Abstract:
Extensions to the concept of using a power line carrier to convey a data record from the secondary side of a first transformer to a receiver in a power distribution substation include receiving the data record over a secondary data path in the event that the primary path is not available. The data record received over the secondary path through a second transformer rather than the first transformer must not interfere with other data transmissions from other transmitters and needs to identify the source of the transmission. An alternative to using a secondary data path through second transformer rather than the first transformer is to provide a data bridge around an opening in the primary path. This abstract is drafted to aid those searching for relevant patents and does not represent a legal limit on the scope of claims arising from patents claiming priority to this application.

Description:
BACKGROUND OF THE INVENTION  
     1. Field of the Invention  
       [0001]     This invention relates generally to the field of data communications over power lines. This form of communication, called power line carrier (PLC), introduces a high frequency analog signal onto a power cable used to convey power in a portion of an electric distribution network. The analog signal is received at a distant receiver through the use of a pick up coil or other means of decoupling an analog signal from a power line.  
         [0002]     Power line carrier is used by some information collection systems to send measurements and other information about the operation of a transformer, related equipment, and conditions in the vicinity of the transformer such as in a vault. The information is sent in a data record over one of the three phases of the feeder bus to a centralized location such as a switchyard where the information is pulled from the phase of the feeder bus by a coil or other means and provided to a receiver which also receives information about the operation of other distribution transformers.  
         [0003]      FIG. 1  introduces the environment relevant to the present invention. A portion of an electrical distribution network is shown as network  100 . Network  100  has feeder bus  104 , feeder bus  108 , and feeder bus  112 . A representative voltage for operation of these feeder buses may be 13 Kv but other systems may operate at 27 Kv, 34 Kv or some other voltage. The power on these three buses is provided to a set of local distribution networks  116  to server loads  120 ,  124 , and  128 . The voltage on these local distribution networks is apt to be 120 volts, but it could be 277 volts, 341 volts or some other voltage. In some cases these loads represent a building or even a portion of a very large building. Depending on the amount of load, the local distribution network may be coupled to one, two, or three feeder buses ( 104 ,  108 ,  112 ). Even when the load can consistently be serviced by just one feeder bus, a desire for reliability leads to providing a redundant path for providing service in case of equipment failure, scheduled maintenance, load balancing, or other needs.  
         [0004]     The local distribution networks  116  are coupled to the feeder buses  104 ,  108 , and  112  through transformers  150  and related equipment. The transformers convert the relatively higher voltage on the primary side  154  of the transformers  150  to the low voltage on the secondary side  158  of the transformers  150 .  
         [0005]     The transformers  150  have breakers  162  on the primary side to isolate the transformers  150  from the feeder buses. The transformers  150  have network protectors  166  on the secondary side  158  of the transformers  150  to isolate the transformers  150  from the local distribution networks  116  as needed to protect the transformers from current flowing from the distribution networks to the primary side  154  of the transformers (known as back feed).  
         [0006]     Additionally, some networks include sets of fuse links  170  between the network protectors  166  and the local distribution networks  116 . Some networks including sets of primary fuse links  174  between the breakers  162  and the feeder buses  104 ,  108 , and  112 .  
         [0007]     The feeder buses  104 ,  108 , and  112  are can be isolated by a set of substation breakers  204  from the transmission network  208  which is ultimately connected to a set of power sources represented here by turbine  212 .  
         [0008]      FIG. 1  shows a small portion of the network which may have more feeder buses and many more local distribution networks  116  providing power to many more loads. These loads may be distributed around a portion of a city. The various transformers  150  may be in pits (vaults) near the various loads. Thus it is convenient to inject analog signals onto the power lines so that the analog signals can be picked off by coils at the substation and fed to a receiver  220 . The precise way that the analog signals are removed from the power line is not relevant to the scope of the present invention, but one typical means for acquiring the analog carrier signal is through a Rogowski air coil as is known in the art. These analog signals are often in the frequency range of 40 KHz to 70 KHz which is much higher than the frequency of the power being distributed over the network. (For example one common frequency for power grids is 60 Hertz although other frequencies are used throughout the world and can be used in connection with the present invention).  
