[0002] In an industrial power distribution system, power generated by a power generation company may be supplied to an industrial or commercial facility wherein the power may be distributed throughout the industrial or commercial facility to various equipment such as, for example, motors, welding machinery, computers, heaters, lighting, and other electrical equipment. At least some known power distribution systems include switchgear which facilitates dividing the power into branch circuits which supply power to various portions of the industrial facility.

Circuit breakers are provided in each branch circuit to facilitate protecting equipment within the branch circuit. Additionally, circuit breakers in each branch circuit can facilitate minimizing equipment failures since specific loads may be energized or de- energized without affecting other loads, thus creating increased efficiencies, and reduced operating and manufacturing costs. Similar switchgear may also be used within an electric utility transmission system and a plurality of distribution substations, although the switching operations used may be more complex.

[0003] Switchgear typically include multiple devices, other than the power distribution system components, to facilitate providing protection, monitoring, and control of the power distribution system components. For example, at least some known breakers include a plurality of shunt trip circuits, under-voltage relays, trip units, and a plurality of auxiliary switches that close the breaker in the event of an undesired interruption or fluctuation in the power supplied to the power distribution components. Additionally, at least one known power distribution system also includes a monitor device that monitors a performance of the power distribution system, a control device that controls an operation of the power distribution system, and a protection device that initiates a protective response when the protection device is activated.

[0004] In at least some other known power distribution systems, a monitor and control system operates independently of the protective system. For example, a protective device may de-energize a portion of the power distribution system based on its own predetermined operating limits, without the monitoring devices recording the event. The failure of the monitoring system to record the system shutdown may mislead an operator to believe that an over-current condition has not occurred within the power distribution system, and as such, a proper corrective action may not be initiated by the operator. Additionally, a protective device, i. e. a circuit breaker, may open because of an over-current condition in the power distribution system, but the control system may interpret the over-current condition as a loss of power from the power source, rather than a fault condition. As such, the control logic may undesirably attempt to connect the faulted circuit to an alternate source, thereby restoring the over-current condition. In addition to the potential increase in operational defects which may occur using such devices, the use of multiple devices and interconnecting wiring associated with the devices may cause an increase in equipment size, an increase in the complexity of wiring the devices, and/or an increase in a quantity of devices installed.

BRIEF DESCRIPTION OF THE INVENTION [0005] In one aspect, method for operating a centrally controlled power distribution system is provided. The power distribution system includes a plurality of circuit breakers, each circuit breaker coupled to a single node electronics unit, the node electronics unit includes a plurality of processors and a memory, and the node electronics unit is communicatively coupled to at least one central control processing unit through an associated network. The method includes triggering a first node electronics unit process with a processor interrupt, and triggering a second node electronics unit process with at least one of a background polling of a plurality of process execution flags and a scheduled processor interrupt.

[0006] In another aspect, apparatus for operating a centrally controlled power distribution system is provided. The power distribution system includes a plurality of circuit breakers, each circuit breaker coupled to a single node electronics unit, said node electronics unit includes a processor and a memory, and the node electronics unit is communicatively coupled to at least one central control processing unit through an associated network. The apparatus includes a software program code segment configured to trigger a first node electronics unit process with a processor interrupt, trigger a second node electronics unit process with at least one of a background polling of a plurality of process execution flags and a scheduled processor interrupt.

BRIEF DESCRIPTION OF THE DRAWINGS [0007] Figure 1 is an exemplary schematic illustration of a power distribution system; [0008] Figure 2 is an exemplary schematic illustration of a node power system; [0009] Figure 3 is an exemplary schematic illustration of a central control processing unit that may used with the power distribution system shown in Figure 1; [0010] Figure 4 is an exemplary schematic illustration of a node electronic unit that may used with the power distribution system shown in Figure 1; [0011] Figure 5 is an exemplary schematic illustration of a circuit breaker that may used with the power distribution system shown in Figure 1 ; and [0012] Figure 6 is an expanded schematic block diagram of an exemplary node electronics unit shown in figure 4.

[0013] Figure 7 is a flow chart illustrating an exemplary method for operating the node electronics unit shown in Figure 6.

