System for detecting earth faults in photovoltaic systems

Abstract

The present invention relates to the detection of faults and particularly relates to a system for detecting earth faults in a photovoltaic system (PVS). The method carried out by the system comprises: referencing the PVS to earth; balancing the potential difference between (+) and (-) against earth; detecting earth fault current; limiting the fault current to values that do not affect the continuity of the electricity generation service; identifying the circuit or branch of the PVS with the earth fault; preventing the PVS from disconnecting as a result of the earth fault; and generating an alert signal to report or inform of the existence of an earth fault.

Description

[0001] SYSTEM FOR DETECTING GROUND FAULTS IN SYSTEMS

[0002] PHOTOVOLTAICS

[0003] BACKGROUND.

[0004] Currently, Photovoltaic Systems (PV systems), which will be used interchangeably throughout this text, have significantly improved their efficiency, substantially increasing the use of solar energy. This has required ever-increasing generation capacity, consequently necessitating higher voltage levels at these power plants. All of the above, and especially the increased voltage levels, also increase the likelihood of faults, both between the positive and negative poles and to ground faults.

[0005] A direct current (DC) photovoltaic (PV) array must have a ground fault protection device. Ground fault detection is very common in alternating current (AC) systems; however, it is not common practice when dealing with direct current (DC) systems.

[0006] In alternating current systems, ground fault detection is performed using protective relays (51 N) connected to the secondary windings of current transformers. The primary winding of these transformers carries the ground fault current from the power system. For ground fault detection in three-phase AC systems, it is crucial that the source be connected in a wye (star) configuration and solidly grounded, or grounded through an impedance when fault current values ​​are very high. When the three-phase source lacks a ground reference connection, it is necessary to add a component to the three-phase source to facilitate current flow and provide a path for the ground fault currents.

[0007] Electrical system failures can occur for various reasons, including environmental conditions that directly influence the deterioration of the insulation in the sheathed cables that interconnect any electrical system, including PV modules. Direct causes include high temperatures, UV rays, very dry environments, or excessively humid environments to the point where conductors can become submerged in water. Indirect causes include overvoltages induced by lightning strikes. Other causes may include insulation aging, poor connections, mechanical damage during installation, and pests, among others.For ground faults to exist, there must be a flow of current circulating through the ground, which requires two conditions: First: that there is a path for the current to flow and Second: that there is a potential difference that makes the current flow.

[0008] The first condition requires that the system have only one grounding point. Once this ground reference point is established, the path for the fault current is determined, and current transformers connect it to the 51N, 51NT, or 51G protection relays. The second condition is met whenever the circuit is energized. This mechanism is widely used to protect three-phase AC electrical systems against ground faults, but ground fault detection is not common practice in DC systems. Based on this reasoning, we consider this a novel way to detect ground faults in DC systems in general and in PV systems in particular.

[0009] There are proposed methods for detecting ground faults adaptable to DC systems in general and PV systems in particular. For example, Japanese patent JP2005168156A refers to a ground fault countermeasure device used in a power generation system, and more specifically to a ground fault countermeasure device used in a solar power generation system. Specifically, it refers to a plurality of modules that constitute a power generation device and a power conditioner for supplying power generated by these modules to a load system or a power system. It has opening / closing means provided between the modules and the power conditioner, and when each of the opening / closing means is detected, based on a pre-established opening / closing method, a ground fault is detected.A ground fault countermeasure device comprising control means for identifying a module in which a ground fault has occurred by controlling the opening and closing of the device. However, it appears to have some operational drawbacks that make it unreliable. For example, it does not appear to control the magnitude of the ground fault current; it also fails to identify the circuit in the system that has the ground fault; its configuration produces a general disconnection and then requires a method of testing each circuit until the faulty circuit is found, and it may not reduce the risk of fire in the system. On the other hand, US patent 7529069B1 discloses a ground fault detection and location device for electrical systems, using the device in conjunction with specific circuit analysis methods, utilizing the information generated by the ground fault detection and location device.The device comprises a voltmeter, an ammeter, a frequency generator, and a variable power supply, thus providing a variety of signals and analyses to be performed on a grounded circuit. The device includes a main unit and a remote unit, which can be a portable unit. As described, the device allows for the detection and location of ground faults. It also describes methods for generating various signals that are fed into the electrical distribution system and monitored by various means, including one or more remote units, such that it can be implemented as a dedicated permanent installation or as a temporary portable system, even computer-controlled.According to the description in this patent, and particularly with regard to photovoltaic systems, it is clear that it does not control the magnitude of ground faults, nor does it provide a method for disconnecting the fault and the inverter, aspects that are important in a system like this. Our invention provides a strategy through which we propose a system for detecting ground faults in photovoltaic systems.