         [0009]     Co-pending and commonly assigned U.S. patent application Ser. No. 11/113,843 for Signal Decoding Method and Apparatus describes one system to decode information sent by phase shift keying over one of several possible carrier frequencies. For purposes of this application, it is not necessary to focus on having more than one carrier frequency as the present invention can be implemented in a system using one carrier frequency. While Phase Shift Keying is a known method for increasing the information density in a data transmission, the details of Phase Shift Keying are not relevant to an understanding of the present invention.  
         [0010]     A preferred location for injecting the analog signal containing information about the operation of a transformer and related equipment is on the secondary side  158  of the transformer between the transformer  150  and the network protector  166 . Transmitter  216  is shown in  FIG. 1  to illustrate this location. Placement of transmitter  216  in this location allows for the injection of the analog signal onto the relatively low voltage, secondary side of the transformer  150 . Traversing the transformer from secondary side to primary side provides only a slight attenuation of the high frequency carrier signal. As the path for the data on the power line carrier signal is from transmitter  216  on the secondary side  158  of the transformer  150  to the primary side  154 , then through the breaker  162 , primary fuse  174 , feeder bus  104 , substation breaker  204 , pick-up coil (not shown) and ultimately to receiver  220 , the data path is not impacted by opening of the network protector relay  166  or fuses  170 . However, if either the breaker  162  or the primary fuse  174  for the phase carrying the power line carrier signal opens, then the data about the operation of the transformer and related information cannot get back to the receiver  220  on the normal path.  
         [0011]     It would be a useful improvement to the prior art to have the capacity for a power line carrier signal to have a secondary communication path from the transmitter near the transformer  150  to the receiver  220  that would be used events such as breaker  162  being open or primary fuses  174  being open.  
         [0012]     It would be a useful improvement to the prior art to have the capacity to bridge data around an open device that so that the open device does not block or inhibit a communication path to the receiver.  
         [0013]     It would be a useful improvement to the prior art to provide alternative data paths to enhance the likelihood that a data record could reach the receiver even in the event that one or more barriers exist for the data record to reach the receiver.  
       BRIEF SUMMARY OF THE INVENTION  
       [0014]     The present invention is directed to a number of ways to increase the likelihood that at least one communication path is available for the transmission of a data record between a transmitter and a receiver over a portion of an electrical distribution network.  
     
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0015]      FIG. 1  depicts a portion of an electrical distribution network in order to explain the environment and context of the present invention.  
         [0016]      FIG. 2  shows the electrical distribution network with an open fuse that blocks the primary data path between transmitter  216  and receiver  220 .  
         [0017]      FIG. 3  shows a smaller portion of the network with transmitters on the load distribution network side of the secondary side fuses.  
         [0018]      FIG. 4  illustrates the use of data bridges around network protectors.  
         [0019]      FIG. 5  illustrates the use of data bridges around both the network protectors and the relevant secondary side fuses.  
         [0020]      FIG. 6  illustrates the use of transmitters with the capacity to inject data records onto both sides of a network protector so that an open network protector is not a barrier to data movement to the receiver.  
         [0021]      FIG. 7  illustrates the use of a repeater to pick up and retransmit data records around an open network protector.  
         [0022]      FIG. 8  illustrates the use of an alternative data path to allow a data record to be passed directly from a first transmitter to a second transmitter and to be transmitted by that second transmitter. 
     
    
     DETAILED DESCRIPTION  
       [0023]     The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown for the sole purpose of conveying the concepts of this invention to those of skill in the art. The actual scope of the invention is not limited by the precise embodiments used to teach the concepts but by the scope of the claims granted in connection with this application.  
