Abstract:
An apparatus for monitoring and measuring analog signal levels, current and reflected power (SWR) in an electric utility substation environment. The apparatus includes selective measurement capabilities for at least five individual frequencies, respectively, and includes programmable event recording and remote alarms. The apparatus will provide data to support in-band spectral analysis of recorded events, and can be located at any point along an associated communication path. The apparatus is non-intrusive and will not affect any existing signals present on an associated communication path.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to the measurement of analog signals on a communication path, and more particularly for communication paths used in electric utility system protection. 
       BACKGROUND OF THE INVENTION 
       [0002]    Electric Utilities use electronic communication systems in combination with Protection Relays to monitor transmission line conditions and provide control change commands when the transmission lines experience fault conditions. These fault conditions require immediate action to avert wide scale power outages and damage to expensive substation equipment. These Relays require a means to communicate these protection control states and command changes. Various communication paths are used to transmit and receive these critical commands. These communication methods include (but are not limited to) Power Line Carrier (PLC), Audio Tone, Analog and Digital Microwave, Fiber Optics and Spread Spectrum Radio. The physical location of the communication equipment is primarily within a relay house of a utility substation, and therefore is exposed to excessive environmental conditions including excessively high voltages, especially during fault conditions. 
         [0003]    Two of the communication paths, Power Line Carrier (30 kHz to 500 kHz) and Audio Tone Systems (300 Hz to 4000 Hz) often multiplex many channels (frequencies) on a single path. While many newer transmitters and receivers now have some type monitoring of their own signals and some also the path in general, it is believed that no monitoring apparatus presently exists to independently monitor the communication path, or has the ability to monitor any selectable frequency. 
         [0004]    Power Line Carrier Communications used for Power System Protection utilize the Electric Utility transmission line as the communication path. Various components are used to convert the transmission line into a viable path for Power Line Carrier (PLC) frequencies. If these components are not aligned properly, the misalignment can cause conditions that will adversely affect the signal. One method of determining proper system alignment is measuring the reflected power or Standing Wave Ratio (SWR). Power Line Carrier Systems are adjusted for minimal reflected power to assure maximum power transfer across the transmission line. Many things connected to the Transmission line affect the reflected power of the PLC system and conditions are constantly changing. Monitoring of reflected power (SWR) is an effective way to assure that the changing conditions of the transmission line do not adversely affect the original alignment of the PLC System and render it ineffective when needed. It is believed that present monitoring apparatus cannot externally monitor various frequency selective reflected power (SWR) measurements and assign alarm or status limits as programmed by the user. 
         [0005]    The majority of monitoring devices presently manufactured for the Electric Utility substations now incorporates the ability to time stamp events that occur within the associated monitoring device that can be synchronized with satellite clocks. The time stamped events provide recorded event timelines that can be used to evaluate, locate, and remedy the defect on the communication path of the utility substations system. However, no substation hardened communication monitoring devices are believed to exist with the capability to monitor and retrieve such time stamped events locally or to a remote control site. 
         [0006]    The present inventors recognize that Spectral Analysis of the Power Line Carrier path provides an opportunity for the Electric Utilities to evaluate the integrity of their control (or Trip) frequencies during the actual fault. During fault conditions, excessive noise conditions exist that can achieve the same levels of the control frequencies. In-band spectral analysis provides the user the ability to determine the Signal to Noise Ratio (SNR) during those conditions and provide valuable information for remedying mis-operations or loss of carrier signals. 
       SUMMARY OF THE INVENTION 
       [0007]    In general, the present invention is a monitoring device or apparatus for use in power company substations, designed to provide programmable analog communications monitoring in the frequency range from 300 Hz to 500 kHz. The present monitoring device is capable of measuring up to five frequency selective voltages or currents simultaneously with various bandwidth options. Monitoring two channels at the same frequency (one for voltage and one for current) will provide reflected power (SWR) readings. The device is designed to be substation hardened. It has a built-in user programmable event recorder and a satellite clock input for event synchronization with other substation devices. When programmed by the user, time synchronized data recording will be performed that will provide the data needed for later review of in band Spectral Analysis of desired events. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The following drawings, in which like items may have the same reference designations, are illustrative of embodiments of the present invention and are not intended to limit the invention as encompassed by the claims forming part of the application, wherein: 
           [0009]      FIG. 1  is a general system block diagram identifying a desired location of where the invention can be used in an Electric Utility Substation relay house, for an embodiment of the invention; 
           [0010]      FIG. 2  is a Power Line Carrier system block diagram identifying a location where the invention can be used, for an embodiment of the invention; 
           [0011]      FIG. 3  shows that it is represented by the combination of  FIGS. 3A and 3B  as described immediately below; 
           [0012]      FIGS. 3A and 3B  represent a block circuit schematic diagram for a Power Communications Monitor for an embodiment of the invention; 
           [0013]      FIGS. 4A through 4E  show a firmware block diagram (flowchart) for the invention; 
           [0014]      FIG. 5  is a filter FPGA (Field Programmable Gate Array) block schematic diagram, for an embodiment of the invention; and 
           [0015]      FIG. 6  is a block diagram illustrating the application of the present invention in a substation incorporating a plurality of transmitters and receivers, for an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    In the system block diagram of  FIG. 1 , for two Substations A and B, as shown in blocks  2 ,  4 , respectively, include there between a coaxial cable communication path  12  that typically utilizes Power Line Carrier transmission requiring one Power Communications Monitor device  15  or  16 , for one embodiment of the invention. In another embodiment of the invention, a four wire bidirectional audio tone system can be utilized, in which the communication path  12  is connected to one wire pair and the receive path is connected to the other wire pair, whereby two identical Power Communications Monitor devices  15 ,  16 , respectively, are required for bidirectional monitoring capability. A detailed description of the present inventive Power Communications Monitor devices  15  and/or  16  is provided below. In this example, the communication path  12  is meant to convey a coaxial cable communication path. 
