Abstract:
Fault detection and power network quality monitoring are performed for a power line network using power line communications (“PLC”) signal transceiving and data processing capabilities. Power line signals are continuously received and processed to obtain signal data representative of power line network operating conditions that are expressed in the received power line signals. The harmonic content and noise signature of the signal data are evaluated with reference to known fault signature data and power line network topology properties for detecting and identifying the location of an existing or anticipated fault in the power line network and assessing power transmission quality of the network.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 60/380,142 filed May 6, 2002, which is incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to the field of data communications over conventional utility electric power conveying media, and more particularly to using power line communications (“PLC”) equipment to detect and identify the location of an existing or anticipated fault in an electric power distribution network and to monitor the quality of the power network. 
     BACKGROUND OF THE INVENTION 
     A conventional utility electric power generating facility supplies electric power to electric power users over a vast and expansive electric power distribution grid containing many interconnected electric power line networks. The power line networks, which can be of various sizes, convey low, medium or high voltage electric power. Each of the networks includes such power transmission equipment elements as overhead electric power transmission wires, electric power transmission line connectors, surge arrestors and step-down electric power transformers. 
     Maintenance of the power line networks from which a larger power distribution grid is constructed is a major and ongoing effort. Each of the individual power networks of the grid usually contains a large number of power equipment elements that can conceivably fail in part or completely for a variety of causes, which include exposure to the external environment and end of useful life, to create a partial or complete discontinuity in the network at the element. When a power network element experiences a predetermined failure level, a fault is created in a power line network at the element that prevents satisfactory transmission of electric power downstream of the location of the fault, thereby cutting off the supply of electric power to downstream power users. 
     Power equipment components can fail either gradually or substantially instantaneously to create a fault in a power line network. A substantially instantaneous fault can be created, for example, upon the complete severing of a connection between a transmission wire and another transmission wire or power wire connector, such as may occur when a utility pole to which a transmission wire is connected falls in a storm. The power company typically learns of this fault from the power user, who no longer is receiving electric power service, soon after the fault initially occurs. 
     A power company, however, does not usually become aware of a gradual equipment failure, which may eventually become a fault, until the failure becomes so severe that a fault actually occurs. Consequently, the power company does not have the necessary information to perform preventive maintenance on the failing element before the fault occurs. For example, a power transformer, which is known to degrade gradually over time, may begin to operate at less than an optimal level, yet still operate at a level that permits a satisfactory, uninterrupted supply of electric power to downstream power users. In this circumstance, the downstream power users continue to have satisfactory power service while the operating level of the transformer is initially degrading. The power users, therefore, do not notify the power company of any problem with power service. Thus, the power company is not aware of an existing or worsening equipment failure and the potential that the equipment failure can eventually become a fault. Ultimately, an insulation failure in the transformer equipment may develop into a major failure event or fault in the power network. The power company, however, typically learns that the transformer equipment has reached the end of its useful life only after a fault in the network is created. 
     Therefore, a need exists for method and system for obtaining information concerning operating status of power line network elements and using the element operating status information to detect and identify the location of an existing or anticipated (future) fault in the network. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, power line communications (“PLC”) equipment collects signal data representative of signals continuously received from a power line that is part of a power line network, and performs network monitoring and analysis processing on the signal data to detect and identify the location and the nature of an existing or anticipated fault in the power network and to determine operating status of power line network elements and. In a preferred embodiment, the network monitoring and analysis processing determines that a composite received signal includes predetermined fault characteristics and uses frequency domain or time domain reflectometery techniques to determine and record the signature associated with the network topology and anomaly detection. In an alternative preferred embodiment, the processing analyzes the collected signal data to determine the presence of high frequency components that may be representative of anticipated equipment failures. In a further preferred embodiment, the processing analyzes the collected signal data to determine the presence of harmonics related to power quality monitoring and FCC compliance and also to power factor. In another preferred embodiment, conventional ground current and current and voltage detection circuitry is coupled to the PLC equipment to permit collection of data representative of ground currents and the currents and voltages of signals present on the power line. This ground current and signal current and voltage data also is used in the network monitoring and analysis processing. 
