US20020110311A1

US20020110311A1 - Apparatus and method for providing a power line communication device for safe transmission of high-frequency, high-bandwidth signals over existing power distribution lines

Info

Publication number: US20020110311A1
Application number: US09/915,459
Authority: US
Inventors: Paul Kline
Original assignee: Current Technologies LLC
Current assignee: Current Technologies LLC
Priority date: 2001-02-14
Filing date: 2001-07-26
Publication date: 2002-08-15
Also published as: US20040246107A1; US7187276B2

Abstract

The fiber optic isolator of the present invention transports data signals between high voltage power lines and a communications interface device, bypassing a step down transformer to low voltage power. The communication interface device includes a low voltage power line as well as telecommunications and wireless interfaces. The signals are coupled and de-coupled off of a high voltage power line by a power line coupler. The fiber optic isolator gets the signals (in light form) and transports them to and from the communications interface device. This insulates the system from current flow between the high voltage power lines and the communications interface.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119(e) from provisional application No. 60/268,519, filed Feb. 14, 2001. The 60/268,519 provisional application is incorporated by reference herein, in its entirety, for all purposes.[0001]

FIELD OF THE INVENTION

The present invention is drawn to a power line communications system for transmitting and receiving high frequency, high bandwidth signals safely over power lines. The system comprises a power line coupler, a fiber optic isolator and a communications interface to various media. The present invention is related to a portion of the system concerned with the fiber optic isolator and communications interface.

BACKGROUND

With well-established power distribution systems (PDSs) already in place throughout much of the world, an efficient power line communication system (PLCS) could provide more users with high-speed telecommunications access with the minimum investment of “add-on” devices.

The infrastructure for providing broadband Internet access is presently insufficient to meet demand. A power distribution system (PDS), however, could be an ideal vehicle for carrying communications signals in order to meet this demand. Development of a power line communication system (PLCS) would therefore provide more users with high-speed telecommunications access. Since the PDS is already built, the time required to implement a PLCS would be minimal.

Of course, there are a series of problems to be overcome before a PDS can be used as an efficient, high-speed power line communications medium. The following issues, while not exhaustive, are representative considerations of what such a system would require in order to use an existing PDS to transport communication data: a sufficient signal to noise ratio, non-disruptive installation of the “add on” device; safety means such that users and circuitry are protected and isolated from stray current; a signal carrier with a frequency sufficient to support high data transfer rate (e.g. 10 Mbps); means for the data signal to bypass a distribution transformer without loss; bidirectional data transmission; coupling devices that do not interfere with data signal handling; an independent power source for electronic conditioning circuitry at power line interfaces; a power line interface that is impervious to extreme environmental conditions; and means for the data to be readily routed to intended locations without loss.

Given the advantages of being able to use the existing PDS for high-speed data communication, an effective method is required to couple and decouple the signals onto and off of a high or medium voltage power line. The coupling and decoupling of the data signal must be at a level sufficient to maintain an adequate signal to noise ratio in order to discern between the data signal and noise or interference on the line. For any method developed, a significant challenge lies in being able to mitigate the adverse effects of the high voltage 50-60 Hz power signal might have on the communications signal. Additionally, safety from high voltage is of concern.

Whyte, et al. in U.S. Pat. No. 4,142,178 observe: “The use of the distribution network conductors for the transmission of carrier communication signals presents many problems not encountered in high voltage transmission line communication systems. Some of these problems include the poor high frequency impedance characteristics and the high level of electrical noise present on the distribution network conductors which, along with the plurality of distribution transformers and power factor correction capacitors attached to the distribution network, rapidly attenuate the communication signals.”

Whyte teaches using a direct circuitry from a line coupler to a remote data terminal thus bypassing the PDS transformer, which is the primary source of data attenuation. The main use for the transmission of communication signals addressed by Whyte was to perform distribution functions such as automatic reading of utility meters and selective load control. Those functions are still desirable, but the function of high speed, high bandwidth communication transmission preclude direct connection from a transformer to remote data terminals economically.