[0010] Therefore, an object of the present invention is to provide a system for detecting ground faults in photovoltaic systems, enabling the detection of the ground fault. Another object of the present invention is to provide a system for detecting ground faults in photovoltaic systems that allows the identification of the circuit or branch exhibiting the ground fault.

[0011] Another object of the present invention is to provide a system for detecting ground faults in photovoltaic systems, which allows confirmation of the presence of a ground fault in an identified branch.

[0012] Yet another object of the present invention is to provide a system for detecting ground faults in photovoltaic systems, which reports and issues a warning of the presence of ground faults in a safe and reliable manner.

[0013] Another object of the present invention is to have a system for detecting ground faults in photovoltaic systems, the procedure of which allows in principle referencing the photovoltaic system to ground.

[0014] Another object of the present invention is to have a system for detecting ground faults in photovoltaic systems, the procedure of which allows balancing the potential difference of (+) and (-) against ground.

[0015] Another additional object of the present invention is to have a system for detecting ground faults in photovoltaic systems, which allows limiting the fault current to values ​​that do not affect the continuity of the electricity generation service.

[0016] These and other objects of the present invention will be appreciated in greater and better detail by interpreting the Figures that accompany this description:

[0017] BRIEF DESCRIPTION OF THE FIGURES Figure 1-a shows a diagram with three different arrangements for detecting these AC ground faults for a simple system with one source and one load.

[0018] Figure 1-b shows the method for detecting ground faults when there are several circuits powered by the same source.

[0019] Figure 2 shows the basic components of a PV system, in which the operating voltage of the PV system depends on the number of PV modules connected in series.

[0020] Figure 3-a shows a floating DC direct current system

[0021] Figure 3-b shows a grounded negative DC system

[0022] Figure 3-c shows a system grounded by means of a voltage divider

[0023] Figure 4 shows the simplified scheme of another type of photovoltaic system, consisting of several branches, where each branch can be made up of several photovoltaic modules in series called strings.

[0024] Figure 5-a shows the schematic of the ground fault current path in a photovoltaic system with a resistor-based voltage divider.

[0025] Figure 5-b shows an alternative to the voltage divider of Figure 5-a consisting of two batteries in series.

[0026] Figure 6 shows the schematic of the elementary ground fault protection circuit in 64FV photovoltaic systems.

[0027] Figure 7 shows the implementation of the photovoltaic system protection system of the present invention. Figure 8 shows a simplified representation of the concentrator logic module of the system of the present invention.

[0028] Figure 9-a schematically represents the differential magnetic detector (DDM) device used in the present invention for detecting ground faults in photovoltaic systems

[0029] Figure 9-b shows the operating scheme of the direct current detector (DCD) associated with the voltage divider of the present invention.

[0030] DETAILED DESCRIPTION OF THE INVENTION

[0031] In alternating current (AC) systems, ground fault detection is performed using protective relays connected to the secondary windings of current transformers. The primary winding of these transformers carries the ground fault current from the power system. For ground fault detection in three-phase AC systems, it is crucial that the source be connected in a wye (star) configuration and also be solidly grounded or grounded through an impedance when the fault current values ​​are very high. Figure 1-a shows a diagram with three different arrangements for detecting these AC ground faults in a simple system with one source and one load. This figure shows a schematic diagram of a three-phase transformer, with its three secondary windings (100) connected in a wye configuration, forming a common neutral point (105), which supply a load (102) via a three-pole circuit breaker (101).The neutral is connected to ground (106). The transformer is protected with overcurrent relays (104) fed by current transformers (103) located at three different points: at the neutral (105), at the output of the coils (100), and at the output of the switch (101). Each of these has different arrangements of current transformers to fulfill the same function of detecting ground faults in AC systems.

