ES2930209B2 - Ground fault locator for an electrical circuit, electrical circuit and method of locating ground faults - Google Patents

Description

DESCRIPTION

Ground fault locator for an electrical circuit, electrical circuit and method of locating ground faults

TECHNIQUE SECTOR

The present invention belongs to the technical field of ground fault detectors in an electrical circuit. More particularly it belongs to the technical field of ground fault locators and ground fault location methods.

BACKGROUND OF THE INVENTION

Electrical systems increasingly require more efficient operations and controlled processes. In this aspect, power electronics, and specifically converters, for example, inverters, rectifiers or bidirectional converters, acquire great importance. A system with a considerable set of converters is usually subject to a direct current microgrid, where the transmission of power between the different connected devices is carried out by direct current wiring.

Although these systems have a higher efficiency than conventional distribution systems, their protection is of particular relevance to avoid dangers to human health as well as to the devices involved in the system. Not many inventions are capable of protecting these systems as a whole without sacrificing coordination between multiple protections, particularly against ground faults, which are the most common faults in this type of systems. It is estimated that between 60% and 80% of electrical failures are caused by ground faults.

Generally, ground faults occur due to degradation of the insulation of the active parts of the electrical system. This occurs gradually due to overvoltages, overcurrents, heating, wear over time,... In this way the fault resistance, which is inverse to the severity of the defect, will decrease until it is zero, where the ground fault will be the most serious possible. Additionally, another difficulty lies in the type of grounding of this type of systems, which are usually high impedance or neutral isolated from ground, so a first ground fault is difficult to detect due to the low fault currents. .

Some inventions manage to detect or even locate faults in the direct current section of the network, such as in patent US 2016/0336899 A1 “PHOTOVOLTAIC SYSTEMS WITH ABNORMALITY DETECTION ARCHITECTURE”, where DC/DC converters are used, that is, current converters. continuous in direct current, like relays current differentials for photovoltaic systems based on the current difference at the input and output of said converter. If the branch controlled by the DC/DC converter has the defect, that converter will detect the current and trigger the alarm.

Differential protections can also be used in electrical drives of AC/AC converters, that is, converters from alternating current to alternating current, with a single network connection. In “T. Gruhn, J. Glenney and M. Savostianik, "Type B Ground-Fault Protection on Adjustable Frequency Drives," in IEEE Transactions on Industry Applications, vol. 54, no. 1, pp. 934-939, Jan.-Feb. 2018.”, it is proposed to place the neutral of a transformer rigidly or with low impedance and place a toroid that measures the differential current in the phases of the low side of said transformer. In this way, if a fault occurs, the current measured by the toroid is different from zero, and it must trip. However, several problems arise in this type of inventions. If the faults occur on the direct current side, the toroid can saturate, and with a single differential the area where the ground fault occurs cannot be distinguished.

Other inventions such as US patent 9007735 B2 “FAULT DETECITON, ISOLATION, LOCATION AND RECONNECTION SYSTEMS AND METHODS” use rigidly grounded artificial midpoints referred to as “probe power units”. These systems are static and require communication between them in order to have selectivity when triggering when a defect occurs. Both systems are only focused on the central direct current zone of a microgrid but are capable of locating ground defects and even defects between phases.

In other systems and methods, such as that described in the invention patent ES 2798348 B2 “METHOD AND SYSTEM FOR DETECTION OF GROUND FAILURES IN ELECTRICAL INSTALLATIONS WITH CONVERSION BETWEEN DIRECT CURRENT AND ALTERNATING CURRENT” a grounding resistance is used in a single neutral point of the installation to protect electrical drives of AC/AC converters with an intermediate direct current stage. These types of systems are linear, so with a single ground point the defect is easily detectable. If there are multiple connections to the intermediate direct current network and several network connections, the system becomes complicated and a single ground point cannot distinguish between drives, network sides, or direct current areas where the defect occurs.

Finally, in the invention ES 2869451 A1 “SYSTEM AND METHOD FOR LOCATION OF EARTH FAULTS IN DIRECT CURRENT ELECTRICAL INSTALLATIONS” multiple connections are used to a single direct current system with several batteries.

This switching system allows the variation of the grounding resistance with the objective of locating the percentage of impedance of direct current sources where the ground fault occurs. In the case of linear systems for converting direct current into alternating current, such as an electric vehicle, said invention is capable of detecting ground faults also on the alternating current side, not being valid when the system is meshed by inserting many converters.

With the previously mentioned inventions, the protection of electrical systems with multiple converters can be solved by coordinating them. However, it is necessary to have systems and methods for detecting ground faults in systems with multiple converters that make it possible to correct the deficiencies presented by the previous state of the art, avoiding communication between many protections, or having several protections and being able to collect all of them. in one, or increasing the degree of detection thereof, being able to discern the area where the defect occurs regardless of the topology of the system with converters.

GENERAL DESCRIPTION OF THE INVENTION

The present embodiments of the invention are intended to address all of the limitations presented in the prior art.

The present invention makes it possible to locate ground faults in an electrical circuit from voltage measurements at various points of the electrical circuit.

A first aspect of the present invention relates to a ground fault locator, also known as a ground fault locating device, for an electrical circuit; understanding the locator:

- electrical connections to electrically connect points of an electrical circuit to ground, each electrical connection having a switch;

- a voltage meter configured to measure voltage waves of electrical connections with the switch closed;

- processing means communicatively connected to the tension meter, the processing means being configured to perform the following steps:

a) receive a measurement of a voltage wave from at least one of the electrical connections;

b) estimate a continuous voltage of a continuous component of the wave of measured voltage and/or estimating an alternating voltage from an alternating component of the measured voltage wave;

c) upon determining that an absolute value of the estimated direct voltage exceeds a ground fault threshold and/or determining that an absolute value of the estimated alternating voltage exceeds a ground fault threshold, close the switch of one of the electrical connections different from the at least one electrical connection of step a) so that the voltage meter measures a voltage wave of the electrical connection different from the at least one electrical connection of step a);

d) receiving the measurement of the voltage wave of the electrical connection other than at least one electrical connection of step a);

e) determine that a portion of an electrical circuit has a ground fault, the determination of the portion of the circuit being based on the measurement of the voltage wave of the electrical connection other than the at least one electrical connection of step a) .