DETAILED DESCRIPTION OF THE INVENTION [0014] Figure 1 illustrates an exemplary schematic illustration of a power distribution system 10, used by an industrial facility for example. In an exemplary embodiment, system 10 includes at least one main feed system 12, a power distribution bus 14, a plurality of power circuit switches or interrupters, also referred to herein as a circuit breakers (CB) 16, and at least one load 18, such as, but not limited to, motors, welding machinery, computers, heaters, lighting, and/or other electrical equipment.

[0015] In use, power is supplied to a main feed system 12, i. e. a switchboard for example, from a source (not shown) such as, an electric generator driven by a prime mover locally, or an electric utility source from an electrical substation. The prime mover may be powered from, for example, but not limited to, a turbine, or an internal combustion engine. Power supplied to main feed system 12 is divided into a plurality of branch circuits by a plurality of busbars configured to route the power from a branch feed breaker and a bus-tie breaker to a plurality of load circuit breakers 16 which supply power to various loads 18 in the industrial facility.

In addition, circuit breakers 16 are provided in each branch circuit to facilitate protecting equipment, i. e. loads 18, connected within the respective branch circuit.

Additionally, circuit breakers 16 facilitate minimizing equipment failures since specific loads 18 may be energized or de-energized without affecting other loads 18, thus creating increased efficiencies, and reduced operating and manufacturing costs.

[0016] Power distribution system 10 includes a circuit breaker control protection system 19 that includes a plurality of node electronics units 20 that are each communicatively coupled to a digital network 22 via a network interface controller switch 23 such as, but not limited to, an Ethernet switch 23. Circuit breaker control protection system 19 also includes at least one central control processing unit (CCPU) 24 that is communicatively coupled to digital network 22. In use, each respective node electronic unit 20 is electrically coupled to a respective circuit breaker 16, such that CCPU 24 is communicatively coupled to each circuit breaker 16 through digital network 22 and through an associated node electronic unit 20.

[0017] In one embodiment, digital network 22 includes, for example, at least one of a local area network (LAN) or a wide area network (WAN), dial-in- connections, cable modems, and special high-speed ISDN lines. Digital network 22 also includes any device capable of interconnecting to the Internet including a web- based phone, personal digital assistant (PDA), or other web-based connectable equipment.

[0018] In one embodiment, CCPU 24 is a computer and includes a device 26, for example, a floppy disk drive or CD-ROM drive, to facilitate reading instructions and/or data from a computer-readable medium 28, such as a floppy disk or CD-ROM. In another embodiment, CCPU 24 executes instructions stored in firmware (not shown). CCPU 24 is programmed to perform functions described herein, but other programmable circuits can likewise be programmed. Accordingly, as used herein, the term computer is not limited to just those integrated circuits referred to in the art as computers, but broadly refers to computers, processors, microcontrollers, microcomputers, programmable logic controllers, application specific integrated circuits, and other programmable circuits. Additionally, although described in a power distribution setting, it is contemplated that the benefits of the invention accrue to all electrical distribution systems including industrial systems such as, for example, but not limited to, an electrical distribution system installed in an office building.

[0019] Figure 2 is an exemplary schematic illustration of a node power distribution system 29 that can be used with power distribution system 10 (shown in Figure 1) and more specifically, with circuit breaker control protection system 19 (shown in Figure 1). Node power distribution system 29 includes a power source 30 that is electrically coupled to node electronic units 20 through a node power distribution bus 32. In an exemplary embodiment, power source 30 is an uninterruptible power supply (UPS). In one embodiment, power source 30 receives power from power system 10 and then distributes this power to node electronic units 20 through node power distribution bus 32. In an alternative embodiment, power is not supplied to power source 30, but rather, power source 30 supplies power to node electronic units 20 using an internal power supply, such as, but not limited to, a plurality of batteries (not shown). In another alternate embodiment, node electronic units 20 are powered by secondary current available from current sensor 82 and/or voltage sensor 84. In this embodiment, circuit breaker control protection system 19 would not include node power distribution system 29, power source 30, or node power distribution bus 32.