[0032] Figure 1-b illustrates the method for detecting ground faults when multiple circuits are fed from the same source, making it necessary to identify which distribution circuit has experienced a fault. This figure shows a three-phase system consisting of a transformer (110) that feeds a node (121), which in turn feeds two power distribution circuits (119 and 120) controlled by circuit breakers (117 and 118). The transformer's neutral (122) is connected to ground (123). The protection scheme, comprised of a current transformer (111) and a current relay (112), can detect ground faults at any point in the system, including the distribution circuits (119 and 120), but cannot distinguish which circuit has the fault.The protection scheme consisting of the three current transformers (113) and the current relay (114) can detect ground faults in the distribution circuit (119) and will cause the circuit breaker (117) to open; however, it will not be able to detect faults in circuit (120). The protection scheme consisting of the three current transformers (115) and the current relay (116) can detect ground faults in the distribution circuit (120) and will cause the circuit breaker (118) to open; however, it will not be able to detect faults in circuit (119). In this way, the ground fault protection schemes (113 and 114) or (115 and 116) can discriminate in which of the AC distribution circuits (119 or 120) a ground fault is present.Electrical system failures can occur for various reasons, including environmental conditions that directly influence the deterioration of the insulation in the sheathed cables that interconnect any electrical system, including PV modules. Direct causes include high temperatures, UV rays, very dry environments, or excessively humid environments to the point where conductors can become submerged in water. Indirect causes include overvoltages induced by lightning strikes. Other causes may include insulation aging, poor connections, mechanical damage during installation, and pests, among others.For ground faults to occur, a current must flow through the ground. This requires two conditions: a path for the current to flow and a potential difference to drive the current. The first condition requires the system to have only one ground connection point, as shown in (106) of Figure 1-a and (123) of Figure 1-b. Once this ground reference point is established, the path for the fault current is defined, and current transformers (103) connect it to the protective relays (104). The second condition is met whenever the circuit is energized. This mechanism is widely used to protect three-phase AC electrical systems against ground faults, but ground fault detection is not common practice in DC systems.This is a novel aspect that determines one of the main objectives of our invention since it is a novel concept of detecting ground faults in DC systems in general and in PV systems in particular.

[0033] Although DC systems are less complex than AC systems, ground fault detection in PV systems is not yet widespread. However, the need to increase generation capacity in PV systems requires increasing the number of cells connected in series, which in turn increases the DC generation voltage. As voltage increases, so does the likelihood of short-circuit and ground faults in the DC system. At this point, protection against short-circuit faults (from positive to negative) becomes critical, as does protection against ground faults involving insulation failures in the cables and equipment that make up the PV system.Given that in PV systems there is no increase in current when a short circuit occurs between positive and negative terminals, as happens in traditional systems, it is necessary that ground fault detection in PV systems be performed with elements that allow for sensitivity at the lowest possible values. Faults between positive and negative terminals must be detected and cleared using overcurrent protection devices, for which fuses and / or thermomagnetic circuit breakers are available. Several patented solutions exist for detecting ground faults to address this problem and prevent physical damage to the PV system, as well as economic losses due to the system being out of power.

[0034] The present invention aims to detect ground faults using magneto-electronic devices that offer sensitivity and selectivity without interrupting the PV system's generation. This eliminates the need to disconnect the system from the electrical grid due to a ground fault. This is achieved as follows: A PV module transforms sunlight into electrical energy. This energy flows in only one direction, hence it is called direct current (DC). This current can be stored in a battery for later use. To use the energy stored in the battery or the energy produced directly by the photovoltaic modules, it must be converted into alternating current (AC), the form in which it can be used by all domestic, commercial, and industrial appliances. The DC-to-AC conversion is performed by an inverter. An inverter is powered by DC at two poles and outputs AC in one or three phases.The inverter is the link and boundary between the DC system and the AC system. The present invention is focused on providing protection to what can be defined as the DC area.

[0035] A 2-pole circuit breaker, preferably a thermal-magnetic type (MCB), connects the PV module to the inverter. The inverter output is connected via a switch to a single-phase or three-phase transformer with the appropriate ratio for connection to the existing AC electrical grid. As shown in Figure 2, the basic components of a PV system are displayed. The operating voltage of the PV system depends on the number of PV modules connected in series, as can be seen in the figure, and can reach voltages between 600 and 1500 Ved. The PV system consists of several branches (209), each of which can be made up of several photovoltaic modules (201) connected in series, called strings. Each branch or string is protected by an MCB (204), which also serves as a disconnect switch for the concentrating node (200). The PV system may include a battery bank (202) that is connected to the concentrating node via the MCB (203).The concentrator node (200) is connected to an inverter (206) via a main switch (205). The inverter (206) converts the DC from the photovoltaic modules (201) to AC to power a transformer (208) via a switch (207). The transformer output is connected to an existing AC network. These PV systems can operate grounded or floating; both modes have advantages and disadvantages, but in either case, it is very important to detect ground fault currents.