The locator and method for detecting ground faults in electrical systems according to the present invention is of particular use in electrical installations where the presence of converters is high, having several stages of alternating current (AC) and direct current (DC). The present invention is applicable, for example and without limitation, to DC microgrids with/without grid connection, with different stages of direct current (photovoltaic or batteries) and even with electrical drives such as wind turbines or motors.

Since the voltage meter is configured to measure voltage waves of the electrical connections with the switch closed, the measurement of a voltage wave of one of the electrical connections can be enabled by closing the switch of said electrical connection.

The estimate or estimates in stage b) are made based on the measurement received in stage a). The measurement received in step a) is a measurement taken by the tension meter.

The ground fault thresholds are predefinable, that is, definable before taking the measurement received in stage a). Ground fault thresholds can be predefined, for example, based on an electrical circuit configuration.

In some embodiments, the ground fault threshold values are substantially zero volts. These embodiments allow the voltage difference between ends of the electrical connections to be substantially zero volts if the electrical circuit is fault-free. In this way, it is possible to minimize the energy dissipation caused by the ground fault locator while the electrical circuit does not present faults.

A threshold value greater than zero volts allows greater versatility in the location of electrical connections in an electrical circuit, since it is not necessary to connect electrical connections to points in the electrical circuit that have ground voltage.

The determination of stage c) allows ground faults to be detected. The electrical voltage measurement in step d) allows determining in which portion of an electrical circuit the ground fault is present, as explained later with reference to some embodiments.

In step e) the portion of an electrical circuit with a ground fault is determined or, in other words, a location of a ground fault of an electrical circuit is determined.

In some embodiments, each of the electrical connections comprises a current limiting impedance on each side of the electrical connection switch. In other words, the switch electrically connects the current-limiting impedance on one side of the switch to the current-limiting impedance on the other side of the switch. The use of a current limiting impedance on each side of the switch allows the current flowing through the switch to be reduced compared to embodiments in which there is only the current limiting impedance of a single side of the switch. In this way, damage caused by a ground fault can be minimized. Current limiting impedances are, for example, resistors.

In some embodiments, the processing means are configured to estimate the direct voltage and/or estimate the alternating voltage of step b) based on a fast Fourier transform of the voltage wave measurement received in step a). The processing means may be configured to estimate the measured voltage wave based on the measurement of the received voltage wave. The continuous voltage estimate of step b) may be the continuous component of the Fourier transform, in other words, the frequency-free component of the Fourier transform of the voltage wave estimate. The alternating voltage estimate from step b) may be an alternating component of the Fourier transform of the voltage wave estimate. Although in these examples the Fourier transform is used, for example, the fast Fourier transform, to estimate the voltage(s) of step b), in other alternatives these estimates are made without using the Fourier transform. The fast Fourier transform allows Quickly extract information required to locate the ground fault.

In some embodiments, the processing means are configured to perform step c), comprising step c) keeping the switches of the rest of the electrical connections open upon determining that the absolute value of the estimated continuous voltage exceeds the ground fault threshold. and/or determine that the absolute value of the estimated alternating voltage exceeds the ground fault threshold. In this way, only the switch of the electrical connection other than the at least one electrical connection of step a) is closed; the switches of the rest of the electrical connections, including the at least one electrical connection of stage a), being open. In this way, the precision of locating the ground fault can be increased, since a voltage of a single electrical connection is measured instead of a sum of voltages of several of the electrical connections.

Additionally, by observing the polarity of the voltage it can be estimated whether the fault takes place on the positive pole (direct current component in the negative grounding device) or if it takes place on the negative pole (direct current component in the negative grounding device). the positive grounding device).

In some embodiments, the processing means is configured to keep the switch of one of the electrical connections normally closed and to keep the switches of the rest of the electrical connections normally open; the at least one electrical connection of step a) being a single electrical connection and the switch of the electrical connection of step a) being normally closed. In this way, the voltage meter measures the voltage wave of a single electrical connection, avoiding the need to close and/or open switches of other electrical connections to take the measurement of the voltage wave received in step a).

In some embodiments, the processing means is configured to perform the determination of step e) by comparing the absolute value of the continuous voltage estimate of step b) with an absolute value of an estimate of a continuous voltage of a continuous component of the voltage wave of the electrical connection other than the at least one electrical connection of step a); the processing means being configured to indicate that the ground fault is closer to the electrical connection with the highest absolute value of the direct voltage estimate than to the electrical connection with the lowest absolute value of the direct voltage estimate. These embodiments make it possible to more precisely locate ground faults of a portion of an electrical circuit, the portion being configured to have direct voltage. Specifically, a relatively greater absolute value with respect to the other absolute value indicates greater proximity between the ground fault and the electrical connection with the greater absolute value than between the ground fault and the electrical connection with the lowest absolute value.

In some embodiments, the processing means are configured to determine in step e) that the portion of the electrical circuit with a ground fault is between two electrical connections, the two electrical connections having voltage waves with the two highest absolute values. of DC voltage estimates of a DC component compared to the absolute values of DC voltage estimates of a DC component of the voltage waves of the rest of the electrical connections. It has been observed that this is the usual location of ground faults in a portion of the circuit configured to have direct voltage.

In some embodiments, the processing means are configured to generate an alarm signal based on the measurement of the voltage wave of the electrical connection other than the at least one electrical connection of step a). The alarm signal allows you to alert of a ground fault in a specific portion of an electrical circuit.

In some embodiments, the alarm signal comprises location data for a portion of a circuit determined in step e). This alarm signal can be used to detect a location of a ground fault.

