Abstract:
A method and apparatus is disclosed for providing protection against arc flash during maintenance on a low voltage power circuit including a circuit breaker having a specified trip function for responding to a fault is provided. The specified trip function is overridden with a maintenance trip function that results in reduced arc energy in the fault during a trip over arc energy during a trip with the specified trip function. The specified trip function is restored following maintenance.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of U.S. patent application Ser. No. 10/373,583, filed Feb. 25, 2003, allowed and pending, which claims the benefit of U.S. provisional patent application Ser. No. 60/359,544, filed on Feb. 25, 2002, and U.S. provisional patent application Ser. No. 60/438,159 filed on Jan. 6, 2003, the contents all of which are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates generally to power distribution systems including circuit breakers, and more particularly to a method and apparatus for a circuit protection system providing adjustable circuit breaker trip curves in-situ. 
     In power distribution systems, power is distributed to various loads and is typically divided into branch circuits, which supply power to specified loads. The branch circuits also can be connected to various other power distribution equipment, such as, transformers that step down the supply voltage for use by a specific piece of electrical equipment. 
     Due to the concern of an abnormal power condition in the system, i.e., a fault, it is known to provide circuit protective devices, e.g., circuit breakers to protect the various loads, as well as the power distribution equipment. The circuit breakers seek to prevent or minimize damage and typically function automatically. The circuit breakers also seek to minimize the extent and duration of electrical service interruption in the event of a fault. 
     It is further known to utilize upstream circuit breakers having pre-programmed time delays so that the downstream circuit breakers are provided with an opportunity to clear the fault before the upstream circuit breaker opens or trips. In a known zone selective interlock system, a downstream circuit breaker can be in direct communication with an upstream circuit breaker through wiring such that the downstream circuit breaker sends a signal to the upstream circuit breaker placing the upstream circuit breaker in a restrained mode. In the restrained mode, the circuit breaker temporarily restrains from opening or tripping until after a pre-determined time delay has timed out. The circuit breakers each have pre-programmed time delay settings incorporated therein. This type of system provides for time delays based upon pre-set, invariable time periods associated with the upstream circuit breaker. Thus, the upstream circuit breaker will delay tripping by a pre-set period of time regardless of the location of the fault in the power distribution system. 
     The circuit breakers, can be arranged in a hierarchy or tree configuration having a plurality of layers or levels with the upstream circuit breakers closer to the power source and the downstream circuit breakers closer to the loads. In order to minimize service interruption, the circuit breaker nearest the fault will first attempt to interrupt the fault current. If this first circuit breaker does not timely clear the fault, then the next upstream circuit breaker will attempt to do so. However, this can result in the problem of a circuit breaker multiple levels upstream from a fault being tripped when the fault is detected, which causes power loss to the multiple levels of loads downstream that should otherwise be unaffected. 
     Such a system does not delay the upstream circuit breakers based upon an optimal time period to provide the downstream circuit breaker with the opportunity to clear the fault. Where a circuit has downstream circuit branches and circuit breakers having differing temporal properties, such as, for example, clearing time or pre-set delay time of the circuit breakers, such a system fails to account for these differences. This increases the risk of damage to the system where an upstream circuit breaker has a pre-set time delay that is too long based on the location of the fault. This also decreases the efficiency of the system where an upstream circuit breaker has a pre-set time delay that is too short based on the location of the fault and opens before the downstream circuit breaker has a full opportunity to clear the fault. This system also suffers from the drawback of the need to hardwire the upstream circuit breakers with each of the downstream circuit breakers. In a multi-tiered and multi-source system, this can require a complex and costly wiring scheme. 
     Accordingly, there is a need for circuit protection systems incorporated into power distribution systems that decrease the risk of damage and increase efficiency of the power distribution system. There is a further need for protection systems that can vary the zones of protection and the time delays of protection as the power distribution system changes and provide optimized protection without sacrificing selectivity. 
     SUMMARY OF THE INVENTION 
     In one aspect, a method of protecting a circuit having a first circuit breaker and a second circuit breaker downstream of the first circuit breaker is provided. The method comprises detecting a fault in the circuit with the fault being downstream of the second circuit breaker, determining a dynamic delay time for opening the first circuit breaker, and opening the first circuit breaker after the dynamic delay time has elapsed. 
     In another aspect, a method of protecting a circuit having a first circuit breaker arranged upstream of a plurality of second circuit breakers is provided. The method comprises detecting a fault in the circuit, determining a location of the fault, determining a dynamic delay time for opening the first circuit breaker based at least in part upon the location of the fault, and delaying opening the first circuit breaker until after the dynamic delay time has elapsed. 
     In yet another aspect, a protection system coupled to a circuit having a first circuit breaker arranged upstream of a plurality of second circuit breakers is provided. The system comprises a network and at least one control processing unit operatively controlling the first circuit breaker and the plurality of second circuit breakers. The network is communicatively coupled to the circuit, the first circuit breaker, the plurality of second circuit breakers and the control processing unit. The control processing unit determines a dynamic delay time for opening the first circuit breaker if a fault is detected in the circuit. The control processing unit delays opening the first circuit breaker until after the dynamic delay time has elapsed. 
     In a further aspect, a power distribution system is provided which comprises a circuit having a plurality of circuit breakers, at least one power source and at least one load. The plurality of circuit breakers are arranged with at least one first circuit breaker upstream of a plurality of second circuit breakers. The system further comprises a network and at least one control processing unit operatively controlling the plurality of circuit breakers. The network is communicatively coupled to the control processing unit and the circuit. The control processing unit determines a dynamic delay time for opening the first circuit breaker if a fault is detected in the circuit. The control processing unit delays opening the first circuit breaker until after the dynamic delay time has elapsed. 