Use of a low voltage power distribution system as a data communications carrier within a premise is well known. Abraham, U.S. Pat. No. 6,014,386 teaches a communications network within a building using the AC wiring as the infrastructure of the network. Different types of appliances using digital signals may be included within the network. The Abraham patent uses an impedance matching scheme to direct a specific signal to a specific location. Couplers at a control location have unique impedances that are matched by corresponding couplers elsewhere within the building. Thus, specific signals will be de-coupled based an impedance match. Abraham also teaches the use of dielectric inductors in circuit with capacitors to tune the impedance characteristics of couplers.

In a similar manner, Abraham in U.S. Pat. No. 5,625,863 teaches the distribution of multiple video signals distributed within a building using the building's AC wiring as the distribution system. Unique impedance settings direct the signals to unique locations. Abraham in U.S. Pat. No. 5,818,127 describes a distribution system for FM signals within a building by use of the building's AC wiring.

Abraham in U.S. Pat. No. 5,717,685 describes the coupling of data signal on and off a building's AC wiring infrastructure. His invention uses capacitive circuits in serial connection. The circuitry also includes air-core transformers. This arrangement allows impedance tuning of the specific couplers. While Abraham claims a system with a fiber optic source for an input signal in his U.S. Pat. No. 6,014,386 patent, there is no description as to the use of fiber optic isolators.

Abraham also states that the utility firm may use the communications system to communicate utility meter information over the PDS.

Methods for avoidance of distribution transformers are well known. Perkins in a series of patents including U.S. Pat. No. 4,473,816 teaches a communications signal bypassing a multi-phase power transformer where the signal uses the PDS as a carrier. The signal is bidirectional and uses conductive material to affect the bypass. The invention uses multiple capacitors in parallel to neutralize the coupling impedance. Further, the winding ratio, R, between the primary and secondary windings ratio is maintained in the signal frequency across the signal bypass. Signal carrier frequency is in the 3-10 KHz range. Similarly, Perkins in U.S. Pat. No. 4,473,817 teaches a communications signal bypassing a single-phase power transformer.

Kennon, U.S. Pat. No. 4,644,321 uses a non-intrusive coupler to capture the data signal. Kennon teaches the use of a toroid having a multiplicity of turns of a conductor that is in circuit with an amplifier and receiver. The toroid core is non-conductive. The signal thus inductively de-coupled is amplified and used for a load management and filed configuration utility terminal. The system requires a battery for circuitry management.

Brown, U.S. Pat. No. 5,949,327 teaches the use of transformer bypass by coupling using capacitors connected to the primary and secondary terminals of the step transformer. Brown recognizes the need for multiple couplings at different points within the EDN (Electrical Distribution Network or, as referred to in the present description as PDS). Brown also teaches that the communication system use a high frequency signal carrier technique such as CDMA.

Moore, U.S. Pat. No. 5,210,519, describes a communication system that couples data signal from a transmission source using an inductor and de-couples the data at the receiver. This methodology is applied in a closed network and requires selective de-coupling as opposed to routing of the signal. Further, Moore teaches the use of a second transformer for reversing any inductor core saturation that may have occurred in the data de-coupling. This method requires time division of the data coupler between data coupling and saturation neutralization.

Dzung, European Pat. Application EP948143, describes a high voltage power line communication system that combines multiple source data signals, couples the combined signal onto multiple power lines using capacitive coupling and de-couples and demodulates the signals, separating and converting the signals back to the original form at the receiver.

Power lines can be located in areas with extreme environmental conditions.

Thus, the mechanical design must ensure proper operation when exposed to these extreme conditions and also maintain the required level of safety. Furthermore, any methods developed should be designed so as to have minimal impact to service of customers during installation.

