Patent Application
20240266823
This disclosure relates generally to protection against electrical faults.
Electrical faults are unintended situations in the distribution of electrical power at a site, such as a residential home. Electrical faults can be dangerous. They can pose a safety hazard to people and can also cause significant damage to equipment. For example, electrical faults can cause electric shock, which can lead to serious injuries or even death.
Electrical faults can also cause fires and explosions. Electrical faults can also cause equipment damage and failures.
Traditionally, devices such as circuit breakers, fuses, ground fault circuit interrupters, and surge protection devices are used to protect against certain types of faults.
However, these devices are fairly unsophisticated and provide only the most basic protection against only the most basic types of faults. For example, if a circuit is carrying too much current, one of these devices may interrupt the circuit to halt the flow of electricity entirely.
Embodiments of the disclosure have other advantages and features which will be more readily apparent from the following detailed description and the appended claims, when taken in conjunction with the examples in the accompanying drawings, in which:
The figures and the following description relate to preferred embodiments by way of illustration only. It should be noted that from the following discussion, alternative embodiments of the structures and methods disclosed herein will be readily recognized as viable alternatives that may be employed without departing from the principles of what is claimed.
The concepts described in this disclosure are applicable both to grid connected electrical systems and to electrical systems operated in an islanded mode. For systems operated in islanded mode, the system is disconnected from the grid and the “islanded” electrical system is being powered with a battery system, a photovoltaic system, the battery of an electric vehicle, or any other source like a generator or a fuel cell. Most of these sources have limited current and fault current protection compared to systems that are connected to the electrical grid. Protection in electrical distribution systems is generally provided by circuit breakers that provide current overload protection and short circuit protection for a grid connected system. For islanded systems, traditional breakers may not provide adequate protection.
Some of the protection concepts in this disclosure change the protection behavior based on the state of the system. Some also add protection mechanisms that are not available in legacy systems. One example is bi-directional overload protection.
In some cases, a whole panel protection scheme takes into account information from the state of the electrical distribution system outside the panel, as well as enhancing overload protection at the branch level. Traditional systems protect only at the branch-level.
Some or all of the protection strategies outlined here can be implemented inside of a home or commercial/industrial product (e.g. in an inverter or a battery storage system). The protection schemes can also be implemented in a separate controller coordinating with distributed sensing and protection devices. Features can be implemented individually or combined in any combination and not limited to the combinations that are expressly described in this disclosure. Some features may be described together, but they are not required to always be used together.
The electrical panel (100) includes a main breaker (2) or a combination of a breaker and a microgrid interconnection device (MID) (1) that connects the panel to the AC distribution network. In this example, it also measures grid and home side voltages, and provides the information about grid-connected and islanded state. Inside the panel are several branch circuits with circuit breakers (3), an intelligent, active, and bi-directional power distribution box (4) connecting an AC circuit to a DC Panel (5). Inside of the DC Panel there are several DC protection devices to distribute DC voltage to loads.
A number of AC branch circuits are connected to AC loads (8) through wiring devices (7). An AC branch can be used to connect a source (9) like a photovoltaic (PV) system and its inverter to the panel. The PV AC/DC is feeding power into the panel. The source (9) may be a bi-directional (AC) EV charger, and a circuit of the panel may be connected to the bi-directional (AC) EV charger. On the DC panel, there are similar loads/sources connected. All of these sources could have a DC/DC converter to manage them and to bring the voltage to a common DC voltage.
The electrical panel includes the following hardware features. An edge compute unit takes data in the panel (e.g., differential and common mode voltage and differential and common mode current readings, temperatures, state of relays and breaker) and communicates to other connected devices like AC/DC inverters, DC/DC converters, EV chargers, battery systems, and wiring devices. The edge compute unit is also aware of the status and the power quality of the power grid that it is connected to. Being cloud connected, the edge computing device of the panel sends information to the cloud and receives information from the cloud.
Algorithms for energy management system functions, safety functions, load identification and diagnostics functions are being executed by the local computing device or by the cloud computing hardware using the data sent from one or more panels. The compute architecture could use a single edge compute unit, or multiple compute units (clients) at a branch or module (multiple branches) level that feed the information to a central compute unit (server) inside of the panel serving as a gateway to connect to the cloud.