         [0017]    With further reference to  FIG. 1 , note that more than two Substations can be connected via associated communication paths  12  simultaneously. However, regardless of the connection of a plurality of Substations via communication paths  12 , the operation of the present Power Communications Monitor  15  or  16  will not be affected. Since the channels being monitored are user selectable via user control of the present Monitor  15  or  16 , the present Monitor  15  can be programmed to measure voltages and current relative to user selected frequencies. As shown, Substation A may include amongst other components a transmitter  13  receptive of an output signal from a protective relay (not shown) via input line  3 , and a receiver  14  for providing an input signal along line  5  to the protective relay (not shown). The present Power Communications Monitor  15  bidirectionally monitors, the transmitter  13  and receiver  14 . As further shown in the simplified block diagram of  FIG. 1 , Substation B includes substantially the same component configuration as Substation A. More specifically, the components of Substation B include a present Power Communications Monitor  16 , a transmitter  17 , a receiver  18 , an output line  7  from another protective relay (not shown), and an input line  9  connected to the protective relay. Substation A is shown in block  2 , and Substation B in block  4 , and show the protective relaying communication system for Substation A, B, respectively. The Communication Path  12  can be provided by any viable present technology. However, in this example, the present Power Communications Monitor  15 ,  16 , respectively, is designed to measure analog signals where power line carrier (RF) signals are sent over the power transmission lines, from which the signals are coupled to the coaxial cable of the Communication Path  12 , in this example. Also note that within a single substation, such as Substation A, this Substation itself may include a plurality of individual component configurations as represented by block  2  or block  4 . Regardless of the number of such substations employed, different frequencies are utilized to represent different protection channels within an individual substation, or substations along a shared communications path. 
         [0018]    An example of the operation of Substations A and B, as represented by component blocks  2 ,  4 , respectively, will now be provided. In Substation A when the transmitter  13  is keyed or energized via a control signal received from protective relay output line  3 , transmitter  13  responds by transmitting a user programmed frequency to be received by both monitor  15 , and receiver  18  of Substation B. Upon receiving the frequency signal from transmitter  13 , receiver  18  responds by changing the state of the input line  9  to cause the associated protective relay to change from one operational state to another desired operational state, for example, to indicate a fault has occurred in Substation A. Similarly, in Substation B, when transmitter  17  is keyed or energized via the state of protective relay output line  7  changing, transmitter  17  responds by transmitting a voltage signal having a user programmed frequency to be responded to by receiver  14  and monitor  15  of Substation A. In response to receiving the control signal of a desired frequency from transmitter  17 , receiver  14  changes the state of relay input line  5  to cause the associated protective relay to respond by performing a desired action to indicate a fault has occurred in Substation B. Note that the Power Communications Monitor  15  is responsive to the signal from transmitter  17  for directing that signal to receiver  14 . Similarly Power Communications Monitor  16  is responsive to receiving a control signal from Power Communications Monitor  15  for transfer to receiver  18 . In effect, as will be described in further detail below, the present monitor  15 , and/or  16  are transparent to the associated communication path  12  in which they are installed. 
         [0019]    The Power Communications Monitor  15  of Substation A can be programmed to monitor user selective levels of voltage having a user selected frequency. The monitor  15  records the time and date of events indicating specific analog communication conditions in the associated Substation A in this example, along with data, such as indicative of voltage and current of the event to permit a user to compute VSWR, and perform spectral analysis. By computing the voltage standing wave ratio (VSWR), a user obtains an indication of the associated reflected power at Substation A. Similarly, the present Power Communications Monitor  16  located in Substation B is user programmed for monitoring event associated levels of voltage and current at a given frequency, for time and date stamping events for recording, and for providing the recorded data for a user to permit computation of VSWR (reflected power) at each event, along with spectral analysis, relative to Substation B. 