         [0024]     In one embodiment of the present invention, a data record is placed onto a carrier signal by a transmitter and subsequently removed from the power line and processed by a receiver. For a data record that is conveyed, perhaps by phase shift keying, perhaps over a period of 390 milliseconds, each transmitter is allotted a time slot for transmission. For example transmitter one is provided with a time slot of 390 milliseconds starting 60 seconds after a synchronizing event (such as the initial provision of power to the transmitter), transmitter two gets a time slot at 60.4 seconds which is 400 milliseconds after transmitter  1  begins sending a data record in its time slot and shortly after the cessation of transmission of the 390 millisecond data signal. Transmitter  3  is given a time slot at 60.8 seconds after the synchronizing event and every 60 seconds thereafter. Thus, a single input to the receiver coming from a single coil connected to a single phase of one feeder bus could process data transmissions from one hundred and fifty transmitters operating on a single power line carrier frequency and receive a data record from each transmitter once a minute. Additional transmitters could be supported if the gap between successive transmissions for each transmitter was increased from one minute to a longer period. For each additional power line carrier frequency used, another one hundred and fifty transmitters could be processed once a minute (assuming that the difference on carrier frequency does not appreciably alter the 390 millisecond length of time needed to transmit the data record).  
         [0025]     Additional transmitters could be serviced by a receiver if those transmitters were connected to a different phase of the three phase power and additional pick-up coils were added to connect the receiver to the data sent over that additional phase.  
         [0026]     Those of skill in the art will be familiar with mechanisms to recognize that more than one transmitter is transmitting on a given frequency at a given time such that the transmitters must be resynchronized or are allocated different time slots or instructed to transmit on different frequencies in order to avoid conflict.  
         [0027]     As the data record transmitted by the transmitter includes a unique identifier for that transmitter (such as an assigned transmitter ID number), the receiver uses the material in the data record to identify the transmitter rather than looking at some combination of the frequency, feeder bus, and time slot. Thus, it does not matter how the data record gets to the receiver as long as the data record gets to the receiver.  
         [0028]     Turning to  FIG. 2 , a primary fuse  174  on the B phase between feeder bus  104  and the primary of transformer  224  is open. Thus the primary path for communication between transmitter  216  and receiver  220  is interrupted. A secondary path exists between transmitter  216  and receiver  220  through network protector  232  past intact fuses  170  onto local distribution network  116  through another set of fuses  170  and network protector  236  and transformer  228 , breaker  240 , intact fuses  174 , onto feeder bus  108  and to receiver  220 . Receiver  220  processes the data record and notes the transmitter ID belongs to the transmitter associated with transformer  224  despite the fact that transformer  224  is attached to feeder bus  104  and this data record was pulled from feeder bus  108 . As the time slots allocated for transmitter  216  is different from the time slot allocated to transmitter  217 , it is not necessary that transmitter  216  use a different carrier frequency than transmitter  217 , even if the data records are transmitted along the same path. Note that this secondary path for communicating information about transformer  224  travels to receiver  220  over feeder bus  108  rather than feeder bus  104  so that information about the status of the transformer  224  and related equipment can be provided to receiver  220  while substation breaker  250  is open as the data record is passed through closed substation breaker  254 . Thus conditions at transformer  224  and in related equipment can be assessed before the transformer is put into service.  
         [0029]     An additional secondary path between transmitter  216  and receiver  220  exists through intact fuses  170 , network protector  250 , transformer  254 , breaker  258 , primary fuses  174 , and feeder bus  112 . The existence of more than one secondary communication path between transmitter  216  and receiver  220  is not a problem.  
         [0030]     If both the primary and the secondary communication paths are open, or if the primary communication path is not open but more than one secondary communication path is open, or if the primary communication path is open and more than one secondary communication path is open, the receiver  220  will receive the same data record during the same time slot via two or more different feeder buses ( 104 ,  108 ,  112 ). The receiver will simply write the data record into memory reserved for that transmitter (as the source transmitter is knowable based on the contents of the data record). As one data record may be received and processed slightly slower than the another copy of that same data record, the later processed data record will either be discarded as redundant or simply overwrite the earlier processed identical data record. A data record would be identifiable as redundant if the data record included a transmission time stamp. Whether duplicate data records are deleted or used to replace identical data records, there is no harm to the receipt of two data records containing the same information.  