A second aspect of the present invention relates to a ground fault locator according to the first aspect of the invention and to protections for an electrical circuit, the processing means being configured to select at least one of the protections and activate the at least one. of the protections selected, the selection being based on the measurement of the voltage wave of the electrical connection other than the at least one electrical connection of step a). Since the measurement of the voltage wave of the electrical connection other than the at least one electrical connection of step a) allows locating the ground fault of an electrical circuit, this measurement can be used to activate a protection configured to protect against faults. to ground at the location of the ground fault determined in step e).

A third aspect of the present invention refers to an electrical circuit, the electrical circuit comprising a ground fault locator according to the first aspect of the invention and one or more converters, the electrical connections of the locator connecting points of the electrical circuit to ground; and the processing means being configured so that the alternating component of step b) has a frequency equal to a fundamental frequency of a polyphase portion of the electrical circuit.

In some embodiments, the electrical circuit points are at least one neutral point of a polyphase portion of the electrical circuit and/or at least a midpoint of a portion of the electrical circuit configured to have direct voltage; and the ground fault threshold values being substantially zero volts. In this way, the at least one neutral point and the at least one midpoint of the portion of the circuit configured to have direct voltage have the ground voltage if the electrical circuit does not have ground faults. In this way, since the electrical connections connect these points to ground, no current flows through the electrical connections if there is no ground fault and consequently the voltage measured by the voltage meter is substantially zero volts. The midpoint of the portion of the electrical circuit configured to have direct voltage is a point at a voltage less than the maximum voltage of the circuit portion and greater than the minimum voltage of the circuit portion. Given a portion of the circuit with a maximum voltage Vcc+ and a minimum voltage Vcc-, the midpoint voltage is preferably:

The connection to the midpoint allows the ground fault detection capability of the ground fault locator to be improved compared to embodiments in which the ground fault threshold values are substantially zero volts but the electrical circuit points to which The electrical connections of the locator are connected to points at the maximum voltage Vcc+ and/or at the minimum voltage Vcc-. This is because the midpoint voltage is different from the maximum Vcc+ and minimum Vcc- voltages of, for example, respectively a positive pole and a negative pole of the portion of the circuit configured to have direct voltage. Therefore, in the event that ground faults occur on the positive pole or the negative pole, the locator can detect these ground faults. On the contrary, if the points to which the electrical connections are joined were points of the positive pole at the maximum voltage Vcc+, a ground fault in said positive pole would not be detectable by the locator because the voltage of the positive pole would be the same as the ground voltage and consequently no current would flow through the electrical connections, not exceeding the ground fault threshold value of substantially zero volts. The expert in the field understands that, for equivalent reasons, the connection to the neutral point allows the ground fault detection capacity to be improved.

Furthermore, if the points to which the electrical connections are connected were points of the positive pole at the maximum voltage Vcc+, in the event that a second ground fault occurred in the circuit, the current could flow through the first ground fault. instead of circulating through the electrical connections of the ground fault locator, making it difficult or impossible to detect the second ground fault. On the contrary, if the points to which the electrical connections are connected are the midpoints, the detection of the second ground fault would be facilitated.

In some embodiments, the processing means is configured to perform the determination of step e) by comparing the absolute value of the alternating voltage estimate of step b) with an absolute value of an estimate of an alternating voltage of an alternating component of the voltage wave of the electrical connection other than the at least one electrical connection of step a), the alternating component having a frequency equal to the fundamental frequency of the polyphase portion of the electrical circuit; the processing means being configured to indicate that the ground fault is closer to the electrical connection with the highest absolute value of the alternating voltage estimate than to the electrical connection with the lowest absolute value of the alternating voltage estimate. In this way, two alternating components are compared with the frequency equal to the fundamental frequency of the polyphase portion of the electrical circuit. These embodiments make it possible to more precisely locate ground faults of a portion of an electrical circuit, the portion being configured to have voltage at the fundamental frequency of the polyphase portion of the electrical circuit. Specifically, an absolute value, such as an effective value or an amplitude, relatively larger than the other absolute value, indicates greater proximity between the ground fault and the electrical connection with the largest absolute value than between the ground fault and the electrical connection with the lowest absolute value.

In some embodiments, the processing means are configured to determine in step e) that the portion of the electrical circuit with a ground fault is between two electrical connections, the two electrical connections having voltage waves with the two highest absolute values. of alternating voltage estimates of an alternating component compared to the absolute values of the alternating voltage estimates of an alternating component of the voltage waves of the rest of the electrical connections; the alternating component having a frequency equal to the fundamental frequency of the polyphase portion of the electrical circuit. It has been observed that this is the usual location of ground faults in a portion of the circuit configured to have alternating voltage.

In some embodiments, the processing means are configured to perform the determination of step e) based on a measurement of an alternating voltage of an alternating component of the voltage wave of the electrical connection other than the at least one electrical connection of step a), having the alternating component a frequency equal to a switching frequency of a converter of the electrical circuit. A non-zero measurement of alternating voltage at said frequency or a measurement of alternating voltage at said frequency whose amplitude or rms value is greater than, respectively, the amplitude or rms value of the alternating voltage at said frequency of other electrical connections is indicative that the ground fault is not in the portion of the circuit directly connected to the electrical connection other than the at least one electrical connection of stage a). Specifically, a non-zero measurement of alternating voltage at said frequency or a measurement of alternating voltage at said frequency whose amplitude or rms value is greater than, respectively, the amplitude or rms value of the alternating voltage at said frequency of other electrical connections is indicative that a converter with said switching frequency electrically connects the ground fault with the electrical connection other than the at least one electrical connection of step a). This is because the alteration produced by the ground fault interacts with the converter, generating an alternating voltage at said frequency in the portion of the circuit connected to the converter on the side of the converter other than the side of the converter connected to the ground fault.