[0036] DC systems can operate in three ways: a first way called “floating”, as shown in Figure 3-a, in which, in this mode the PV system is isolated from the earth, if one of the poles (302) makes contact with the earth (306), there would be no current in circulation until, if the other pole (303) makes contact with the earth, then a short circuit occurs from positive to negative, therefore neither of the poles is connected to the earth and in this arrangement it is not possible to detect earth faults since there is no path for the current to circulate through the earth and return to the source.In a second configuration, called “grounding one of the poles,” as shown in Figure 3-b, the negative pole (313) is already grounded (316). Therefore, fault detection is only possible when the positive pole (312) is grounded, causing a short-circuit fault. Consequently, although there is a ground connection, it only detects ground faults at the ungrounded pole. Finally, the third configuration can be called “referencing the system to ground by means of a voltage divider,” as shown in Figure 3-c. In this configuration, the PV system is partially grounded, allowing a ground fault (326) at any point in the PV system before the inverter (325) to cause a current to flow through the grounding point (327) of the voltage divider (328). This offers advantages for use in detecting ground faults, such as those described in the present invention.

[0037] According to the present invention, the system consists of conditioning the PV system as illustrated in Figure 4. In this system, the PV system consists of several branches (408), each branch can consist of several photovoltaic modules (401) connected in series called strings, each branch or string has protection by an ITM (403) which also serves as a disconnector with the concentrating node (400),The PV system includes a battery bank (402) connected to the concentrator node via an ITM (403). The concentrator node (400) is connected to the inverter (406) via the main switch (404). The PV system is grounded (407) through the voltage divider (405), whose resistors must have the same value so that the voltages at each of the (+) and (-) terminals are equal with respect to ground (407). A DC current detector (DCD) (410) is connected to the ground connection of the voltage divider (405) to measure the current (413) flowing through the ground. Under normal conditions, all currents (411) flow to the (+) terminal of the concentrator node, from there to the (+) terminal of the inverter (406), and eventually to the battery (402). A ground fault (412) at any point in the PV system produces a current (413) that necessarily flows through the grounding point of the voltage divider (405). On the other hand,In each of the branches (408) composed of two conductors emanating from the concentrating node (400), the current is evaluated by the differential magnetic detector (DDM) (409) to determine if a differential current exists and to quantify it. The differential current at this point indicates the presence of a ground fault in that branch. Therefore, the PV system is conditioned to achieve the objective of the present invention by means of the following actions: referencing the PV system to ground using a voltage divider (405),This allows balancing the potential difference of (+) and (-) against ground regardless of the value of the voltage divider resistors, provided both are the same value in ohms. This grounding of the PV system (405) should preferably be unique for the entire PV system so that any fault current at any point in the system must flow through this grounding point and can be quantified. Being the only grounding point of the PV system allows quantifying the magnitude of a ground fault current. The voltage divider (405) allows limiting the maximum magnitude of the fault current by setting the divider resistor values ​​based on the maximum current that the PV system operator establishes as acceptable or convenient. Therefore,The PV system operator is permitted to set the maximum ground fault current value such that it does not damage the PV system components and does not affect the continuity of the PV system's power generation service. Therefore, by complying with the above, obtaining the resistance values ​​of the voltage divider (405) to ground the common point of the divider will prevent the PV system from disconnecting due to a ground fault. Furthermore, the proposed scheme is improved by adding a battery bank (402) that would provide the necessary energy for the ground fault detectors to operate during periods of low sunlight. If this battery bank were of high capacity, it could store the energy generated during the day for use at night.

[0038] Even though this principle makes it possible to detect and conveniently handle ground faults in a PV system, the present invention emphasizes the philosophy of ensuring that a ground fault exists in the PV system by applying two different methods for fault detection. The first method involves detecting a current circulating through the DCD (410) connected directly to the common point of the divider (405) without identifying the faulted circuit. The second method involves detecting the magnetic field produced by the differential current, which represents the ground fault current in the faulted circuit. This second method allows for the identification of the faulted circuit by installing DDMs (409), one in each circuit or string.

[0039] This identification is performed at the point where each branch (408) or string connects to the concentrating node (400). This requires devices capable of detecting a difference in the currents of the two conductors, positive and negative, of each branch or string. These devices are the ground fault current detectors in each branch, and we have named them Differential Magnetic Detectors (DDM) (409). The DDMs must be located in each branch or circuit near the switches (403) so that the faulted branch can be easily isolated from the concentrating node (400). These devices must identify which circuit is carrying the ground fault current, which is simultaneously flowing through the grounding point of the voltage divider (405).The DDM (409) identifies a fault current by detecting the magnetic field produced by the difference between the input and output currents of each branch; that is, it obtains the differential current of the circuit. This is done indirectly by comparing the magnetic fluxes generated by the currents flowing through the two wires (positive and negative) in each branch or string. Details of the measurement procedure for this type of device have been proposed and presented in Mexican patent MX370515. Confirmation of the presence of a ground fault in an identified branch can be performed using a logic gate (AND) that combines the results of the two detection methods: the current signal detected by detector (410) with the differential current detected by each of the detectors (409).To generate indicators and report the presence of a ground fault, illuminated LEDs or any other type of indicator can be used, including, in certain configurations, dry contacts for local or remote audible alarms. It is highly advisable to ground the PV system using a voltage divider (405) to reduce the magnitude of the fault current, thereby reducing the power dissipation and the possibility of overheating of conductors and other PV system components through which this current would flow. This allows the system to continue operating without the need to trip the main circuit breaker (404).

