System for optically detecting an electrical arc in a power supply

A system for optically detecting an electrical arc in a power supply. The system includes a light pipe, a photodetector optically coupled to the light pipe, and a signal processor connected to the photodetector.

BACKGROUND

This application discloses an invention that is related, generally and in various embodiments, to a system for optically detecting an electrical arc in a power supply. The system and may be utilized with a power supply having a plurality of power cells. Various embodiments of a power supply having a plurality of power cells are described, for example, in U.S. Pat. No. 5,625,545 to Hammond (“the '545 patent”).

Systems for optically detecting an electrical arc are known in the art. In general, when an electrical arc occurs, the light resulting from the arc is optically detected, and the detection may be utilized to interrupt the power that is supplying the electrical arc. However, known systems for optically detecting electrical arcs are not necessarily suitable for many applications.

Known systems for optically detecting electrical arcs are generally susceptible to a single point of failure, and thus are not particularly well-suited for applications which require a particular level of redundancy. Also, in various devices, electrical arcs can occur in a variety of locations. For such a device, electrical arcs can occur in locations which are not quickly detected by known optical arc detection systems. Consequently, the detection of such arcs is often delayed, thereby allowing the arcs to cause significant damage to the device prior to their detection. In many instances, the damage is significant enough to render the device inoperable.

SUMMARY

In one general respect, this application discloses a system for optically detecting an electrical arc in a power supply. According to various embodiments, the system includes a light pipe, a photodetector optically coupled to the light pipe, and a signal processor connected to the photodetector.

In another general respect, this application discloses a power supply. According to various embodiments, the power supply includes a plurality of power cells. At least one of the power cells includes at least a portion of a light pipe, a photodetector optically coupled to the light pipe, and a signal processor connected to the photodetector.

Aspects of the disclosed invention may be implemented by a computer system and/or by a computer program stored on a computer-readable medium. The computer-readable medium may comprise a disk, a device, and/or a propagated signal.

DETAILED DESCRIPTION

FIG. 1illustrates various embodiments of a system10for optically detecting an electrical arc. The system10includes a light pipe12, a photodetector14optically coupled with the light pipe12, and a signal processor16electrically connected to the photodetector14. The system10may be utilized to optically detect an electrical arc in a variety of applications. For example, the system10may be utilized to optically detect an electrical arc in a power supply having a plurality of power cells. Various embodiments of a power supply having a plurality of power cells are described, for example, in U.S. Pat. No. 5,625,545 to Hammond (“the '545 patent”), which is hereby incorporated by reference in its entirety. For ease of explanation purposes, the system10will be described in the context of optically detecting an electrical arc in a power supply which is similar to the power supply described in the '545 patent. However, the system10may also be utilized to optically detect an electrical arc in applications other than a power supply.

Various embodiments of the light pipe12are illustrated inFIG. 2. The light pipe12includes a first end18and a second end20, and may be of any suitable length. According to various embodiments, the light pipe12is configured to capture light present at its first end18and transmit the captured light along the length of the light pipe12to its second end20. According to various embodiments, the light pipe12is also configured to capture light present along its length and transmit the captured light along the length of the tight pipe12to its second end20. Thus, in operation, when light associated with an electrical arc is proximate any portion of the light pipe12, the light is captured and transmitted along the length of the light pipe12to its second end20.

Returning toFIG. 1, as indicated hereinabove, the light pipe12is optically coupled with the photodetector14. Such optical coupling may be realized by positioning an end of the light pipe12(e.g., the second end20of the light pipe12) proximate the photodetector14. For applications where the second end20of the light pipe12is positioned proximate the photodetector14(e.g., see Fig. X), light captured at the first end18of the light pipe12and/or along its length is transmitted to the photodetector14via the second end20of the light pipe12.

The photodetector14may be any suitable type of photodetector. For example, according to various embodiments, the photodetector14is a photodiode having an anode and a cathode as is known in the art. For embodiments where the photodetector14is a photodiode, the photodiode may be a P-N photodiode, a P-I-N photodiode, etc., and may have a spectral range of approximately350to1100nanometers. According to other embodiments, the photodetector14is a phototransistor.

