Patent Application
20100013496
Information about the status of a building's electrical service (voltage and current distribution system) at the time of a fire or failure incident is often sought after the incident has occurred. The importance of this information is seen in the need to determine the cause and origin of fires within a building or property containing electrical distribution systems. Determining the history of the electrical branch circuit status at the time of the fire is described in the NFPA 921 document titled GUIDE FOR FIRE AND EXPLOSION INVESTIGATIONS. The methods described in this document are time consuming and can be inaccurate due to the damaging effects of extreme environmental attack or to suppression and overhaul operations by the attending Fire Department. Key information that could help in the analysis of the condition of the electrical systems just before and during the occurrence of a disastrous incident is often lost which makes it difficult for those investigating the scene to make sense of the remaining evidence.
Prior art suggests the use of detectors which sense current overloads, arcs, or high temperatures, and which even can shut off power to the affected branch circuits. U.S. Pat. No. 5,627,719 titled ELECTRICAL WIRING SYSTEM WITH OVERTEMP PROTECTION proposes to remove power when a certain temperature is reached. US Application Number 2007/0070568 titled ARC DETECTION CIRCUIT proposes an improved, more accurate method of detecting arcs. Both of these, however, do nothing to shed light on the origin and spread of a fire that does occur.
Prior art also suggests the use of fault diagnostic monitors for load centers or other equipment. U.S. Pat. No. 4,857,918 titled FAULT DIAGNOSTIC APPARATUS FOR ELECTYRIC APPLIANCE suggests the use of such a monitor for an air conditioner. U.S. Pat. No. 6,212,049 titled LOAD CENTER MONITOR FOR ELECTRICAL POWER LINES suggests the use of such a monitor for monitoring and analyzing circuit breakers.
What is needed and is not provided in prior art or available as a commercial product is a method of preserving certain state and operational characteristics of branch circuits at the time of a major catastrophic incident such as a fire, and which will maintain storage of the data after severe environmental stress has occurred and further, which will allow the retrieval of this data after some time has passed. This method should be robust and preferably independent of other systems in the house including power from those systems.
Energized electrical distribution systems are useful indicators in the investigation of a fire as well as major loss incidents such as flooding or mechanical damage. To date, investigators have relied on a time intensive technique called arc mapping to help them determine a point of origin for the fire. The theory is that an energized electrical circuit located in the area of origin for the incident will be affected first. Damage to its insulation will occur early in the incident timeline which will affect the integrity of the conductor isolation, resulting in an electrical arc. This in turn immediately trips a circuit breaker or blows a fuse which prevents further arcs from occurring on that particular circuit.
If multiple circuits travel through the area of origin, they also are affected and will loose their insulation in a similar manner. The result is a constellation of arc's, or a map with the area of origin at its center. The state of the circuit breakers is also useful information after an incident has occurred. To be useful in a typical room situation, certain elements are needed:
If these elements are not present, the analysis of data obtained from an arc mapping exercise may be compromised and the results uncertain. Even under ideal circumstances, there are issues with this approach:
It is an object of the present invention to provide an electric branch circuit black box device which will avoid the problems noted above.
The addition of a branch circuit black box provides the investigator with sequence and/or time of the respective circuit arcs occurring which adds another dimension to the arc map data. Further, this device will contain a special event characterization memory which will be able to survive the destructive environment present. This in turn will enable better resolution of the area of origin in the analysis of the data.
A branch circuit black box for use in a building's electrical system having service entrance, current protection switches (circuit breakers or fuses), and a power distribution system in accordance with an embodiment of the present invention includes a plurality of sensors positioned adjacent to the distribution wires, wherein the sensor data is collected, analyzed and stored by a non volatile memory for the purpose of recovering time-of-incident state and operational information for resolution analysis after the incident has occurred in a building or system.
A branch circuit black box 7 for use in detecting, storing, and subsequently recovering the electrical activity, and operational state of an electrical system at the time of an incident involving damage to a facility is shown in
In a preferred embodiment, the branch circuit black box includes a plurality of sensors 13 that detect the electrical activity or status on branch circuits emanating from the service panel 1. The electrical parameters recovered include, primarily, detection and storage of voltage, and time, however it is sometimes also desirable to capture current and temperature. A processor 10 is included which comprises primarily control logic and a non-volatile memory 11 that stores recent branch circuit 3a, 3b, 3c, and 4 activity detected by any of the sensors 13 wherein a change in the voltage triggers it's capture and storage, along with the time of the change. It is preferable to store the time when measurements are taken to establish sequential relationships between electrical activities occurring on the different branch circuits.