[0040] An illustrative, but not limiting, example of the parameters used in the system proposed in the present invention consists of determining the value of the voltage divider resistors for a 250 VDC system to limit the ground fault current to 500 milliamperes. For example, the simplified form shown in Figure 2 allows visualization of the fault current path as shown in Figure 5-a, in which the battery (502) is the source that powers the circuit, and resistors R1 (505) and R2 (506) of the voltage divider (504) limit the current under fault and non-fault conditions, while also serving as a ground reference. Theoretically the RF value (507) will be infinite under “no fault” conditions, therefore the IR1 (508) and IR2 (509) currents will be equal and will have a value of around 0.25 amperes, while the fault current (510) will be 0 amperes.Under direct fault conditions, when the (+) node is directly connected to ground, the value of RF (507) will be equal to zero. In this condition, the maximum fault current will circulate and will be limited only by R2 (506). The value of the fault current “IF” (510) will be equal to the current IR2 (509) and will be around 0.5 amperes, while IR1 (508) will be very close to 0 amperes. To quantify the fault current, a DCD (511) direct current detector element is inserted in the grounding cable.

[0041] To limit fault current and prevent damage to the electrical system, values ​​of approximately 0.5 amperes have been proposed as the maximum ground fault current. However, other values ​​can be established as needed. Figure 5-a illustrates that for a direct (+) to ground fault, assuming the RF value is set to "0", resistor R2 is the only component limiting the fault current. In this case, the fault current is limited to a maximum of 500 milliamperes for any voltage level. Therefore, a different resistance value for the voltage divider is determined for each voltage level.An alternative to the voltage divider described in Figure 5-a is the arrangement proposed in Figure 5-b, where the voltage divider (520) consists of the batteries (523 and 524) connected in series, and the midpoint (521) is connected to ground (527) through resistor R0 (525). This resistor acts as a ground fault current limiter, so that if a positive-to-ground fault occurs, the value of RF (526) will be equal to 0. Therefore, the value of IF (528) will only be limited by the value of R0 (525), with the battery (523) as the sole source. To quantify the fault current, the DCD (522) is inserted in the grounding circuit.

[0042] In a more detailed and explanatory concept of the present invention in a PV installation, one of the preferred implementation methods of the system of the present invention is described below, following the procedure described. Given the extensive areas where PV modules are installed in a plant, it is very important that they be separated into several circuits; therefore, it is necessary to monitor and detect ground faults in each circuit independently.As shown in Figure 7, in one of the preferred implementation modes of the present invention consists of a system for the protection of the PV system composed of a voltage divider (705) to reference the PV system to ground, a Concentrating Logic Module (CLM) (710) of PV system ground fault detection devices, in which a particular mode is shown individually in Figure 6, (which can be referred to as 64FV following the nomenclature defined by the ASA).As shown in Figure 7, the proposed system for detecting ground faults in a PV system consists of: a voltage divider (705) to ground the PV system, which includes the ground fault current limiting resistors; a direct current ground fault detector (DCD) (706); a plurality of differential magnetic current detectors (DDMs) (707), distributed in each of the monitored branches; and a battery bank (702) (not essential), which would provide power to the PV system in the absence of photovoltaic generation. The Concentrating Logic Module (CLM) (710) receives the signal from the DCD (706) indicating the presence of a ground fault for the 64FV logic signal (from Figure 6).The MLC (710) also receives signals from the Differential Magnetic Detectors (DDM) (707 and 708), which identify the faulted circuit. The detector signals are carried to the MLC via multi-conductor cable (709) with shielding. The Logic Concentrator Module (MLC) (710) groups the 64FV protection devices shown in Figure 6, one for each branch or protected circuit. It signals the occurrence of a transient fault with three current levels using visual or other signals, in this case, yellow LEDs with manual reset. In the event of a permanent fault, the red LED illuminates to indicate the fault locally, and a relay with dry contacts is activated to transmit this signal to remote locations, such as an alarm annunciator or a digital event recorder. The voltage divider consists of a pair of resistors of the same value connected in series, with their common point connected to ground.The resistor values ​​are determined to limit the ground fault current to a maximum of approximately 500 milliamperes, while simultaneously balancing the voltages with respect to ground under normal operating conditions. In this configuration, there is a single voltage divider for the entire PV system, while the grounding conductor passes through the DCD to quantify the ground fault current.

