Patent Application
20120098347
This invention relates to electronic circuit breakers and particularly to an improved circuit breaker that enters a non-fault-protecting mode of operation, using an auxiliary power source, after a trip signal has been produced.
When operating an electronic circuit breaker it is highly desirable that any functions performed to upgrade the software or firmware of the breaker's microcontroller be accomplished without interruption and without sacrificing protection of the load. In a traditional electronic circuit breaker, once tripped, the microcontroller controlling the breaker has no power and is inaccessible. Thus, in past known electronic circuit breakers the microcontroller state is on or off, mirroring the closed or open position, respectively, of the breaker contacts.
To perform a firmware upgrade, the breaker either needs to 1) be removed from the load center, or 2) perform fault protection during the upgrade process, or 3) enter a mode of operation where fault protection is not required. With respect to 1), removing the breaker from the load center is not ideal for firmware upgrades in terms of maintenance time and wear on the breakers and associated equipment, as well as the safety aspects of breaker removal. With respect to 2) there is microprocessor overhead required to provide fault protection during the upgrade process or determining if the breaker can enter a mode of operation where fault protection is not required. One example of updating the firmware while providing protection requires two separate program sections and a separate boot section. To ensure protection is uncompromised, the new program would have to be written into a separate section of memory while the existing program continues to detect for fault protection. Then, once the new program is validated, the processor would have to do a reset, and the boot section of the microcontroller would have to track which firmware program to use in the future in order to always point to the newest program. Additional processor overhead is required to handle the case when a fault is detected, and the new program is being written to the program section to ensure the breaker can't enter a hazardous mode of operation.
Today's residential electronic circuit breakers (AFCI) monitor and protect against many different types of fault conditions. When a circuit breaker trips, it is advantageous to know what type of fault the circuit breaker interrupted in order to accurately and rapidly correct the fault condition. The electronic modules in such circuit breakers are capable of indicating the interrupted fault only when the electronics are powered. Normally this requires re-closing the circuit breaker with its manual handle to power the electronic module. However, re-closing the circuit breaker to indicate the cause of the interrupted fault also means re-energizing the fault if the fault is still present. In order to safely re-close the circuit breaker, an electrician must open the load center and remove the line load and neutral load wires from the circuit breaker. It would be desirable to have a secondary means of powering the electronic module to allow the electronic module to indicate the interrupted fault, without the need to re-energize the fault at levels that would be considered hazardous, thus eliminating the need to remove the load wires from the circuit breaker.
In accordance with one embodiment, an electronic circuit breaker includes controllable mechanical contacts adapted to connect a primary power source to at least one load, and control circuitry for monitoring the flow of power from the primary power source to the load, detecting fault conditions, producing a trip signal in response thereto, and automatically opening the contacts. A primary power source supplies power to the control circuitry when the contacts are closed, and an auxiliary power source supplies power to the control circuitry when the contacts are open.
By supplying the control circuitry with power from an auxiliary power source while the breaker contacts are open, this breaker system avoids any need to close the circuit breaker onto a hazardous fault to determine the reason the circuit breaker tripped. It also avoids any need to remove branch circuit wiring from the circuit breaker, or to remove the circuit breaker from a load center, in order to update firmware, to indicate the cause of a trip, or to perform branch wiring diagnostics.
In one implementation, at least one sensor is coupled to the power flow from the primary power source to the load and produces an output signal representing a characteristic of the power flow, and the control circuitry samples data derived from the output signal and processes that data to detect fault conditions. The control circuitry also detects failures in the data sampling and produces a trip signal in response to a preselected number of detected failures in the data sampling. The control circuitry may detect failures of in the data sampling by detecting the absence of zero crossing in an AC voltage supplied by the primary power source to the load, as will occur upon manually opening the contacts with the breaker handle, thus causing the control circuitry to issue a trip signal.
The invention may best be understood by reference to the following description taken in conjunction with the accompanying drawings, in which:
Although the invention will be described in connection with certain preferred embodiments, it will be understood that the invention is not limited to those particular embodiments. On the contrary, the invention is intended to cover all alternatives, modifications, and equivalent arrangements as may be included within the spirit and scope of the invention as defined by the appended claims.