     In yet a further aspect of the invention, a method of providing protection against arc flash during maintenance on a low voltage power circuit including a circuit breaker having a specified trip function for responding to a fault is provided. The specified trip function is overridden with a maintenance trip function that results in reduced arc energy in the fault during a trip over arc energy during a trip with the specified trip function, and the specified trip function is restored following maintenance. 
     In another aspect of the invention, a low voltage circuit breaker protecting from arc flash resulting from faults in a protected low voltage power circuit is provided. The circuit breaker includes separable contacts, current sensors sensing current in the protected low voltage power circuit, a trip unit responsive to the current sensors tripping open the separable contacts in response to a specified trip function, and maintenance means overriding the specified trip function with a maintenance trip function that results in reduced arc energy in the fault during a trip over arc energy during a trip with the specified trip function. 
     The above-described and other features and advantages of the present disclosure will be appreciated and understood by those skilled in the art from the following detailed description, drawings, and appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of a power distribution system; 
         FIG. 2  is a schematic illustration of a module of the power distribution system of  FIG. 1 ; 
         FIG. 3  is a response time for the protection system of  FIG. 1 ; 
         FIG. 4  is a schematic illustration of a multiple source power distribution system; 
         FIG. 5  is a schematic illustration of a portion of the system of  FIG. 4  with a fault occurring downstream of Feeder Circuit Breaker  1 ; 
         FIG. 6  is a schematic illustration of the portion of the system of  FIG. 4  with a fault occurring downstream of Feeder Circuit Breaker  2 ; 
         FIG. 7  is a schematic illustration of the portion of the system of  FIG. 4  with a fault occurring downstream of Main Circuit Breaker  1 ; 
         FIG. 8  is a schematic illustration of a portion of the system of  FIG. 4  with a Tie Circuit Breaker in an open or tripped state; and 
         FIG. 9  is a schematic illustration of the portion of the system of  FIG. 8  with a Main Circuit Breaker  2  in an open or tripped state. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings and in particular to  FIG. 1 , an exemplary embodiment of a power distribution system generally referred to by reference numeral  10  is illustrated. System  10  distributes power from at least one power bus  12  through a number or plurality of circuit breakers  14  to branch circuits  16 . 
     Power bus  12  is illustrated by way of example as a three-phase power system having a first phase  18 , a second phase  20 , and a third phase  22 . Power bus  12  can also include a neutral phase (not shown). System  10  is illustrated for purposes of clarity distributing power from power bus  12  to four circuits  16  by four breakers  14 . Of course, it is contemplated by the present disclosure for power bus  12  to have any desired number of phases and/or for system  10  to have any desired number of circuit breakers  14 . 
     Each circuit breaker  14  has a set of separable contacts  24  (illustrated schematically). Contacts  24  selectively place power bus  12  in communication with at least one load (also illustrated schematically) on circuit  16 . The load can include devices, such as, but not limited to, motors, welding machinery, computers, heaters, lighting, and/or other electrical equipment. 
     Power distribution system  10  is illustrated in  FIG. 1  with an exemplary embodiment of a centrally controlled and fully integrated protection, monitoring, and control system  26  (hereinafter “system”). System  26  is configured to control and monitor power distribution system  10  from a central control processing unit  28  (hereinafter “CCPU”). CCPU  28  communicates with a number or plurality of data sample and transmission modules  30  (hereinafter “module”) over a data network  32 . Network  32  communicates all of the information from all of the modules  30  substantially simultaneously to CCPU  28 . 
     Thus, system  26  can include protection and control schemes that consider the value of electrical signals, such as current magnitude and phase, at one or all circuit breakers  14 . Further, system  26  integrates the protection, control, and monitoring functions of the individual breakers  14  of power distribution system  10  in a single, centralized control processor (e.g., CCPU  28 ). System  26  provides CCPU  28  with all of a synchronized set of information available through digital communication with modules  30  and circuit breakers  14  on network  32  and provides the CCPU with the ability to operate these devices based on this complete set of data. 
     Specifically, CCPU  28  performs all primary power distribution functions for power distribution system  10 . Namely, CCPU  28  performs all instantaneous overcurrent protection (IOC), short time overcurrent, longtime overcurrent, relay protection, and logic control as well as digital signal processing logged in single, central location, i.e., CCPU  28 . CCPU  28  is described herein by way of example as a central processing unit. Of course, it is contemplated by the present disclosure for CCPU  28  to include any programmable circuit, such as, but not limited to, computers, processors, microcontrollers, microcomputers, programmable logic controllers, application specific integrated circuits, and other programmable circuits. 
     As shown in  FIG. 1 , each module  30  is in communication with one of the circuit breakers  14 . Each module  30  is also in communication with at least one sensor  34  sensing a condition or electrical parameter of the power in each phase (e.g., first phase  18 , second phase  20 , third phase  22 , and neutral) of bus  12  and/or circuit  16 . Sensors  34  can include current transformers (CTs), potential transformers (PTs), and any combination thereof. Sensors  34  monitor a condition or electrical parameter of the incoming power in circuits  16  and provide a first or parameter signal  36  representative of the condition of the power to module  30 . For example, sensors  34  can be current transformers that generate a secondary current proportional to the current in circuit  16  so that first signals  36  are the secondary current. 
     Module  30  sends and receives one or more second signals  38  to and/or from circuit breaker  14 . Second signals  38  can be representative of one or more conditions of breaker  14 , such as, but not limited to, a position or state of separable contacts  24 , a spring charge switch status, a lockout state or condition, and others. In addition, module  30  is configured to operate or actuate circuit breaker  14  by sending one or more third signals  40  to the breaker to open/close separable contacts  24  as desired, such as open/close commands or signals. In a first embodiment, circuit breakers  14  cannot open separable contacts  24  unless instructed to do so by system  26 . 