As stated above, public safety is an absolute requirement. Any system using the PDS must isolate the end user (and public in general) from exposure to electric current. The PDS steps medium and high voltage power down to low voltage power (approximately in the 100-240 volt range) using transformers. Transformers are designed to filter out and ground high frequency signals as a safety precaution. Since a high frequency signal carrier is the ideal medium for high bandwidth data transfer, a communications data delivery system needs to circumvent the transformer filtration process while preserving safety protection.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a safe interface to a power line coupler for use with a power line communication system (PLCS).

It is still another object of the present invention to provide a bypass between a high voltage power line coupler and across a power distribution transformer.

It is a further object of the present invention to provide a bypass across a power distribution transformer wherein the data signal is preserved and consistent on either side of each of the transformer.

It is yet another object of the present invention to provide electrical current isolation between components and circuits within the PLCS by use of dielectric materials between components of the PLCS.

It is another object of the present invention to provide a high speed power line communication system (PLCS) using inductive signal coupling where the coupler's core stay's unsaturated.

It is yet another object of the present invention to provide a PLCS that performs data packet management.

It is a further object of the present invention to provide a power line coupler for use with a PLCS that is non-intrusive.

It is still a further object of the present invention to provide a power line coupler for use with a PLCS that inductively draws operating power from the power line.

It is a further object of the present invention to provide a power line coupler device for use with a PLCS that is self-contained and is nearly impervious to environmental conditions.

It is another object of the present invention to provide a PLCS that uses a toroid inductor to inductively couple and de-couple signals to and from a power line.

It is yet another object of the present invention to provide a power line coupler that provides an electro-optical transducer to interface with a fiber optic insulator.

It is still another object of the present invention to provide a non-intrusive power line coupler that is hinged for ease of installation.

It is still a further object of the present invention to provide a quality monitoring feedback system whereby a power company.

The PDS topology can be used to deliver high-speed communications to residential homes in a cost effective way. Applications for such communication systems include high speed Internet, telephony, video conferencing and video delivery. This recitation of applications is not meant to be exhaustive.

The system involves coupling and de-coupling communications data between a data source and a PDS. High frequency signals allow high bandwidth transfers (the higher the frequency of the data carrier, the more cycles per unit time available for data transfer). The carrier should exhibit high signal to noise characteristics relative to the underlying system of a 50 or 60 Hz PDS. (The U.S. standard is 60 Hz, but most countries use a 50 cycle per second power system.)

The data signals are coupled on to and off of the power line with a power line coupler (PLC). One embodiment of the present invention uses an inductive method to couple and de-couple data signals off of the power line. A toroid with conductive windings is placed around the power line. This method effectively provides a transformer between the power line and the PLC thus facilitating the transmission and receiving of the data signal. For the PLC side of the transformer, the number of windings and the orientation of the windings around the magnetic toroid is guided by the desire to maximize the flux linkage.

The type of signal used on this channel can be almost any signal used in communications (CDMA, TDMA, FDM, OFDM to name a few). A wideband signal such as CDMA that is relatively flat in the spectral domain is preferred to minimize radiated interference to other systems while delivering high data rates.

Since communications signals are very high frequency, a step down transformer would filter a signal coupled on the power line. The present invention avoids this by bypassing the transformer with a power line bridge (PLB). The PLB de-couples data signals from the medium or high voltage line a short distance from a transformer. The PLB interfaces between the power line on the primary of the transformer and the LV line on the secondary of the transformer. (The primary is the side of the transformer where the relatively high voltage enters; the secondary is the side of the transformer where the stepped down, lower voltage exits the transformer.)

The PLB is used to prevent the relatively high voltage from passing to the transformer's secondary side yet allowing the communications signal to pass between the PDS on either side of the transformer by using an isolator. A preferred embodiment of the present invention is to use an optical medium. The de-coupled signal from the relatively high voltage power line is converted to light energy (i.e. light signal) by using a transducer and transmitting the light signal over a nonelectric conductive but light conductive medium. In a like manner, light signals from the light conductive medium are converted to electrical signals for coupling to the power line.