Residential load centers may contain a main breaker and multiple branch circuit breakers. Each breaker can be built to execute different protection algorithms as appropriate. Each breaker for example can execute algorithms to detect short circuits, overloads, or arcing faults. Some breakers might also have other smart features and are cloud connected.
The panel may provide multiple new protection functions that is important for a distribution system that is energized by different AC and DC sources (sometimes concurrently), can be connected and powered by the electrical grid and operate while disconnected from the grid (islanded mode), and/or is connected to devices capable of bi-directional current flow.
In order to provide protection, the panel may include a combination of any or all protection, sensing, and actuation hardware described here:
These functions can be implemented inside the electrical panel or the functions can be distributed throughout the electrical system implemented in separate building blocks or collocated in systems connected to the electrical distribution system including several panels and subpanels.
The panels described here may also provide a holistic solution where sensors are placed at each branch, algorithms are executed not only at the branch level but at a higher level after multiple sensors have been aggregated. This has the advantage that a more complete protection system can be built for the electrical distribution system taking the input of multiple circuits into account. Each branch circuit of the panel has a current sensor and a relay in combination with the circuit breaker. Using the current value as input and the relay as actuator, the panel can complement or replace the protection functions of the breaker while adding protection solutions that involve multiple branches enabling zone protection of the distribution system. Each branch circuit has a current sensor that can sense one or multiple of the following currents: AC current, DC current, common mode current, direction of current flow. Each of the breaches can have a voltage sensor downstream of the relay to indicate if the branch is energized when turned off.
Using the panel's branch relays and the disconnect device (MID) for the grid connection, each load can be isolated and the entire distribution system can be isolated using the MID. In the case of multiple panel installations, each function can be coordinated between panels through the compute unit communicating to other panels directly or through the cloud. The electrical system might have different energy sources and the MID could open putting the installation in islanded mode while energy sources connected to the branch circuits power the panel.
Local implemented protection and energy management system (EMS) features may include any or all of the following. The panel through its branch sensor can detect the state of the EMS by sensing:
Using the EMS awareness features, the panel can give a warning for power quality conditions, like brown out, leakage currents to alert the owner/operator that something is wrong. There can be several alert levels for warnings and faults. A warning might be sent just to the app of the operator phone, where a fault (e.g. an isolation fault) can de-energize that circuit branch.
Another set of warnings can be sent to the installer / electrician application to give awareness of the state of the panel before a circuit is de-energized. The electrician then can troubleshoot the fault condition more quickly by knowing what had led to opening a circuit.
One of the advantages of having a holistic view through the panel is that protection now can be coordinated with several breakers or panels. Zone protection can be implemented. For example, several breakers of the basement could trip due to a flooding event. The panel can command that all branches in the basement zone be de-energized protecting the entire zone. If the system is powered by multiple panels, virtual zones including branch circuits from each panel may be grouped together.
External sensors can be used to trigger zone protection. For example, a water sensor can trigger the panel to shut down power in the compromised zone, e.g. de-energizing the circuits in the basement or laundry area. A water flow sensor for example can indicate a problem in the plumbing or an appliance the panel will react accordingly. A smoke detector or environmental sensor could be an indication a hazardous condition could be the input to the panel to control circuits to react to it.
A catastrophic event to the structure can be caused by external events like flooding due to a hurricane, a wildfire, or other events. The panel can respond to sensors or input external from the house, or from a command triggered externally to put the structure into an electrically save state.
Virtual sub-panel/Zone protection: In traditional electrical systems with backup generation, a sub-panel is installed that is fed by a breaker in the main panel through a transfer switch. The subpanel again has a main breaker with a rating. This panel can group branch circuits together to form a virtual sub panel and define a virtual main breaker rating for this group of circuits. If the rating of the sum of the currents exceeds the virtual main breaker rating, load shedding can reduce the current draw for this subset of circuits, or the virtual main breaker can trip resulting in de-energizing all the circuits in this group.