     System  26  utilizes data network  32  for data acquisition from modules  30  and data communication to the modules. Accordingly, network  32  is configured to provide a desired level of communication capacity and traffic management between CCPU  28  and modules  30 . In an exemplary embodiment, network  32  can be configured to not enable communication between modules  30  (i.e., no module-to-module communication). 
     In addition, system  26  can be configured to provide a consistent fault response time. As used herein, the fault response time of system  26  is defined as the time between when a fault condition occurs and the time module  30  issues an trip command to its associated breaker  14 . In an exemplary embodiment, system  26  has a fault response time that is less than a single cycle of the 60 Hz (hertz) waveform. For example, system  26  can have a maximum fault response time of about three milliseconds. 
     The configuration and operational protocols of network  32  are configured to provide the aforementioned communication capacity and response time. For example, network  32  can be an Ethernet network having a star topology as illustrated in  FIG. 1 . In this embodiment, network  32  is a full duplex network having the collision-detection multiple-access (CSMA/CD) protocols typically employed by Ethernet networks removed and/or disabled. Rather, network  32  is a switched Ethernet for managing collision domains. 
     In this configuration, network  32  provides a data transfer rate of at least about 100 Mbps (megabits per second). For example, the data transfer rate can be about 1 Gbps (gigabits per second). Additionally, communication between CCPU  28  and modules  30  across network  32  can be managed to optimize the use of network  32 . For example, network  32  can be optimized by adjusting one or more of a message size, a message frequency, a message content, and/or a network speed. 
     Accordingly, network  32  provides for a response time that includes scheduled communications, a fixed message length, full-duplex operating mode, and a switch to prevent collisions so that all messages are moved to memory in CCPU  28  before the next set of messages is scheduled to arrive. Thus, system  26  can perform the desired control, monitoring, and protection functions in a central location and manner. 
     It should be recognized that data network  32  is described above by way of example only as an Ethernet network having a particular configuration, topography, and data transmission protocols. Of course, the present disclosure contemplates the use of any data transmission network that ensures the desired data capacity and consistent fault response time necessary to perform the desired range of functionality. The exemplary embodiment achieves sub-cycle transmission times between CCPU  28  and modules  30  and full sample data to perform all power distribution functions for multiple modules with the accuracy and speed associated with traditional devices. 
     CCPU  28  can perform branch circuit protection, zone protection, and relay protection interdependently because all of the system information is in one central location, namely at the CCPU. In addition, CCPU  28  can perform one or more monitoring functions on the centrally located system information. Accordingly, system  26  provides a coherent and integrated protection, control, and monitoring methodology not considered by prior systems. For example, system  26  integrates and coordinates load management, feed management, system monitoring, and other system protection functions in a low cost and easy to install system. 
     An exemplary embodiment of module  30  is illustrated in  FIG. 2 . Module  30  has a microprocessor  42 , a data bus  44 , a network interface  46 , a power supply  48 , and one or more memory devices  50 . 
     Power supply  48  is configured to receive power from a first source  52  and/or a second source  54 . First source  52  can be one or more of an uninterruptible power supply (not shown), a plurality of batteries (not shown), a power bus (not shown) and other sources. In the illustrated embodiment, second source  54  is the secondary current available from sensors  34 . 
     Power supply  48  is configured to provide power  56  to module  30  from first and second sources  52 ,  54 . For example, power supply  48  can provide power  56  to microprocessor  42 , data bus  42 , network interface  44 , and memory devices  50 . Power supply  48  is also configured to provide a fourth signal  58  to microprocessor  42 . Fourth signal  58  is indicative of what sources are supplying power to power supply  48 . For example, fourth signal  58  can indicate whether power supply  48  is receiving power from first source  52 , second source  54 , or both of the first and second sources. 
     Network interface  46  and memory devices  50  communicate with microprocessor  42  over data bus  44 . Network interface  46  can be connected to network  32  so that microprocessor  42  is in communication with CCPU  28 . 
     Microprocessor  42  receives digital representations of first signals  36  and second signals  38 . First signals  36  are continuous analog data collected by sensors  34 , while second signals  38  are discrete analog data from breaker  14 . Thus, the data sent from modules  30  to CCPU  28  is a digital representation of the actual voltages, currents, and device status. For example, first signals  36  can be analog signals indicative of the current and/or voltage in circuit  16 . 
     Accordingly, system  26  provides the actual raw parametric or discrete electrical data (i.e., first signals  36 ) and device physical status (i.e., second signal  38 ) to CCPU  28  via network  32 , rather than processed summary information sampled, created, and stored by devices such as trip units, meters, or relays. As a result, CCPU  28  has complete, raw system-wide data with which to make decisions and can therefore operate any or all breakers  14  on network  32  based on information derived from as many modules  30  as the control and protection algorithms resident in CCPU  28  require. 
     Module  30  has a signal conditioner  60  and an analog-digital converter  62 . First signals  36  are conditioned by signal conditioner  60  and converted to digital signals  64  by A/D converter  62 . Thus, module  30  collects first signals  36  and presents digital signals  64 , representative of the raw data in the first signals, to microprocessor  42 . For example, signal conditioner  60  can includes a filtering circuit (not shown) to improve a signal-to-noise ratio first signal  36 , a gain circuit (not shown) to amplify the first signal, a level adjustment circuit (not shown) to shift the first signal to a pre-determined range, an impedance match circuit (not shown) to facilitate transfer of the first signal to A/D converter  62 , and any combination thereof. Further, A/D converter  62  can be a sample-and-hold converter with external conversion start signal  66  from microprocessor  42  or a clock circuit  68  controlled by microprocessor  42  to facilitate synchronization of digital signals  64 . 
     It is desired for digital signals  64  from all of the modules  30  in system  26  to be collected at substantially the same time. Specifically, it is desired for digital signals  64  from all of the modules  30  in system  26  to be representative of substantially the same time instance of the power in power distribution system  10  . 