When a fault is detected by the circuit breaker, the microcontroller 14 generates a trip signal that is supplied to the trip circuit 13 to automatically open the breaker contacts 12 and thus interrupt the flow of electrical current to the load 11. The microcontroller also typically stores information identifying the reason for the trip, such as the detection of a ground fault or an arcing fault.
To enable the microcontroller 14 to be used while the breaker contacts 12 are open, power can be supplied to the microcontroller 14 from an auxiliary power source 20, such as a battery, by closing a switch 20a. This connects the auxiliary power source 20 to the voltage regulator 18, which in turn powers the microcontroller 14. It will be appreciated that the battery might be plugged directly into the breaker without the need for a switch.
There are several reasons why it may be desirable to have the capability of operating the microcontroller 14 while the breaker contacts 12 are open. For example, it is desirable to be able to upgrade the firmware of the microcontroller 14 or perform branch wiring diagnostics without the need to remove the breaker from a load center and/or to avoid the need for additional processor overhead within the electronic breaker. As another example, it is desirable to be able to access the microcontroller to determine the type of fault that produced a trip, while the breaker contacts have been opened by a trip signal.
The flow chart in
Referring to
In the “Fault Detection” path, step 33 samples the data that is used to detect fault conditions (e.g., data derived from the voltage monitoring circuit 16), and then step 34 uses the sampled data in algorithms that are executed to detect when a fault has occurred. As long as no fault is detected, step 35 yields a negative answer, which returns the system to step 33 to continue sampling data from the voltage monitoring circuit 16. This loop continues as long as data continues to be sampled at step 33 and no fault condition is detected by the algorithms executed at step 34.
In the concurrent, parallel “System Diagnostic Detection” path, step 36 detects when there is a failure of the sample data, such as by detecting a start-of-sampling failure (e.g., the non-occurrence of zero crossings of the primary AC voltage). This is a standard fail-safe diagnostic feature in electronic circuit breakers, typically executed by a conventional watchdog timer in the firmware and thus represents no additional processor overhead to the microcontroller 14. Step 37 counts the failures detected at step 36 and determines when the number of consecutive failures reaches a preset “failure count” that indicates a real failure has been detected. As long as step 37 yields a negative answer, the system is returned to step 36 to continue watching for sample data failures. This loop continues as long as the preset “failure count” is not met. If the breaker is manually turned off, i.e. the contacts 12 are opened, the system times out and an affirmative answer is given.
An affirmative answer at either step 35 or step 37 causes a trip signal to be generated at step 38. The trip signal is sent to the trip circuit 13, which opens the main contacts 12 to remove the primary power source 10 from the breaker system. After the trip signal is issued at step 38, an alternate mode of operation is started at step 39.
The alternate mode of operation continues only if the switch 20a has been closed to connect the auxiliary power source 20 to the voltage regulator 18 to supply power to the microcontroller 14. If the auxiliary power source 20 is connected, the microcontroller continues to receive power, and thus various operations can be carried out by the microcontroller. When the microcontroller is powered by the auxiliary power source 20, the start-of-sampling event does not occur because the main contacts 12 are open. Thus, several watchdog timeouts occur in succession, which causes an affirmative response at step 37, the generation of a trip signal at step 38, and the start of the alternate mode of operation at step 39. In the alternate mode of operation, the trip signal is always present, so if the main contacts 12 are closed, the trip circuit 13 immediately re-opens those contacts. If the auxiliary power source is removed, e.g., by opening the switch 20a or by a battery reaching the end of its life, the alternate mode of operation is terminated. This provides a self-protection feature when the auxiliary power is present.
In the illustrative example of
Using the existing diagnostic test for primary AC voltage zero-crossings requires no additional processor overhead to determine when to enter the alternate mode of operation. Processor overhead is defined as using additional clock cycles or more power to execute an operation prior to issuing the trip signal. The watchdog timer is typically part of the standard firmware for an electronic breaker, so there is no additional overhead or additional timing constraints.
While particular embodiments and applications of the present invention have been illustrated and described, it is to be understood that the invention is not limited to the precise construction and compositions disclosed herein and that various modifications, changes, and variations may be apparent from the foregoing descriptions without departing from the spirit and scope of the invention as defined in the appended claims.