In some embodiments, the processing means are configured to perform the determination of step e) based on a measurement of an alternating voltage of an alternating component of the voltage wave of the electrical connection other than the at least one electrical connection of stage a), having the alternating component a frequency equal to a third harmonic of a converter of the electric circuit. The third harmonic of the converter is the third harmonic of an input voltage and/or an output voltage of the converter. A non-zero measurement of alternating voltage at said frequency or a measurement of alternating voltage at said frequency whose amplitude or rms value is greater than, respectively, the amplitude or rms value of the alternating voltage at said frequency of other electrical connections is indicative that the ground fault is not in the portion of the circuit directly connected to the electrical connection other than the at least one electrical connection of step a). Specifically, a non-zero measurement of alternating voltage at said frequency or a measurement of alternating voltage at said frequency whose amplitude or rms value is greater than, respectively, the amplitude or rms value of the alternating voltage at said frequency of other electrical connections is indicative that a converter with said third harmonic electrically connects the ground fault with the electrical connection other than the at least one electrical connection of step a). This is because the disturbance produced by the ground fault interacts with the converter, particularly if the converter comprises passive electronic components such as diodes, generating an alternating voltage at the frequency of the third harmonic in the portion of the circuit connected to the converter by the side of the converter other than the side of the converter connected to the ground fault.

A fourth aspect of the present invention refers to a method of locating ground faults of an electrical circuit, the electrical circuit comprising one or more converters; and understanding the method the stages:

a) measure a voltage wave to ground from a point in the electrical circuit;

b) estimating a direct voltage from a direct component of the measured ground voltage wave and/or estimating an alternating voltage from an alternating component of the measured ground voltage wave;

c) upon determining that an absolute value of the estimated direct voltage exceeds a ground fault threshold and/or determining that an absolute value of the estimated alternating voltage exceeds a ground fault threshold, measure a ground voltage from another point on the electrical circuit, the other point of the electrical circuit being different from the point in step a);

d) measure a voltage wave to ground from the other point of the electrical circuit;

e) determining that a portion of an electrical circuit has a ground fault, the determination of the portion of the circuit being based on the measurement of the voltage wave in step d).

A fifth aspect of the present invention relates to the method of the fourth aspect of the present invention realized by the ground fault locator of the first aspect of the present invention or by the electrical circuit of the third aspect of the present invention.

The different aspects and embodiments of the invention defined above can be combined with each other, as long as they are mutually compatible.

Additional advantages and features of the invention will become apparent from the following detailed description and will be particularly noted in the appended claims.

BRIEF DESCRIPTION OF THE FIGURES

In order to help a better understanding of the characteristics of the invention according to examples of practical embodiments thereof, a set of drawings is attached as an integral part of the description in which, for illustrative purposes, the following has been represented. following:

Figure 1 shows a part of an electrical circuit according to some embodiments of the invention.

Figure 2 shows a ground fault locator according to some embodiments of the invention.

Figure 3 shows a ground fault locator according to some embodiments of the invention.

Figure 4 shows a method according to some embodiments of the invention. Numerical references of the figures:

(the) First alternating-direct converter;

(lb) First DC-AC converter;

(1c) Second AC-DC converter;

(ld) Second DC-AC converter;

(le) First continuous-continuous converter;

(lf) Second continuous-continuous converter;

(2a) First transformer;

(2b) Second transformer;

(3a) First electrical conductor;

(3b) Second electrical conductor;

(4) Three-phase impedance;

(5) Rotating electric machine;

(6) Electrical energy accumulator;

(7) Set of photovoltaic panels;

(81), (82), (83), (84), (85), (86) Capacitors;

(91), (92), (93), (94), (95), (96) Resistances;

(10a) First connection to a neutral point;

(10b) Second connection to a neutral point;

(10c) Third connection to a neutral point;

(10d) Fourth connection to a neutral point;

(10e) Fifth connection to a midpoint;

(10f) Sixth connection to a midpoint;

(10g) Seventh connection to a midpoint;

(10h) Eighth connection to a midpoint;

(10i) Ninth connection to a midpoint;

(10j) Tenth connection to a midpoint;

(10k) Eleventh connection to a midpoint;

(10l) Twelfth connection to a midpoint;

(11a), (11b), (11c), (11 d), (11 e), (11 f) Frequency signals;

(12) Grounding subsystem;

(13) Normally closed switch;

(14) Normally open switch;

(15) Grounding resistance;

(16) Land;

(17) Tension meter;

(18) Switch controller;

(19) Switch control signal;

(20) Processing means;

(21) Alarm signal;

(22) Fuse;

(23) Additional resistances;

(24) First stage of measuring a voltage wave to ground from a point in an electrical circuit;

(25) Second stage of estimating a direct voltage of a continuous component of the measured ground voltage wave and/or estimating an alternating voltage of an alternating component of the measured ground voltage wave;

(26) Third stage of comparing an absolute value of the estimated direct voltage with a ground fault threshold and/or comparing an absolute value of the estimated alternating voltage with a ground fault threshold;

(27) Fourth stage of closing one or more of the electrical connection switches; (28) Fifth stage of measuring a voltage wave to ground from another point of the electrical circuit;

(29) Sixth stage of determining a portion of an electrical circuit with a ground fault;

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

In view of this description and figures, the person skilled in the art will be able to understand that the invention has been described according to some embodiments thereof, but that multiple variations can be introduced in said embodiments, without leaving the object of the invention as such. has been vindicated.

We now proceed to make a description of a preferred embodiment of the invention, for a non-limiting example system of an electrical system with converters.