     Modules  30  sample digital signals  64  based, at least in part, upon a synchronization signal or instruction  70  as illustrated in  FIG. 1 . Synchronization instruction  70  can be generated from a synchronizing clock  72  that is internal or external to CCPU  28 . Synchronization instruction  70  is simultaneously communicated from CCPU  28  to modules  30  over network  32 . Synchronizing clock  72  sends synchronization instructions  70  at regular intervals to CCPU  28 , which forwards the instructions to all modules  30  on network  32 . 
     Modules  30  use synchronization instruction  70  to modify a resident sampling protocol. For example, each module  30  can have a synchronization algorithm resident on microprocessor  42 . The synchronization algorithm resident on microprocessor  42  can be a software phase-lock-loop algorithm. The software phase-lock-loop algorithm adjusts the sample period of module  30  based, in part, on synchronization instructions  70  from CCPU  28 . Thus, CCPU  28  and modules  30  work together in system  26  to ensure that the sampling (i.e., digital signals  64 ) from all of the modules in the system are synchronized. 
     Accordingly, system  26  is configured to collect digital signals  64  from modules  30  based in part on synchronization instruction  70  so that the digital signals are representative of the same time instance, such as being within a predetermined time-window from one another. Thus, CCPU  28  can have a set of accurate data representative of the state of each monitored location (e.g., modules  30 ) within the power distribution system  10 . The predetermined time-window can be less than about ten microseconds. For example, the predetermined time-window can be about five microseconds. 
     The predetermined time-window of system  26  can be affected by the port-to port variability of network  32 . In an exemplary embodiment, network  32  has a port-to-port variability of in a range of about 24 nanoseconds to about 720 nanoseconds. In an alternate exemplary embodiment, network  32  has a maximum port-to-port variability of about 2 microseconds. 
     It has been determined that control of all of modules  30  to this predetermined time-window by system  26  enables a desired level of accuracy in the metering and vector functions across the modules, system waveform capture with coordinated data, accurate event logs, and other features. In an exemplary embodiment, the desired level of accuracy is equal to the accuracy and speed of traditional devices. For example, the predetermined time-window of about ten microseconds provides an accuracy of about 99% in metering and vector functions. 
     Second signals  38  from each circuit breaker  14  to each module  30  are indicative of one or more conditions of the circuit breaker. Second signals  38  are provided to a discrete I/O circuit  74  of module  30 . Circuit  74  is in communication with circuit breaker  14  and microprocessor  42 . Circuit  74  is configured to ensure that second signals  38  from circuit breaker  14  are provided to microprocessor  42  at a desired voltage and without jitter. For example, circuit  74  can include de-bounce circuitry and a plurality of comparators. 
     Microprocessor  42  samples first and second signals  36 ,  38  as synchronized by CCPU  28 . Then, converter  62  converts the first and second signals  36 ,  38  to digital signals  64 , which is packaged into a first message  76  having a desired configuration by microprocessor  42 . First message  76  can include an indicator that indicates which synchronization signal  70  the first message was in response to. Thus, the indicator of which synchronization signal  70  first message  76  is responding to is returned to CCPU  28  for sample time identification. 
     CCPU  28  receives first message  76  from each of the modules  30  over network  32  and executes one or more protection and/or monitoring algorithms on the data sent in all of the first messages. Based on first message  76  from one or more modules  30 , CCPU  28  can control the operation of one or more circuit breakers  14 . For example, when CCPU  28  detects a fault from one or more of first messages  76 , the CCPU sends a second message  78  to one or more modules  30  via network  32 , such as open or close commands or signals, or circuit breaker actuation or de-actuation commands or signals. 
     In response to second message  78 , microprocessor  42  causes third signal  40  to operate or actuate (e.g., open contacts  24 ) circuit breaker  14 . Circuit breaker  14  can include more than one operation or actuation mechanism. For example, circuit breaker  14  can have a shunt trip  80  and a magnetically held solenoid  82 . Microprocessor  42  is configured to send a first output  84  to operate shunt trip  80  and/or a second output  86  to operate solenoid  82 . First output  84  instructs a power control module  88  to provide third signal  40  (i.e., power) to shunt trip  80 , which can separate contacts  24 . Second output  86  instructs a gating circuit  90  to provide third signal  40  to solenoid  82  (i.e., flux shifter) to separate contacts  24 . It should be noted that shunt trip  80  requires first source  52  to be present, while solenoid  82  can be operated when only second source  54  is present. In this manner, microprocessor  42  can operate circuit breaker  14  in response to second message  78  regardless of the state of first and second sources  52 ,  54 . Additionally, a lockout device can be provided that is operably connected to circuit breaker  14 . 
     In addition to operating circuit breaker  14 , module  30  can communicate to one or more local input and/or output devices  94 . For example, local output device  94  can be a module status indicator, such as a visual or audible indicator. In one embodiment, device  94  is a light emitting diode (LED) configured to communicate a status of module  30 . In another embodiment, local input device  94  can be a status-modifying button for manually operating one or more portions of module  30 . In yet another embodiment, local input device  94  is a module interface for locally communicating with module  30 . 
     Accordingly, modules  30  are adapted to sample first signals  36  from sensors  34  as synchronized by the CCPU. Modules  30  then package the digital representations (i.e., digital signals  64 ) of first and second signals  36 ,  38 , as well as other information, as required into first message  76 . First message  76  from all modules  30  are sent to CCPU  28  via network  32 . CCPU  28  processes first message  76  and generates and stores instructions to control the operation of each circuit breaker  14  in second message  78 . CCPU  28  sends second message  78  to all of the modules  30 . In an exemplary embodiment, CCPU  28  sends second message  78  to all of the modules  30  in response to synchronization instruction  70 . 