[0020] Figure 3 is an exemplary schematic illustration of CCPU 24.

CCPU 24 includes at least one memory device 40, such as, but not limited to, a read only memory (ROM) 42, a flash memory 44, and/or a random access memory (RAM) 46. CCPU 24 also includes a central processor unit (CPU) 48 that is electrically coupled to at least one memory device 40, as well as an internal bus 50, a communications interface 52, and a communications processor 54. In an exemplary embodiment, CCPU 24 is a printed circuit board and includes a power supply 56 to supply power to a plurality of devices on the printed circuit board.

[0021] Additionally, in an exemplary embodiment, internal bus 50 includes an address bus, a data bus, and a control bus. In use, the address bus is configured to enable CPU 48 to address a plurality of internal memory locations or an input/output port, such as, but not limited to communications interface 52 through communications processor 54, and a gateway interface 57, through a gateway processor 58. The data bus is configured to transmit instructions and/or data between CPU 48 and at least one input/output, and the control bus is configured to transmit signals between the plurality of devices to facilitate ensuring that the devices are operating in synchronization. In the exemplary embodiment, internal bus 50 is a bi- directional bus such that signals can be transmitted in either direction on internal bus 50. CCPU 24 also includes at least one storage device 60 configured to store a plurality of information transmitted via internal bus 50.

[0022] In use, gateway interface 57 communicates to a remote workstation (not shown) via an Internet link 62 or an Intranet 62. In the exemplary embodiment, the remote workstation is a personal computer including a web browser.

Although a single workstation is described, such functions as described herein can be performed at one of many personal computers coupled to gateway interface 57. For example, gateway interface 57 may be communicatively coupled to various <BR> <BR> individuals, including local operators and to third parties, e. g. , remote system operators via an ISP Internet connection. The communication in the example embodiment is illustrated as being performed via the Internet, however, any other wide area network (WAN) type communication can be utilized in other embodiments, <BR> <BR> i. e. , the systems and processes are not limited to being practiced via the Internet. In one embodiment, information is received at gateway interface 57 and transmitted to node electronic unit 20 via CCPU 24 and digital network 22. In another embodiment, information sent from node electronic unit 20 is received at communication interface 52 and transmitted to Internet 62 via gateway interface 57.

[0023] Figure 4 is an exemplary schematic block diagram of single node electronics unit 20. In the exemplary embodiment, node electronics unit 20 is a unitary device mounted remotely from CCPU 24 and breaker 16. For example, node electronics unit 20 can be separate from, but proximate to circuit breaker 16. Node electronics unit 20 includes a communications interface 70 that is coupled to digital network 22. In the exemplary embodiment, communication interface 70 communicates over network 22 using Fast Ethernet protocol at about 100 Mbps. In another embodiment, node electronics unit 20 includes a plurality of communication interfaces 70 that couple to an equal number of independent networks 22 which, in turn, each couple to independent CCPUs 24. Such an architecture provides a redundancy that facilitates operation of power distribution system 10. A number of independent, redundant communications interfaces 70, networks 22 and CCPUs 24 is determined by a predetermined redundancy requirement of a user. Each communication interface 70 couples electrically to a node processor 72 to transmit data received from a respective CCPU 24 to node processor 72 and to transmit data received from node processor 72 to respective CCPU 24. In an alternative embodiment, node electronics units 20 include a plurality of node processors 72. At least one of the plurality of node processors 72 may comprise a self-powered processor. A self-powered processor receives power from a self-power supply circuit 73. In an embodiment wherein a self-powered processor is used, the self-powered processor is configured to conserve electrical energy when power supply 80 is unable to supply the electrical requirements of the node electronics units 20. It should be appreciated that, in one embodiment, the self-powered processor conserves energy by being configured to execute only predetermined processes such that the self powered- processor conserves energy. In such a case, self-powered processor is configured for fast wakeup, i. e. an abbreviated initialization process when first powered. It should be further appreciated that, in another embodiment, the fast wakeup configuration allows the self-powered processor to conserve energy by executing only predetermined processes. Self-powered processor is additionally configured to modify its clock speed and processing to coordinate its power usage with power available through self-power supply circuit and power supply 80. Node processor 72 includes a memory, a communication processor and a command interpreter within.