[0043] Regarding the ground fault protection device in 64FV photovoltaic systems of Figure 6, it consists of an electronic circuit that can be powered by voltages of 24, 48 or 120 Ved, which contains discrete electronic elements for its operation such as comparators and logic circuits, which operate with external analog signals, one signal from a differential magnetic detector (DDM), which is shown illustratively in Figure 9-a, and another from a direct current detector (DCD) of Figure 9-b.

[0044] More specifically, what is shown in Figure 6 is the 64FV protection circuit (Ground fault detector in Photovoltaic Systems) which consists of a logic circuit powered by two external signals, one signal from a differential magnetic detector (DDM) and another from the direct current detector (DCD).The DDM (Differential Magnetic Detector) is composed of two Hall effect sensors (600) whose output signals are filtered and mixed (601) and then passed to a conditioning stage (602) before being carried to the logic module through a multi-conductor cable with shielding mesh (603). This signal is distributed to three intensity level comparators, level 1 (604), level 2 (605) and level 3 (606), which, depending on the magnitude of the fault current, will cause the light emitting diodes (611) to turn on and latch. The latching occurs through the action of the memory switches (Flip Flop) (609). This mechanism will allow the detection of transient faults that may occur in the monitored circuit or branch (example: momentary fault occurring during an atmospheric discharge). To reset the turned-on diodes, the button (615) must be pressed.Thus, to confirm and declare that there is a permanent fault in the circuit or branch, the signal from the ground fault current detector (GFCD) (607) is required. This signal is amplified (616) and carried by a shielded cable (603) to the comparator (608) of the logic module. If the GFCD signal reaches the level set in comparator 608, its output is activated to turn on LED 617. The logic gate (AND) (610) checks for the presence of the two signals, one from comparator (605) and the other from comparator (608). If both signals are present, LED (612) turns on and the relay (613) is activated, whose contacts (614) will close to indicate the presence of a ground fault in the monitored circuit.

[0045] In this way, the analog signal from the DDM is distributed to different comparators set to different current intensity levels, for example, low, medium, and high. These comparators activate their output depending on the magnitude of the fault current, causing light-emitting diodes (LEDs) to illuminate and latch. These LEDs indicate the occurrence of a transient fault, such as a momentary fault during a lightning strike. For example, when a fault that could be considered transient occurs, the LED(s) where the received signal exceeds the level set on the comparator illuminate. The LEDs remain illuminated due to the latching elements (flip-flops). This mechanism allows for the detection of transient faults that may occur in the monitored circuit or branch. To reset the illuminated LEDs, the reset button must be pressed.In the case of a fault that can be considered permanent, it is determined by the presence of two conditions of the PV system using an AND logic gate. The first condition is the detection of a current flowing to ground through the grounding point by the DCD (Direct Current Detector), and the second condition is the detection of a differential current in the faulted circuit by a DDM (Dynamic Current Detector). The analog signal from the DCD is evaluated by a comparator preset to a certain current level. When the preset current level is exceeded, the comparator's output is activated, which is considered a present logic value and indicates the presence of a ground fault current.The signal from the DDM is evaluated by the average level comparator. If the magnitude of the differential current exceeds the preset level of the comparator, its output is activated. This output is considered a logic present value and indicates the presence of a differential current, detected indirectly by its magnetic field, thus indicating a ground fault current in the monitored circuit. An AND gate evaluates the presence of both signals, DCD and DDM. If both outputs are present, the AND gate output is activated, turning on a fourth LED and an output relay. The LED and relay will remain activated as long as a ground fault exists. The activated relay keeps its contacts closed, which can be used to transmit information about the presence of a ground fault in a given circuit to remote monitoring or recording stations.

