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Sunday, August 14, 2011

Broadband Power Line Communication

Electrical voltage is big and alternatively slow, while a data signal's voltage is small and alternatively fast. Since these waves have different frequencies, there is no cross interference when combining them.

BPL Combines a data signal and an electrical signal

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1. Background

2. Acronyms/Definitions
3. Business Case
4. Benefits
5. Risks/Issues
6. Companies
7. Links

  • The overlapping signals are divided and the data signal is extracted by the PLC adaptor. This makes it possible to send data signals through power lines.
  • Electrical power is transmitted over high voltage transmission lines, distributed over medium voltage, and used inside buildings at lower voltages. Powerline communications can be applied at each stage. Most PLC technologies limit themselves to one set of wires, but some can cross between two levels (for example, both the distribution network and premises wiring).

2. Acronyms/Definitions
  1. Attenuation Distortion - The distortion of an analog signal that occurs during transmission when the transmission medium does not have a flat frequency response across the bandwidth of the medium or the frequency spectrum of the signal. Attenuation distortion occurs when some frequencies are attenuated more than other frequencies. When an analog signal of constantamplitude across its frequency spectrum suffers attenuation distortion, some frequencies of the received signal arrive being greater in amplitude (louder), relative to other frequencies.
    1. Signal Attenuation by Active Devices: Devices such as relays, transistors, and rectifiers create noise in their respective systems, increasing the likelihood of signal degradation. Arc-fault circuit interrupter (AFCI) devices, required by some recent electrical codes for living spaces, may also attenuate the signals.
    2. Signal Attenuation by Passive Devices: Transformers and DC-DC converters attenuate the input frequency signal almost completely. "Bypass" devices become necessary for the signal to be passed on to the receiving node. A bypass device may consist of three stages, a filter in series with a protection stage and coupler, placed in parallel with the passive device.

    HV transmission lines actually represent a far better medium for BPL because they are much more uniform and have none of the discontinuities inherent in the many devices installed on distribution lines. The net result is that BPL signals have less attenuation on HV lines, therefore increasing the distance they can travel. They are also more amenable to noise-mitigation techniques than distribution lines are.

  2. BPL – Broadband over Power Lines - Uses PLC by sending and receiving information bearing signals over power lines to provide access to the Internet.
  3. Couplers - Transfer the communications signal to and from medium voltage and low voltage power lines in a BPL or PLC network, and also serve to read, in real-time, the current of the electrical distribution grid.

  4. OFMD - Orthogonal Frequency-Division Multiplexing - (Essentially identical to coded OFDM( COFDM) and discrete multi-tone modulation (DMT), is a frequency-division multiplexing(FDM) scheme used as a digital multi-carrier modulation method. A large number of closely-spaced orthogonal sub-carriers are used to carry data. The data is divided into several parallel data streams or channels, one for each sub-carrier.

    Power lines are unshielded and will act as antennas for the signals they carry, and have the potential to interfere with shortwave radio communications. Modern BPL systems use OFDM modulation, which allows them to mitigate interference with radio services by removing specific frequencies used.

  5. PLC - Power line Communication (power line carrier ) also known as Power line Digital Subscriber Line (PDSL)

  6. PLT - Power Line Telecom - A system for carrying data on a conductor also used for electric power transmission. (aka PLN – Power Line Networking)

  7. Regenerator - A device that boosts the distance a BPL signal can travel by decoding the message, filtering the message content from any noise on the lines, then recoding and transmitting the message.

  8. Repeater - An outdated approach to boosting a BPL signal. A repeater re-ampliphies the signal plus any noise the signal picked up ultimately causing the degradation of the signal (see regenerator).

3. Business Case
  • The transmission Smart Grid will require broadband, low-latency, secure connectivity between all transmission stations and from these stations to their control centers. With such a platform in place, faster and more reliable control, protection, and grid status information becomes possible. Synchrophasor measurements, combined with advanced digital protection (such as line differential relaying) will allow cycle-by-cycle system assessment and response. More powerful central computers will interact with these remote subsystems to create faster simulations and to convey grid conditions instantaneously to system operators in new, more easily understood ways. Power electronic-enabled devices, such as Flexible AC Transmission Systems (FACTS), high-voltage (HV) DC, and bulk storage, will respond in milliseconds to signals issued either centrally or locally. As the speed and penetration of grid technologies increases, transmission control will evolve from quasi-steady state to dynamic.