The clocks of each node processor 72 in the plurality of node electronics units 20 in power distribution system 10 are synchronized by a synchronization pulse received from at least one CCPU 24. Node electronics units 20 determines which synchronization signal received synchronizes the node processors 72.

[0024] Node processor 72 is electrically coupled to a memory device 74, such as, but not limited to a flash memory device, an analog digital (A/D) converter 76, and a signal conditioner 78. Node processor 72 is communicatively coupled to communications interface 70. Memory device 74 is also communicatively coupled to node processor 72 for exchanging data, and program instructions. In one embodiment, memory device 74 is a single device including a program area and a data area. In an alternative embodiment, memory 74 is a plurality of devices, each including an area for a program, data and configuration constant information. In an embodiment wherein a plurality of node processors 72 are used, memory 74 includes a separate device dedicated to each node processor 72 and a shared memory area accessible and modifiable by each node processor 72. Node processor 72 is electrically coupled to A/D converter 76 to receive digital signals representing analog signals received from signal conditioner 78. Analog signals from sensors located remotely from circuit breaker 16 and node electronics unit 20 monitor electrical parameters associated with respective circuit breaker 16. The analog signals are received by signal conditioner 78 from CT input 82 and PT input 84. CT input 82 is electrically coupled to an input CT and a burden resistor (not shown). Input current flowing through the burden resistor induces a voltage drop across the burden resistor that is proportional to the input current. The induced voltage is sensed at signal conditioner 78 input. Signal conditioner 78 includes a filtering circuit to improve a signal to noise ratio of the incoming signal, a gain circuit to amplify the incoming signal, a level adjustment circuit to shift the incoming signal to a pre-determined range, and an impedance match circuit to facilitate a signal transfer to A/D converter 76. In the exemplary embodiment, A/D converter 76 is a sample and hold type of A/D converter. The sample and hold feature facilitates synchronization of electrical parameter measurements in node electronics units 20. A/D converter 76 samples signal conditioner 78 output when commanded by node processor 72, which issues synchronization commands as directed by CCPU 24. In an exemplary embodiment, node electronics unit 20 is a printed circuit board and includes a power supply 80 to power a plurality of devices on the printed circuit board.

[0025] In one embodiment, node electronics unit 20 receives signals input from a plurality of devices, such as, but not limited to, a current transformer 82, and a potential transformer 84, and/or a circuit breaker 16. A plurality of inputs from the circuit breaker 16 are provided as status input 86, and these inputs may include inputs, such as, but not limited to, an auxiliary switch status, and a spring charge switch status. In one embodiment, current transformer 82 includes a plurality of current transformers, each monitoring a different phase of a three phase power system, and at least one current transformer monitoring a neutral phase of the three phase power system. In another embodiment, potential transformer 84 includes a plurality of potential transformers, each monitoring a different phase of a three-phase power system. An actuation relay module 88 is communicatively coupled to node processor 72 and module 88 is also coupled to an actuation power module 90. Status input module and actuation power module 90 are electrically coupled to circuit breaker 16 through a standard wiring harness.

[0026] In one embodiment, node electronics unit 20 includes a second node processor 72 that executes a program code segment that determines local control and protection actions to be used to determine breaker commands when communications between node electronics unit 20 and CCPU 24 is lost. The second node processor is powered from an electrical source onboard the node electronics unit separate and independent from the control system power supply that supplies the other components of node electronics unit 20. In this embodiment, first node processor 72 is configured to execute a program code segment that controls all other functions of nod electronics unit 20, including, but, not limited to, communications functions performed by communications interface 70, input functions performed by signal conditioner 78, A/D 76, and status input 86, and output functions performed by actuation relay 88 and actuation power module 90. Second node processor 72 includes a memory separate and independent from memory unit 74.

