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    • 专利摘要:
    Method and system for detecting earth faults in electrical installations with conversion between direct current and alternating current, based on the measurement of voltage or the measurement of current, of an earthing device connectable between a neutral point of the power transformer and earth or between an artificial neutral and earth, which allows detecting earth faults, discriminating whether the fault is in direct current or alternating current. (Machine-translation by Google Translate, not legally binding)
    公开号:ES2798348A1
    申请号:ES202030579
    申请日:2020-06-15
    公开日:2020-12-10
    发明作者:Granados José Manuel Guerrero；Gaona Carlos Antonio Platero
    申请人:Universidad Politecnica de Madrid；
    IPC主号:
    专利说明:

    [0002] METHOD AND SYSTEM FOR DETECTION OF EARTH FAULTS IN ELECTRICAL INSTALLATIONS WITH CONVERSION BETWEEN DIRECT CURRENT AND ALTERNATING CURRENT
    [0003] OBJECT OF THE INVENTION
    [0005] The present invention refers to a system and method for detecting ground faults in electrical installations for converting between alternating current and direct current capable of detecting this type of fault while being at any point in the electrical circuit, with it in operation.
    [0007] The ground fault detection system and method according to the present invention is useful in electrical installations connected to an electrical network by means of a transformer that has a connection for the neutral in the secondary, or failing that, it has a artificial neutral. The present invention has application, for example and without limitation, in the sector of variable speed drives, renewable energies in wind or solar photovoltaic technology, among others.
    [0009] BACKGROUND OF THE INVENTION
    [0011] Any electrical system installed must be protected both to guarantee the safety of people and to ensure the proper functioning of the facilities and avoid damage that may cause possible faults due to numerous factors.
    [0013] Among the possible faults, the most common are earth faults, which can be caused, for example, by defects in the insulation due to aging or high operating temperatures, uninsulated cables in contact with surfaces at earth potential, etc ... Ground faults alone may not cause significant damage in the case of limited fault or isolated neutral systems where the return circuit is open or the ground capacities that allow it are small and considerably limit the output current. return by land. However, a second ground fault can close the circuit with low impedance, producing a high current that could damage equipment and people.
    [0015] In the field of electrical fault diagnosis and protection, ground fault detection is a field with numerous inventions already designed. Although most of these devices are configured to detect only in direct current or alternating current.
    [0017] The increasing introduction of power electronics in electrical systems with the aim of controlling different electrical drives means that systems now have an important part of hybrid networks in terms of a combination of alternating current (AC) and direct current (DC). Therefore, the protection elements must be numerous if they are only capable of detecting in certain parts of the system where the current is only AC or DC.
    [0019] In already known earth fault detection systems, it is usual to have the following means:
    [0020] • Detection by injection of alternating current of a frequency different from that of operation between a point of the electrical installation and ground that gives a reading of said current if there is a ground fault. This system is valid for direct and alternating current systems.
    [0021] • Detection by injection of direct current in the electrical installation that gives a reading of said current if there is a ground fault. It is valid for alternating current systems, losing efficiency in direct current systems.
    [0023] In addition, the following inventions can be considered as more current systems of protection and detection of earth faults:
    [0025] US6992490 B2 (01.31.2006) Honda Motor Co., Ltd. (100%), GROUND FAULT DETECTION DEVICE.
    [0026] US6927955 B2 (08/09/2005) Canon Kabushiki Kaisha (100%), APPARATUS AND METHOD OF DETECTING GROUND FAULTS IN POWER CONVERSION SYSTEM.
    [0028] EP2856591 B1 (04/19/2017) Li, Huaqiang, SYSTEM AND METHOD FOR HIGH RESISTANCE GROUND FAULT DETECTION AND PROTECTION IN POWER DISTRIBUTION SYSTEMS.
    [0030] In the first of the mentioned inventions (US6992490 B2), the apparatus is capable of detecting direct current faults with the detection system in the direct current zone by reading resistors placed in series with the IGBTs of the converters. However, the invention does not contemplate the detection of faults in alternating current.
    [0032] A second invention to take into account (US6927955 B2) is a direct current earth fault detector that, by injecting alternating current with a commutator switch and reading the waveform in both poles on the direct current side, makes it possible to distinguish if the The fault is in the positive pole or the negative pole of the DC bus of a converter.
    [0034] Finally, in the last invention (EP2856591 B1) a ground positioning system in the alternating current source of an alternating current side is proposed. However, the system only detects faults in the electrical drive that is located on the opposite side of the converter. In this invention, the phase and ground currents are recorded, as well as the voltage in the direct current bus or the speed of the drive among others, which implies a lot of measurement instrumentation.
    [0036] Likewise, it is convenient to develop new systems and methods for the detection of earth faults, capable of detecting in which area of the system the fault in question is located (alternating current or direct current), since this would speed up repair and / or maintenance tasks. . Furthermore, it would be advantageous if such detection systems and methods were capable of detecting the ground faults using only voltage or current measurements, since this would considerably reduce its cost of manufacture and / or implementation and improve its modularity.
    [0038] Some of these methods are reflected in the state of the art in the following patents.
    [0040] ES2716482 A1 (18.12.2018) Platero Gaona, Carlos Antonio, SYSTEM AND METHOD OF DETECTION OF FAULTS TO GROUND OR AGAINST THE CHASSIS IN DIRECT CURRENT SYSTEMS WITH INVERTERS POWERED FROM BATTERIES.