One embodiment of the present invention uses a fiber optic cable as the isolator. The isolator is a light pipe that bypasses the transformer. Fiber optic cable is a dielectric thus insulating the PDS on the secondary transformer side from relatively high voltage.

The signal is next modulated and de-modulated by a first modem. The signal goes through a data router and then a second modem. The router serves the purpose of matching data packets with specific messages and destinations. The second modem modulates and de-modulates the signal in a form consistent with transport over a LV power line.

The light signal is converted back to an electronic signal and then coupled onto the LV power line (LV coupler). In an embodiment of the present invention a second isolator is inserted in the system between the second modem and the data router for conversion of the light signal to electrical signal. Additionally the isolator proves an additional layer of safety because of the dielectric quality of the second isolator.

The high speed, high frequency signal is then delivered, over the LV power line to the end user's residence or place of business. A power line interface device (PLID) serves as the gateway between the end user's various data appliances and local area network (LAN) and the high speed data transport.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 discloses the typical electric distribution topology of the prior art. [0044]
FIG. 2 illustrates typical electric distribution topology modified for communication in accordance with the present invention. [0045]
FIG. 3 illustrates a block diagram of the AP in accordance with the present invention. [0046]
FIG. 4 illustrates a block diagram of the PLB in accordance with the present invention. [0047]
FIG. 5 illustrates a conceptual diagram of a power line coupling in accordance with one embodiment of the present invention. [0048]
FIG. 6 illustrates a diagram of a self-contained power line coupling in accordance with one embodiment of the present invention.[0049]