[0027] In use, the status inputs 86 and signals received from current transformer 82, and potential transformer 84, are conditioned by signal conditioner 78 and transmitted to A/D converter 76, where the analog signals are converted to digital signals for input to node processor 72. Node processor 72 executes software that is resident on memory 74. The software instructs node processor 72 to receive digital signals from A/D converter 76 and logical status signals from circuit breaker 16 through status input 86. Node processor 72 compares the input signals to parameters determined by software executing on node processor 72 and parameters in control and protective actions received from CCPU 24 through network 22 and communications interface 70. Node processor 72 determines local control and protective actions based on the input signals and the control and protective actions received from CCPU 24. If node processor 72 and CCPU are communicating properly, a local block signal received from CCPU 24 inhibits node processor 72 from using the local control and protective actions from determining a set of breaker control actions. The breaker control actions are a set of signals that command circuit breaker 16 to operate in a predetermined manner. The presence of the local block signal indicates the communication state between node processor 72 and CCPU 24. If the local block signal is present in signals received from CCPU 24, Node processor uses CCPU 24 control and protective actions to determine breaker control actions. If the local block signal is not present, node processor 72 uses local control and protective actions to determine breaker control actions. Node processor 72 transmits breaker control action through actuation relay module 88, actuation power module 90, and the standard wiring harness.

[0028] Data received from A/D converter 78 and status input 86 by node processor 72 are transmitted to CCPU 24 via node electronics unit 20, and digital network 22. The data sent is to CCPU 24 is pre-processed data from node processor 72, in that, the data sent to CCPU 24 is sent in its raw form, before processing by node processor 72 takes place. The data transmitted to CCPU 24 via node electronics unit 20 is processed by CCPU 24, which transmits a signal to node electronics unit 20 via digital network 22. In the exemplary embodiment, node electronics unit 20 actuates circuit breaker 16 in response to the signal received from CCPU 24. In one embodiment, circuit breaker 16 is actuated in response to <BR> <BR> commands sent only by CCPU 24, i. e. , circuit breaker 16 is not controlled locally, but rather is operated remotely from CCPU 24 based on inputs received from current transformer 82, potential transformer 84, and status inputs 86 received from node electronics unit 20 over network 22.

[0029] Figure 5 is an exemplary schematic illustration of circuit breaker 16 that is electrically coupled to node electronics unit 20. In the exemplary embodiment, circuit breaker 16 includes a switch assembly that includes movable and/or stationary contacts, an arc suppression means, and a tripping and operating mechanism. Circuit breaker 16 auxiliaries include only a trip coil 100, a close coil 102, an auxiliary switch 104, a spring charge switch 106, and a motor 108. Circuit breaker 16 does not include a trip unit. Auxiliary switches and sensors are coupled to node electronics unit 20 through a standard wiring harness 110, which may include both copper wiring and communications conduits. Current sensor 82, and voltage sensor 84 are coupled to node electronics unit 20 through a cable 112 that may include copper wiring and/or communications conduits. Circuit breaker 16 is a unitary device mounted proximate to CCPU 20, current sensor 82, and voltage sensor 84.

[0030] In use, actuation signals from node electronics unit 20 are transmitted to circuit breaker 16 to actuate a plurality of functions in circuit breaker 16, such as, but not limited to, operating a trip coil 100, operating a close coil 102, and affecting a circuit breaker lockout feature. An auxiliary switch 104 and spring charge switch 106 provide a status indication of circuit breaker parameters to node electronics unit 20. Motor 108 is configured to recharge a close spring (not shown) after circuit breaker 16 closes. To close circuit breaker 16, a close coil 102 is energized by a close signal from actuation power module 90. Close coil 102 actuates a closing mechanism (not shown) that couples at least one movable electrical contact (not shown) to a corresponding fixed electrical contact (not shown). The closing mechanism of circuit breaker 16 latches in a closed position such that when close coil 102 is de-energized, circuit breaker 16 remains closed. When breaker 16 closes, an "contact of auxiliary switch 104 also closes and a"b"contact of auxiliary switch 104 opens. The position of the"a"and"b"contacts is sensed by node electronics unit 20. To open circuit breaker 16, node electronics unit 20 energizes trip coil (TC) 100.

