Patent Application
20220005663
The field of the invention relates generally to circuit protection devices, and more specifically to an arc flash reduction system for an overcurrent protection fuse.
Fuses are widely used as overcurrent protection devices to prevent costly damage to electrical circuits. Fuse terminals typically form an electrical connection between an electrical power source and an electrical component or a combination of components arranged in an electrical circuit. One or more fusible links or elements, or a fuse element assembly, is connected between the fuse terminals, so that when electrical current flowing through the fuse exceeds a predetermined limit, the fusible elements melt and open one or more circuits through the fuse to prevent electrical component damage.
Mitigating certain types of electrical arc flash conditions for large amperage fuses in high voltage, high current electrical power systems presents particular challenges that have yet to be completely addressed by existing arc flash reduction measures and systems. Improvements are desired.
Non-limiting and non-exhaustive embodiments are described with reference to the following Figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified.
Electrical power systems in industrial and commercial facilities typically operate at higher voltages and with high current than other electrical power systems. Higher voltage, higher current circuitry presents increased potential energy for electrical arcing events as an overcurrent protection fuse operates to open such circuitry and protect load-side circuits and equipment from damage that may otherwise be caused when electrical fault conditions occur. Higher voltage, higher current circuitry likewise presents a possibility of undesirable electrical arcing conditions apart from electrical fault conditions, including but not necessarily limited to service and maintenance procedures performed by electrical power system personnel in and around electrical panels and the like where circuit protectors such as overcurrent protection fuses are located. Improved arc flash mitigation features are accordingly desired from both circuit protection and safety perspectives. Method aspects will be in part apparent and in part explicitly discussed in the description below.
It is understood that the electrical power system 100 in a commercial or industrial facility may include many circuit protectors 102 of the same or different type to protect branch circuitry in the power system, to protect different loads 106 connected to the power system, and to meet specific needs at various different points in the electrical power system 100. Various access points to different parts of the electrical power system 100 are typically provided in different locations in the commercial or industrial facility for service and maintenance, including but not limited to inspection and/or replacement of overcurrent protection fuses. For certain service or maintenance procedures to be performed while the electrical power system is “live” or energized, electrical arcing conditions and arc flash hazards are of particular concern to electrical power system personnel that are in the vicinity of the panel. Apart from service and maintenance procedures, electrical arcing in certain circumstances can compromise the desired circuit protection when the circuit protector 102 does not or cannot act quickly enough to interrupt the circuit path between the line-side circuitry 104 and the load-side circuitry 106. While such conditions are described in the context of an overcurrent protection fuse 102, other types of circuit protectors may present similar issues.
The overcurrent protection fuse 102 (separately shown in the example of
The blade terminals 114, 116 of the fuse 102 include respective mounting apertures 118, 120 of varying size and shape that are used to complete bolt-on connection to respective conductors of the line-side and load-side circuitry 104, 106 in the power system 100 shown in
The fuse 102 in one contemplated embodiment is a large amperage fuse such as a known Class L fuse that is designed to meet the demands of higher voltage, higher current circuitry in the electrical power system 100 represented by the line-side circuitry 104 and the load-side circuitry 106. For example, the fuse 102 may be a Class L fuse installed in a switchboard mains and feeder circuit in the power system 100, other power distribution circuitry in the power system 100, or in a motor control center of the power system 100. In an exemplary motor control application, the fuse 102 may be a Class L fuse providing branch-circuit protection in the power supply (the line-side circuitry 104) for one or more large motors (the load side-circuitry 106), and may provide short circuit and overload protection to the motors via time delay features built-in to the fuses 102.
UL listed Class L fuses suitable for use as the fuse 102 are available from a variety of electrical fuse manufacturers, including but not necessarily limited to Eaton's Bussmann Business of St. Louis, Mo. In one exemplary embodiment the fuse 102 may be a known Class L fuse having a voltage rating of about 600 VAC or less, an amperage rating of 300 A to 6000 A, and an interrupting rating of 200 kA VAC RMS Sym. In another exemplary embodiment the fuse 102 may be a known Class L fuse having a voltage rating of 600 VAC/300 VDC, an amperage rating of about 600 A to 2000 A, and an interrupting rating of 300 kA VAC RMS Sym or 100 kA VDC. Known Class L fuses may include time-delay features or may be fast acting as desired for use in the power system 100.