         [0020]    In  FIG. 2 , a power line carrier system is shown in greater detail than  FIG. 1 . In  FIG. 2 , the positioning of the present Power Communication Monitor  15 ,  16  of the present invention can be anywhere in a coaxial cable communication path of a power utilities substation. The monitor  15 ,  16  provides monitoring of multiple protection channels on the communication or associated coaxial communication path. The Monitor  15  or  16  can be placed in other locations within the electrical power system coaxial cable communication path. In this example, monitor  15  is connected between a hybrid  55  within a communication relay house 2 of Substation A, and a line tuner  64 . In Substation B, monitor  16  is connected between a hybrid  58  in communication relay house 4, and a line tuner  61 , for example. For their locations shown, Monitors  15  and  16  monitor any signals that have been multiplexed or appear individually onto the associated communication path. It is common for four transmitters and four receivers to be utilized in substations 2 and/or 4, respectively, whereby the monitors  15  and  16  can record events on channels being monitored. 
         [0021]    With further reference to  FIG. 2 , Substation A now represented by block  50  includes the series connection of a line trap  66 , CCVT (coupling capacitor voltage transformer)  65 , and line tuner  64 . The line tuner  64  is also bidirectionally connected to a present Power Communications Monitor  15 , the latter being located in a Communications/Relay House 2, in this example. Note that the component configuration in the Communications/Relay House 2 is substantially the same as in block  10  for Substation A of  FIG. 1 , except for the addition of a hybrid  55  bidirectionally connected between monitor  15 , and transmitter  13  and receiver  14 , as shown. Similarly, for Substation B as shown by block  51 , components including a line trap  63 , CCVT  62 , and line tuner  61  are connected in series, with the line tuner  61  being bidirectionally connected to a Power Communications Monitor  16 , the latter being located within a Communications/Relay House 4. The only difference between the configuration of the components within Communications/Relay House 4 and the components configurations shown in Substation B of block  11  of  FIG. 1 , is the addition of a hybrid  58  in Communications/Relay House 4, with the hybrid  58  being bidirectionally connected to monitor  16 , and also bidirectionally connected to both transmitter  17  and receiver  18 , as shown. The common connection between line trap  66  and CCVT  65  is connected to one end of a transmission power line  52  also serving as a communications path between Substations A and B. In Substation B, the common connection between the line trap  63  and CCVT  62  is connected to the other end of the transmission power line  52 , as shown. Note that in a typical substation, such as Substation A or B, the coaxial cable communication path is typically located between an associated Line Tuner and associated transmitter/receiver. 
         [0022]    More specifically, with further reference to  FIG. 2 , the component configuration shown in blocks  50  and  51  for Substations A and B, respectively, provide a more detailed representation of electrical power companies or utilities power line carrier protective relaying communication systems, in this example. Transmission power line  52  provides the utilities high voltage transmission line that in this example also serves as the utilities power line carrier (RF) communication path, as previously indicated. The operation of transmitters  13  and  17  is as previously described relative to  FIG. 1 . Hybrids, such as  55  and  58 , are required when more than one power line carrier channel is present on a single communication path, such as served by transmission power line  52 , in this example. More specifically, hybrid  55  is designed to provide the proper line impedance and necessary electrical isolation between transmitter  13  and receiver  14 . Similarly, hybrid  58  is designed to assure the proper line impedance and electrical isolation between transmitter  17  and receiver  18 , in this example. As previously indicated, a Power Communications Monitor  15  is included in Substation A, and a Power Communications Monitor  16  is included in Substation B. The use of the two Power Communications Monitors  15  and  16  as shown provides for optimized monitoring capability relative to signals and events. However, only a single Power Communications Monitor  15  or  16  is required if a less optimized system is acceptable, in this example. 
         [0023]    With yet further reference to  FIG. 2 , the CCVT  65  (Coupler Capacitor Voltage Transformer) included in Substation A is required for coupling RF signals to transmission power line  52 , in this example. Similarly, CCVT  62  in Substation B provides for coupling RF signals to transmission power line  52 . The line tuner  64  in Substation A provides an adjustable inductor that is “tuned” to cancel the capacitive reactance introduced by CCVT  62  and CCVT  65  (of Substation B). Line tuner  64  also includes an impedance matching transformer. Line Tuner  61  provides in Substation B a similar function to line tuner  64  in Substation A. Note that typical power line carrier transmitters  13 ,  17  have a 50 or 75 ohm impedance output. The impedance of the transmission power line  52  typically can have a large variance of impedance values, but usually can range between 200 and 500 ohms. The impedance matching transformers of line tuners  64  and  61  are adjusted to best match the output impedance of their associated transmitters  13 ,  17 , respectively, to the impedance of the transmission power line  52 . When properly adjusted, line tuner  64  and  61  provide maximum power transfer of RF signals to the transmission power line  52  serving as a communication path, in this example. Accordingly, as indicated, each of the line tuners  64  and  61  provide the same function within their associated Substation A and B represented by blocks  50 ,  51 , respectively. Line trap  66  in Substation A serves to maximize the power transfer of RF signals between substations, particularly remote substations such as might be represented by Substations B. When line trap  66  is properly tuned, it provides a high impedance relative to RF signals on the transmission power line path  52  serving as a communication path. Line trap  63  at Substation B provides the same function as line trap  66  at Substation A. 