     Accordingly, system  26  can control each circuit breaker  14  based on the information from that breaker alone, or in combination with the information from one or more of the other breakers in the system  26 . Under normal operating conditions, system  26  performs all monitoring, protection, and control decisions at CCPU  28 . 
     Since the protection and monitoring algorithms of system  26  are resident in CCPU  28 , these algorithms can be enabled without requiring hardware or software changes in circuit breaker  14  or module  30 . For example, system  26  can include a data entry device  92 , such as a human-machine-interface (HMI), in communication with CCPU  28 . In this embodiment, one or more attributes and functions of the protection and monitoring algorithms resident on CCPU  28  can easily be modified from data entry device  92 . Thus, circuit breaker  14  and module  30  can be more standardized than was possible with the circuit breakers/trip units of prior systems. For example, over one hundred separate circuit breakers/trip units have been needed to provide a full range of sizes normally required for protection of a power distribution system. However, the generic nature of circuit breaker  14  and module  30  enabled by system  26  can reduce this number by over sixty percent. Thus, system  26  can resolve the inventory issues, retrofittability issues, design delay issues, installation delay issues, and cost issues of prior power distribution systems. 
     It should be recognized that system  26  is described above as having one CCPU  28  communication with modules  30  by way of a single network  32 . However, it is contemplated by the present disclosure for system  26  to have redundant CCPUs  28  and networks  32  as illustrated in phantom in  FIG. 1 . For example, module  30  is illustrated in  FIG. 2  having two network interfaces  46 . Each interface  46  is configured to operatively connect module  30  to a separate CCPU  28  via a separate data network  32 . In this manner, system  26  would remain operative even in case of a failure in one of the redundant systems. 
     Modules  30  can further include one or more backup systems for controlling breakers  14  independent of CCPU  28 . For example, system  26  may be unable to protect circuit  16  in case of a power outage in first source  52 , during the initial startup of CCPU  28 , in case of a failure of network  32 , and other reasons. Under these failure conditions, each module  30  includes one or more backup systems to ensure that at least some protection is provided to circuit breaker  14 . The backup system can include one or more of an analog circuit driven by second source  54 , a separate microprocessor driven by second source  54 , and others. 
     Referring now to  FIG. 3 , an exemplary embodiment of a response time  95  for system  26  is illustrated with the system operating stably (e.g., not functioning in a start-up mode). Response time  95  is shown starting at T 0  and ending at T 1 . Response time  95  is the sum of a sample time  96 , a receive/validate time  97 , a process time  98 , a transmit time  99 , and a decode/execute time  100 . 
     In this example, system  26  includes twenty-four modules  30  each connected to a different circuit breaker  14 . Each module  30  is scheduled by the phase-lock-loop algorithm and synchronization instruction  70  to sample its first signals  36  at a prescribed rate of 128 samples per cycle. Sample time  96  includes four sample intervals  101  of about 0.13 milliseconds (ms) each. Thus, sample time  96  is about 0.27 ms for data sampling and packaging into first message  76 . 
     Receive/validate time  97  is initiated at the receipt of synchronization instruction  70 . In an exemplary embodiment, receive/validate time  97  is a fixed time that is, for example, the time required to receive all first messages  76  as determined from the latency of data network  32 . For example, receive/validate time  97  can be about 0.25 ms where each first message  76  has a size of about 1000 bits, system  26  includes twenty-four modules  30  (i.e., 24,000 bits), and network  32  is operating at about 100 Mbps. Accordingly, CCPU  28  manages the communications and moving of first messages  76  to the CCPU during receive/validate time  97 . 
     The protection processes (i.e., process time  98 ) starts at the end of the fixed receive/validate time  97  regardless of the receipt of first messages  76 . If any modules  30  are not sending first messages  76 , CCPU  28  flags this error and performs all functions that have valid data. Since system  26  is responsible for protection and control of multiple modules  30 , CCPU  28  is configured to not stop the entire system due to the loss of data (i.e., first message  76 ) from a single module  30 . In an exemplary embodiment, process time  98  is about 0.52 ms. 
     CCPU  28  generates second message  78  during process time  98 . Second message  78  can be twenty-four second messages (i.e., one per module  30 ) each having a size of about 64 bits per module. Alternately, it is contemplated by the present disclosure for second message  78  to be a single, multi-cast or broadcast message. In this embodiment, second message  78  includes instructions for each module  30  and has a size of about 1600 bits. 
     Transmit time  99  is the time necessary to transmit second message  78  across network  32 . In the example where network  32  is operating at about 100 Mbps and second message  78  is about 1600 bits, transmit time  99  is about 0.016 ms. 
     It is also contemplated for second message  78  to include a portion of synchronization instruction  70 . For example, CCPU  28  can be configured to send second message  78  upon receipt of the next synchronization instruction  70  from clock  72 . In this example, the interval between consecutive second messages  76  can be measured by module  30  and the synchronization information in the second message, if any, can be used by the synchronization algorithm resident on microprocessor  42 . 
     Once modules  30  receive second message  78 , each module decodes the message and executes its instructions (i.e., send third signals  40 ), if any, in decode/execute time  100 . For example, decode/execute time  100  can be about 0.05 ms. 
     In this example, response time  95  is about 1.11 ms. Of course, it should be recognized that system response time  95  can be accelerated or decelerated based upon the needs of system  26 . For example, system response time  95  can be adjusted by changing one or more of the sample period, the number of samples per transmission, the number of modules  30 , the message size, the message frequency, the message content, and/or the network speed. 
     It is contemplated by the present disclosure for system  26  to have response time  95  of up to about 3 milliseconds. Thus, system  26  is configured to open any of its circuit breakers within about 3 milliseconds from the time sensors  34  sense conditions outside of the set parameters. 