Figure 1 shows a part of an electrical circuit that can be used as a non-limiting example of the invention to explain it in detail. The electrical circuit partially illustrated in Figure 1 comprises several converters; specifically it comprises a first AC/DC converter (1a), a first DC/AC converter (1b), a second AC/DC converter (1c), a second DC/AC converter (1d), a first DC/DC converter ( 1e) and a second DC/DC converter (1f). The electrical circuit comprises a first transformer (2a), a second transformer (2b), a rotating electrical machine (5) and a three-phase impedance (4). The first transformer (2a), the second transformer (2b), the rotating electrical machine (5) and the three-phase impedance (4) are in areas of the electrical circuit configured to have alternating voltage. The electrical circuit comprises an electrical energy accumulator (6) and a set of photovoltaic panels (7). The electrical energy accumulator (6) and the set of photovoltaic panels (7) are in areas of the electrical circuit configured to have direct voltage.

As illustrated in Figure 1, the converters (1a), (1b), (1c), (1d), (1e), (1f) are electrically linked to each other through an area of the electrical circuit configured to have direct voltage. . This zone configured to have direct voltage comprises resistors (91), (92), (93), (94), (95), (96) and capacitors (81), (82), (83), (84), (85), (86). The capacitors (81), (82), (83), (84), (85), (86) make it possible to reduce a ripple of a voltage in the area configured to have direct voltage. The area configured to have direct voltage has a first electrical conductor (3a) and a second electrical conductor (3b).

The electrical circuit partially illustrated in Figure 1 comprises a ground fault locator such as, for example, the locator partially illustrated in Figure 2 or the locator partially illustrated in Figure 3. The locator comprises electrical connections to electrically connect points of an electrical circuit to ground. Specifically, the locator comprises a first connection (10a) to a neutral point of the circuit, a second connection (10b) to a neutral point of the circuit, a third connection (10c) to a neutral point of the circuit, a fourth connection (10d) to a neutral point of the circuit, a fifth connection (10e) to a midpoint of the circuit, a sixth connection (10f) to a midpoint of the circuit, a seventh connection (10g) to a midpoint of the circuit, an eighth connection ( 10h) to a midpoint of the circuit, a ninth connection (10i) to a midpoint of the circuit, a tenth connection (10j) to a midpoint of the circuit, an eleventh connection (10k) to a midpoint of the circuit, a twelfth connection (10l) to a midpoint of the circuit.

Circuit midpoints are portions of the circuit configured to be at ground voltage, that is, the midpoints are at ground voltage if the circuit is fault-free. The neutral points of the electrical circuit are also configured to have ground voltage, that is, the neutral points are at ground voltage if the circuit is fault-free.

The resistors (91), (92), (93), (94), (95), (96) and/or the capacitors (81), (82), (83), (84), (85), (86) may be part of the locator or may be part of an electrical circuit that is not part of the locator.

Figure 2 shows the electrical connections (10a), (10b), (10c), (10d), (10e), (10f), (10g), (10h), (10i), (10j), (10k) , (10l) of the locator. The first connection (10a) comprises a normally closed switch (13) and the rest of the electrical connections comprise normally open switches (14). The electrical connections (10a), (10b), (10c), (10d), (10e), (10f), (10g), (10h), (10i), (10j), (10k), (10l) They connect the respective points of the electrical circuit with a grounding resistor (15). The grounding resistor (15) is electrically connected to ground (16). The grounding resistance (15) is an example of a current limiting impedance.

The electrical connections (10a), (10b), (10c), (10d), (10e), (10f), (10g), (10h), (10i), (10j), (10k), (10l) They are electrically connected to each other by means of fuses (22). The fuses allow you to avoid short circuits caused by an undesirable closing of two switches (13), (14) simultaneously.

A set that includes the electrical connections (10a), (10b), (10c), (10d), (10e), (10f), (10g), (10h), (10i), (10j), (10k) , (10l), the fuses (22) and the grounding resistor (15) can be considered a grounding subsystem (12).

The locator comprises a voltage meter (17) configured to measure voltage waves of the electrical connections (10a), (10b), (10c), (10d), (10e), (10f), (10g), (10h ), (10i), (10j), (10k), (10l) with the switch (13), (14) closed. Specifically, the voltage meter (17) comprises terminals connected to two ends of the grounding resistor (15) so that the voltage meter (17) is configured to measure a voltage drop in the grounding resistance. earth (15).

The tension meter (17) is communicatively connected to the processing means (20). The processing means (20) are communicatively connected to a controller (18) of the switches (13), (14). The processing means are connected to the electrical circuit so that they receive frequency signals (11) from the electrical circuit. The frequency signals (11) may be, for example, signals indicative of the switching frequency of switches of one or more converters of the electrical circuit and/or signals indicative of alternating voltage frequencies of one or more polyphase portions of the electrical circuit. Figure 1 illustrates an example in which the frequency signals (11) are frequency signals (11a), (11b), (11c), (11 d), (11e), (11f) indicative of the switching frequency of the respective converters (1a), (1b), (1c), (1d), (1e), (1f).

Figure 3 shows a portion of a ground fault locator equal to the locator shown in Figure 2 except that it includes additional resistors (23) to limit current to the ground (16). As illustrated in Figure 3, the electrical connections (10a), (10b), (10c), (10d), (10e), (10f), (10g), (10h), (10i), (10j ), (10k), (10l) comprise a resistor on each side of each of the switches (13), (14). The additional resistors (23) allow the risk of short circuit between two neutral points, two midpoints and/or between neutral point and midpoint due to the simultaneous closing of two or more of the switches (13), (14) to be considerably reduced. at the cost of losing resolution in the detection of a voltage indicative of a ground fault, since the fault voltage drop is distributed in three regions, a voltage drop in one of the additional impedances (23), a voltage drop in the grounding resistance (15) and a voltage drop in the ground fault, decreasing the voltage drop in the grounding resistance (15). The additional resistors (23) are examples of current limiting impedances. Each of the additional resistances (23) can be equal to the rest of the additional resistances.

As can be deduced from Figures 2 and 3, the voltage meter (17) is configured to measure a voltage to ground of the electrical connections (10a), (10b), (10c), (10d), ( 10e), (10f), (10g), (10h), (10i), (10j), (10k), (10l) with the switch(es) (13), (14) closed. Specifically, the voltage meter (17) is configured to measure a voltage drop of the grounding resistance (15).