         [0024]    With reference to the Power Communications Monitor  15 ( 16 ) of  FIGS. 3A and 3B , and further reference to  FIG. 2 , operation of the present invention will now be described. In the preferred embodiment of the invention, terminal  20  receives an analog signal RF IN (Radio Frequency) from Hybrid  55 ( 58 ) that enters the primary winding of current transformer  100 . The current transformer  100  provides impedance matching, and electrical isolation between the monitor and the coaxial cable path. In typical operation, the primary winding current can range from 1 μa (microampere) to 2 amperes), for example, whereby the actual level of current is programmed by a user in setting the amplitude of RF IN. The secondary winding of current transformer  100  is connected to a current load resistor  101 . If the current in the secondary winding of transformer  100  does not exceed xy milliamps (typically does not exceed a 2 volt drop across resistor  101 ), then it passes unattenuated through switch  102  to the current anti-alias filter buffer amplifier  104 , which in this example has a gain of 0.499. If the current level exceeds xy milliamps, then the switch  102  (a solid state switch controlled by CPU  200 ) is activated via CPU  200  responding to the user&#39;s setting of RF IN, and the signal passes through the 40 dB input attenuator  103  for current measurement. Otherwise, RF IN passes unattenuated through switch  102 . The signal then passes to the current anti-alias filter buffer amplifier  104 . The current anti-alias filter buffer amplifier  104  reduces the signal level by 0.499, in this example. The signal then passes through the current anti-alias lowpass filter  105  which filters out all frequencies above 10 MHz, and passes lower frequencies. The signal then passes through the input gain operational amplifier  106  for current measurement. Gain of amplifier  106  is set by CPU  200  to one of five different gain setting. In this example, the settings are 1, or 5.64, or 31.8096, or 179.40614, or 1011.8551). The gain setting is set by CPU  200  in response to a user&#39;s prior programming for the amplitude of RF IN. The signal then enters an associated 16 bit current A/D (Analog-to-Digital Converter)  107 , which converts the analog signal to a digitized signal that is inputted to the filter FPGA  207 . The components between RF IN terminal  20  and the filter FPGA  207  provide measurement of current magnitude. 
         [0025]    In the preferred embodiment, terminal  21  is receptive of an analog signal RF OUT from Line Tuner  61 ( 64 ) that enters the primary winding of voltage transformer  108 , the secondary winding of which is connected to a resistive load  109 . The voltage transformer  108  provides impedance matching, and electrical isolation between the monitor and the coaxial cable path. A High Level Detector  116  monitors the voltage level across load  109 . If the voltage exceeds 5 volts, the High Level Detector  116  outputs an INTR0 signal to CPU  200 , in this example. CPU  200  responds by activating switch  110  to pass the signal through the 40 dB attenuator circuit  111 . The signal then passes from attenuator circuit  111  through switch  110  to amplifier  112 . Otherwise, the signal passes unattenuated through switch  110  to amplifier  112 . The voltage anti-alias filter buffer amplifier  112  reduces the signal level by 0.499, in this example. The signal then passes through the voltage anti-alias lowpass filter  113 , which filters out all frequencies above 10 MHz, and passes lower frequencies. The signal then passes through the input gain control amplifier  114  for voltage measurement. As with amplifier  106 , the gain of amplifier  114  is set to one of five different gain settings (1, 5.64, 31.8096, 179.40614 &amp; 1011.8551) controlled by CPU  200 , in response to a user&#39;s prior programming of the amplitude of RF OUT. The signal then enters a 16 bit voltage Analog-to-Digital Converter  115 , which converts the associated analog signal into a digitized signal, in this example. The digitized signal is inputted to the filter FPGA  207 . The components between RF OUT terminal  21  and Filter FPGA  207  provide for measurement of voltage amplitude. The present monitors  15 ,  16  provide the capability of measuring up to five frequency selective voltages or currents simultaneously with various bandwidth options. 
         [0026]    An external device is used to provide a timing reference. Terminal  22  is receptive of an IRIG-B series time code format signal. This input which has two electronic formats. Hardware jumper switch  117  is manually controlled to select which mode of the IRIG-B time code format is desired (modulated or unmodulated). If unmodulated, the Opto-coupler  118  deciphers the unmodulated signal and converts it to 3.3V CMOS (Complementary Metal Oxide Semiconductor) signal. If modulated, the signal will be isolated by transformer  119 , and then pass through from the secondary winding of transformer  119  to buffer amplifier  120 . Transformer  119  also provides impedance matching between the monitor and communication path. The output signal from buffer amplifier  120  passes to anti-aliasing lowpass filter  121 , which passes signals having frequencies below 10 KHz. The output signal from filter  121  is passed through buffer amplifier  122  to analog-to digital-converter  123 , which digitizes the signal and inputs it to FPGA  207  (Field Programmable Gate Array). 