     Referring to  FIG. 4 , an exemplary embodiment of a multi-source, multi-tier power distribution system generally referred to by reference numeral  105  is illustrated with features similar to the features of  FIG. 1  being referred to by the same reference numerals. System  105  functions as described above with respect to the embodiment of  FIGS. 1 through 3 , and can include the same features but in a multi-source, multi-layer configuration. System  105  distributes power from at least one power feed  112 , in this embodiment a first and second power feed, through a power distribution bus  150  to a number or plurality of circuit breakers  14  and to a number or plurality of loads  130 . CCPU  28  can include a data transmission device  140 , such as, for example, a CD-ROM drive or floppy disk drive, for reading data or instructions from a medium  145 , such as, for example, a CD-ROM or floppy disk. 
     Circuit breakers  14  are arranged in a layered, multi-leveled or multi-tiered configuration with a first level  110  of circuit breakers and a second level  120  of circuit breakers. Of course, any number of levels or configuration of circuit breakers  14  can be used with system  105 . The layered configuration of circuit breakers  14  provides for circuit breakers in first level  110  which are upstream of circuit breakers in second level  120 . In the event of an abnormal condition of power in system  105 , i.e., a fault, protection system  26  seeks to coordinate the system by attempting to clear the fault with the nearest circuit breaker  14  upstream of the fault. Circuit breakers  14  upstream of the nearest circuit breaker to the fault remain closed unless the downstream circuit breaker is unable to clear the fault. Protection system  26  can be implemented for any abnormal condition or parameter of power in system  105 , such as, for example, long time, short time or instantaneous overcurrents, or excessive ground currents. 
     In order to provide the circuit breaker  14  nearest the fault with sufficient time to attempt to clear the fault before the upstream circuit breaker is opened, the upstream circuit breaker is provided with an open command at an adjusted or dynamic delay time. The upstream circuit breaker  14  is provided with an open command at a modified dynamic delay time that elapses before the circuit breaker is opened. In an exemplary embodiment, the modified dynamic delay time for the opening of the upstream circuit breaker  14  is based upon the location of the fault in system  105 . Preferably, the modified dynamic delay time for the opening of the upstream circuit breaker  14  is based upon the location of the fault with respect to the circuit breakers and/or other devices and topology of system  105 . CCPU  28  of protection system  26  can provide open commands at modified dynamic delay times for upstream circuit breakers  14  throughout power distribution system  105  depending upon where the fault has been detected in the power flow hierarchy and the modified dynamic delay times for the opening of each of these circuit breakers can preferably be over an infinite range. Protection system  26  reduces the clearing time of faults because CCPU  28  provides open commands at modified dynamic delay times for the upstream circuit breakers  14  which are optimum time periods based upon the location of the fault. It has been found that the clearing time of faults has been reduced by approximately 50% with the use of protection system  26 , as compared to the use of contemporary systems. 
     Referring to  FIG. 5 , an exemplary embodiment of a portion of power distribution system  105  having a two-tier circuit with a main- 1  circuit breaker (CB)  415  upstream of feeder  1  CB  420  and feeder  2  CB  425 , which are in parallel. Power flow is from transformer  412  through main- 1  CB  415 , feeder  1  CB  420  and feeder  2  CB  425 , to loads  431 ,  432 . In the event of a fault X occurring between feeder  1  CB  420  and load  431 , the existence of the fault and the location of the fault is determined by CCPU  28  in the manner as described above and as schematically represented by reference numeral  450 . The nearest circuit breaker upstream of the fault X, i.e., feeder  1  CB  420 , is placed into “pickup mode” by CCPU  28  and waits a pre-defined delay time before being opened. The modified dynamic delay time for the opening of main- 1  CB  415  (the next nearest circuit breaker that is upstream of fault X) is then determined by zone selective interlock (ZSI) routine  426 . In an exemplary embodiment, ZSI routine  426  is an algorithm, or the like, performed by CCPU  28 . CCPU  28  determines the dynamic delay times for the opening of any number of upstream circuit breakers  14  and provides open or actuation commands to open the circuit breakers at the dynamic delay times. 
     In an exemplary embodiment, the modified dynamic delay time for main- 1  CB  415  is determined from the sum of the pre-defined delay time and the clearing time of feeder  1  CB  420 . The pre-defined delay time is set to best service load  431 . The clearing time of a circuit breaker, such as feeder  1  CB  420 , is dependent on the type of circuit breaker. The delay time for opening of main- 1  CB  415  is then modified based upon the value determined by CCPU  28 , as schematically represented by reference numeral  475 . This allows feeder  1  CB  420  the optimal time for feeder  1  CB  420  to clear the fault X before main- 1  CB  415  opens. The modified dynamic delay time determined by ZSI routine  426  reduces potential damage to system  105 . The modified dynamic delay time also increases the efficiency of system  105  by delaying the opening of main- 1  CB  415  for the optimal time period to provide the downstream circuit breaker, feeder  1  CB  420 , with the full opportunity to clear the fault X so that other loads, i.e., load  432 , can still receive power. 
     Referring to  FIG. 6 , the portion of power distribution system  105  having a two-tier circuit is shown with a fault X occurring between feeder  2  CB  425  and load  432 . In the manner described above, the existence and location of fault X is determined, as represented by reference numeral  450 . ZSI routine  426  determines the dynamic delay time for opening of main- 1  CB  415 , as represented by reference numeral  475 . Where feeder  2  CB  425  has a different pre-defined delay time set to best service load  432  and/or a different clearing time than feeder  1  CB  420 , ZSI routine  426  will determine a different dynamic delay time for the opening of main- 1  CB  415 . The difference in the two modified dynamic delay times for the opening of main- 1  CB  415  ( FIGS. 5 and 6 ) is based upon the location of fault X in system  105  with respect to feeder  1  CB  420  and feeder  2  CB  425 . 