The change of state from opening to closing and from closing to opening of the switches (13), (14) is controlled by control signals (19) generated by the controller (18). In some non-illustrated embodiments the processing means (20) comprise the controller (18).

As the neutral points and the midpoints electrically connected to the electrical connections (10a), (10b), (10c), (10d), (10e), (10f), (10g), (10h), (10i), (10j), (10k), (10l) are at the ground voltage (16), if the circuit does not have ground faults, the voltage drop in the grounding resistance (15) is substantially zero volts. More specifically, as the normally closed switch (13) electrically connects the ground (16), see figure 2 or 3, with a neutral point with the same voltage as the ground (16), see figure 1, the current that circulates through The first connection (10a) is zero amperes, the voltage drop across the grounding resistance (15) being measured as substantially zero volts.

In the event that a ground fault occurs in the electrical circuit partially illustrated in Figure 1, the current that circulates through the first connection (10a) increases, increasing in absolute value a voltage drop in the grounding resistance. (fifteen). The voltage meter (17) measures a first voltage wave of the grounding resistance (15) and transmits the measurement of the first voltage wave to the processing means (20).

The processing means (20) are configured to carry out a first stage a) of receiving the measurement of the first voltage wave of the first connection (10a).

The processing means (20) is configured to perform a step b) of estimating a direct voltage of a continuous component of the measured voltage wave and/or estimating an alternating voltage of an alternating component of the measured voltage wave. These estimates allow you to determine possible locations of the ground fault. These estimates may be estimates of frequency components of the measured voltage wave. For example, estimates of the frequency components can be obtained by computing a fast Fourier transform of an estimate of the measured voltage wave, estimating the measured voltage wave from the measurement of the voltage wave.

To more accurately detect the location or location of a ground fault of the electrical circuit, the processing means (20) may be configured to estimate the direct voltage of the direct component of the measured voltage wave and an alternating voltage of a component alternating for each fundamental frequency of the electrical circuit, each alternating component having a fundamental frequency of the electrical circuit. For example, in the electrical circuit partially illustrated in Figure 1, the fundamental frequencies may be a first fundamental frequency of the voltage of the first transformer (2a), a second fundamental frequency of the voltage of the second transformer (2b), a third fundamental frequency of the voltage of the three-phase impedance (4) and a fourth fundamental frequency of the voltage of the rotating electrical machine (5).

The frequency of the alternating voltage whose absolute value is greater than substantially zero volts makes it possible to delimit possible locations of a ground fault in the circuit, the frequency of the alternating voltage coinciding with the fundamental frequency of the voltage in said possible locations. For example, if the only portion of the circuit configured to have a voltage at the third fundamental frequency is the three-phase impedance (4), if a frequency of the alternating voltage whose absolute value is greater than substantially zero volts is equal to the third fundamental frequency , this is indicative that the ground fault is in the three-phase impedance (4).

In another example, the first fundamental frequency is equal to the second fundamental frequency and the electrical circuit comprises no further portions configured to have an alternating voltage with a frequency equal to the first fundamental frequency; then a frequency of the alternating voltage whose absolute value is greater than substantially zero volts equal to the first fundamental frequency is indicative that the ground fault is in the first transformer (2a) and/or in the second transformer (2b).

The absolute value of the alternating voltage may be, for example, an rms value of the alternating voltage or an amplitude of the alternating voltage.

An estimated direct voltage greater than the value of substantially zero volts is indicative of a ground fault in a portion of the electrical circuit, the portion of the electrical circuit being configured to have direct voltage. An absolute value of the alternating voltage greater than the value of substantially zero volts is indicative of a ground fault in a portion of the electrical circuit, the portion of the electrical circuit being configured to have alternating voltage.

The processing means (20) are configured to perform a step c) that comprises opening the normally closed switch (13) and closing a normally open switch (14) of another of the electrical connections (10b), (10c), (10d). ), (10e), (10f), (10g), (10h), (10i), (10j), (10k), (10l).

When opening the normally closed switch (13) and closing the normally open switch (14), the current that circulates through the grounding resistance (15) ceases to be the current that circulates through the normally closed switch (13) and passes to be the current that circulates through the normally open switch (14) that has been closed. In this state of switches (13), (14) the voltage meter (17) measures a second voltage wave of the grounding resistance (15) and transmits the measurement to the processing means (20).

The processing means (20) may be configured, for example, to select which of the normally open switches (14) to close based on the measurement of the first voltage wave. For example, the processing means may be configured to close a normally open switch (14) whose electrical connection is connected to a point of a portion of the circuit configured to have voltage with a fundamental frequency, the fundamental frequency being equal to the frequency of the estimated alternating and/or direct voltage with an absolute value greater than substantially zero volts.

The processing means (20) are configured to carry out a step d) of receiving the measurement of the second voltage wave of the electrical connection different from the first connection (10a).

The processing means (20) are configured to perform a step e) of determining a portion of the electrical circuit, the portion having a ground fault; the determination being based on the measurement of the second voltage wave. This determination can be made in different ways as explained below.

Step e) may comprise comparing an absolute value of the continuous voltage estimate of step b) with an absolute value of an estimate of a continuous voltage of a continuous component of the second voltage wave of the electrical connection different from the first. connection (10a). This improves the accuracy of ground fault detection in portions of the circuit configured to have direct voltage. A greater absolute value of the direct voltage estimate of step b) with respect to the absolute value of the direct voltage estimate of the electrical connection other than the first connection (10a) is indicative that the ground fault is closer to the point electrically connected to the first connection (10a) than to the point electrically connected to the electrical connection other than the first connection (10a). Conversely, a lower absolute value of the direct voltage estimate of step b) with respect to the absolute value of the direct voltage estimate of the electrical connection other than the first connection (10a) is indicative that the ground fault is The point electrically connected to the electrical connection other than the first connection (10a) is closer than the point electrically connected to the first connection (10a).