         [0027]    The Central Processing Unit (CPU)  200  controls all of the peripheral components in the system, which include the Complex Programmable Logic Device or Chip Selector (CPLD)  201 , the CPU Flash Memory  202 , the Real Time Clock (RTC)  203 , the Event Flash Memory  204 , the Static Random Access Memory (SRAM)  205 , the Communication Field Programmable Gate Array (FPGA)  206 , and the filter FPGA  207 . The CPU  200  is a 150 MHz digital signal processor (Texas Instruments TMS320VC33), in this example. The Chip Selector  201  is an Altera Max2 CPLD, which is used by the CPU  200  to select a device for reading data from or writing data into. The CPU Flash Memory  202  stores the present monitor&#39;s  15 ( 16 ) firmware. The Real Time Clock (RTC)  203  includes a Static RAM (SRAM) not shown, and is used by an interconnected device to keep time even in the event of loss of the IRIG-B satellite signal, and hold the user boot configuration while the unit is powered down. The Event Flash Memory  204  provides an event recorder database capable of recording up to 32,767 events, in this example, which is not meant to be limiting. The SRAM  205  is the memory for the CPU  200 . The Communications FPGA (Field Programmable Gate Array)  206  controls bidirectional signal flow associated with the Ethernet port  213 , USB (universal serial bus) port  214 , and SD (secure digital interrupt) Card port  215  functions. 
         [0028]    The Filter FPGA  207  performs SLM (Selective Level Meter) filtering, IRIG-B filtering, TRIG-B UART (universal asynchronous receiver/transmitter), and Communication UART. FPGA  207  also is controlled by CPU  200  to output control signals via Buffer  208  to selectively operate a plurality of alarm switches  209  to selectively provide one or a combination of ALARM 1 through ALARM 4 signals, and/or drive Light Emitting Diode (LED) array  210  for selectively activating one or a combination of LED 1 through LED 8 to alert a user to fault conditions. The FPGA  207  is also controlled via CPU  200  to provide bidirectional signal flow via RS-232 port  211 , and RS-485 port  212 . 
         [0029]    The main Power Supply  300  converts input voltages ranging from 24 to 150 VDC to a 12 VDC output. Power Supply  301  is a redundant supply used in case of Power Supply ( 300 ) failure. The low voltage Power Supply  302  converts the 12 VDC to +1.2VDC, +1.8VDC, +3.3VDC, +5 VDC and −5VDC for connection to various of the components of the present system. 
         [0030]    The CPU  200  is programmed to control operation of the present monitoring system  15  ( 16 ). Firmware flowcharts as shown in  FIGS. 4A through 4E  provide details for the programming of CPU  200 , and the operation of the present system as described in greater detail below. Necessary calculations by a user based upon stored detected signals provide data for user calculation of SWR, rms voltage and current, wattage, and so forth, can be calculated via use of software library No. rts30gr.lib of Texas Instruments, for example. Note each substation in a power utility system can have ten or more channels multiplexed on a single path. Two channels may be at the same frequency with one channel representing voltage, and the other channel current, for use in making the aforesaid necessary calculations for the associated substation. 
         [0031]    Further reference is now made to the flowchart or firmware block diagram for the present monitor  15 ( 16 ) shown in  FIGS. 4A-4E . In  FIG. 4A , in broad terms, step  346  provides Interrupt INTR0 control signal, a high level detection interrupt. Sublevel steps included in step  346  include  347 , in which the INTR0 signal is outputted from high level detector  116  causing CPU  200  to respond by operating switch  110  to change state for passing the RF OUT signal through 40 dB attenuator  111 , as previously described. After a predetermined period of time, in substep  348  CPU  200  operates to deactivate switch  110 , returning it to its normal or rest state as shown in  FIG. 3 . At that time the control program returns to where it last left off. 
         [0032]    With further reference to  FIG. 4B , step  349  is an Interrupt INTR1 associated with a 50 microseconds loop. Step  349  includes substeps  350  that monitors the A/D converters  107 ,  115 ,  123  for long or short overloads. In step  351 , if the aforesaid modulated IRIG-B option is set, the IRIG-B A/D converter data is loaded into A/D  115 . In step  352  the SLM or selective level meter data from the Process SLM 0 through 4 Filters are processed relative to the associated five frequencies or channels, respectively. The data is obtained from the third operational amplifier  106  and associated A/D  107  for current. Next in step  353  SLM 0 through 4 channel or frequencies are processed, from operational amplifier  114  and associated A/D  115  for voltage. In substep  354  a “12 State Machine” is provided to calculate the following values:
       00. SLM 1 Vrms01; SLM 2 Vrms02; SLM 3 Vrms03; SLM 4 Vrms or SLM 1 Arms 04; SLM 5 Vrms or SLM 2 Arms05; SLM 1 dBm06; SLM 2 dBm07; SLM 3 dBm08; SLM 4 dBm09; SLM 5 dBm/event_clock/aux_timers10; and Level detector/GUARD/TRIP Timers 11. An Event Recorder saves these values in a local database.
 
The values are used by the user to extract the data from ports  211 - 214 .
 
In substep  355  the program returns to where it last left off.