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, the typical electric distribution topology of the prior art is illustrated. Medium voltage (MV) half loop power delivery system, as illustrated, is common to the U.S. PDS. Many transformers are used. Each transformer services a few homes or small businesses. Many other countries, such as the European states, use a high voltage delivery system with many end users serviced from a transformer. The present invention applies to either environment. [0050]
The present invention may be implemented in a high voltage and medium voltage PDS environment. For purposes of this description and subsequent claims, the high and medium voltage portion of the PDS is described as “primary” voltage (PV). The low voltage portion of the system is described alternatively as LV or “secondary” voltage (SV). These terms are arbitrary but used to improve clarity of the description. Similarly, the side of a transfer where the PV line enters is called the “primary” side. The SV side of the transformer is referred to as the “secondary” side of the transformer. [0051]
A [0052] sub-station 10 delivers PV power to a half loop distribution point, pole dip 12. The power is delivered in parallel to multiple transformers 20 over a PV power line 14. After the transformer is stepped down to a SV power (in the range of 100 to 240 VAC), several end user premises 26 are serviced via a SV power line 24. The step down transformer 20 grounds high frequency signals for safety purposes. Since a high data transfer (high bandwidth) power line communication delivery system requires a high frequency signal carrier, an object of the present invention is to avoid the removal of the high frequency signal by the transformer 20. It is noted that the PV power lines 14 may be above ground or subterranean. The transformers 20 may be aerial mounted on a pole or pad mounted on the ground.
Referring to FIG. 2 the typical electric distribution topology as shown in FIG. 1 as modified for communication in accordance with the present invention is illustrated. A point of presence [0053] 40 (POP), the terminus for high frequency, high bandwidth data signal, serves as the gateway to the digital communications world. It both sends and receives data to the end user over the PDS. A backhaul link 42 connects the POP 40. Data is manipulated and coupled and de-coupled from the PV power line at an aggregation point 44 (AP). A more detailed description of the AP follows in the FIG. 3 discussion.
The PDS is viewed as having three channels: PV power line; SV power line; and the premise's wiring. The first channel (the PV cable) has the least amount of noise and least amount of reflections. This channel has the highest potential bandwidth for communications. This is important because it is the channel that concentrates all of the bandwidth from the other channels. The type of signal used on this channel can be almost any signal used in communications (CDMA, TDMA, FDM, OFDM to name a few). A wideband signal such as CDMA that is relatively flat in the spectral domain is preferred to minimize radiated interference to other systems while delivering high data rates. [0054]
The second channel (SV line from the transformer to the premise) and third channel (premise wiring) have noise present from electrical appliances and reflections due to the “web” of wires. These channels can support a lower bandwidth than the PV channel and they need a more intelligent (with more overhead) modulation schemes. There are several companies with chip sets to achieve good communications for local area networks (LANs) such as: Adaptive Networks (Newton, Mass.), Inari (Draper, Utah), Intellion (Ocala, Fla.), DS[0055] 2 (Valencia, Spain) and Itran (Beer-Sheva, Israel). These devices would work well for the SV and premise channels.
Data signal and power are carried over the [0056] PV power line 14 as previously stated. A power line bridge 46 (PLB) allows the data signal to bypass the transformer 20 thus avoiding the grounding of the high frequency data signal. More description of the PLB follows in the FIG. 4 description. The data signal after manipulation is delivered to the end user's premise. The data signal enters premise via the SV wiring. The end user may have a local area network (LAN) or have individual digital appliances.
In one embodiment of the present invention, the signal is carried through the premise's wiring and is available to various [0057] digital appliances 29, 30, including PC's, by a power line interface device 28 (PLID). The PLID 28 plugs into a standard electrical socket and allows the digital appliance to send and receive digital data. An alternative embodiment as described later, uses a communications interface located outside of the premise and the data signal is directly fed to the premise.
Referring next to FIG. 3, a block diagram of the AP in accordance with the present invention is illustrated. The [0058] AP 44 is the point where digital data is coupled and de-coupled to the PV power line. Additionally, the data is processed so that it can be readily communicated. Data signal communication to and from POP 40 is provided by the backhaul link 42.
A [0059] backhaul interface 50 allows direct communication with POP 40. The signal is passed through a signal modem 52 (PV modem). An isolator 54 is used to prevent electric current from flowing between the PDS and the components leading to the POP 40. The isolator 54 is made from dielectric material. The isolator, in a preferred embodiment of the present invention, is a fiber optic light pipe. More description of the isolator and its components occurs in the description referring to FIG. 6.
The isolator [0060] 54 bridges between the PV modem 52 and a power line coupler 56 (PLC). The PV modem 52 within the AP 44 conditions the signal for transmission over the PV power line 14. When data is transmitted by the end user and is de-coupled off of the PV power line, the PV modem 52 conditions the signal for transmission back to the POP 40.
In one embodiment of the present invention the [0061] PLC 56 comprises, along with other components, an inductor having a toroid (donut-like) shaped core. The toroid core has permeability qualities to maximize signal to noise ratio. More description of a preferred embodiment for the PLC is presented below. The inductor component couples and de-couples a high frequency signal to and from the power line without invading the power line. Once the data signal has been coupled to the PV power line, it is transported on the PV power line 14.
Referring to FIG. 4, a block diagram of the PLB in accordance with the present invention is illustrated. The [0062] PLB 46 bypasses the transformer 20 linking the data signal between the PV power line and the SV power line. At either end of the PLB 46 is a coupler. A PV coupler 60 couples and de-coupes signal with a PV power line 14. A SV coupler 72 couples and de-coupes signal with a SV power line 24.
An isolator is present between the [0063] PLB end couplers 60,72 and the interior of the PLB 46. The isolators, a PV isolator 62 and a SV isolator 70, are composed of dielectric material and insulate the balance of the PLB from potential electrical damage and user injury. A preferred embodiment of the isolator uses fiber optic material. The isolator will be discussed in more detail below.