    BPL is a technology that allows data to be transmitted over utility power lines. BPL has been implemented by the U.S. and other countries on medium-voltage distribution lines, but it had never been applied to HV lines. HV-BPL can provide a secure, low-cost alternative to the conventional expensive and time consuming option of deploying optical fiber communications systems along 69 kV and 138 kV transmission lines.

  • All power line communications systems operate by impressing a modulated carrier signal on the wiring system. Different types of powerline communications use different frequency bands, depending on the signal transmission characteristics of the power wiring used. Since the power wiring system was originally intended for transmission of AC power, the power wire circuits have only a limited ability to carry higher frequencies. The propagation problem is a limiting factor for each type of power line communications.

  • Data rates over a power line communication system vary widely. Low-frequency (about 100-200 kHz) carriers impressed on high-voltage transmission lines may carry one or two analog voice circuits, or telemetry and control circuits with an equivalent data rate of a few hundred bits per second; however, these circuits may be many miles long. Higher data rates generally imply shorter ranges; a local area network operating at millions of bits per second may only cover one floor of an office building, but eliminates installation of dedicated network cabling.

Communications between grid operators and customers over BPL

4. Benefits
  1. Existing Infrastructure - The extensive powerline infrastructure already available appears to allow people in remote locations to access the Internet with relatively little equipment investment by the utility. Also, such ubiquitous availability would make it much easier for other electronics, such as televisions or sound systems, to hook up.

  2. BPL Backhaul - One possible solution is to use BPL as the backhaul for wireless communications, for instance by hanging Wi-Fi access points or cell phone base stations on utility poles, thus allowing end-users within a certain range to connect with equipment they already have. In the near future, BPL may also be used as a backhaul for WiMAX networks.

  3. Rural Broadband - Many rural areas still lack high-speed Internet service, "five-per-mile to 15-per-mile" market. Those are cooperatives that have between five to 15 customers per linear mile of transmission lines – too few to be served by incumbent broadband providers, but enough to make a BPL business model work. he said. "and if you've got the network in place, you can read meters, you can do fault detection, you can do demand management – all the things the major utilities want to do, but have to fork out a ton of money for the network that supports it."

  4. Street Light Control - Utilities can control streetlights and other devices by communicating over the power line. Anchorage's streetlights will be controlled through power line networking. In the Anchorage project, for instance, the streetlights can be dimmed slightly when there is a substantial amount of snow present because the reflection off the snow provides some illumination. Lights can also be dimmed and increased as traffic swells and fades. In the Anchorage example, radio frequency chips couldn't be used because of potential for signal interference.

  5. Additional Services over Street Light Control - Applications can also be added on top of light control. In Quebec, the government is collecting data from motion sensors and LED lights linked into a power-line network to see if the system can alert safety teams about the existence of recent accidents or pinpointing their location. Oslo is trying to meld a pedestrian safety application into its power-line streetlight network. The Norwegian city has seen power consumption for streetlights decline by 50 percent and maintenance decline by 30 percent. Streetlights rigged with power lines can keep track of city buses or trains: a small LCD screen can then precisely pinpoint when the next one arrives.

  6. Signal Coverage - The primary advantage of power line arises from the fact that it has better signal coverage than wireless. Power line networking chips allow communication signals to travel on the same wires that go to the lights. As a result, rapid, finely tuned commands can be shuttled from a utility without worries that other radios or environmental disturbances will hamper.

  7. Security - More secure than wireless and less prone to interference from neighbor networks.

5. Risks/Issues
  • Transformers Block Signal - BPL has developed faster in Europe than in the United States due to a historical difference in power system design philosophies. Power distribution uses step-down transformers to reduce the voltage for use by customers. But BPL signals cannot readily pass through transformers, as their high inductance makes them act as low-pass filters, blocking high-frequency signals. So, repeaters must be attached to the transformers. In the U.S., it is common for a small transformer hung from a utility pole to service a single house or a small number of houses. In Europe, it is more common for a somewhat larger transformer to service 10 or 100 houses. For delivering power to customers, this difference in design makes little difference for power distribution. But for delivering BPL over the power grid in a typical U.S. city requires an order of magnitude more repeaters than in a comparable European city.