The operation of the branch circuit black box 7 is not limited to only capturing voltage during state transitions, and it may also synchronously capture the state of the voltage on the branch circuits 3a, 3b, 3c, and 4 on a periodic basis, wherein the period is shorter than expected electrical events normally occur and is typically from seconds to small fractions of a second.
Those skilled in the art will recognize that if the sensors 13 and processing 10 are sophisticated enough, additional computed results can be derived from these, including average or rms voltage or current, power, average power, and power factor.
Non-contact voltage sensing is well known in the art, commercial versions of these devices are available and need not be discussed here in detail. A method of voltage sensing is described in U.S. Pat. No. 4,804,922 titled VOLTAGE SENSOR, which discusses the sensing technique, and includes a filter to discriminate signal information in the frequency range of interest. Commercial detectors are available to measure electrostatic field or surface potential. U.S. Pat. No. 5,517,123 titled HIGH SENSITIVITY INTEGRATED MICROMECHANICAL ELECTROSTATIC POTENTIAL SENSOR describes a highly integrated and sensitive device for measuring voltage without contacting the object. Non-contact current sensing is also well known in the art and can be accomplished by using, for example, solid state Hall or Magnetoresistors as described in U.S. Pat. No. 4,539,520 titled REMOTE CURRENT DETECTOR and Number 4283643 titled HALL SENSING APPARATUS. As discussed in the prior art, these sensors 13 produce low voltage level signals which must be protected from system and environmental noise, and thus may include an amplifier to boost the signal level higher above the ambient noise of the chosen location for the branch circuit black box 7. The electronic functions 13, 10, and 11 shown in FIG. 2 can be implemented in various ways, including discrete electronics, separate modules, or integrated onto one monolithic substrate.
A key feature of this system is the ability to retain information in robust non volatile memory 11 which is connected to the processor 10. This memory will preferably be contained within in the Branch Circuit Black Box 7 and may actually be the same as the memory holding the operating system. However, because of its function during a catastrophic situation, the branch circuit black box 7 non volatile memory 11 may be exposed to severe heat and water and must maintain its storage function after such a situation. It must also be protected from mechanical damage and from tampering by individuals wishing to alter or destroy its contents. It may be desirable, for example, to encase the circuitry in heavy gauge steel or place it in a protected location where it is not easily removed and is protected from heat. The removal of the non volatile memory and extraction of information therein may be facilitated by use of special tools owned by investigators or by forensic engineers.
Even when power is interrupted or normal functionality is lost, the non volatile memory 11 will still contain the information originally recorded about the system. The memory is preferably solid state or magnetic in nature, however other methods may be used which do not require any power to sustain the contents. Battery hold-up of volatile memory may be a good choice if the battery itself can be made to be robust. Integrated (chip level) battery techniques can keep the memory powered for sufficient time duration to allow investigators time to recover it.
Normal operating power for the circuitry in the branch circuit black box 7 should be very small and many methods are available for providing it such as energy harvesting techniques, or long-life batteries such as lithium cells. Preferably, the circuitry is self-powering and harvests energy from the environment, wherein power is scavenged from energy in the fields of the wires themselves, and stored in batteries or capacitors. However, other methods may be used, including harvesting energy from photovoltaic cells sensitive to light.
It may be advantageous to use periodic wireless transmission of the data to a processor for central storage located amid several branch circuit black box sensor arrays. Texas Instruments makes wireless interface ICs which are useful for RF communication to nearby devices and which work well with their MSP430 processors.
In the operational examples discussed in this section, the branch circuit black box 7 must already have been in place when a fire or incident occurs. When the investigator visits the scene of an incident, the memory will already contains the electrical activity and status which occurred before, during, and shortly after the fire. If the extreme environment of a catastrophe damages the branch circuit black box 7 so as to make it non-functional, all events leading up to that time will still be safely recorded into non volatile memory 11.
Investigators will retrieve the non volatile memory 11 and forward it to engineers who will then remove it, interrogate it, and obtain the “history” of the incident for analysis of electrical activity and status at times surrounding the occurrence of the incident.