       
 
         [0034]    Interrupt INTR2 step  356  shown in  FIG. 4C . This step is carried out by substeps  357  through  364 . In substep  357  a voltage and current A/D converter overload controller (not shown) output is monitored to provide the blocking mechanism for AGC (automatic gain control) when there is an overload. In step  358  the wideband RMS current and voltages are obtained from the FPGA  207 . CPU  200  responds to INTR1, whereby if the auto mode attenuator  103  and/or gain of amplifier  106  is charged until the overload is overcome. In step  359 , if a current overload is detected in A/D  107  converter an overload interrupt is generated by FPGA  207  as INTR1. Substep  360  detects whether there is a voltage overload relative to A/D converter  115 , and if so, generates a voltage overload interrupt as INTR2, and CPU  200  responds by checking FPGA  207  to determine if A/D  107  or  115  is overloaded. If the latter, then if in an auto mode Attenuator  111  and/or amplifier  114  gain is changed. Regardless, the overload is not corrected if a user is in a manual mode. In Substep  361  IRIG-B Interrupt is generated to interrupt CPU  200  to get the latest satellite time. In step  362  a COMM port Interrupt signal is generated via a received byte from the Serial Port-RS-232/RS-485 (see  FIG. 5 ). It interrupts CPU  200 . In step  363  a USB 0 port Interrupt signal is generated when data is available from USB, to permit CPU  200  to access the data. In substep  364  the program returns to where it last left off before pursuing step  356 . 
         [0035]    Interrupt INTR3 step  365  is now entered as shown in  FIG. 4D . This step includes substep  366  that causes a COMM FPGA  206  Interrupt signal to be generated to read Ethernet port  213 . In step  367  the program returns to where it left off. 
         [0036]    Reference is now made to the flowchart of  FIG. 4E . Main step  368  is followed by step  369  to set the CPU  200  registers (not shown). Step  370  is then entered to provide initialization of various parameters. In step  371  a WHILE Loop  380  is entered into. Note that a WHILE Loop in most computer languages, is a control flow statement that allows code to be executed repeatedly based on a given Boolean condition. The While Loop can be thought of as a repeating if statement, for maintaining previous processed information or data. More specifically, in this example, the WHILE Loop  380  allows the monitor system to pickup where it left off from an interrupt. Step  372  provides a uart (universal asynchronous receiver transmitter) interface which transmits and receives data external to the monitor  15  ( 16 ), and is software driven to insure the transmission of data. Step  373  provides a software driven download setup for external applications, such as an embedded web server, to permit a user to check the settings or programming of the monitor. Step  374  packages generated real time data from CPU  200  for external applications to be available at an output port ( 211 - 214 , respectively). Step  375  provides for packaging recorded event data on the SD card for external applications. Step  376  provides packages in the SD card FFT (Fast Fourier Transform) data for external applications. Step  377  transmits uart (universal asynchronous receiver transmitter) data to any port. Step  378  provides for operation of a software event recorder and alarm controller database stored in Event Flash  204 . 
         [0037]      FIG. 5  is a block schematic diagram of the FILTER FPGA  207  of  FIG. 3 . As shown, the digitized signals from A/D  115  are received by a Wideband RMS Voltage  500  module which calculates Wideband RMS Voltage values from the digitized signals, and inputs the values to controller  514 . The voltage representative digitized signals from AD  115  are also inputted to demodulators  501  through  505 , which in turn provide demodulated signals thereof to SLM (selective level meter) filters  506  through  510 , respectively. The filtered output signals from SLM filters  506  through  510  are inputted into controller  514 . Digitized current representative signals from A/D converter network  107  are inputted to a Wideband RMS Current calculator module  511 , which calculates RMS current values therefrom, and inputs the values to controller  514 . Switch  516  is operative to connect either the voltage A/D  115  signals to demodulators  504  and  505 , or the current A/D  107  signals to demodulator  504  and  505 . CPU  200  controls controller  514  to operate switches  516  and  117 . Either switch  516  or  517  is activated to measure current via associated demodulators  504 ,  505 , respectively, to permit RMS calculation by a user. Switch  517  is operative to selectively connect either voltage A/D  115  signals or current A/D  107  signals to demodulators  504  and  505 , respectively, to further permit a user to calculate RMS values therefrom. 
         [0038]    With further reference to  FIG. 5 , an IRIG-B signal from A/D  123  is inputted into an IRIG demodulator  512  that demodulates the serial time code format for input to an IRIG filter  513 , to provide the latest timing signals. The output of filter  513  is inputted to controller  514 . Also, an IRIG-B unmodulated signal is inputted to controller  514  from A/D  123 . Controller  514  provides an interface to external buses. COMM UART  515  (Communicator for universal asynchronous receiver transmitter) provides an interface with all communication options via the RS-232 and RS-485 signal lines or ports. 
         [0039]    With further reference to  FIG. 3 , as previously mentioned, the present monitor  15 ,  16 , is relatively transparent to the substation in which it may be located somewhere in the coaxial cable communication path. For example, a monitor  15 ,  16  connected as shown in  FIG. 2 , with RF IN terminal  20  connected to hybrid  55 ,  58 , respectively, and RF OUT terminal  21  connected to line tuner  64 ,  61 , respectively, the impedance of the primary winding of transformer  100  is maintained as low 0.1 ohm, whereas the impedance of the primary winding of transformer  108  maintained at about 40 kilohms. As a result, even if the power is not being applied to monitor  15  or  16 , or during the powering of monitor  15 ,  16 , the connection between hybrid  55  and line tuner  64 , and hybrid  58  and line tuner  61 , will be maintained via monitors  15 ,  16 , respectively. 