A [0064] PV modem 64 modulates and de-modulates the signal to and from the PV isolator. The PV modem conditions the high frequency signals for transmission over the PV power line 14. The SV modem 68 conditions the signal for communication over a SV power line. In one embodiment of the present invention, a data router 66 is between the SV modem 68 and the PV modem 64. The function of the data router 66 is to prioritize and gather packets from all of the devices on SV power line side PV power line side. The data router 66 provides data packet management of end user transmission.
The signal (going to the end user) is coupled onto the SV power line by the [0065] SV coupler 72. The SV power line 24 delivers the power service to an end user premise 26. A “web” of wires distributes power and signal within the premise. The user draws power on demand by plugging an appliance into a power outlet. In a similar manner, the user may use a power line interface device 28 (PLID) to digitally connect data appliances to receive and send data signals carried by the power wiring.
A [0066] PLID 28 can have a variety of interfaces to the subscriber's equipment 29, 30.
Some examples are RJ-11 Plain Old Telephone Service (POTS), RS-232, USB, and 10 Base-T. A subscriber can have [0067] multiple PLIDs 28 on the same internal wiring.
Referring to FIG. 5, a conceptual diagram of a power line coupling in accordance with one embodiment of the present invention is illustrated. The prior disclosed embodiments of the PLCS include a [0068] PLB 46. The embodiment conceptualized in FIG. 5 replaces the PLB 46 with a self-contained power line coupler 100, a fiber optic isolator 130 and a communications interface 140. Further, the transformer 20 is depicted as pole mounted. The Communications Interface 140 separates signal carried over the PV power line 14 into three components: SV power line 24; wireless link 150; and telephone line 160.
Referring to FIG. 6, a diagram of a self-contained power line coupling in accordance with one embodiment of the present invention is illustrated. The self-contained PLC is packaged in a [0069] weatherproof housing 102 to militate against harsh weather and environment conditions. The PV power line 14 passes through sealed openings in the container. A data signal coupler 104 couples and de-couples data signals transported by the PV power line 14. One embodiment of the present invention uses a magnetic toroid shaped inductor. Windings 108 are placed around the inductor 104 to facilitate flux linkage of the data signal. The number of windings and the winding orientation is selected to maximize flux linkage. The permeability of the magnetic core is chosen for maximum coupling with the high frequency data signal. The permeability characteristics must also prevent low frequency (50-60 Hz) power line signal saturation of the toroid core to allow the data signal to couple and de-couple.
The toroid has direct electrical connection to the signal conditioning electronics used for transmitting and receiving the data signal. Transmit and receive circuitry [0070] 110 carries data signal to signal conditioning electronic components. As depicted in FIG. 6, the transmit circuitry 112 and the receive circuitry 114 are in parallel. Another embodiment of the present invention employs two data signal coupling toroids as opposed to one data signaling coupling toroid as depicted. One coupler for receiving and one for transmitting in order to optimize the flux linkage for the two cases.
The design of the transmit side is done to maximize the power of the drive signal in order to keep the signal to noise ratio of the coupled signal at least to the level acceptable for the overall communications system. The receive side contains a low noise amplifier designed to handle the lowest acceptable transmit signal level of the system. At a system level, the modulation and signaling scheme is done to minimize interference between transmit and receive signals. [0071]
The signal conditioning circuitry is connected to the fiber optics interface via an electro-[0072] optical transducer 116, such as laser diodes. The transducer converts an electrical signal to a light signal in the receive circuitry 114. The transducer converts light signals to electrical signals in the transmit circuitry 112. The light signal is transmitted to and from a light pipe 130 to a fiber-optic isolator 120 (fiber optic line or cable). The data signals are communicated back and forth between the PLC 100 and the Communications Interface 140 via a fiber optic line 120. The Fiber Optic Isolator breaks any electrical path between the two devices and provides the inherent safety required by the power distributors.
With the PLC being a “closed” system, power for the electronics must be derived internally. Although batteries may be an option, replacement would be costly and impractical. As a result, the PLC contains a [0073] power draw toroid 106 having magnetic characteristics appropriate for coupling 60 Hz signals that will inductively draw some of the 60 Hz signal off of the power line charging a power supply 118 component. The power supply 118 powers the PLC electronics.
For additional safety, the [0074] PLC housing 102 is constructed with high dielectric, corrosive resistant materials and is designed to significantly reduce any possible exposure to the high voltage potential present on the power line. The fiber optic isolator 120 and light pipe 130 is the only connection between the PLC 100 and the communications interface 140. Further, the light pipe 130 is encased in the insulated housing 102. The housing's 102 first priority is to protect exposure to the high voltage potential. It is also designed to ensure proper operation under extreme environmental conditions.
In another embodiment of the present invention, a “hinged” toroid design allows for easy installation and minimal impact to customer service. The toroid simply snaps around the power line using existing utility tools and techniques. [0075]
The [0076] communications interface 140 communicates with the PLC 100 via the fiber optic isolator 120. Received signals are separated into digital data signals and any other communication signal that may be carried by the PV power line. FIG. 5 depicts three types of leads from the communications interface: 120/240 V power line 24 (SV power line); wireless link 150; and telephone link 160. The SV power line receives current from the transformer 24. The digital data signal is coupled on and off the SV power line 24 within the communications interface.
The description of one embodiment of the present invention for the [0077] PLB 46 providing a means for converting light signals received via a PV isolator to coupled digital data signals as delivered to a premise over SV power line has been offered above. The communications interface implements the coupling and de-coupling of digital data signal on and off the SV power line in a similar fashion.
A system as disclosed herein is useful to provide data services to the residential market place at 10 Mbps. This makes an entire new range of applications practically available. Each device that is connected to the power would (if desired) have an address and would be accessible remotely. Some examples include remote utility meter reading, Internet Protocol (IP)-based stereo systems, IP-based video delivery systems, and IP telephony, although these are not meant as limitations. [0078]
The present invention has been described in terms of preferred embodiments, however, it will be appreciated that various modifications and improvements may be made to the described embodiments without departing from the scope of the invention. [0079]