The following example shows how the preferred embodiment works in the case shown in
In this example the B3 branch circuit breaker 8c tripped at 8:01:20, followed by B1 branch circuit breaker 8a trip at 8:11:01. The activity and the time of the activity are thus captured and stored in the memory. Capturing and storing of the branch circuit electrical activity may be asynchronously triggered by either voltage or current transitions on particular branches, however other detected parameters reaching an preset threshold value can cause the capture of data as well, such as temperature, conductivity, phase relationship, harmonic noise, or any other electrical property which may signify the occurrence of an incident (fire, flood, loss of air flow to equipment, presence of explosive gas, failure etc).
In a second embodiment, only the discrete energized state information is required and measured analog values are not required. During manufacture or at installation time, the branches and desired state configuration is pre-determined, along with the state transition threshold to trigger storage. An example memory record is shown below:
In this example, the branch B3 circuit breaker 8c tripped at 8:01:20, followed by branch B1 circuit breaker 8a trip at 8:11:01, but only the discrete state information is retained in the memory. The trigger and threshold applied here can be, for example, the opening of more than one circuit breaker, separated by more than 0.1 second, and less than 30 min of time. This embodiment is simpler than example 1 due to only requiring a discrete time event monitor and thus can be lower in cost than the first embodiment.
In a third embodiment, the temperature at the Branch Circuit Black Box is recorded along with the other parameter information:
In this example, the temperature at the conductors where the branch circuit black box 7 is located exceeded a threshold of 160 F, which triggered the memory to read data. However, none of the breakers has tripped yet.
In a fourth embodiment, parameter and/or state information can be recorded along with time in a “continuous loop” fashion. For example, data is simply streamed into the memory which functions as a FIFO with continuous looping capability . . . never stopping the recording of parameter information and time of capture until either commanded to, or until some significant pre-determined state change occurs (loss of more than 1 branch circuit, temperatures above 100 F, currents exceeding 30 A, etc).
Example memory records for such a system are shown below, with state changes occurring on branch B13a at time 25,2019 seconds and on branch B34 at 25,2020 seconds, where time is kept as a count of seconds. The advantage of this system is that the memory controls and time-keeping requirements of this system are simplified since an external trigger is not required, thus not requiring any special circuitry or threshold setting. For this example, the memory store trigger is dependant upon the energized/de-energized branch state changes, and can, for example be more than 2 circuit breakers tripping within 5 minutes of each other, but greater than 0.5 seconds. It is also possible, but not necessary for this embodiment to function, for an internal temperature operated switch to open at 150 F, which will halt the memory access after the last record is written:
In variations of embodiment four, different properties can be used to force termination of memory access in anticipation of possible harsh environment.
In a fifth embodiment, environmental hardening of the device may be implemented by some combination of heat shielding, hermetic packaging, use of high temperature substrates, special coatings, and/or positioning it in a location where it is not exposed to any expected harsh environments, for example, embedded in concrete or cinder block and covered by a metal plate. This will reduce risk of data loss due to exposure to hostile conditions such as high temperatures. It is also possible for the non-volatile memory to be located in a protected position, separate from the rest of the circuitry. Another option is for the non-volatile memory to be located in another system such as an energy management, HVAC control, or alarm panel. In these cases, a more robust memory communication bus/connection will be required and a wireless link may be preferable.
In a sixth embodiment, the Branch Circuit Black Box is used in other systems or subsystems, wherein the system's power feed is available and accessible at a single point and then distributes throughout the system. Examples include an aircraft, automobiles, or watercraft, but also may include any system or device containing a network of power arranged as branches or in a star distribution such as appliances, machines, or other devices. It is often desirable and useful to know how the power state or usage changed within a complex system or structure just prior to a problem or incident occurring. The branch circuit black box 7 can provide this information which can be useful in troubleshooting problems and resolving failures.
Use in spacecraft is also envisioned. In these cases, the properties which will trigger the branch circuit black box 7 to store information may include radiation, velocity, altitude, roll-rate, loss of navigation, loss of control, and many other possibilities.
In all of these embodiments, the key information retained, and stored into non volatile memory is information about the branch circuit states including the unique sequence and the time of the “change of state” on each branch circuit. Other results could be calculated or derived from inputs available near the service entrance or the panel and also stored in the non-volatile memory. Some of these might include:
The present application claims benefit of and priority to Provisional Patent Application Ser. No. 61/132,843 entitled BRANCH CIRCUIT BLACK BOX FILED Jun. 23, 2008, the entire contents of which are hereby incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| 61132843 | Jun 2008 | US |