         [0031]     Note that with the present location of the transmitter  216 , the opening of breaker  226  or one of the fuses  174  in combination with the opening of network protector  232  and the fuse set  170  on the B phase would make transmitter  216  isolated as a data record could not travel on the primary or any secondary communication path.  
         [0032]      FIG. 3  shows a smaller portion of a network. In  FIG. 3 , transformer  2150  can provide power from feeder bus  108  to load  128  through local distribution network  116  and transformer  3150  can provide power from feeder bus  104  to load  128  through local distribution network  116 .  FIG. 3  differs from  FIG. 2  in that the transmitters  216  and  217  have been moved. Transmitter  216  is now beyond fuse set  3170 . Transmitter  217  is now beyond fuse set  2170 . With the placement of transmitter  216  as shown in  FIG. 3 , transmitter  216  can provide a data record to local distribution network  116  even if network protector  3166  opens. The data record from transmitter  216  can convey information about transformer  3150  and associated equipment to receiver  220 .  
         [0033]     As the transmitters  216  and  217  are used to convey more and more information about the transformer and related equipment, it becomes more and more important that a data path be maintained in order to provide information that may help remote operations people in discerning whether equipment, such as a network protector opened properly to avoid back feeding the transformer or opened without sufficient justification. As the information in the data record is used to provide more and more information, it may become appropriate to provide a bridge around components that are apt to block the primary data communication path.  
         [0034]      FIG. 4  illustrates this concept.  FIG. 4  introduces a data bridge  404  providing a low impedance pathway for high frequency signals such as the carrier frequencies and a high impedance pathway to block the low frequency signals such as the 50 or 60 Hertz current used in many power distribution systems. A data bridge of this type could be composed of a high pass filter or a band pass filter to allow the carrier frequencies to have a low impedance pathway. An example of when such a data bridge would be useful is when all feeds to a spot node have an interruption of some type and at least one of the interruptions is exclusively in the network protector. If load  128  includes some end user facilities with faulty cogeneration equipment, it is possible that the cogeneration equipment could back feed the local distribution network  116  such that network protector  3166  opens. If breaker  2162  and network protector  2166  were already open, there would not any viable path from transmitters  216  and  217  to the receiver  220  unless the data records passed over data bridge  404  around the open network protector  3166 . These data records would convey the voltage level of the local distribution network  116  which would cause the operators to consider faulty cogeneration equipment rather than a faulty network protector  3166  as the cause of the open network protector.  
         [0035]      FIG. 5  shows a variation of the data bridge concept shown in  FIG. 4 . In  FIG. 5 , the data bridges  408  and  410  extend around fuse sets  3170  and  2170  in addition to network protectors  3166  and  2166 .  
         [0036]     An advantage of a data bridge as shown in  FIGS. 4 and 5  over the exclusive reliance on a secondary communication path over the local distribution network  116  is that the best path for the data record from the transmitter  216  to the receiver  229  is through its network transformer  3150  and through the original feeder bus  104 .  
         [0037]     The secondary communication path from transmitter  216  to receiver  220  over local distribution network  116  and transformer  2150  is not the desired path back to the substation. The secondary communication path has a great deal more signal attenuation. This extra attenuation arises in part from uncontrolled impendence mismatches on the network. The various figures shown to illustrate the present invention do not convey the extended distances that may exist between transformers that feed the same local distribution networks (such as  116 ). The distance between the secondary side of transformer  3150  and the secondary side of transformer  2150  is often 600 to 1000 feet apart.  
         [0038]     Thus, when feeder bus  104  is in service (substation breaker  3204  is closed) but network protector  3166  is open, the data path from transmitter  216  to receiver  220  through the data bridge ( 404  or  408 ) has much less attenuation of the data signal than the secondary communication path through transformer  2150 .  