     In a preferred embodiment, the PLC equipment separates line noises from communication signals by collecting and analyzing PLC silent data representative of electrical signals traveling on the power line network during PLC silent periods, i.e., during predetermined time intervals when PLC data communications and control signals are not scheduled for transmission over the network or are expected not to be transmitted. The PLC silent data can include, as suitable, the polarity, amplitude, phase, and frequency of an electric signal on the power line network and, for an electric signal reflected by an element of the power line network, an electrical signature, such as an impulse response. For example, a PLC silent signal can be a composite of a stimulus signal, which contains a set of specifically spaced sine waves that are useful for extracting frequency domain reflection signature from the power line network, and the reflected stimulus signal, which may additionally contain electrical signatures generated by power line network elements causing the reflection. The PLC silent period signal detection simplifies some network monitoring and analysis processing implementations, where there are a suitable number of silent periods available, by allowing for a straightforward method of monitoring the network response and noise signatures during these periods to look for faults, or phenomena that may lead to faults in the near future, on the network. In cases of heavily loaded networks, where there may not be enough silent periods available for continuous power quality monitoring, a method of extracting a known signal from a composite signal can be used, with the resultant signal being used as a network response signature for the purposes of network monitoring. The PLC silent data can include, as suitable, the polarity, amplitude, phase, and frequency of an electric signal on the power line network and, for an electric signal reflected by an element of the power line network, an electrical signature, such as an impulse response. For example, a PLC silent signal can be a composite of a stimulus signal, which contains a set of specifically spaced sine waves that are useful for extracting frequency domain reflection signature from the power line network, and the reflected stimulus signal, which may additionally contain electrical signatures generated by power line network elements causing the reflection. 
     In a preferred embodiment, power quality analysis logic (“PQAL”) is included with or coupled to the PLC equipment and performs a power quality evaluation by processing the collected PLC silent data or a composite signal data with the extracted background noise to determine the presence of harmonics and power factor distortions. The processing performed by the PQAL includes analyzing the signal data associated with PLC silent intervals or signal (active) intervals whose noise signatures have been extracted with reference to fault signature data representative of power line network fault conditions and expected signal response and signal transfer function associated with the topology of the network. The PQAL, based on the fault evaluation, generates a fault alarm or a warning when an existing or anticipated fault is detected. In an exemplary preferred embodiment for detecting an anticipated fault, an anticipated fault is identified upon detection of the higher frequency harmonics that would be injected onto the power line network when insulation breakdown occurs at a failing transformer. In addition, the PQAL performs further fault evaluation processing to generate fault location data, which identifies the location of the element in the network creating an electric signal discontinuity condition that corresponds to an existing or anticipated fault. In a preferred embodiment, evaluation of historical records containing frequency and time domain response signatures, transfer function parameters, network impedance, and noise signatures helps to determine nature and location of an anticipated or existing fault. In a further embodiment, the PQAL, based on the fault evaluation, generates a power quality estimate that is representative of the power transmission quality of the network. 
     In a preferred embodiment, the PLC equipment transmits predetermined signals onto the power line to provide that additional signal data can be collected from the power line for use in the network monitoring and analysis processing. In one preferred embodiment, a PLC transceiver, in addition to collecting PLC silent data already existing on the line, generates fault event PLC silent data signals having combinations of predefined transitions and transmits the fault event signals during the PLC silent intervals. The fault event data signals can be PLC or other suitable wideband signals. The PLC transceiver processes reflections of the fault event data signals, which a failing or failed element of the power line network causes and which are received during PLC silent periods, and stores in a memory transmission and received fault event data representative of the transmitted and received fault event data signals, respectively. The PQAL performs a fault evaluation using the received fault event data and, optionally, the transmission fault event data and any other PLC silent data collected at the PLC transceiver. 