For some embodiments where the photodetector14is a photodiode, the photodiode is reverse-biased, operates in the photoconductive mode, and may generate a measurable level of dark current. For such embodiments, the cathode of the photodetector14is connected to a power source22and the anode of the photodetector14is connected to the signal processor16. The power source22may form a portion of the system10or may be external to the system10. For other embodiments where the photodetector14is a photodiode, the photodiode is zero-biased and operates in the photovoltaic mode. For such embodiments, the photodetector14is not connected to the power source22and the cathode of the photodetector14is connected to the signal processor16.

In operation, when the photodetector14optically detects light associated with an electrical arc (e.g., when light associated with an electrical arc is captured by the light pipe12and is transmitted to the photodetector14), the photodetector14generates a current which is representative of the intensity of the detected light. The generated current may include a photocurrent component and a dark current component. The photocurrent component may be considered an arc component of the generated current, and the dark current component may be considered a non-arc component of the generated current.

As indicated hereinabove, the signal processor16is electrically connected to the photodetector14. The signal processor16may be implemented in any suitable manner. For example, according to various embodiments, the signal processor16is implemented as a signal processing circuit. Various embodiments of such a signal processing circuit are illustrated inFIG. 3. The signal processing circuit30ofFIG. 3includes an RC filter circuit32and a trip circuit34which are each electrically connected to the photodetector14. The RC filter circuit32operates to remove unwanted information (e.g., information representative of the dark current component) from the signal generated by the photodetector14. The trip circuit34operates to output a signal when the voltage applied to the trip circuit34reaches or exceeds a predetermined threshold.

According to other embodiments, the signal processor16is implemented as a digital signal processor. Various embodiments of such a digital signal processor are illustrated inFIGS. 4 and 5. The digital signal processor40ofFIG. 4includes a filter module42and a comparator module44in communication with the filter module42. The filter module42is configured to generate a signal representative of the photocurrent component of the signal generated by the photodetector14. The comparator module44is configured to compare a value of the filtered signal to a threshold value, and generate an output based on which of the two values (i.e., the value of the filtered signal or the threshold value) is larger. The modules42,44may be implemented in hardware, in firmware, in software, or in any combination thereof. According to various embodiments, the functionality of the modules42,44may be combined into a single module or distributed over more than two modules.

The digital signal processor50ofFIG. 5includes a filter module52, an amplitude module54and a frequency module56. The filter module52is configured to generate a signal representative of the photocurrent component of the signal generated by the photodetector14. The amplitude module54is in communication with the filter module52, and is configured to analyze the amplitude of the filtered signal. The frequency module56is also in communication with the filter module52, and is configured to analyze the frequency of the filtered signal. Collectively, the amplitude module54and the frequency module56operate to spectrally break down the filtered signal. By analyzing both the amplitude and frequency of the filtered signal, the digital signal processor50may determine the specific type of arcing which has occurred, and generate an output based on the analysis. The modules52,54,56may be implemented in hardware, in firmware, in software, or in any combination thereof. According to various embodiments, the functionality of the modules52,54,56may be combined into a single module or distributed over more than three modules.

In some implementations of the system10, the filtering function may be applied external to the digital signal processors ofFIGS. 4 and 5(e.g., by an RC filter). For embodiments where the signal generated by the photodetector14is an analog signal, the system10may also include an analog-to-digital converter (not shown) electrically connected to the photodetector14and the digital signal processor to convert the analog signal generated by the photodetector14to a digital signal which is suitable for the digital signal processor,

FIG. 6illustrates various embodiments of a power supply60. The power supply60may be similar to the power supply described in the '545 patent. The power supply60includes a multi-winding device62such as a transformer or a transformer-like device, a plurality of power cells64connected to the multi-winding device62, and a main control66connected to each of the power cells64. The power supply60may also include a main contactor68which is connected to the power input of the power supply60, to the multi-winding device62, and to the main control66. The main contactor76may be a three-phase contactor connected to three power lines of a three-phase distribution system, and may comprise any number of auxiliary contacts as is known in the art. According to various embodiments, the main contactor68may be a vacuum contactor, and may be rated for the full current and voltage of a load (e.g., a motor) coupled to the power supply60.