This group of branch breakers can be a subset of breakers in a single panel, or it can be a number of branch breakers from different panels and subpanels grouped together to form a virtual sub-panel. One could for example group all breakers together that feed the heating and cooling circuits in a house. The circuits in a virtual sub-panel can be grouped and controlled via local communications in a microprocessing unit like a gateway that is part of a panel. They could also be grouped together via cloud connectivity forming a virtual sub-panel spanning a house, a campus, or a neighborhood.
Virtual sub-panels can include branch circuits from different panels that are on the same physical installation or even across the cloud at different locations. Using virtual sup-panels one can group circuits together to give them a combined virtual main breaker, for example grouping all the building system loads (HVAC, water heater) together; or grouping zones or load types together in a virtual panel. This could be used to give these circuits a combined virtual ampere rating, designating a certain capacity to these circuits.
Virtual sub-panels can be used to identify protection zones. It is used to prevent the spread of faults by de-energizing an entire zone or adjacent zones when faults occur. Using the concept of virtual sub-panels, several zones can be created for the same loads and sources. One zone can be used for load control, one zone can be used for protection with some of the loads overlapping in both zones.
Dynamic overload/custom overload protection
The traditional load center consists of a main breaker connected to the 240V/120V distribution transformer of the grid and several branch circuits protected by circuit breakers, distributing electricity to the loads of the house. The circuit breaker of a load center generally has a rating of 120V and 15A or 20A. There are other breakers for dedicated loads like A/C that have higher ratings and can be 120V single pole or 240V double pole breakers.
Protection against electrical overloads, short circuits, arc faults, or ground faults is provided by these branch circuit breakers. The protection is static, generally meant to protect the wire of the branch from overheating.
Of course if all branches are loaded at 100%, the capacity of the main breaker would be exceeded and it would trip, de-energizing the entire dwelling. With the introduction of multiple sources, grid-connected operation, and islanded operation, the available current of the entire panel may also fluctuate and be limited to the generating source or sources. It might be that the available fault current is a lot smaller than the breaker rating. Another scenario might be that the combination of sources that is being back fed into the panel from the branch circuits exceeds the allowable maximum current of the panel. To provide protection, dynamic trip-time curves may be used. A trip-time curve is a curve of allowable duration as a function of current. If the current exceeds the allowable duration specified in the trip-time curve, then the circuit should be tripped (de-energized). Implementing trip-time curves electronically provides more flexibility in defining and changing the levels of protection.
Bi-directional trip-time curves: As shown in
It is useful to be aware of which circuits can source power into the panel. One feature of a bi-directional trip-time curve is to disallow current flow into the panel for normal electrical loads, thus preventing the operator to “backfeed” circuits with a generator of other source, or to prevent faulty devices to feed power back into the panel. A unidirectional trip-time curve will only allow current flow in one direction. This backfeed protection mechanism will also prevent motor loads from feeding “re-generative” power back into the panel and protect the panel and other assets connected to it.
I2t curves based on load detection: The branches of the panel can be de-rated by implementing an electronic trip-time curve at lower currents, freeing up capacity for other high current loads such as vehicle chargers or heat pumps. The panel through its branch circuits may learn the load characteristics of each connected circuit and over time will know what is connected. Through load-disaggregation the panel is able to identify the loads connected and can model load profiles. This information is used to provide a custom trip-time curve for the connected load or loads. This enables the panel to provide branch-level equipment protection custom for each branch.
Dynamic overload: When the system is in islanded mode and powered by inverter sources or generators, the overall power through the load center can be reduced. Very often there is a light load on a branch circuit far below the rating of the branch. One can load shed every circuit that is not essential to power things like the refrigerator or the HVAC system and reduce the amount of load to the sources. A panel may know how much current draw has been on each circuit in the past. We can derate each circuit with a dynamically changed overload curve to keep as many circuits on as possible. The overload curve is dependent on the total available electrical power to the panel.