     In another preferred embodiment, a destination PLC transceiver processes a fault event data signal, which was received during a PLC silent period and which a source PLC transceiver transmitted during the PLC silent period, and stores in its memory transfer fault event data representative of the received fault event data signal. The PQAL, at either the source or destination PLC transceiver, uses the transfer and associated transmission fault event data to perform a fault evaluation on the portion of the power line network between the source and destination PLC transceivers. The fault event data is transmitted between the source and destination PLC transceivers, as desired, on PLC data communications signals, based on instructions that the PLC transceiver performing the fault evaluation transmits to the other PLC transceiver on PLC data communications signals. 
     In a further preferred embodiment, a plurality of PLC transceivers is on the power line network and each of the PLC transceivers transmits to a PLC head end unit, over the power line network and on PLC data communications signals, PLC silent data that includes fault event data. The PLC head unit, which contains conventional PLC transceiver equipment, uses the PLC silent data to perform a high level network fault evaluation. In still another preferred embodiment, each of the PLC transceivers transmits to the PLC head end unit the fault alarm, fault location and power network quality estimate data results of the fault evaluations performed at the respective PLC transceivers. 
     In a further preferred embodiment, the PQAL in the PLC transceiver controls and causes transmission of time domain reflectometry (“TDR”) data signals onto the power line network during the PLC silent periods. The PLC transceiver stores TDR data representative of reflected TDR data signals received at the PLC transceiver during the PLC silent periods. The PQAL uses the TDR data, together with any other available PLC silent data, in a fault evaluation to more precisely identify the location of an existing or anticipated fault. 
     In a further preferred embodiment, the PQAL in the PLC transceiver controls and causes transmission of frequency domain reflectometry (“FDR”) data signals onto the power line network during the PLC silent periods. The PLC transceiver stores FDR data representative of reflected FDR data signals received at the PLC transceiver during the PLC silent periods. The PQAL uses the FDR data, together with any other available PLC silent data, in a fault evaluation to more precisely identify the location of an existing or anticipated fault. 
     In still another preferred embodiment, the PQAL performs a fault evaluation using PLC silent data and channel quality data which is stored at the PLC transceiver and was collected based on monitoring of PLC signals during the PLC active period. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects and advantages of the present invention will be apparent from the following detailed description of the presently preferred embodiments, which description should be considered in conjunction with the accompanying drawings in which: 
         FIG. 1  is a block diagram of a preferred embodiment of a power line communication transceiver including power quality analysis logic in accordance with the present invention. 
         FIG. 2  is a time domain representation of power line signal transmission during the PLC active and silent periods and illustrates the results of PQAL processing at a PLC transceiver in accordance with the present invention. 
         FIG. 3  is a block diagram of a preferred embodiment of a power line network distribution system including a PLC head end unit and high, medium and low voltage power line networks including PLC transceivers containing respective PQALs in accordance with the present invention. 
         FIG. 4  is a time domain representation of a preferred embodiment of a time domain reflectometery power line signal transmitted during the PLC silent interval in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The use of electrical signals traveling on a power line communications (“PLC”) network to perform power line network fault evaluation and quality monitoring is illustrated below in connection with a conventional, prior art PLC transceiver which further includes power quality analysis logic (“PQAL”) in accordance with the present invention. The addition of the PQAL to the conventional PLC transceiver is substantially a software modification requiring relatively few hardware changes and readily permits collection of data representative of power line signals on the network, during both PLC active and PLC silent intervals, for use in a power line network fault evaluation. The conventional PLC transceiver provides for a physical and electronic signal connection to the power line network, which includes the functionalities of generating and injecting wideband signals onto the power line network and receiving and processing power line signals. For the purpose of explaining the preferred embodiment, it is assumed that the PLC transceiver uses a signal above about 60 Hz and below about 100 MHz, and has the capability to transmit and receive signals in the frequency band spanning from 0 Hz (DC) to about 300 Mhz. It is to be understood that, in accordance with the present inventive technique, the PQAL can be included within or coupled to any device having power line network signal transmitting and receiving capabilities and associated data signal processing and storage capabilities. It is to be further understood that, for purposes of illustration, the PQAL is shown as a separate block and also that the PQAL could be implemented as a plurality of functions embedded in other existing modules of a system in accordance with the present invention and/or a plurality of extensions to the existing modules of the system or a combination thereof. 