         [0040]    Note further that a user can program CPU  200  in a manual mode to permit the user to extract stored data from the event/memory  204  for obtaining the times and dates of successive events, and data from the SD Card for calculating and displaying a Fast Fourier Transform (FFT) output data to provide spectrum analysis associated with given ones of the events. The user in order to calculate an FFT must select one frequency or channel between 30 kHz to 0.5 MHz, in this example. The user also selects the bandwidth they wish to view, whereby the user can program a monitor  15  or  16  to select up to five different bandwidths. Also, a user can program CPU  200  for putting the associated monitor  15 ,  16  into an automated mode, which will restrict a user to only have the ability to measure the VSWR subject to a given event. 
         [0041]    A user determines the current level range for detection by the present monitor  15 ,  16 . A user can make this selection via Ethernet port  213  or USB port  214 , the selection being made via Communication FPGA  206  inputting the selection to CPU  200 . In turn, CPU  200  responds to the current level selection by setting the gain for operational amplifier  106 . In a similar manner, the gain for operational amplifier  114  is set in response to the voltage level range for detection set by a customer or user. 
         [0042]    With further reference to  FIG. 3 , the Filter FPGA  207  (also see  FIG. 5 ), permits up to five channels or frequencies to be processed, as previously described. For each of the demodulators  501  through  505 , the CPU  200  sets the output or intermediate frequency (IF) outputted from each demodulator. The SLM filters  506  through  510  block frequencies from 5 kHz and above, and pass IF signals having frequencies lower than 5 kHz, whereby the IF signals passed are inputted into controller  514 , as previously mentioned. The controller  514  provides signals for a given event to the CPU  200 , whereby the CPU  200  directs the event signals for storage to the Event Flash  204 . 
         [0043]    With further reference to  FIGS. 3A and 3B , note that Alarm lines 1 through 4, and LED&#39;s 1 through 8, are activated when events first occur, and thereafter, all subsequent events are recorded. With regard to typical events that can be recorded, such events may include High Frequency Detected, Center Frequency Detected, Low Frequency Detected, Signal Out of Range High, Signal Out of Range Low, SWR out of Range. Further, the aforesaid listing of events is not meant to be limiting, numerous other events may occur. Note further that the CPU Flash memory  202  stores the programming for firmware for the CPU  200 . Also, the RTC  203  maintains timing to be independent of the satellite provided IRIG-B signal, when a monitor  15 ,  16  is turned off. The SRAM  205  continuously stores ongoing operations during a particular period of operation, and is reset when power is turned off. In other words, SRAM  205  is a volatile memory. Note further that the CPU Flash memory  202  receives data from the FPGA  207  every 50 microseconds, in this example. 
         [0044]    With further reference to  FIG. 2 , the Substation A when the protective relay output line  3  changes state as a result of a change in state of its associated protective relay (not shown), the state change such as a change from a 0 to a 1 state, or vice versa, triggers transmitter  13  to output a signal to hybrid  55 . As previously mentioned, the signal has a user predetermined frequency. Transmitter  13  typically uses FSK (frequency shift key) or AM (amplitude modulation) keying, as previously programmed by a user (typically the power company). Also, with regard to a given transmitter, such as transmitter  13 , a user typically selects a frequency for the signal ranging 300 Hz to 500 kHz. 
         [0045]    Note that the demodulated signals provided to controller  514  via SLM filters  506  through  510  provide demodulated waveforms having sine and cosine portions, presenting a complex wave with a real and imaginary portion. The signals are provided to CPU  200 . As previously mentioned, the CPU  200  for each event, stores the time and date of the event, an indication whether the event is represented by a high frequency, low frequency, center frequency, low level signal, or by the VSWR being out of range. The CPU  200  also puts data into the SD Card for permitting a user to retrieve these data and compute an FFT analysis thereof to permit spectrum analysis. Operation of monitor  16  in Substation B is substantially the same as that described for monitor  15  and Substation A. When a given monitor  15  or  16  receives a transmitted signal from another substation, the monitor can only use the signal to record that an event has occurred, and that the event was caused by shifting in frequency previously programmed. 
         [0046]    The Communications FPGA  206  controls Ethernet port  213 , and USB port  214  using database and address buses connected to CPU  200 . 
         [0047]    The buffer  208  provides a user with voltage isolation between the FPGA  207  and the Alarm lines 1 through 4. A user can manually program their connection to any of the Alarm lines. Also, a user can program CPU  200  to activate each of the LED 1-8 light emitting diodes to each show an individual event occurrence. 
         [0048]    The RS-232 port  211  is typically hardwired to a communication device, individually and with a protocol for point-to-point connection. The RS-485 port  212  can be hardwired to communicate with a plurality of devices. 
