-way data over existing medium voltage (MV) and low voltage (LV) electrical wiring. This avoids the cost of installing new data cables or wireless networks.
BPL uses some of the same radio frequencies as over-the-air radio. Modern BPL uses smart techniques like Wavelet-OFDM to avoid interfering with frequencies already in use.
The BPL OPERA standard is mainly used by internet service providers (ISPs) in Europe. In North America, it's used by some utilities for smart meters and managing electricity loads.
Ultra-High Frequency PLC
Even faster data can be sent over power lines using very high frequencies, from 2–20 GHz. This technology, sometimes called E-Line, sends signals as a wave traveling along the surface of a single wire.
These systems claim to offer very fast, two-way communication, over 1 Gbit/s in each direction. They can even carry multiple Wi-Fi channels and TV signals. Because they use such high frequencies, they can avoid interference issues that lower-frequency systems might have.
Standards for PLC
Different groups have created standards for powerline networking.
Inside homes, the IEEE 1901 standards explain how existing AC wires should be used for data. This standard includes technologies like HD-PLC and HomePlug AV. Products following IEEE 1901 can often work together.
For power grid use, the IEEE approved a low-frequency standard called IEEE 1901.2 in 2013. Other groups like the ITU-T have also developed standards, such as G.hn for high-speed powerline communication.
In Spanish: Power Line Communications para niños
See also
- HomePNA
- KNX (standard)
- Multimedia over Coax Alliance
- Residential gateway