         [0039]      FIG. 6  provides another solution that provides two communication paths such that the opening of the network protector  2166  or  3166  or the fuses  2170  or  3170  cannot isolate the transmitters  616  and  617  from receiver  220 . The solution illustrated in  FIG. 6  calls for the dual injection of the data record from each transmitter to both a position between the secondary of the transformer ( 2150  and  3150 ) and the network protector ( 2166  and  3166 ) and between the fuses ( 2170  and  3170 ) and the local distribution network  116 . As discussed above, if both the primary and the secondary communication paths are open, the receiver  220  will receive the same data record during the same time slot via two different feeder buses ( 104  and  108 ). One of skill in the art can appreciate that when network protector  3166  is closed and fuse set  3170  is intact, there is no advantage to the dual injection of the data record. The receiver will simply write the data record into memory reserved for that transmitter (as the source transmitter is knowable based on the contents of the data record). As one data record may be received and processed slightly slower than the other copy of that same data record, the later processed data record will either be discarded as redundant or simply overwrite the identical data record. In either event, there is no harm to the receipt of two data records containing the same information.  
         [0040]     The dual injection concept in  FIG. 6  could be applied to inject the data record on either side of the network protector  2166  or  3166  without also providing a route around fuses  2170  and  3170  as those fuse sets may not exist in particular system, may be remote from the network protectors, or may not be viewed as a frequent source of interruption of the secondary communication pathways.  
         [0041]      FIG. 7  illustrates an alternative to a data bridge as shown in  FIGS. 4 and 5 . In  FIG. 7 , the data records transmitted by transmitters  216  and  217  in their respective time slots are received by repeater receiver  716  and then retransmitted in the appropriate time slots by repeater transmitter  726 . The timeslot to be used could be discerned based on the identity of the original transmitter as discerned from the data record, from a time slot indication provided in the data record, or by noting the time of receipt of the data record.  
         [0042]     To illustrate this point, transmitter  217  transmits a data record 1 A in time slot  1 . This data record is obtained from the bus by a pick-up coil or alternative means and processed by repeater receiver  716 . Transmitter  216  transmits a data record 3 A in time slot  3 . This data record is read by repeater receiver  716 . During the next time slot  1 , transmitter  217  transmits a data record 1 B in time slot  1  while repeater transmitter  726  could retransmit data record 1 A. As this would be two transmitters transmitting during the same time slot, some data could be lost as the data records may not be identical between data record 1 A and data record 1 B. In order to avoid this potential for loss, the repeater transmitter  726  does not transmit any data records unless the most recent data record from transmitter  216  indicates that network protector  3166  is open. (Alternatively, the repeater transmitter  726  could receive status information directly from network protector  3166 .) Thus, repeater transmitter  726  does not retransmit data records from either transmitter  216  or any other transmitter (such as  217 ) unless there is a known need to bridge around open network protector  3166 . Repeater receiver  716  and repeater transmitter  726  could be two separate components or different functionalities of one device.  
         [0043]     In a like manner, repeater receiver  717  and repeater transmitter  727  operate to selectively retransmit data records obtained and processed at repeater receiver  717 . The data records are injected above network protector  2166  if the network protector  2166  is open (as indicated by the data record from transmitter  217  or data received from network protector  2166 ).  FIG. 7  shows the repeater receivers acquiring the data record from the local distribution side of fuses  2170  and  3170 . The repeater receivers could also be connected to acquire the data record between the fuses  2170  and  3170  and the network protectors  2166  and  3166 .  
         [0044]      FIG. 8  illustrates another strategy for providing for an alternative communication path from a transmitter to the receiver in the substation. In  FIG. 8 , the transmitters  2216  and  2217  are located between the secondary of the transformers  2150  and  3150  and the network protectors  2166  and  3166 . In the event that a fuse on the B phase of the set of primary fuses  3174  opens, the primary communication path between transmitter  2216  and receiver  220  is interrupted. The secondary communication path from transmitter  2216  and receiver  220  is through network protector  3166 . If the secondary communication path is blocked as network protector  3166  is open, then the transmitter  2216  knowing that the network protector  3166  is open can opt to use an alternative path.  