Claims

I claim:

1. A method of safely transporting high-frequency signals over power transmission lines, comprising the steps of:

coupling and de-coupling high-frequency electrical signals on a first power transmission line;

converting said high-frequency electrical signals to light signals and light signals to said high-frequency electrical signals with an electro-optical transducer for coupling and de-coupling said high-frequency electrical signals to and from a non-electrically conductive but light conductive medium.

2. The method of claim 1, further comprising performing said steps within a non-electrically conductive enclosure.

3. The method of claim 1, wherein said light conductive medium is a fiber-optic isolator.

4. The method of claim 3, wherein said fiber-optic isolator is a fiber-optic transmission line.

5. The method of claim 3, further comprising transmitting said light signals to and from an interface device for digital appliances.

6. The method of claim 3, further comprising:

transmitting said light signals to and from a second electro-optical transducer to for coupling and de-coupling said high-frequency electrical signals to and from an opposite end of said fiber-optic isolator; and

coupling and de-coupling said high-frequency electrical signals on a second power transmission line;

so as to form an electrically isolated power line bridge.

7. An apparatus for safely transporting high-frequency signals over power transmission lines, comprising:

coupler means for coupling and de-coupling high-frequency electrical signals on a first power transmission line;

an electro-optical transducer capable of converting said high-frequency electrical signals to light signals and light signals to said high-frequency electrical signals; and

a non-electrically conductive but light conductive medium adjacent said transducer for coupling and de-coupling said light signals.

8. The apparatus of claim 7, further comprising a non-electrically conductive enclosure for at least said coupler means and said transducer.

9. The apparatus of claim 7, wherein said light conductive medium comprises a fiber-optic isolator.

10. The apparatus of claim 9, wherein said fiber-optic isolator is a fiber-optic transmission line.

11. The apparatus of claim 9, further comprising an interface device for digital appliances connected to an opposite end of said fiber-optic isolator.

12. The apparatus of claim 9, further comprising:

a second electro-optical transducer connected to an opposite end of said fiber-optic isolator for coupling and de-coupling said high-frequency electrical signals and said light signals to and from an opposite end of said fiber-optic isolator; and

a second coupling means for coupling and de-coupling said high-frequency electrical signals on a second power transmission line so as to form an electrically isolated power line bridge.