         [0049]    In summary, the user of a monitor  15 ,  16  is provided the ability to select signal frequencies and/or channels for recording events as they occur on the associated communication path. A user can also select the bandwidth to be recorded relative to the selected frequencies. Also, a user can select or program data desired to be recorded to provide a user the ability to compute from past event occurrences the FFT from the data in order to perform spectrum analysis. In other words, monitors  15 ,  16  provide real time measurements and the ability to record data for immediate or later use by a user to observe events happening at given times in order to determine if a particular substation is operating properly. As required, a user can reprogram signal frequencies and voltage levels, at any time. Another important feature provided by monitor  15 ,  16  is to permit a user to program the monitor to record data at regular set intervals for providing trending analysis. For example, a recording can be provided every hour, every twenty-four hours, and so forth. Such data recording would be conducted regardless of whether there is the occurrence of a particular event. 
         [0050]    With reference to  FIG. 6 , as previously indicated, in a power substation a plurality of transmitters and receivers may be used. In the example shown, five transmitters  601  through  605  are being utilized, along with four receivers  610  through  613 . Each of the transmitters  601  through  605  upon receiving a change of state signal from an associated protective relay (not shown) transmit a signal of a user preset frequency, with the frequencies between transmitters  601  and  605  each typically being different. A resistive hybrid  614  is receptive of output signals from transmitter  601  and  602 , and in this example serves to multiplex the two signals together should they occur at the same time. Similarly, resistive hybrid  616  is receptive of output signals from transmitter  603  and  604 , and serves to multiplex the two signals together even if they occur at the same time. Output signals from resistive hybrid  614  and resistive hybrid  616  are inputted into a resistive hybrid  618 , which in turn multiplexes the aforesaid output signals together. The output of resistive hybrid  618  is inputted to another resistive hybrid  620 , which is also receptive of an output signal from transmitter  605 . The output from resistive hybrid  620  can be representative of the multiplexed combination of the output signals from transmitter  601  through  605 , the multiplexed signals being inputted into a skewed hybrid  622 . The skewed hybrid  622  is bidirectionally connected to a present Power Communications Monitor (PCM)  626 , the latter being bidirectionally connected to the line tuner  628 , as shown. The interconnection of the present monitor  626  to the skewed hybrid  622  and line tuner  628  is substantially the same as the above-described interconnection of a present monitor  15  to a line tuner  64  and hybrid  55 . However, in this example, the monitor  626  may at times have to simultaneously process five transmitted signals of different frequencies multiplexed together, in this example. With further reference to  FIG. 5 , the transmitted signals are respectively demodulated by demodulators  501  through  505 , and passed through associated SLM filters  506  through  510 , respectively, to controller  514 . These signals are then further processed for recording the occurrences of the related events and the event/memory  204 , and recording data in the SD card for later use by a user to calculate associated Fast Fourier Transforms (FFT) therefrom, to permit spectrum analysis. 
         [0051]    With further reference to  FIG. 6 , a second present monitor or PCM  624  is receptive of output signals from the skewed hybrid  622  for processing signals received from other substations that may be connected to the associated substation, for outputting the signals indicative of the occurrence of events from these other substations, which output signals are individually received by receiver  610  through  613 , respectively. 
         [0052]    It should be noted that in power line carrier channels or coaxial communication paths, the purpose of hybrid circuits is to enable the connection of two or more transmitters together on one coaxial cable without causing intermodulation distortion due to the signal from one transmitter affecting the output stages of the other transmitter, in addition to other purposes as indicated above. Also in typical power substations the purpose of line tuners in conjunction with coupling capacitors (CCVT, for example) is to provide a low impedance path for the carrier energy to the transmission line and a high impedance path to the power frequency energy. The line tuner/coupling capacitor combination provides a low impedance path to the power line by forming a series resonant circuit tuned to the carrier frequencies. However, the capacitance of the coupling capacitor or CCVT is a high impedance to the power frequency energy. Although not shown in the figures, coupling capacitors have a high impedance at power frequencies, whereby a path to ground must be provided for the capacitor to function properly, and is typically provided by a drain coil (not shown) in the present figures. Also, typically, the carrier energy on the transmission lines must be directed toward a remote line terminal and not towards a substation bus, and must also be isolated from bus impedance variations. Line traps provide this isolation function, and are usually provided by a parallel resonant circuit which is tuned to the carrier energy frequency. The parallel resonant circuit provides a high impedance at its tune frequency, thereby causing most of the carrier energy to flow toward a remote line terminal. Also, a coil (not shown) of the line trap provides a low impedance path for the flow of power frequency energy, which is typically substantially large. As a result, the coils used in typical line traps must be large in terms of physical size. The use of line tuners, resistive hybrids, skewed hybrids, CCVT&#39;s, and line traps are well known in the power industry. 
         [0053]    Although various embodiments of the present invention have been shown and described, they are not meant to be limiting. Those of skill in the art may recognize certain modifications to these embodiments, which modifications are meant to be covered by the spirit and scope of the appended claims.