Step e) may comprise comparing an absolute value of the alternating voltage estimate of step b) with an absolute value of an estimate of an alternating voltage of an alternating component of the second voltage wave of the electrical connection other than the first connection (10a), the two alternating voltages having a frequency equal to a fundamental frequency of a polyphase portion of the electrical circuit. This allows improving the accuracy of ground fault detection in portions of the circuit configured to have alternating voltage at said fundamental frequency. A greater absolute value of the estimation of the alternating voltage of step b) with respect to the absolute value of the estimation of alternating voltage of the electrical connection other than the first connection (10a) is indicative that the ground fault is closer to the point electrically connected to the first connection (10a) than to the point electrically connected to the electrical connection other than the first connection (10a). Conversely, a lower absolute value of the estimate of the alternating voltage of step b) with respect to the absolute value of the estimate of alternating voltage of the electrical connection other than the first connection (10a) is indicative that the ground fault is The point electrically connected to the electrical connection other than the first connection (10a) is closer than the point electrically connected to the first connection (10a).

The determination of step e) may be based on a measurement of an alternating voltage of an alternating component of the second voltage wave of the electrical connection other than the first connection (10a), the alternating component having a frequency equal to a third harmonic of an electrical circuit converter. This way of locating a ground fault makes it possible to improve the precision of the location. If the electrical circuit includes a converter between the ground fault and the point electrically connected to the electrical connection other than the first connection (10a), the ground fault causes the point to receive a voltage with a frequency equal to the third harmonic, having the voltage an absolute value greater than a voltage with the same frequency but from an electrical connection connected to a point in the circuit that is not separated from the ground fault by the converter.

The determination of step e) may be based on a measurement of an alternating voltage of an alternating component of the second voltage wave of the electrical connection other than the first connection (10a), the alternating component having a frequency equal to a frequency switching of an electrical circuit converter. This way of locating a ground fault improves the accuracy of the location. If the electrical circuit comprises a converter between the ground fault and the point electrically connected to the electrical connection other than the first connection (10a), with the converter being driven with the switching frequency, the ground fault causes the point to receive a voltage with a frequency equal to the switching frequency, the voltage having an absolute value greater than a voltage with the same frequency but from an electrical connection connected to a point in the circuit that is not separated from the ground fault by a converter driven with said switching frequency.

Step c) may comprise closing the switches of all electrical connections other than the first connection (10a), preferably so that no more than one switch is closed simultaneously. This allows the determination of step e) to be carried out based on measurements of voltage waves of all electrical connections (10a), (10b), (10c), (10d), (10e), (10f), ( 10g), (10h), (10i), (10j), (10k), (10l). To ensure that the fundamental frequencies of all polyphase portions of the electrical circuit are measured, each of the switches can be kept closed for a time equal to the inverse value of the lowest fundamental frequency of the circuit voltages.

The processing means (20) may be configured to generate an alarm signal based on the measurement of the second voltage wave of the electrical connection other than the first connection (10a). In this way, not only is a location of a ground fault determined based on the measurement of the second voltage wave, but the alarm signal is also issued. The alarm signal may comprise location data for the portion of the circuit that has been determined to have the ground fault.

The electrical circuit may include protections to minimize electrical damage, the damage being caused by ground faults. The protection conferred by each electrical protection may depend on the location of the ground fault. Therefore, the protection to activate may depend on the location of the ground fault, that is, the protection to activate can be selected based on the measurement of the second voltage wave of the electrical connection different from the first connection (10a ).

The condition that no third harmonic appears in the ground voltage measurement of one of the electrical connections implies that the activated switch (13), (14) is in the same area as the defect, that is, there is no electronics. power between the fault and the neutral/middle point at which said voltage is measured.

Figure 4 shows a ground fault detection method (100) according to some embodiments of the invention. This method (100) can be implemented with the ground fault locator illustrated in Figure 2 or with the ground fault locator illustrated in Figure 3. In a first stage (24) of the method (100) a wave of voltage to ground from a point in an electrical circuit. In a second stage (25) of the method (100), a direct voltage is estimated from a continuous component of the ground voltage wave measured in the first stage (24) and/or an alternating voltage is estimated from an alternating component of the ground voltage wave measured in the first stage (24). In a third stage (26), an absolute value of the estimated direct voltage in the second stage (25) is compared with a ground fault threshold and/or an absolute value of the estimated alternating voltage is compared in the second. stage (25) with a ground fault threshold. In the event that none of the absolute values are higher than the respective ground fault threshold, we return to the first stage (24) of measuring the ground voltage wave at a point in the electrical circuit, preferably without changing the state of any of them. of the switches of the locator's electrical connections. In the event that at least one of the absolute values is higher than the threshold, the method optionally advances to a fourth stage (27) of closing one or more of the switches of the electrical connections to enable a fifth stage (28) in the which measures a voltage wave to ground from another point in the electrical circuit. In a sixth step (29) of method (100), a portion of the electrical circuit is determined, the portion having a ground fault.

In this text, the term “comprehends” and its variants (such as “understanding”, etc.) should not be understood in an exclusive way, that is, they exclude the possibility that what is described includes other elements, steps, etc.

On the other hand, the invention is not limited to the specific embodiments that have been described but also encompasses, for example, the variants that can be carried out by the average person skilled in the art (for example, regarding the choice of materials, dimensions , components, configuration, etc.), within what is clear from the claims.