Such high voltage, high current loads on such Class L fuses 102 creates rather severe electrical arcing potential. While Class L fuses are engineered to contain electrical arcing inside the housing 110 as the fuse 102 operates in response to a specified fault current, electrical arcing conditions can sometimes be unpredictably severe and/or difficult to control or extinguish in certain cases. If arcing is not effectively controlled or extinguished, even for a well-designed electrical fuse 102, an undesirable release of significant amounts of concentrated radiant energy may result in a fraction of a second, resulting in an undesirable high temperature and pressure condition in the ambient environment of the fuse 102. Likewise, it is possible for electrical power system personnel to inadvertently create an electrical arcing condition when performing service and maintenance procedures while the power system 100 is “live” and the fuse 102 (and other electrical conductors and components proximate the fuse 102) are energized under the high voltage, high current load.
To mitigate arc flash concerns in the scenarios described above, an arc flash mitigation network 120 is connected in parallel to the fuse 102 to respond to electrical arcing conditions that the fuse 102 has not responded to in a desired timeframe. The arc flash mitigation network 120 in the example shown includes a semiconductor switch 122 and an arc mitigation fuse 124 connected in series to one another and in parallel to the fuse 102. In view of the fact that two overcurrent protection fuses are now present, the fuse 102 is referred to hereinafter as the “main” fuse providing primary overcurrent protection to the load-side circuitry 106 while the arc mitigation fuse 124 serves a limited, secondary role only in certain conditions as described below.
The semiconductor switch 122 in an exemplary embodiment is a silicon controlled rectifier, sometimes referred to as a thyristor, connected in parallel to the main fuse 102 such that the voltage across the main fuse 102 is input to a gate 126 of the silicon controlled rectifier 122. In normal operation, the silicon controlled rectifier 122 is off and exhibits high resistance such that all of the current present flows through the main fuse 102. As such, the arc mitigation fuse 124 is disconnected through the semiconductor switch 122 and current does not flow through the arc mitigation fuse 124.
When the voltage across the main fuse 102 reaches a predetermined level, however, the voltage applied to the gate 126 causes the silicon controlled rectifier 122 to switch on and provide a low resistance circuit path that conducts current in the parallel circuit path through the silicon controlled rectifier 122 and to the arc mitigation fuse 124. As such, the current is shunted or diverted away from the main fuse 102 and through the parallel current path by the silicon controlled rectifier 122 and to the arc mitigation fuse 124.
The arc mitigation fuse 124, in turn, is selected to have a lower amperage rating than the main fuse 102 and will respond much more quickly to the current than the main fuse 102 otherwise would or could. The faster opening of the arc mitigation fuse 124 reduces the electrical arcing potential and reduces a severity of any arc flash event that may occur while electrically isolating the load-side circuitry 106 from the line-side circuitry 104.
The semiconductor switch 122 and the arc mitigation fuse 124 may be particularly advantageous in certain overcurrent conditions wherein the main, high amperage fuse 102 by itself does not operate fast enough to minimize arc flash energy. The low amperage fuse 124 in the parallel current path that is switched on by the semiconductor switch 122 in response to the applied voltage provides a much quicker response time to reduce arc flash energy. In general, however, the arc flash mitigation network 120 is configurable to respond to any other circuit condition in which arc flash energy reduction is desired.
The high and low amperage ratings of the respective fuse 102 and the fuse 124, as well as the gate voltage needed to switch the silicon controlled rectifier 126 on, may be strategically selected in combination to optimally respond to specific overcurrent conditions that may arise in a given electrical power system 100. The arc flash mitigation network 120 is voltage dependent in view of the large amperage rating of the main fuse 102 and the corresponding high amperage current of the power system 100, and avoids complications of a current-dependent arc flash mitigation network in such a high current power system.
In a contemplated embodiment, the semiconductor switch 122 is responsive to a predetermined change in voltage drop across the main fuse 102 as applied to the gate 126 of the silicon controlled rectifier to achieve faster operation in certain voltage and current ranges that the main fuse element is slower to respond than desired from an arc flash reduction perspective. When the voltage drop reaches a certain level, the silicon controlled rectifier connected in parallel with the main fuse 102 is enabled to shunt the current through the silicon controlled rectifier for interruption via the low ampacity fuse 124 that is sized and selected to react much faster than the main fuse 102.
By selecting the voltage change that turns the semiconductor switch 122 on, the parallel current path and the arc mitigation fuse 124 may be selectively used (or not) to respond to different voltage events representing the current flowing through the main fuse 102. The semiconductor switch 122 may accordingly respond to some overcurrent conditions but not others, and may therefore complement the response time of the main fuse 102 only when needed. When not needed, the semiconductor switch 122 is off and the arc mitigation fuse 124 is electrically isolated from the current such that the main fuse 102 solely provides the circuit protection.