       FIG. 1  shows a preferred embodiment of a conventional orthogonal frequency division multiplexing (“OFDM”) PLC transceiver  10  coupled to a power line network element  12  and further including PQAL  14  in accordance with the present invention. See, for example, U.S. patent application Ser. No. 10/211,033, filed Aug. 2, 2002 and U.S. application Ser. No. 10/309,567, filed Dec. 4, 2002, each of which is assigned to the assignee of this application and incorporated by reference herein, for a description of conventional PLC transceiver construction and operation. The inventive PLC transceiver is shown in FIG.  1  and described below as containing, in addition to the PQAL  14 , conventional functional PLC transceiver blocks for processing PLC and other power line signals. The PLC transceiver blocks generate, and transmit and receive, power line signals, such as conventional PLC control and data communications signals. In addition, the PLC transceiver blocks perform power line signal processing, including conventional PLC signal processing, and store and process power line signal data that the PQAL can use in fault evaluation processing. It is to be understood that the PLC transceiver blocks of the inventive PLC transceiver described below as performing data or signal processing operations constitute a software module, a hardware module or a combined hardware/software module. In addition, each of the modules suitably contains a memory storage area, such as RAM, for storage of data and instructions for performing processing operations in accordance with the present invention. Alternatively, instructions for performing processing operations can be stored in hardware in one or more of the modules. Similarly, the PQAL  14  can constitute a software module, a hardware module or a combined hardware/software module. 
     Referring to  FIG. 1 , the PLC transceiver blocks establish the physical connection and electronic signal link between the power line network element  12  and a data input/output (“I/O”) device, such as a computer, as is known in the prior art. The following PLC transceiver blocks are connected to one another in sequence and operate (i) to connect the PLC transceiver to the I/O device that provides input data, and (ii) to generate and transmit onto the power line network a PLC signal containing the input data: coding  16 , interleaving  18 , modulation  20 , mapping/pilot insertion  22 , inverse fast fourier transform (“iFFT”)  24 , cyclic extension windowing and filtering  26  and digital-to-analog converter (“DAC”), radio frequency (“RF”) transmitter and power line coupler  28 . The PLC transceiver blocks  36 ,  38 ,  40  and  42 , in combination, constitute PLC receiver logic  41 . 
     Further, the following PLC transceiver blocks are connected in sequence and operate (i) to receive a PLC data signal from the power line network, and (ii) to extract the digital data that is carried on the received PLC signal: power line coupler, RF receiver and analog-to-digital converter (“ADC”)  30 , timing and frequency synchronization and cyclic extension removal  32 , FFT  34 , demapper/channel correction  36 , demodulation  38 , deinterleaving  40  and decoding  42 . The PLC transceiver blocks  16 ,  18 ,  20  and  22 , in combination, constitute PLC transmitter logic  43 . As is known well known in the art, the PLC transceiver blocks  28  and  30  are connected to the power line network element  12  and convert digital data to power line signals and vice versa, respectively. Also as is well known in the art, the PLC transceiver blocks  24  and  34  process digital data transmitted on and received from the power line network between the time domain and the frequency domain. 
     In addition, the PLC transceiver  10  includes a conventional PLC software controller  50  and a data and control signal bus  52 . The bus  52  couples the controller  50  to each of the PLC transceiver blocks  16 ,  19 ,  20 ,  22 ,  24 ,  26 ,  28 ,  30 ,  32 ,  34 ,  36 ,  38 ,  40  and  42 . As is known in the prior art, the controller  50  transmits control signals to, and exchanges data signals with, each of the PLC transceiver blocks  16 ,  18 ,  20 ,  22 ,  24 ,  26 ,  28 ,  30 ,  32 ,  34 ,  36 ,  38 ,  40  and  42  to establish a signal link between the power line network element  12  and an I/O device, which is coupled to the PLC transceiver blocks  16  and  42 . 