The power supply60may be utilized to deliver a three-phase AC voltage to a motor, and the voltage can vary from application to application. For example, according to various embodiments, the power supply60may be utilized to deliver 4160 volts (vac) to the motor, 6600 volts (vac) to the motor, 10,000 volts (vac) to the motor, or other AC voltage levels.

Each power cell64is a device which includes an AC-DC rectifier, a smoothing filter, an output DC-to-AC converter, and a local control70. According to various embodiments, the local control70may include for example, the signal processor16ofFIG. 1. The local control70of each power cell64is in communication with the main control66. Each power cell64may be constructed to low-voltage standards, accepts three-phase AC input powder, and output a single-phase AC voltage. At least one of the power cells64of the power supply60also includes the system10ofFIG. 1. For purposes of clarity, portions ofFIG. 6are shown in a conventional one-line format, and only some of the components of the power cells64(e.g., the local control70) are shown inFIG. 6. For example, although at least one power cell64includes a photodetector14and a signal processor16as described with respect to the system10ofFIG. 1, such components are not shown inFIG. 6. Although the power supply60is shown as having nine power cells64inFIG. 6, one skilled in the art will appreciate that the power supply60may include any number of power cells64, and the number of power cells64included in the power supply60can vary from application to application.

FIG. 7illustrates various embodiments of one of the power cells64. As shown inFIG. 7, the first end18of the light pipe12is positioned external to the power cell64and the second end20of the light pipe12is positioned proximate the photodetector14. As electrical arcs may occur in areas external to the power cell64, the portion of the light pipe12external to the power cell64may capture light resulting from such an arc and transmit the light along its length to the photodetector14. According to other embodiments, the first end18of the light pipe12is positioned internal to the power cell64and the second end20of the light pipe12is positioned proximate the photodetector14.

FIG. 8illustrates various embodiments of one of the power cells64. As shown inFIG. 8, the power cell64includes power electronics72and a plurality of capacitors74. The photodetector14is positioned to define a field of view76within the power cell64. When positioned in such a manner, the photodetector14is able to optically detect an electrical arc occurring at any point within the field of view76. As electrical arcs are most likely to occur in the area where the power electronics72are positioned, and the field of view76includes the area where the power electronics72are positioned, the photodetector14is able to optically detect electrical arcs originating from the power electronics72, either directly or indirectly via the light pipe12. For purposes of clarity, the light pipe12is not shown inFIG. 8.

FIG. 9illustrates various embodiments of a power supply80. The power supply80may be similar to the power supply60ofFIG. 6, but is different in that the power supply80may include a bypass control82, at least one contactor84connected to the bypass control.82, and at least one bypass switch86connected to the bypass control82. The at least one contactor84and the at least one bypass switch86are also connected to an individual power cell64. According to various embodiments, the power cell80includes a plurality of contactors84, wherein each respective contactor84is connected to a different power cell64.

The bypass control82and the main control66are configured to communicate with one another via communication link88. Communication link88may be embodied as, for example, a wired connection or a fiber optic link. The communications between the main control66and the bypass control82may be in any suitable form. The bypass control82may be implemented in any suitable manner. For example, according to various embodiments, the bypass control82is implemented as a programmable logic device. The bypass control82is operative to receive a communication from the main control66, and to transmit a signal to at least one of the contactor84and the bypass switch86in response thereto. The signal transmitted to the contactor84and/or the bypass switch86may be a low-voltage signal (e.g., 36 volts). According to various embodiments, the power supply80may include a plurality of bypass controls82, wherein each bypass control82is in communication with the main control66and is connected to a contactor84and/or a bypass switch86associated with a particular power cell64.