The fuse 130 includes a housing 132 and terminal blades 134, 136. The housing 132 is comparatively smaller than the housing 110 of the main fuse 102 (
In
While different examples of main fuses 102 and arc mitigation fuses 130, 140 have been described, still others are possible. While exemplary voltage and current ratings of Class L fuses are described in relation to the main fuse 102 to illustrate examples of high voltage, high current demands of the electrical power system 100 that present arc flash concerns, other types and classes of main fuses 102 having similar or different voltage current ratings are possible in further and/or alternative embodiments. Likewise, arc mitigation fuses having housing or terminal structure or amperage ratings different than that shown in the drawings and described above may be used in combination with various types and classes of main fuses 102 to accomplish similar benefits.
Also, semiconductor switches other than a silicon controlled rectifier are possible in other embodiments of an arc flash mitigation network with similar effect and similar advantages. Various different types of silicon controlled rectifiers may also be used with similar effect and similar advantages. More than one silicon controlled rectifier or its equivalent may also be used in the same arc flash mitigation network 120 with more than one arc mitigation fuse in the network to provide still further variations in response times to different current conditions. In embodiments having more than one semiconductor switch in an arc flash network, the various semiconductor switches may have the same or different voltage response to switch them on and may accordingly operate in combination according to the voltage drop across the main fuse or may operate individually to different voltage drops as needed or as desired.
The arc flash mitigation network 202 in the example shown includes a pair of semiconductor switches 122a, 122b connected in an anti-parallel arrangement with one another and in parallel to the main fuse 102. That is, the semiconductor switches 122a, 122b are connected in parallel to one another, but with their polarities reversed as shown. The semiconductor switches 122a, 122b are further provided in combination with the arc mitigation fuse 124 defining a series-connected shunt current path through the arc mitigation fuse 124. Like the arc flash mitigation network 100, the semiconductor switches 122a, 122b are silicon controlled rectifiers, sometimes referred to as thyristors, although other types of semiconductor switches may likewise be utilized as discussed above in further and/or alternative embodiments with similar effect.
As in the arc mitigation network 100, the arc mitigation fuse 124 in the arc mitigation network 202 has a lower amperage rating than the main fuse 102 and has a comparatively smaller package size than the main fuse 102. In contemplated embodiments, the arc mitigation fuse 124 may be the fuses 130 or 140 as shown and described in
The fuse element or fuse element assembly in the arc mitigation fuse 124 has a lower amperage rating than the main fuse 102, which provides for a comparatively smaller package size of the arc mitigation fuse 124 relative to the main fuse 102. The lower amperage rating of the arc mitigation fuse 124 may be a specified fraction of the higher amperage rating of the main fuse, such as one half or one third. The arc mitigation fuse 124 may include a short circuit fuse element only, while the main fuse 102 may provide for short circuit and overload protection with time delay features. As such, and depending on circuit conditions, the main fuse 102 may desirably respond to interrupt circuit conditions that the arc mitigation fuse 124 could not and in such conditions the arc mitigation network 202 plays no role in interrupting the circuit.
The semiconductor switches 122a, 122b in the arc mitigation network are each responsive to an input 204, such as a predetermined change in voltage drop across the main fuse 102 as shown. In the arc mitigation network 202 the input 204 is applied to each gate 126 of the respective silicon controlled rectifiers 122a, 122b to achieve faster operation in certain voltage and current ranges that the main fuse 102 is slower to respond than desired from an arc flash reduction perspective. In normal operation, the voltage input 204 is below a predetermined threshold and the silicon controlled rectifiers 122a, 122b are in a nonconductive or “off” state wherein no current flows in the arc mitigation network 202. As a result all of the current flows through the high amperage main fuse 100 in the normal operation of the power system 200.
When the voltage input 204 reaches a predetermined threshold, however, the silicon controlled rectifiers 122a, 122b assume an “on” state to become conductive and divert the current away from the main fuse 102 and to the arc mitigation fuse 124 in the lower resistance shunt current path. The low amperage arc mitigation fuse 124 is strategically sized and selected to react to the diverted current much faster than the high amperage main fuse 102 could or would if the current was not diverted. The anti-parallel connection of the semiconductor switches 122 in the arc flash mitigation network 202 allows the shunting of current to the arc mitigation fuse 124 in each of the respective positive and negative half cycles of AC current. The arc flash mitigation network 202 therefore reduces arc energy and arc flash concerns of AC more effectively than the arc flash mitigation network 100 in certain power systems. The faster opening of the low amperage arc mitigation fuse 124, relative to the high amperage main fuse 102, reduces the electrical arcing potential and reduces a severity of any arc flash event that may occur while electrically isolating the load-side circuitry 106 from the line-side circuitry 102.