[0046] As shown in Figure 9-a, the DDM is a device composed of a ferrite core, split into several parts, in this case shown in two parts, so that it can be disassembled and placed over the conducting wires that carry a direct current, wrapping or embracing them to capture the magnetic field produced by the two conductors simultaneously.It should be mentioned that this type of Differential Magnetic Detector (DDM), as represented in this invention, represents an improved version of the one described in Mexican patent MX 370515 of November 2019, which consists of a core wound with the wires that carry the positive and negative current in order to amplify the magnetic flux that would represent a very small current. More specifically, this improved version of the DDM is composed of a ferrite core, preferably circular in shape (900), split into two parts so that it can be disassembled and placed over the two positive (905) and negative (906) conducting wires that carry a direct current, embracing them to capture the magnetic field produced by the two conductors simultaneously.At the two junction points of the sectioned core are placed two Hall effect detectors (901), one at each junction point, which are responsible for detecting the presence and intensity of a magnetic flux. Under "no fault" conditions, the two currents flowing through the two conductors (905) and 906) produce equal magnetic fields that cancel each other out. However, when a ground fault occurs, a difference in the currents between the two conductors will be produced, and this differential current will generate a magnetic field that will flow through the magnetic core (900). This same magnetic field will be detected by each of the Hall effect sensors (901).The signals produced by the sensors (901) are carried to the electronic board (902) by means of the cables (903). On the board (902), the signals pass through a low-pass filter, to a mixer and then to a conditioner-amplifier. The output signal of the amplifier is available to be carried by a multi-conductor cable (904) to the concentrator logic module (MLC) shown in Figure 8. At the two junction points of the sectioned core, two Hall effect detectors are placed, one at each junction point, which are responsible for detecting the presence and intensity of a magnetic flux.Under "no fault" conditions, the two currents flowing through the two conductors produce equal magnetic fields that cancel each other out. However, when there is a ground fault, a difference in the currents between the two conductors will occur, and this differential current will cause a magnetic field that will flow through the magnetic core, and this same magnetic field will be captured by each of the Hall effect sensors.

[0047] The DCD detector, as schematically represented in Figure 9-b, is associated with the voltage divider, where the DCD detector (920) is an electronic device consisting of a resistor connected between the common point of the voltage divider (921 and 922) and ground (924). When the ground fault current flows through the resistor, it produces a voltage drop, which is amplified and conditioned to be sent to the MLC through cable 923. This potential difference is proportional to the current flowing, and this signal is amplified and sent directly to the concentrating logic module (MLC).

[0048] In accordance with the configuration shown in Figure 8, which serves as an explanation, we have what is called the Concentrating Logic Module (CLM). As shown in this figure, it is an arrangement that can be housed in an enclosure containing multiple 64FV SFV fault detection elements, such as those shown in Figure 6. The rear of the cabinet contains inputs for the signal from the DCD and the signals from the DDM, as well as connection points for the output contacts of each 64FV. The front of the cabinet has four LEDs that indicate the status of each monitored circuit: three for transient fault detectors at levels 1, 2, and 3, and the fourth LED indicating a permanent fault in the monitored circuit. It also has a button to reset all the LEDs.Specifically, a signal is received from DCD (800), which is evaluated by comparator 801. Its output (815) is activated if the value set by comparator (801) has been exceeded, which also illuminates LED (816). It also receives multiple DDM signals (802) from various monitored or supervised circuits. Signal 802 is evaluated by comparators (803, 804, and 805). The comparator outputs are determined by the magnitude of the received signal (low, medium, or high). If the received signal (802) is low, comparator 1's output is activated to produce signal (803), which then activates LED 807, which is latched by the corresponding memory (806). If the signal (802) reaches the medium level, the output of comparator 2 is activated to obtain the signal (804), which activates the “led” 808, being latched by the corresponding memory (806).If signal (802) reaches a high level, comparator output 3 is activated to generate signal (805), which activates LED 809, latching it via the corresponding memory (806). When signal 804 is received, it is fed to the AND gate (810), which activates LED (811) provided it also presents the DCD signal (815). The illumination of LED (811) confirms a fault in circuit 2, as both the DCD signal (815) and the DDM signal are present. The output of gate (810) also activates relay (812), whose dry contacts (813) close upon activation. These contacts can be used to activate remote signaling indicating a ground fault in one of the PV circuits. A push button (814) is used to reset any of the fault indication signals on the LEDs.

[0049] In accordance with all of the above, a system has been proposed that facilitates the protection against ground faults of PV systems, preferably using 64FV type detectors, where in PV systems the magnitude of the ground fault current can be controlled to values ​​less than around 500 milliamperes, applying a grounding scheme using a potential divider with resistors of predetermined values.

[0050] Having described the present invention, the contents of the following are considered novel and therefore claimed as property:

Claims

CLAIMS.

1. A ground fault detection system in photovoltaic systems, characterized in that the procedure consists of: referencing the photovoltaic system to ground; balancing the potential difference of positive and negative against ground; detecting the current of a ground fault; limiting the fault current to values ​​that do not affect the continuity of operation of the photovoltaic system; identifying the circuit or branch that presents the ground fault; and generating signals, reports and reports of the ground fault.

2. The ground fault detection system in photovoltaic systems of claim 1, wherein the referencing of the photovoltaic system is carried out by means of a voltage divider whose resistances are preferably of the same value.