TC 100 acts directly on circuit breaker 16 to release the latching mechanism that holds circuit breaker 16 closed. When the latching mechanism is released, circuit breaker 16 will open, opening the"a"contact and closing the"b"contact of auxiliary switch 104. Trip coil 100 is then de-energized by node electronics unit 20. After breaker 16 opens, with the close spring recharged by motor 108, circuit breaker 16 is prepared for a next operating cycle. In the exemplary embodiment, each node electronics unit 20 is coupled to circuit breaker 16 in a one-to-one correspondence.

For example, each node electronics unit 20 communicates directly with only one circuit breaker 16. In an alternative embodiment, node electronics unit 20 may communicate with a plurality of circuit breakers 16.

[0031] Figure 6 is an expanded schematic block diagram of an exemplary node electronics unit 20 shown in figure 4. Node electronics unit 20 functions to perform at least the following functions, sample a current flow through circuit breaker 16 and/or a voltage across circuit breaker 16 and synchronized to within about 10 microseconds of the sampling of all other node electronics units 20, transmit current and/or voltage measurements and node electronics unit 20 and/or circuit breaker 16 state to central control processing unit (CCPU) 24 through network 22, and receive and decode commands issued by CCPU 24 communicatively coupled through network 22. These functions need to occur with sufficient temporal speed such that all power distribution system 10 control latency requirements are met. For example, in an instantaneous overcurrent (IOC) event at one of circuit breaker 16, a TRIP command should be issued for the affected circuit breaker and executed by the associated node electronics unit 20 within 2.6 milliseconds of the onset of IOC.

[0032] Components of node electronics unit 20 that are identical to node electronics unit 20 components shown n Figure 4 are shown in Figure 6 using the same reference numerals used in Figure 4. Accordingly, node electronics unit 20 includes node processor 72, sample and hold A/D converter 76, communication interface 70, and network 22. Additionally, node electronics unit 20 includes an execution timer 602, external interrupt channel 604 and internal interrupt channel 606.

Sample and hold A/D converter 76 includes a data input from signal conditioner 78 (not shown) via an input channel 608. Sample and hold A/D converter 76 also includes communications paths 610 and 612 to node processor 72 for transmitting a sample command 610 and transmitting digital sampled data 612 [0033] Node processor 72 includes an interrupt handler 614 which receives interrupt requests from external components via channel 604, internal components via channel 606, execution timer 602, and communications interface 70.

Interrupt handler 614 also services interrupt requests generated onboard processor 72.

Node processor 72 includes a polling subroutine 616 operating in a background environment. Polling subroutine 616 executes when interrupt handler 614 is not servicing interrupts, thus utilizing node processor 72 resources only when the resources are not needed to service higher priority requests. Polling subroutine 616 polls a plurality of process execution flags 618 that are set by other processes executing in processor 72. A high priority interrupt may start a process that needs lower priority processes to execute, and may set a process execution flag to request service for the process. Likewise, lower priority processes may spawn other processes by setting an execution flag for that process. Processor 72 is programmed to include functions such as an integrator, a differentiator, an amplifier, a comparator, a voltage reference and a current reference for processor operation during periods of power interruption or poor power quality supplied to node electronics unit 20, when processor 72 may be operating from a self-powered function processing analog input signals.

[0034] In operation, node electronics unit 20 utilizes a software architecture that enables real-time, synchronized monitoring and control of node electronics unit 20 and circuit breaker 16. In this software architecture, node processes are triggered by external or internal interrupts, or through background polling of process execution flags. High priority process components, for example components that need immediate processing for the system to achieve latency goals, are executed within interrupt handler 614. If follow-on low priority processes are to occur, a flag 618 is set for the follow-on process. When interrupt handler 616 is not executing, a low priority polling loop is running, checking the status of process flags 618. If a process's flag is set, its process flag is cleared and the process is executed.

As described above, this process may enable the execution of further follow-on processes by setting their process flags.