     Referring to  FIG. 1 , in accordance with a preferred embodiment of the present invention, the PQAL  14  is coupled to the iFFT  24  and the FFT  34  by data lines  55  and  57 , respectively, and to the PLC controller  50  by input data line  54  and fault evaluation data output line  56 . The PQAL  14  includes a memory (not shown) for storing power line network information and protocol information, which the controller  50  supplies on the line  54 . The power line network information preferably includes power line network topology data representative of the expected signal response of the power line network that extends upstream and downstream from the element  12 . In addition, the PQAL  14  memory includes protocol data, such as PLC protocol layer and PHY layer data, which provides information as to the PLC active and silent periods. The PLC active and silent period information permits the PQAL  14  to control the reception and transmission of power line signals and also reflections of signals generated at the PLC transceiver, which are discussed in detail below, at the PLC transceiver blocks  24 ,  26 ,  28 ,  30 ,  32  and  34 , such that signal data representative of received PLC active and silent signals can be obtained for use in fault evaluation processing in accordance with the present invention. 
     In a preferred embodiment, the memory of the PQAL  14  includes data representative of unique, identifiable signal signatures which can be used to determine that the power line network includes an existing or anticipated fault. The identifiable signatures correspond to those signals that would be generated and transmitted over a power line network when an element in a power transmission system, such as a transformer, surge arrestor or overhead wire, begins to fail. For example, the signature data can include the unique RF signature representative of the corona like discharge imposed on the power line network when a tree branch touches an overhead power transmission wire. 
     In a preferred embodiment, an external source transmits the network topology data to the PLC transceiver  12  on a PLC data communications signal and the controller  50  forwards this network topology data to the PQAL  14  on the line  54 . 
     The PLC transceiver  10  operates as follows in accordance with a preferred embodiment of the invention. The PLC transceiver blocks  30 ,  32  and  34  process power line signals, or composite signals, which are received at the power line element  12  during the PLC silent and active periods. In this embodiment, the power line signals may not be a function of or based on a power line signal transmitted by a PLC transceiver which is on the power line network to which the element  12  is coupled. The FFT block  34  generates digital PLC silent data or composite signal data representative of the received signals and forwards the signal data to the PQAL  14 . The PLC silent data preferably includes the polarity, amplitude, phase and frequency of the received power line signal and also its electrical signature. The composite signal data preferably includes the extracted noise signatures of the network. The PQAL  14  stores in its memory the signal data received from the FFT block  34 . 
     In accordance with the present invention, the PQAL  14  processes the signal data in view of the network topology and fault signature data, which was provided from the controller  50  and stored in its memory, to determine whether the signal data indicates an existing or anticipated fault and which element or elements in the network constitute the discontinuity causing the fault condition. In a preferred embodiment, the processing of the signal data with respect to the stored signatures in the PQAL memory can provide information about the distance between the PLC transceiver and the power line network element that caused the RF signature which is represented in the signal data. In a preferred embodiment, if the PQAL determines that the signal data includes a unique stored signature, important parameters about the event that caused the fault, such as the presence of harmonics or power factor distortions, would be known. Based on the results of the fault evaluation processing, the PQAL  14  generates a fault alarm indicating an existing or anticipated fault. 
     Once a fault is detected, the PQAL  14  performs further processing on the signal data to determine the location and characteristics of the power network element or elements causing the fault, and generates fault location data based on this processing. In a preferred embodiment, the PQAL  14  evaluates the signal data in view of the network topology and a detailed list of element properties to identify the network element or elements causing the fault. Depending on the network complexity, the PQAL performs additional fault evaluation processing, with reference to the signature data, to identify or locate the element. 
     In an alternative preferred embodiment, the PLC transceiver  10  generates signal data from the power line signals received during each successive PLC silent period, and the PQAL  14  creates a history of power line network signal characteristics based on the stored historical PLC silent data for use in the fault evaluation processing. 