Missing current detection/missing power (energy): A panel may be connected to several intelligent power systems in
Ground Fault Circuit Interruption (GFCI) or Residual Current Detection (RCD): The panel has the sensing means to detect ground fault currents. The sensing level can be adjusted to provide various forms of protection, e.g. 6 mA for personnel protection, or 30mA for equipment protection. The panel may measure ground fault levels, keep track of trending, and send the information to the cloud. The panel can provide a warning if ground fault currents are present at a pre-trip level or perform a trip to protect the users or equipment. A fault indication and specifics about the fault condition may be given.
Branch protection may be implemented by a circuit breaker in series with a controllable device like a relay. The relay is controlled by a programmable device like a microprocessor. The microprocessor is aware of the current amplitude and direction through a current sensor sensing the current in the branch going to the load or being sourced from the generating source. The microprocessor implements an electronic trip-time curve that protects for lower currents. This electronic trip-time curve is coordinated with the circuit breaker's protection curve in a way that the relay will trip before the circuit breaker will. This will enable being able to change the trip-time behavior of that branch and coordinating fault protection of several branches to provide more advanced circuit protection.
Using the configuration above, the panel will protect the same way a traditional electrical panel with circuits breakers does, with normal circuit breakers as required by the National Electrical Code (NEC). With the addition of a relay or other electrical disconnect device, different tip-time curves can be implemented using the relay.
An electric protection system also allows for a different trip-time curve to be implemented. Generally a circuit breaker's overload trip-time curve is chosen to provide protection of overheating for the size of the wire used in the branch. The electronics protection system can for example implement different trip-time curves like equipment protection.
The electronic protection system can implement different trip-time curves depending on the direction of current, as shown in
Traditional electrical panels employ circuit breakers or fuses that generally only implement fault algorithms based on the magnitude of the current and the time the current is present. Panels described here may make use of signature analysis on the current and voltage using machine learning algorithms, deep learning methods, or other analytical methods to determine if an unsafe condition exists.
Load ID assisted fault algorithms: Load identification may assist all the fault algorithms. It may be used to remove noise or harmonics to get a cleaner signal of the load current. Once identified, the loads may be compared with a load library in the cloud to determine overall health. A library of load and source faults in the cloud may help identify unhealthy conditions based on the data sent back to the cloud. This mechanism customizes arc fault algorithms described below.
Series arcs: A panel may be connected with several intelligent power systems with its own sensing capability. The current and voltage is reported back to the panel. If a series arcing fault (e.g. due to a loose connection), or a high impedance fault (to ground or at a junction point) the voltage at the load can be substantially lower than at the panel. The panel will compare the voltages and issue a fault state when they are different.
Parallel arc: Parallel arcs (arcing faults to neutral or ground) exhibit intermittent high current spikes that might not trigger the overload or short circuit protection mechanism of regular circuit breakers. A panel may be monitoring each branch circuit and detecting the presence of a parallel arcing fault. The arcing fault algorithm may be dynamically adjusted to account for the available fault current when the panel is in islanded mode.
The electrical panel described here may monitor for abnormal conditions resulting from the grid or the home wiring to ensure safe operation and to ensure the integrity of the home electrical system is safe. This includes monitoring trending over time and comparing key parameters with stored historical values on the panel or in the cloud.
Circuit Isolation/Isolation fault Integrated in each panel is an isolation monitor that will measure the impedance between neutral and ground before energizing the panel.
This may be done for AC and DC circuits. The DC and AC sections of the panel can be isolated independently and from each other.
Overvoltage/Undervoltage and lightning protection/transient voltage protection: Integrated into the main board, main breaker, and/or main branch is a transient voltage suppression (TVS) device, protecting the panel and each branch from overvoltages due to overvoltage conditions coming from the distribution network due to lightning or other transient events. The panel provides comprehensive protection for transient voltage events. In present systems, TVS devices provide passive whole home protection. There is no way to know the state of these devices. The panel may track transient events and count them. A state-of health indication is given after a number of events. The panel may measure the leakage current of transient protection devices or track the clamping voltage to know the health of these devices and indicate when TVS protection is compromised and service is needed.
During an overvoltage event in grid-connected or islanded mode, the panel disconnects that source to protect itself and connected loads. During an undervoltage event, loads and sources are disconnected to protect the equipment. Overvoltage protection can be individualized per source and circuit for the AC circuits or the DC circuits.