[0035] In the exemplary embodiment, high priority processes for execution may include recording the local time of an arriving packet, which is triggered by an interrupt from communications interface 70, initiation of data sampling by sample and hold A/D converter 76, execution timer reset, which is triggered by a timer expiration interrupt, and enabling data sample collection, which is triggered by a data ready interrupt from A/D converter 76. Follow-on processes that may be initiated by the high-priority processes may include low priority execution of command message decoding and execution, synchronization processes as needed, for example, when a particular command message is received, low priority evaluation of communication channel health, reading of a set of data samples from the A/D converter, and loading the set of data samples into a data packet. The data packet is transmitted to CCPU 24 when all of the data sample fields of the data packet's have been filled with new data (since the previous packet transmission).

[0036] The software architecture of node electronics unit 20 enables real-time, synchronized monitoring and control of node electronics unit 20, such as synchronized sampling and transmission of circuit breaker 16 currents and voltages to CCPU 24, and real-time reception and execution of commands issued by CCPU 24.

The software architecture also provides for division of processes into high priority (i. e. immediate--interrupt driven) and low priority categories, execution of high priority tasks that are important for real-time, synchronized node operation, and use of flags and polling to enable execution of lower priority tasks. High priority tasks, which are triggered by interrupts may include recording the local time of an arriving message packet, initiating A/D converter 76 data acquisition, resetting timer 602, and enabling data sample collection. Lower priority tasks, which are triggered through the polling of flags set by other processes may include decoding of received messages and execution of received message commands, evaluation of communication channel health, reading of data samples from A/D converter 76, and transmission of node electronics unit information to CCPU 24.

[0037] Figure 7 is a flow chart illustrating an exemplary method 700 for operating the node electronics unit shown in Figure 6. In the exemplary embodiment, the node electronics unit is a component of a centrally controlled power distribution system wherein the power distribution system includes a plurality of circuit breakers that are each coupled to a single node electronics unit. Each node electronics unit includes a plurality of processors and a memory, and is communicatively coupled to at least one CCPU through an associated network.

Method 700 includes triggering 702 a first node electronics unit process with a processor interrupt. High priority processes may originate internal to the processor and/or external to the processor. An interrupt handler, executing on each processor services each received interrupt. An interrupt may trigger a high priority process such as recording a local time of an arriving message packet, initiation of an A/D converter data sampling and a timer reset, and enabling data sample collection. An interrupt that triggers 702 recording the local time of an arriving message packet is an example of an interrupt from an interrupt source external to processor. Such an interrupt may originate in communications interface. Triggering an initiation of the A/D converter data sampling and the timer reset is an example of an interrupt from an interrupt source internal to processor such as from a timer expiration interrupt. Additionally, a device such as A/D converter may signal a data ready condition to processor using an interrupt. Node electronics unit processor includes a background polling process for processes that are not high priority processes. A lower priority request triggers 704 a second node electronics unit process by background polling of a plurality of process execution flags and/or a scheduled processor interrupt. A device or routine requests servicing of a lower priority process by setting at least one process execution flag, processor polls the process execution flags when processor interrupt handler 614 is not executing, and triggers a low priority process when a process execution flag is set.

A first process initiated by a process execution flag may spawn another second process such that a follow-on process execution flag is set by the first process to enable execution of a follow-on process. In the exemplary embodiment, interrupt handler 614 services the processor interrupts. In an alternative embodiment, interrupts are handled using the processor operating system, and processes are scheduled using the processor operating system.

[0038] Exemplary processes that may be initiated using a process execution flag include decoding of received messages and executing received message commands, evaluating communication channel health, conducting a node electronics unit self-evaluation, reading data samples from a node electronics unit A/D converter, executing local protection, logging diagnostic history, logging event history, reading circuit breaker status, reading node identification, determining identification of systems units, updating system unit identification, executing a synchronization routine, adaptively modifying node electronics unit parameters and process execution, and transmitting node electronics unit information to the CCPUs.

[0039] Node electronics unit parameters may include a local protection function parameter, a communication parameter, a sampling parameter, a diagnostic parameter, and a calibration parameter. Node electronics unit process execution may include a condition for triggering a process, adding a new trigger, replacing an existing trigger, replacing an existing process with an alternate process, adding a new process, removing an existing process. When replacing an existing process with an alternate process, the existing process may be replaced with an alternate process that is resident in the node and the alternate process may be identified by a process description received from a remote source such as a remote processor, a remote controller, a manual entry, an external process server, an external code server, a storage media, and the a process description may include a binary, executable, compilable source code, interpretable source code, or references to resident code blocks.