     In a preferred embodiment where a suitable number of PLC silent periods are available for collecting PLC silent data, the detection of PLC silent signals simplifies network monitoring and analysis processing performed by the PQAL  14  by permitting direct monitoring of the network response signature during the PLC silent periods for determining the presence of faults or phenomena that may lead to faults in the near future on the network. In embodiments where the network is heavily loaded, such that an insufficient number of PLC silent periods is available for continuous power quality monitoring, network monitoring by the PQAL is preferably performed by determining if a composite signal, detected during PLC active periods, includes a known response signature. 
     In a further preferred embodiment, the PQAL  14 , as part of the fault evaluation processing, determines the quality of the power line and generates power line quality estimate data. 
     It is noted that PLC transceiver operation during the PLC active periods continues as in the prior art. The PLC transceiver blocks  30 ,  32 ,  34  receive PLC data communication signals and the PLC receiver logic  41  generates a digital data output based on the received signals. Further, the PLC transmitter logic  43  provides input data to the PLC transceiver blocks  24 ,  26  and  28 , which generate and transmit PLC data communication signals.  FIG. 2  illustrates typical power line signal transmission during the PLC silent and active periods and the data outputs generated at the PLC transceiver  10  based on the fault evaluation processing and also conventional PLC data communications signal processing. In a preferred embodiment, the PQAL  14  also uses channel history quality data collected at the PLC transceiver  10  during the PLC active interval, such as described in U.S. patent application Ser. No. 09/605,064, U.S. patent application Ser. No. 09/290,353, and U.S. Provisional Patent Application No. 60/113,608, filed Dec. 23, 1998, each of which is assigned to the assignee of this application and incorporated by reference herein, in the fault evaluation processing to detect and locate faults. 
     Following fault evaluation processing, the PQAL  14  transmits fault alarm, fault location and power quality estimate data to the controller  50  on the line  56 . The controller  50  then causes the transmission of this fault evaluation data to a desired destination, such as the I/O device connected to the PLC transceiver block  42 . 
     In a preferred embodiment, the controller  50  causes transmission of the fault evaluation data onto the power line network on PLC data communication signals, such that a user having signal communications access or an indirect communications link to the power line network can receive the data. Consequently, higher level network control elements can readily receive and use the fault evaluation data to further analyze and identify the power line network conditions. 
       FIG. 3  illustrates a preferred embodiment of a power line network  90  including a power plant  100  containing a PLC head end unit  102 , a high voltage power network  104  containing a PLC transceiver  110 , medium voltage power networks  106  and  107  containing respective PLC transceivers  210 A and  210 B, and low voltage power networks  108 ,  112  and  114  containing respective PLC transceivers  310 A,  310 B, . . .  310 X,  410 A,  410 B, . . .  410 X and  510 A,  510 B, . . .  510 X. Each of the PLC transceivers in the networks  104 ,  106 ,  107 ,  108 ,  112  and  114  is preferably identical, or substantially similar, in construction and operation as the PLC transceiver  10  described above. The PLC head end unit  102  is a conventional device which has been modified to include software associated with the evaluation of a power line network for faults and power quality conditions based on fault evaluation data generated at the PQAL of a PLC transceiver, as described above. In a preferred embodiment, each of the PLC transceivers in the networks  104 ,  106 ,  107 ,  108 ,  112  and  114  continuously transmits to the PLC head end unit  102  PLC silent data, alarm data, fault location data and power quality estimate on PLC data communications signals. The PLC head end unit  102  uses such data to perform higher level network processing concerning faults and power quality. 
     Thus, the present invention advantageously provides that the presence of a plurality of the networked PLC nodes in a given network can be used in connection with single-ended and multi-node techniques and methods of measurement and network analysis. In a single-ended mode a stimulus signal originates at the point of measurement, whereas in a multi-mode mode a stimulus signal originates in the node not co-located with a node conducting the measurements. In this configuration, the networked environment offers the ability to coordinate multi-mode measurements as well as perform system calibration and synchronization functions. 