Specifically, when the semiconductor switches 122a, 122b operate to shunt the current in the arc mitigation network 202 and divert current away from the main fuse 102, excess energy is more quickly dissipated in the opening of the low amperage arc mitigation fuse 124, reducing the total arc energy potential at the main fuse 102 at the time that the arc mitigation network 202 operates. The arc energy is effectively transferred from the high amperage main fuse 102 to the low amperage arc mitigation fuse 124 at the time that the arc mitigation network 202 operates to more effectively extinguish severe arcing in the low amperage arc mitigation fuse 124. After the low amperage arc mitigation fuse 124 opens in the shunt current path in the arc mitigation network 202, the shunting of the current ceases and the entirety of current present returns to flow through the main fuse 102. At this point, the main fuse 102 takes over and opens to complete the circuit interruption process between the line 104 and load 106.
Because total arc energy potential is decreased by the prior opening of the arc mitigation fuse 124, arc flash energy is reduced for any electrical arcing that may occur in the opening of the main fuse 102. In contrast, without the arc mitigation network 202, all of the arc energy potential would otherwise be fully presented to the high amperage main fuse 102, resulting in more severe arcing over a longer period of time. Enhanced safety of personnel while servicing an energized electrical power system in the vicinity of the high amperage main fuse 102 is realized by the arc mitigation network 202 that dissipates a portion of the arc energy presented that would otherwise be presented to the main fuse 102, which beneficially reduces arc energy potential, severity of arcing and duration of arcing in the high amperage main fuse 102 as it opens.
The exemplary voltage and current ratings of Class L fuses described above in relation to the main fuse 102 are illustrative examples of high voltage, high current demands of the electrical power system 200 that present arc flash concerns, although other types and classes of main fuses 102 having similar or different voltage current ratings are possible in further and/or alternative embodiments. Likewise, arc mitigation fuses having housing or terminal structure or amperage ratings different than that shown in
While the voltage input 204 shown in
The benefits and advantages of the invention are now believed to have been amply illustrated in relation to the exemplary embodiments disclosed.
An embodiment of an arc flash mitigation network for a main overcurrent circuit protector providing primary overcurrent protection to an electrical load has been disclosed. The arc flash mitigation network includes first and second semiconductor switches connected in parallel to the main overcurrent circuit protector and in parallel to one another, and an arc mitigation fuse connected in series to the parallel connected first and second semiconductor switches. An operation of at least one of the first and second semiconductor switches diverts current to the arc flash mitigation fuse in predetermined circuit conditions and wherein a prior opening of the arc mitigation fuse reduces arc flash energy in a subsequent opening of the main overcurrent circuit protector, thereby enhancing safety of personnel while servicing an energized electrical power system in the vicinity of the main overcurrent circuit protector.
Optionally, the first and second semiconductor switches may be connected in reverse polarity to one another. The first and second semiconductor switches may be operative with respect to an input to divert current to the arc mitigation fuse. The input for each of the first and second semiconductor switches may be a voltage across the main overcurrent circuit protector. The first and second semiconductor switches may be silicon controlled rectifiers.
The main overcurrent circuit protector may optionally be a main overcurrent protection fuse having a high amperage rating, and the arc flash mitigation fuse may have a low amperage rating. The low amperage rating may be one half or one third of the high amperage rating. The high amperage rating may be at least 300 A, but may also be less than about 4000 A. The main overcurrent protection fuse may have a voltage rating of about 600 VAC or about 300 VDC.
As further options, the main overcurrent protection fuse may be larger than the arc flash mitigation fuse. The main overcurrent protection fuse may be configured to provide overload protection and short circuit protection. The arc mitigation fuse may be configured to provide short circuit protection only. The main overcurrent protection fuse may also be a time delay fuse.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
This application is a continuation-in-part application of U.S. patent application Ser. No. 17/358,848 filed Jun. 25, 2021 which is a continuation application of U.S. patent application Ser. No. 15/976,209 filed May 10, 2018 and now issued U.S. Pat. No. 11,049,685, the complete disclosures of which are hereby incorporated by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 15976209 | May 2018 | US |
| Child | 17358848 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 17358848 | Jun 2021 | US |
| Child | 17480748 | US |