  • Signal Noise - Power lines are inherently a very noisy environment. Every time a device turns on or off, it introduces a pop or click into the line. Energy-saving devices often introduce noisy harmonics into the line. The system must be designed to deal with these natural signaling disruptions and work around them. Computers / electronics on the same line can cause problems, UPS's on the line will cause problems. Motors will generate noise, which includes A/C units, refrigerators and appliances. On paper it looks pretty good, but in actual use, the system is pretty 'sensitive'. When you start to factor in adding filters here, there, and everywhere to try to limit this noise so you can get communications across, the cost starts increasing past a favorable ROI point.

  • Lack of Standards - Variations in the physical characteristics of the electricity network and the current lack of IEEE standards mean that provisioning of BPL is far from being a standard, repeatable process.

  • Bandwidth - The amount of bandwidth a BPL system can provide compared to cable and wireless is in question. Using power lines to deliver Internet or TV into U.S. homes has perennially lagged way behind DSL.

  • Radio Interference - Older versions of BPL interferes with ham radios and emergency equipment. In April 2008, in a lawsuit brought by the American Radio Relay League ham radio association, a federal court ruled that the FCC had to rewrite its BPL regulations to solve that problem. BPL companies solved that problem by "notching" the frequencies they used to avoid those that interfered with ham radio. Power lines are unshielded and will act as antennas for the signals they carry, and have the potential to interfere with shortwave radio communications. Modern BPL systems use OFDM modulation, which allows them to mitigate interference with radio services by removing specific frequencies used.

6. Companies
  • Ambient (OTCBB: ABTG).- Newton, MA- Ambient Smart Grid™ communications solution is a modular network overlaid on the medium-voltage and low-voltage segments of the power distribution system allowing real-time insight into the operations of the electrical distribution grid while supporting any IP-based application. Ambient's equipment is designed to deliver broadband service over existing power lines. High-speed backhaul connections (which go to the Internet or to private networks) connect the Ambient Smart Grid™ network at any point along the medium voltage circuit allowing for IP data traffic to be carried, via a choice of multiple technologies including BPL, Wi-Fi, cellular, and/or low bit rate power line carrier (PLC).

    Ambient is extending its smart grid partnership with Duke Energy, with plans to supply its multi-modal communications modules to support the millions of smart meters the utility plans to deploy in multiple states over the coming years.

    In January 2010, Verizon Wireless and Ambient Corporation announced the launch of their jointly developed Open Smart Grid Communications Architecture, an integrated smart grid solution and open communications network for utilities deploying smart grid programs.

    While their OTC stock (ABTG.OB) trades at around 9 cents, they have brought in a modest $15 million in revenues from their four-year relationship with Duke Energy (via their nodes that were installed to support a 50,000 smart meter deployment in Cincinnati). Being that Duke’s smart grid team is widely considered to count some of the real visionaries of the industry among its members, it has to be viewed as a major validation for the efficacy of their communications products.

  • Amperion, Lawrence, Mass - A supplier and technical innovator in BPLC (Broadband Power Line Carrier) technology with over 100 patents. Unique to Amperion is its ability to run over distribution and transmission lines, scaling from 110V low voltage all the way up to 138KV high voltage transmission lines. Founded in 2001 by Redleaf Ventures, American Electric Power (AEP), and Cisco Systems, Amperion has deep roots in energy and data communications, Amperion's patents include methods of powering from the grid, RF signal coupling, RF signal filtering, frequency agility, hybrid networks of PLC and wireless, switching algorithms between wireless and PLC, and transmissions over high voltage lines.

7. Links
  • IBM and the International Broadband Electric Communications are running trials of smart grid services using broadband over powerline communications. The two companies hope billions in stimulus money could boost the use of transmission lines for smart grid communication in rural areas.
  • National Energy Technology Laboratory (NETL) - HV-BPL Phase 2 Field Test Report - November 2009; Presentation Februrary 2010


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