Power Quality Abnormalities: The panel monitors the load and source total harmonic distortion (THD) of the various sources (inverter fed or grid) and loads and determine abnormal conditions to notify the user or bring the panel to a safe state.
Load wearout detection: The branch circuits of the panel sense the current signature and send parameters to the local compute or cloud compute platform. The panel tracks historical data and monitor the load, detecting load changes or load degradation over a timespan from seconds, minutes, days, months, and years. The panel may monitor and track the health of itself and its components, store historical data and trends in the cloud, and provide warnings about the health of the panel. Sources connected to the panel or connected to the electrical system may be monitored and trending data is stored and analyzed in the cloud.
The Panel may detect the state of the grid and report grid state conditions like brown-out, black-out, voltage levels, frequency to the cloud or to the utility. It may be aggregated over a neighborhood or region to be able to provide region-wide grid status. Aggregated information from many panels can be used in the cloud to diagnose how grid conditions originate and travel through the grid and that information may provide information valuable to the utility.
The panel incorporates a home awareness mechanism that is used to build a model of the electrical system with all branch circuits, main connection, panels, sub-panels, sources, and loads. This cloud-assisted model may be used to create a schematic of the electrical wiring system and may be used to assist with fault protection algorithms tuned to that system. Without any input from an installer, the load types are identified and a library of what current signatures are created. This helps identify unusual current signatures that can be flagged.
The panel includes an AC/DC converter to connect to DC storage devices like batteries, EVs, or PV. Using the converter, power can be provided during power outages. The health of the power electronic system and their passive components like capacitors and inductors are monitored and stored in the cloud.
Cloud-Connected Protection Features
In the case of multiple panels in one installation, the protection features mentioned here can be extended to cloud or locally connected and communicating panels. Virtual sub-panels can be defined across multiple panels, dynamic overload curves and zones can be defined across multiple panels.
The panels may send branch level information to the cloud. The cloud stores historical parameters and can determine if the behavior of the branch circuits change or drift over time. The algorithms may learn what kind of transient and steady-state signals are present for each branch, learn what type of loads are present and then alert the operator of any anomalies.
The cloud is used to aggregate large amounts of data and keep historical data and trending, keep track of configuration changes of the panel's electrical system and manage inter-panel communications and coordination. Using the data stored of the present state and having the historical data enables cloud-based deep learning algorithms to optimize the protection schemas and analyze the robustness of the individual protection devices. This knowledge then can be used to load shift or reconfigure the electrical system or update individual devices to perform better. Post processing and trending data can be used to give the user or installer a holistic view of the system, pin-point where faults occur and give the electrician information on past faults, fault location, circuits that are regularly overloaded (e.g. a circuit is regularly loaded over 80% capacity but not enough to be tripped). Using the information of cloud-connected panels within a region, decisions in response to an event in a larger geographic area can be made, e.g. in response to a seismic event, flooding, or wildfire. For all faults and fault types, a detailed history log of all fault types are kept and it is used for diagnostic purposes of the overall electrical system and to provide information to an electrician or for system optimization.
Although the detailed description contains many specifics, these should not be construed as limiting the scope of the invention but merely as illustrating different examples. It should be appreciated that the scope of the disclosure includes other embodiments not discussed in detail above. Various other modifications, changes and variations which will be apparent to those skilled in the art may be made in the arrangement, operation and details of the method and apparatus disclosed herein without departing from the spirit and scope as defined in the appended claims. Therefore, the scope of the invention should be determined by the appended claims and their legal equivalents.
This application is a continuation of International Application No. PCT/US24/14480, “Protection Architecture for an Electrical Panel,” filed Feb. 5, 2024; which claims priority to U.S. Provisional Patent Application Ser. No. 63/483,523, “Protection Architecture for an Electrical Panel,” filed Feb. 6, 2023. The subject matter of all of the foregoing is incorporated herein by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| 63483523 | Feb 2023 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/US2024/014480 | Feb 2024 | WO |
| Child | 18609765 | US |