According to various embodiments, the contactor84includes contacts90connected to secondary windings of the multi-winding device62, and a solenoid92connected to the bypass control82. The number of contacts90may vary based on the power supply configuration. The solenoid92is operative to open and close each of the contacts90responsive to a signal received from the bypass control82. The contactor84may be implemented as a three-phase contactor, and may include any number of auxiliary contacts as is known in the art. According to various embodiments, the contactor84may be a vacuum contactor, and may be rated for the full current and voltage of the power cell64to which it is connected.

The bypass switch86may be implemented in any suitable manner. For example, according to various embodiments, the bypass switch86may include a switch94connected to the output of the power cell64, and a switch96connected to the output of another power cell which is connected in series with the power cell64. According to various embodiments, the switches94,96may be interlocked, and the bypass switch86may further include device (e.g., a solenoid) operative to open the switch94and close the switch96responsive to a signal received from the bypass control82.

FIG. 10illustrates various embodiments of a method100for optically detecting an electrical arc. The method100may be implemented by the system10ofFIG. 1, and may be utilized to optically detect an electrical arc in a variety of applications. For example, the method100may be utilized to optically detect an electrical arc within or external to a power cell in a power supply. For ease of explanation purposes, the method100will be described in the context of optically detecting an electrical arc in the power supply80ofFIG. 9. However, the method100may also be utilized to optically detect an electrical arc in other power supplies (e.g., power supply60ofFIG. 6) and in applications other than a power supply.

The process starts at block102, where the photodetector14optically detects light resulting at least in part from an electrical arc which occurs in the power supply80. The electrical arc may occur internal to or external to a power cell64of the power supply80. Thus, the light may be optically detected by the photodetector14directly or via the light pipe12.

From block102, the process advances to block104, where the photodetector14generates a current (i.e., a signal) which is indicative of the intensity of the detected light. The generated current includes a photocurrent component and a dark current, component. The photocurrent component is associated with the light resulting from the electrical arc and the dark current component is associated with something other than the electrical arc (e.g., ambient light).

From block104, the process advances to block106, where the signal processor16receives at least a portion of the signal generated by the photodetector14, processes the received, signal, and generates an output. As described hereinabove, the signal processor16may form a portion of the local control70. The processing of the signal at block106may include, for example, filtering the dark current component of the signal generated by the photodetector14, comparing the signal or the filtered signal to a threshold value, and analyzing the amplitude and/or frequency of the signal or the filtered signal. The output generated by the signal processor16may indicate that no arc has been detected, that an arc has been detected, or that a specific type of arc has been detected.

From block106, the process advances to block108, where the local control70communicates a message to the main control66. The message may indicate, for example, that no arc has been detected, that an arc has been detected, or that a specific type of arc has been detected.

From block108, the process advances to block110, where the main control66receives the message and determines an appropriate course of action. The appropriate course of action may be, for example, to interrupt power to all the power cells, to interrupt power to a particular power cell (e.g., the power cell which includes photodetector which detected the presence of the arc), or to take no action.

If the determination made at block110is to interrupt power to all of the power cells, the process advances from block110to block112. At block112, the main control66outputs a signal which causes the contactor68to interrupt power to the input to the power supply80, thereby interrupting power to each of the power cells64.

If the determination made at block110is to interrupt power to a particular power cell (e.g., the power cell which includes the photodetector which detected the presence of the arc), the process advances from block110to block114. At block114, the bypass control82receives the interrupt message, processes the interrupt message, and sends an interrupt signal to the contactor84associated with the particular power cell64. The interrupt signal causes power to be interrupted to the particular power cell64. Additionally, the bypass control82may also send a bypass signal to the bypass switch86associated with the particular power cell64. The bypass signal causes the switch94to open and the switch96to close, thereby preventing the particular power cell64from contributing to the output voltage of the power supply80while allowing the power supply80to remain operational.

If the determination made at block110is to take no further action, the process advances from block110to block116. At block116, the method100then waits for the next electrical arc to occur. The process flow described hereinabove may be repeated any number of times while the power supply80is operational.

While several embodiments of the invention have been described herein by way of example, those skilled in the art will appreciate that various modifications, alterations, and adaptions to the described embodiments may be realized without departing from the spirit and scope of the invention defined by the appended claims.