         [0045]     The alternative path for sending a data record from transmitter  2216  shown in  FIG. 6  is to send the data record over a communication link  2227  to an input data port on transmitter  2217 . This data record contains an identification of the transmitter that created the data record. Transmitter  2217  would transmit its own data record in the allocated time slot for transmitter  2217  and transmit the data record received from transmitter  2216  during the time slot for transmitter  2216 . Transmitter  2217  would know the time slot for transmitter  2216  through receipt of this information from transmitter  2216  such as within the data record sent by transmitter  2216  or through a previously stored set of information that included the mapping of transmission time slots to specific transmitters for at least those transmitters with a data link connected directly to transmitter  2217 .  
         [0046]     In order to provide for an alternative data communication path for transmitter  2217 , the data record created by transformer  2217  could be passed over data link  2226  to a data port on transmitter  2216  and subsequently transmitted by transmitter  2216  using the time slot for transformer  2217 . Transmitter  2217  would send data records across data link  2226  to transmitter  2216  whenever transmitter  2217  noted that network protector  2166  was open. Thus, the alternative path can be used when the secondary data path is blocked. The alternative path can be used whether or not the primary data path is viable (through transformer  2150  and ultimately through feeder bus  108 ).  
         [0047]     If primary fuse  3174  is restored but network protector  3166  remains open, then two paths exist for the transmission of a data record from transmitter  2216 . During the time slot allocated to transmitter  2216  the data record would travel on the primary data path through transformer  3150  and to receiver  220  through feeder bus  104 . A second copy of the data record from transmitter  2216  would be sent via data link  2227  to transmitter  2217  and then sent by transmitter  2217  on the next instance of the time slot reserved for transmitter  2216  through transformer  2150  and ultimately feeder bus  108 . Note that as transmitter  2217  is sending the data record received from transmitter  2216 , transmitter  2216  is sending a new data record through the primary data path to receiver  220  on feeder bus  104 . Thus, receiver  220  will receive two data records transmitted from transmitter  2216  on subsequent transmission cycles at approximately the same time over feeder bus  104  and feeder bus  108 .  
         [0048]     The handling of this situation turns on how the receiver processes the data records. If the data record has a transmission time stamp from transmitter  2216 , then the duplicate data record received belatedly on feeder bus  108  can be deleted by receiver  220  as redundant. If the receiver  220  simply stores the most recent data record from each transmitter, then the belated data record from transmitter  2216  received via alternative data path on feeder bus  108  could conceivably replace the newer data record recently received over the primary data path on feeder bus  104  (if the newer data record was processed before the belated data record). Due to relative stability of the data sent via the data records in comparison with the frequency of transmission of the data records, this is not a serious problem.  
         [0049]      FIG. 8  uses two links  2226  and  2227  to facilitate the discussion of the explanation of the concept. One of skill in the art will recognize that while two separate communication links could be used, one data link could be used for communication in both directions if the transmitters use bidirectional ports.  
         [0050]     The present invention is incorporated in  FIG. 8  does not require that the two transmitters rely on each other to be the alternative data paths. For example for transmitters A, B, and C, transmitter A could have a data path to transmitter B which has a data path to transformer C which has a data path to transmitter A. Thus, each transmitter is connected to one other transmitter.  
         [0051]     Alternatively, a transmitter such as transmitter  2216  could be connected to more than one transmitter to create two alternative data paths when network protector  3166  prevents use of the secondary data path. Duplicative data records received by the receiver  220  over different feeder buses can be processed as discussed above.  
         [0052]     One or skill in the art will recognize that the alternative embodiments set forth above are not mutually exclusive and that in some cases alternative embodiments can be created that implement two or more of the variations set forth above.  
         [0053]     Those skilled in the art will recognize that the methods and apparatus of the present invention have many applications and that the present invention is not limited to the specific examples given to promote understanding of the present invention. Moreover, the scope of the present invention covers the range of variations, modifications, and substitutions for the system components described herein, as would be known to those of skill in the art.  
         [0054]     The legal limitations of the scope of the claimed invention are set forth in the claims that follow and extend to cover their legal equivalents. Those unfamiliar with the legal tests for equivalency should consult a person registered to practice before the patent authority that granted this patent such as the United States Patent and Trademark Office or its counterpart.