     Referring to  FIG. 7 , the portion of power distribution system  105  having a two-tier circuit is shown with a fault X occurring between main- 1  CB  415  and either feeder  1  CB  420  or feeder  2  CB  425 . In the manner described above, the existence and location of fault X is determined, as represented schematically by reference numeral  480 . Since only main- 1  CB  415  is available to clear fault X, ZSI routine  426  does not modify the dynamic delay time of the opening of main- 1  CB and the main- 1  CB will open in its pre-defined delay, which is typically much less than the dynamic time delay in the previous two examples. 
     Referring to  FIGS. 4 through 7 , CCPU  28  coordinates protection system  26  by causing the circuit breaker  14  nearest to the fault to clear the fault. Protection system  26  variably adjusts the dynamic delay time for opening of the upstream circuit breakers  14  to provide backup protection for the downstream circuit breaker nearest the fault. In the event that the downstream circuit breaker  14  nearest the fault is unable to clear the fault, the next upstream circuit breaker will attempt to clear the fault with minimal additional delay based upon its modified dynamic delay time. As shown in  FIG. 7 , when a fault occurs between a main circuit breaker and a feeder circuit breaker, e.g., main- 1  CB  415  and feeder  1  CB  420 , the minimal delay of the main- 1  CB opening reduces the let-thru energy. This reduces system stress, damage and potential arc energy exposure of operating and service personnel while maintaining selectivity. In an exemplary embodiment, protection system  26  and CCPU  28  allow the implementation of ZSI routine  426  to modify the dynamic delay times for opening of any circuit breakers  14  throughout system  105  without the need for additional wiring coupling each of the circuit breakers to one another. CCPU  28  provides an open command to the upstream circuit breakers  14  for opening at dynamic delay times as determined by ZSI routine  426 . 
     In an exemplary embodiment, ZSI routine  426  is performed at CCPU  28  and interacts with the individual protection functions for each module  30 , which are also determined at the CCPU. ZSI routine  426  could also use pre-set clearing times for circuit breakers  14  or the clearing times for the circuit breakers could be determined by CCPU  28  based on the physical hardware, which is known by the CCPU. The CCPU  28  effectively knows the topology of power distribution system  105 , which allows the CCPU to open the circuit breakers  14  at an infinite range of times. 
     Referring to  FIG. 8 , the portion of power distribution system  105  having a first two-tier circuit branch  490  and a second two-tier circuit branch  790  coupled by a tie CB  700  is shown. In this circuit, the opening of tie CB  700  has created two separate zones of protection in circuit branch  490  and circuit branch  790 , which has a transformer  712 . In the event of a fault, protection system  26  implements ZSI routine  426 , as described above with respect to the two-tier circuit branch of  FIGS. 5 through 7 , independently for each of the circuit branches  490 ,  790 . 
     Referring to  FIG. 9 , the portion of power distribution system  105  is shown when main- 2  CB  715  is open and tie CB  700  is closed. The opening of main- 2  CB  715  and the closing of tie CB  700  has created a new single three-tiered zone of protection with feeder  3  CB  720  and feeder  4  CB  725  in the third tier or level of circuit breakers. The status of all of the circuit breakers, including main- 2  CB  715  and tie CB  700 , is known by CCPU  28 , as represented schematically by reference numerals  450 . In the event of a fault (not shown) in first circuit branch  490  downstream of the feeder  1  CB  420  or the feeder  2  CB  425 , the ZSI routine  426  would modify the dynamic delay time for the opening of main- 1  CB  415 , as described above with respect to  FIG. 5  or  FIG. 6 . 
     In the event of a fault (not shown) in second circuit branch  790  downstream of the feeder  3  CB  720  (or the feeder  4  CB  725 ), the ZSI routine  426  would modify the dynamic delay time for opening of both the tie CB  700  and the main- 1  CB  415 . In an exemplary embodiment, the modified dynamic delay time for the opening of tie CB  700  is determined from the sum of the pre-defined delay time and the clearing time of feeder  3  CB  720  (or feeder  4  CB  725 ). The dynamic delay time for opening of tie CB  700  is then modified based upon the value determined by CCPU  28 , as schematically represented by reference numeral  500 . This provides feeder  3  CB  720  (or feeder  4  CB  725 ) with an optimal time to clear the fault before tie CB  700  is opened. Furthermore, the modified dynamic delay time for the opening of main- 1  CB  415  is then determined from the sum of the modified dynamic delay time and the clearing time of tie CB  700 . The dynamic delay time for opening of main- 1  CB  415  is then modified based upon the value determined by CCPU  28 , as schematically represented by reference numeral  475 . This provides tie CB  700  with an optimal time to clear the fault before main- 1  CB  415  is opened by the open command from CCPU  28 . 
     In the event of a fault between tie CB  700  and feeder  3  CB  720  (or feeder  4  CB  725 ), the dynamic delay time for opening of main- 1  CB  415  is modified from the sum of the pre-defined delay and the clearing time of tie CB  700 . The delay for opening of tie CB  700  would not be modified since it is the nearest circuit breaker upstream of the fault for clearing the fault. 
     In an exemplary embodiment, the protection functions performed at CCPU  28 , including ZSI routine  426 , are based on state information or status of circuit breakers  14 , as well as current. Through the use of protection system  26 , the state information is known by CCPU  28 . The state information is synchronized with the current and the voltage in power distribution system  105 . CCPU  28  effectively knows the topology of the power distribution system  105  and uses the state information to track topology changes in the system. CCPU  28  and ZSI routine  426  utilizes the topology information of power distribution system  105  to optimize service and protection. 