3. The ground fault detection system in photovoltaic systems of claims 1 and 2, characterized in that a direct current detector is connected to the ground connection of the voltage divider, said voltage divider being formed by a plurality of resistors, which are preferably two resistors.

4. The ground fault detection system in photovoltaic systems of claim 3, characterized in that it may be composed of a plurality of direct current sources, preferably two sources connected in series, wherein said sources may be two battery banks.

5. The ground fault detection system in photovoltaic systems of claims 1, 3 and 4, wherein the detection of the ground fault current is carried out by quantifying the current flowing through the earth.

6. The ground fault detection system in photovoltaic systems of claim 1, wherein said referencing of the PV system to ground is preferably unique for the entire PV system.

7. The ground fault detection system in photovoltaic systems of claim 1, characterized in that it allows limiting the maximum magnitude of the fault current, preventing damage to the PV system or its continuity of service, and also having a battery bank.

8. The ground fault detection system in photovoltaic systems of claim 1, characterized in that each branch, photovoltaic circuit or string, is preferably connected to a concentrating node by means of devices capable of detecting a difference in the currents of the two conductors, positive and negative of each branch or string.

9. The ground fault detection system in photovoltaic systems of claims 1 and 8, characterized in that said devices are magnetic differential type detectors.

10. The ground fault detection system in photovoltaic systems of claim 9, characterized in that said magnetic differential detectors are located in each of the branches or circuits and close to the switches so that the faulted branch can be easily separated from the concentrating node.

11. The ground fault detection system in photovoltaic systems of claims 1 and 8, characterized in that the confirmation of the presence of a ground fault in an identified branch is carried out by means of a logic gate (AND) combining the output of the direct current detector with the output of any of the magnetic differential detectors located in each of the branches.

12. The ground fault detection system in photovoltaic systems of claim 11, characterized in that luminous, audible or any other type of indicator signals can be enabled that can be monitored on site or remotely to detect the existence of ground faults in the photovoltaic system.

13. The ground fault detection system in photovoltaic systems of claims 1 to 11, characterized in that a voltage divider is preferably used to reduce the magnitude of the fault current, thereby reducing the power dissipated and the possibility of overheating of conductors and other components of the PV system.

14. The ground fault detection system in photovoltaic systems of claims 1 and 8, characterized in that a battery supplies the voltage divider resistors that limit the current under fault and "non-fault" conditions, while serving as a ground reference.

15. The ground fault detection system in photovoltaic systems of claim 14, characterized in that the fault value is limited to a maximum value of 500 milliamperes for any voltage level, whereby a different resistance value for the voltage divider is determined for each voltage level.

16. The ground fault detection system in photovoltaic systems of claim 1, characterized in that it comprises: a voltage divider for referencing the PV system to ground, a Logic Module Concentrator of ground fault detection devices in PV systems; a direct current ground fault detector; a plurality of magnetic differential detectors; and preferably a battery bank.

17. The ground fault detection system in photovoltaic systems of claims 7 and 16, characterized in that the direct current detector is of the 64FV type.

18. The ground fault detection system in photovoltaic systems of claim 16, characterized in that the concentrating logic module is a board where the signals from the direct current detector and the magnetic differential detectors of each of the branches are received, thereby identifying the faulted circuit, and where said detector signals are preferably conducted by means of multi-conductor cable with shielding mesh.

19. The ground fault detection system in photovoltaic systems of claim 18, characterized in that the concentrating logic module allows signaling the occurrence of a transient fault, emitting local or remote event recording signals 20. The ground fault detection system in photovoltaic systems of claim 16, wherein the ground fault protection device in The 64FV photovoltaic system consists of an electronic circuit that can be powered by voltages of 24, 48 or 120 Ved, containing discrete electronic elements for its operation such as comparators and logic circuits, which operate with external analog signals, a signal from a magnetic differential detector and a direct current detector.

21. The ground fault detection system in photovoltaic systems of claim 16, characterized in that the magnetic differential detector is composed of a metal core that can be split into several parts to be assembled in contact with the conducting cables that carry a direct current, detecting the magnetic field produced by the two conductors.

22. The ground fault detection system in photovoltaic systems of claim 16, characterized in that the direct current detector is associated with the voltage divider, and consists of a resistor connected between the common point of the voltage divider and the ground.

23. The ground fault detection system in photovoltaic systems of claim 16, characterized in that the concentrator logic module can be in the form of a board containing a plurality of fault detection elements in PV systems, with inputs for the signal from the direct current detector and the magnetic differential detector(s), and can also house visibly luminous or audible indicators of the faults presented in the system, and with devices for sending local or remote signals for notification, control or recording of ground fault events of the photovoltaic system.

Images