[0040] Node electronics unit parameters and process execution may be adaptively modified based on system resources, a communication network noise level, a data signal-to-noise ratio, a change in a number of network nodes, a communication channel utilization, a change of authorization of parameters, service requested data, and a change command received from at least one of a remote controller and an external processor. The node electronics unit senses parameters associated with potential system problems and routinely performs system troubleshooting and diagnostic self checks to facilitate maintaining optimal system operation during periods of less than optimal system conditions.

[0041] Node electronics unit parameters and process execution may be adaptively modified based on service requested data that may include system status data, local status data, local health data, communication network data, data signal-to- noise ratio, event history, and error history.

[0042] To facilitate efficient operation during foreseeable operating conditions at least one of the plurality of processors may be configured to operate at a first power consumption, which would be the power consumption level during a normal operating period, and also configured to operate at a second, reduced power consumption, which would occur during periods of a loss of normal power to the node electronics unit as may occur during a fault in the power supply. Additionally, a processor may be programmed to operate as a primary processor and a second processor may be programmed to operate as a secondary processor. The primary processor is operable to perform the functions of a processor in a normal mode and the secondary processor is operable in a sleep mode and may be self powered. The secondary processor may remain in sleep mode until activated by an external signal, such as a loss of power to the node electronics unit or may"wake-up"periodically, based on an internal timer, to determine the status of the node electronics unit and then reenter sleep mode. The secondary processor may be configured to operate with ultra-low power, at very high processor speed, and be capable of a short power-up or initialization time. During periods when the node electronics unit is supplied with normal power, the secondary processor may communicate secondary processor status, secondary processor health, and secondary processor events to the primary processor, and may receive commands, parameters, status information, and health information from the primary processor.

[0043] In the exemplary embodiment, at least one processor is programmed to execute a watchdog timer function for monitoring the health of the other processors. Processor generates a first"heartbeat"signal and transmits the heartbeat signal to each other processor or a predetermined number of the other processors. Each processor that receives the first heartbeat signal and is healthy, responds with a second heartbeat signal, which each processor transmits to the sending processor. The sending processor is programmed to determine the health of the other processors based on heartbeat signals received and the watchdog timer.

[0044] A processor may be programmed to execute a power supply monitoring function that includes logging power supply events, determining a health of the power supply, and transmitting commands based on the determined health, for example, writing power supply status data to a nonvolatile memory, executing a reduced instruction set to conserve power, and transferring processing control to a processor operating at reduced power consumption. The processor may further be programmed to execute a baclcup protection function when operating at reduced power consumption. During reduced power consumption the processor may operate only selected high priority functions using a reduced instruction set and/or reduced clock speed. In the exemplary embodiment, the processor executes the backup protection function using analog signal processing and bypassing the A/D converter to conserve power. As described above, the processor includes functionality that includes an integrator, a differentiator, an amplifier, a comparator, a voltage reference and a current reference for processing the analog input signals. The processor receives analog signals from a source, such as, a current transformer, potential transformer, and/or a status input device, and processes the analog signal using the integrator, the differentiator, the amplifier, the comparator, the voltage reference and the current reference.

[0045] The above-described power distribution system node electronics unit software architecture is cost-effective and highly reliable. The software architecture enables real-time, synchronized monitoring and control of all node electronics units operating on the power distribution system. The software architecture also provides for division of processes into high priority and low priority categories, such that node resources are used efficiently and system latency times may be maintained below predetermined goals. Accordingly, the power distribution system node electronics unit software architecture facilitates protection and monitoring of the power distribution system in a cost-effective and reliable manner.

[0046] Exemplary embodiments of power distribution system node electronics unit components are described above in detail. The components are not limited to the specific embodiments described herein, but rather, components of each system may be utilized independently and separately from other components described herein. Each power distribution system node electronics unit component can also be used in combination with other power distribution system components.

[0047] While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.