     Referring again to  FIGS. 1-2 , in a preferred embodiment, the PQAL  14  causes the PLC transceiver  12  to transmit fault event data signals onto the power line network during the PLC silent periods. The fault event data signals transmissions generate additional PLC silent data for use in fault evaluation processing. The PQAL  14  uses the PLC protocol layer and PHY layer data to coordinate access to the power line network, such that fault event data signals are transmitted onto the power line network only during the PLC silent periods. In this preferred mode of operation, based on fault event data provided by the PQAL  14 , the PLC transceiver blocks  24 ,  26  and  28  generate and transmit onto the power line network at the element  12  fault event data signals. The PQAL  14  stores in its memory transmit fault event data, representative of the transmitted fault event data signals, and reflection fault event data, representative of reflections of the fault event data signals received during the PLC silent periods and then processed at the PLC transceiver blocks  30 ,  32  and  34 . Preferably, the PQAL  14  performs fault evaluation using the transmit and received fault event data. 
     In a further preferred embodiment, the PQAL  14  causes the PLC transceiver  12  to generate wideband time domain reflectometry (“TDR”) signals as the fault event data signals, to transmit these TDR signals onto the power line network at the element  12  during the PLC silent periods, and to receive during the PLC silent periods reflected TDR signals at the PLC transceiver blocks  30 ,  32  and  34 . The TDR signal is preferably a wideband signal because it approaches an ideal impulse signal and, therefore, permits easier signal processing for identification of a fault. In one preferred embodiment, the PQAL  14  generates a wideband OFDM TDR signal, such as shown in  FIG. 4 , for transmission onto the power line network. The PQAL  14  stores in its memory TDR data representative of the reflected TDR signals which are received and processed at the PLC transceiver blocks  30 ,  32  and  34 . In addition, the PQAL  14  memory preferably includes TDR signature data which is representative of the presence of a shorted connection, open connection, resistive connection, etc., in the power line network. 
     In a preferred embodiment, the PQAL  14  uses the TDR data in a fault evaluation to determine characteristics of the power line network under analysis, such as the nature of each discontinuity, and to help detect network faults or anticipated faults. In a further alternative embodiment, the PQAL  14  uses the TDR data to identify a change in the characteristics of a network to prompt further analysis. The PQAL preferably uses the TDR data to determine, with greater resolution, the distance of a discontinuity from the PLC transceiver along a power line network path. 
     In alternative preferred embodiment, the PQAL  14  causes the PLC transceiver  12  to generate frequency domain reflectometry (“FDR”) signals as the fault event data signals and performs processing similar to that described above with respect to the TDR signals to identify a change in the characteristics of a network and determine, with greater resolution, the distance of a discontinuity from the PLC transceiver along a power line network path. In addition, the memory of the PQAL  14  would include an initial signature of the FDR response data which can be used to continuously compare with current response data and identify changes that would be the result of a change occurring in the network or a network device. Further, the FDR data can be used in a fault evaluation algorithm to more precisely identify the location of an existing or anticipated fault. See U.S. Pat. No. 6,466,649, incorporated by reference herein. 
     In a further preferred embodiment, the PQAL uses a combination of PLC silent period data and composite FDR data to further pinpoint the fault location or network anomaly. 
     In another preferred embodiment, the PQAL  14  provides that a shaped pulse like signal is generated and used to provide a time domain response of the network. In another embodiment, a sweep like signal could be used to measure transfer function and S parameters of the network. 
     Thus, the inventive PLC transceiver generates a steady output stream of power line network quality information, fault alarms and fault location data based on processing of power line signals with respect to fault signature, power line network topology and expected power line network signal response information. The PLC transceiver can be operated to generate TDR or FDR data, which can be used to more precisely determine the location of the element or elements detected as causing the existing or anticipated fault. 
     Although preferred embodiments of the present invention have been described and illustrated, it will be apparent to those skilled in the art that various modifications may be made without departing from the principles of the invention.