Claims (1)

1- Ground fault locator for an electrical circuit; the locator being characterized in that it comprises: - electrical connections (10a, 10b) configured to connect the respective points of the electrical circuit with a grounding resistor (15), where the grounding resistor (15) is electrically connected to ground (16), each having electrical connection (10a, 10b) a switch (13, 14), and where the electrical connections (10a, 10b) are electrically connected to each other by means of fuses (22); - a voltage meter (17) configured to measure voltage waves of the electrical connections (10a, 10b) with the switch (13, 14) closed, where the voltage meter (17) comprises terminals connected to two ends of the grounding resistance (15) so that the voltage meter (17) is configured to measure a voltage drop across the grounding resistance (15); - a controller (18) configured to generate control signals (19) and to control, by means of said control signals (19), the change of state from opening to closing and from closing to opening of the switches (13, 14); - processing means (20) communicatively connected with the tension meter (17) and with the controller (18) of the switches (13, 14), the processing means (20) being configured to carry out the following steps: a) receiving a measurement of a voltage wave from at least one of the electrical connections (10a, 10b); b) estimating a direct voltage from a continuous component of the measured voltage wave and/or estimating an alternating voltage from an alternating component of the measured voltage wave; c) upon determining that an absolute value of the estimated direct voltage exceeds a ground fault threshold and/or determining that an absolute value of the estimated alternating voltage exceeds a ground fault threshold, close the switch of one of the electrical connections different from the at least one electrical connection of step a) so that the voltage meter measures a voltage wave of the electrical connection different from the at least one electrical connection of the step to); d) receiving the measurement of the voltage wave of the electrical connection other than the at least one electrical connection of step a); e) determine that a portion of an electrical circuit has a ground fault, the determination of the portion of the circuit being based on the measurement of the voltage wave of the electrical connection other than the at least one electrical connection of step a) . 2- The ground fault locator of claim 1, each of the electrical connections (10a, 10b) comprising a current limiting impedance on each side of the electrical connection switch. 3- The ground fault locator of any one of the preceding claims, the processing means being configured to estimate the direct voltage and/or estimate the alternating voltage of step b) based on a fast Fourier transform of the measurement. of the voltage wave received in step a). 4- The ground fault locator of any of the previous claims, comprising step c) keeping the switches of the rest of the electrical connections open when determining that the absolute value of the estimated continuous voltage exceeds the ground fault threshold and /or determine that the absolute value of the estimated alternating voltage exceeds the ground fault threshold. 5- The ground fault locator of any one of the preceding claims, the processing means being configured to keep the switch of one of the electrical connections normally closed and to keep the switches of the rest of the electrical connections normally open; the at least one electrical connection of step a) being a single electrical connection and the switch of the electrical connection of step a) being normally closed. 6- The ground fault locator of any one of the preceding claims, comprising step e) comparing the absolute value of the continuous voltage estimate of step b) with an absolute value of an estimate of a continuous voltage of a component. continuous voltage wave of the electrical connection other than the at least one electrical connection of step a); the processing means being configured to indicate that the ground fault is closer to the electrical connection with the highest absolute value of the direct voltage estimate than to the electrical connection with the lowest absolute value of the direct voltage estimate. 7- The ground fault locator of any one of the preceding claims, the processing means being configured to generate an alarm signal (21) based on the measurement of the voltage wave of the electrical connection other than the at least an electrical connection from step a). 8- The ground fault locator of claim 7, the alarm signal (21) comprising location data for a portion of a circuit determined in step e). 9- The ground fault locator of any of the preceding claims and protections for an electrical circuit, the processing means being configured to select at least one of the protections and activate the at least one of the protections selected, the selection being based on the measurement of the voltage wave of the electrical connection other than the at least one electrical connection of step a). 10- Electrical circuit, the electrical circuit comprising the ground fault locator of any one of claims 1 to 8 and one or more converters (1a, 1b), the electrical circuit being characterized in that : - the electrical connections of the locator electrically connect points of the electrical circuit to ground; - the processing means are configured so that the alternating component of step b) has a frequency equal to a fundamental frequency of a polyphase portion of the electrical circuit. 11- The electrical circuit of claim 10, the points of the electrical circuit being at least one neutral point of a polyphase portion of the electrical circuit and/or at least one midpoint of a portion of the electrical circuit configured to have direct voltage; and the ground fault threshold values being substantially zero volts. 12- The electrical circuit of claim 10 or 11, comprising step e) comparing the absolute value of the alternating voltage estimate of step b) with an absolute value of an estimate of an alternating voltage of an alternating component of the wave voltage of the electrical connection other than the at least one electrical connection of step a), the alternating component having a frequency equal to the fundamental frequency of the polyphase portion of the electrical circuit; the processing means being configured to indicate that the ground fault is closer to the electrical connection with the highest absolute value of the alternating voltage estimate than to the electrical connection with the lowest absolute value of the alternating voltage estimate. 13- The electrical circuit of any one of claims 10 to 11, the determination of step e) being based on a measurement of an alternating voltage of an alternating component of the voltage wave of the electrical connection different from the at least an electrical connection of step a), having the alternating component a frequency equal to a switching frequency of a converter of the electrical circuit. 14- The electrical circuit of any one of claims 10 to 11, the determination of step e) being based on a measurement of an alternating voltage of an alternating component of the voltage wave of the electrical connection different from the at least an electrical connection of step a), having the alternating component a frequency equal to a third harmonic of a converter of the electrical circuit. 15- Method (100) for locating ground faults in an electrical circuit, the electrical circuit comprising one or more converters; The method being characterized in that it includes the stages: a) measure a voltage wave to ground from a point in the electrical circuit; b) estimating a direct voltage from a direct component of the measured ground voltage wave and/or estimating an alternating voltage from an alternating component of the measured ground voltage wave; c) upon determining that an absolute value of the estimated direct voltage exceeds a ground fault threshold and/or determining that an absolute value of the estimated alternating voltage exceeds a ground fault threshold, measure a ground voltage from another point on the electrical circuit, the other point of the electrical circuit being different from the point in step a); d) measure a voltage wave to ground from the other point of the electrical circuit; e) determining that a portion of an electrical circuit has a ground fault, the determination of the portion of the circuit being based on the measurement of the voltage wave in step d). 16- The method of claim 15 carried out by the ground fault locator of any one of claims 1 to 8 or by the electrical circuit of any one of claims 10 to 14.