     Of course, it is contemplated by the present disclosure for power distribution system  105  to have any number of tiers or levels and any configuration of branch circuits. The dynamic delay time for opening of any number of circuit breakers  14  upstream of the fault could be modified as described above based upon the location of the fault in the power flow hierarchy. Additionally, the zones of protection and the dynamic delay times can change as the power distribution system  105  changes. In an alternate embodiment, ZSI routine  426  can modify the dynamic delay time for opening of the upstream circuit breakers  14  based upon other factors using different algorithms. Protection system  26  allows for the dynamic changing of the delay times for opening of circuit breakers  14  throughout the power distribution system  105  based upon any number of factors, including the location of the fault. Protection system  26  also allows for the upstream circuit breaker  14  to enter the pickup mode as a function of the downstream circuit breaker  14  fault current and pickup settings as opposed to its own current and pickup settings. 
     The embodiments of  FIGS. 1 through 9  describe the implementation of ZSI routine  426  at CCPU  28 . However, it is contemplated by the present disclosure that the use of dynamic delay times for opening of circuit breakers  14  and/or the use of ZSI routine  426  can be implemented in other ways such as, for example, in a distributed control system with supervision by CCPU  28  or a distributed control system with peer to peer communications. In such distributed control systems, the delay time for opening of the upstream circuit breaker  14  will be modified to a dynamic delay time and/or based at least in part on the location of the fault in the power flow hierarchy. The dynamic delay times for the upstream circuit breakers  14  can also be determined and communicated to the upstream circuit breakers and/or circuit breaker actuators operably connected to the breakers. 
     In an exemplary embodiment, protection system  26  using CCPU  28  and ZSI routine  426  replaces the traditional time-current and fixed-delay protection while achieving both selectivity and tight backup protection. The feeder breakers (load-side) are set best to serve their loads reliably, but the main breakers and tie breakers (line-side) dynamically set their delay and current settings to best fit each feeder when that feeder circuit experiences a fault. The determination of a fault can be based on the feeder&#39;s settings and the sensors. In a traditional system, the sensing of a fault at the tie or main breaker is based on the settings at those trips and the current flowing through the respective circuit breakers. If the current magnitude is not sufficient to be recognized as a fault the trip units will not initiate a trip and hence provide no back-up function. There are no additional margins of safety or unnecessary time delays needed to allow the protection system  26  to operate selectively and provide protection to the mechanical limits of the devices used. Protect system  26  also applies within the short-circuit ranges of the devices in power distribution system  105 . When the CCPU  28  senses a fault within the short-circuit range of any load-side device, the next line-side device is ready to operate immediately if the CCPU senses that the load-side device is not clearing the fault, even if the fault may not be in the instantaneous range assigned to the line-side device. This form of backup protection could save many cycles of fault current when a feeder breaker fails to open or if the fault occurs in the switchgear, without sacrificing selectivity. 
     In an embodiment, system  26  can be configured with circuit protection devices, circuit breakers  14  for example, located at service entrances and branch circuits. Load circuit over-current protection can be provided by module  30 , acting as a trip unit in conjunction with CCPU  28 , and current sensors  34  being integrated with the circuit breaker  14 . These devices will continue to measure the circuit currents but the information will be digitized and broadcast over network  32 . The network  32  communicates digital representation of the system parameters, current, and voltage, for example, from multiple points throughout the system and makes this information available to all control devices in the system. The network  32  can also communicate protective device status and has the ability to direct the protective device  14  to take action over the same digital network  32 . For example, optimum switching between protective devices  14  may be accomplished by controlling centrally via CCPU  28  each circuit breaker  14  which has an adjustable time delay that is remotely controllable. Having the system parameters and the ability to control the devices enables this control and communication system to perform all of the functions currently performed by the multitude of control devices and point to point wiring used in known systems. As disclosed, this control functionality can be added virtually via software rather than physically through hardware. 
     A form of over-current protection is provided by the inverse time-over-current characteristics and fixed, or dynamic as discussed above, time delays that can be assigned to each circuit breaker  14  in the system  26 . In a typical main and multiple-feeder system, the main breaker is set at the appropriate current setting to handle the maximum current that the bus may carry, or the sum of the currents of each of the feeders. However, the main breaker may also be set with a current setting equal to that of each of the feeder breakers and a time characteristic that allows it to provide backup protection to each individual feeder at that feeder&#39;s setting. The processor  28  would simultaneously monitor the current at the main bus and each of the branch circuits, reacting to an undesirable current at any point. This provides each branch circuit with secondary backup protection optimally set to supplement the primary protection with no compromise needed to achieve selectivity or to allow the bus current to flow unimpeded. 
     Through utilization of CCPU  28 , control algorithms at a circuit breaker  14  can be duplicated at its respective feeder in the event it or one of its sub-components fails. This approach for the centrally controlled power system  26  works by the central controller&#39;s ability to adjust the circuit breaker trip curves in-situ, based on the current status of the system. Therefore, if a feeder breaker happens to malfunction, for example, the central controller will be notified and will perform adjustments to its supplying breaker. These adjustments include altering the supply breakers trip curves, and/or performing an interpolation calculation. This interpolation calculation involves collecting information from the supply breaker and its remaining feeder breakers. With this information, the conditions at the failed feeder breaker are determined. 
     In an exemplary embodiment of system  26 , circuit breakers  14 , busbars  12  and current sensors  34  are labeled with tags that identify that component&#39;s current rating (and potentially other identifying characteristics). These tags interface with the node electronics associated with the equipment cabinet in which the component is located. Using tags allows for identification of circuit breakers, current sensors and bus-bars based on tags. As such, an embodiment provides a mechanism for identifying the current rating of circuit breakers, current sensors and bus-bars, and a means for communicating these current ratings to appropriate components of the circuit breaker control and protection system (for example, breaker node, central controller). 
     While the instant disclosure has been described with reference to one or more exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope thereof. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the scope thereof. Therefore, it is intended that the disclosure not be limited to the particular embodiment(s) disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.