    [0042] ES2736412 A1 (07.10.2019) Platero Gaona, Carlos Antonio y Guerrero Granados, Jose Manuel, SYSTEM AND METHOD FOR LOCATING EARTH FAULTS IN ALTERNATING CURRENT IN DIRECT CURRENT SYSTEMS WITH INVERTERS.
    [0044] In the first invention, the connection of the midpoint of a direct current bus to ground is evaluated by means of a grounding resistor for different electrical drives. This system is suitable for detecting earth faults in isolated systems where the supply is made in direct current, but this is not the case in systems powered from an alternating current network with a previous rectifier.
    [0046] In the second invention, "System and method for locating ground faults in alternating current in direct current systems with inverters", the system refers to the location of faults on the controlled alternating current side, since it needs pulsed waves of voltage in an earthing device to proceed to the estimation of the fault in percentage of equivalent impedance of the variable frequency side. This system is only valid for controlled circuits, thus not being effective for locating faults in direct current or in alternating current on the grid side.
    [0047] For this reason, the main advantage provided by the present invention is the possibility of distinguishing, by means of a single passive element grounded in the secondary of a transformer of the supply system to the converter or artificial neutral in which a fault detector system is coupled , that there is a ground fault at any point of the installation and that it is also capable of distinguishing between direct or alternating current zones and the section in which it is, considerably reducing maintenance time against this type of faults as well as the instrumentation necessary to detect the defect.
    [0049] DESCRIPTION OF THE INVENTION
    [0051] In one embodiment of the invention, it is intended to address all the limitations, disadvantages, and drawbacks of the systems and methods discussed in the prior art.
    [0053] For this reason, the method and the ground fault detection system in electrical installations with conversion between direct current and alternating current described here are configured to measure voltage / current at a neutral point in the power supply area of electrical installations or in its fault, measure in an artificial neutral between the electrical installation and earth. In this way, the method / device of the present invention detects the fault / fault current when it occurs. Additionally, afterwards, the corresponding treatment is carried out for the emission of the final informational signal on ground fault, if any. The present invention is applicable to converting alternating current to direct current and vice versa.
    [0055] For the detection of ground faults in systems where there are several stages of electrical energy transformation, such as rectifiers to go from alternating current to direct current, or inverters to convert direct current to alternating current, the invention contemplates having at least one transformer of main supply to the circuit with accessible neutral or, failing that, an artificial neutral on the secondary terminals of a transformer on the grid side.
    [0056] In any case, an earthing device will be located between the neutral (zero potential of the circuit) of the system and earth. In the event of a fault at any point in the system, whether it be alternating current or direct current, a fault current will flow through the faulty conductor and return through the earth network to the earthing detection device.
    [0058] To detect the fault current in the grounding device, at least two embodiments of the invention can be considered, either by measuring the current flowing through the device, or fault current, or the voltage between its terminals.
    [0060] The present invention then seeks to address and improve the performance of other inventions in the present state of the art. The main improvement provided by this ground fault detection system in electrical systems is the need for few measuring instruments to detect faults in an electrical system with extensive transformations and deformations in its voltage and current waves. In addition to detecting faults additionally up to the point of injection of power to the grid.
    [0062] To carry out the above, the present invention discloses in a first aspect of the invention, a method for detecting ground faults in electrical installations with conversion between alternating current and direct current, and in a second aspect of the invention, a system detection of ground faults in electrical installations with conversion between alternating current and direct current that is configured to carry out the method of the first aspect of the invention.
    [0064] Therefore, in a first aspect of the present invention, a method of detecting ground faults in electrical installations with conversion between alternating current and direct current is disclosed. The method of the present invention comprises the following steps:
    [0066] a) measure a selected signal between a voltage between terminals of a grounding device connectable between a neutral and a ground, and a circulating current through the grounding device;
    [0068] b) calculating harmonics of the previously measured signal;
    [0070] c) calculate some amplitudes of the signal previously measured at the following fundamental frequencies for each of the harmonics:
    [0072] or zero frequency, f0, for direct current;
    [0074] or network frequency, f1, for a supply with alternating current;
    [0075] or variable frequency, f1 ', of alternating current on a controlled side;
    [0076] d) comparing the amplitudes of each frequency with predetermined values of trigger settings for direct current, alternating current from mains and alternating current on the controlled side;
    [0078] e) calculating a fault polarity in case the amplitude for zero frequency (direct current) exceeds the predetermined value; and
    [0080] f) issue a ground fault signal, when at least one of the following conditions is met:
    [0082] o the amplitude for zero frequency (direct current) exceeds the predetermined value;
    [0084] o the amplitude for mains frequency (alternating current) exceeds the predetermined value; and,
    [0086] or the amplitude for variable frequency (alternating current on controlled side) exceeds the predetermined value.
    [0088] In one embodiment, the step of calculating harmonics is carried out using the Fast Fourier Transform FFT to the measured voltage signal as follows:
    [0092] where:
    [0094] j: is the system's operating zone according to the wave frequency;
    [0096] k: is the harmonic to be evaluated according to the operating zone, these being multiples and submultiples of the fundamental frequency of the zone in question; in the case of direct current, this value is 0 and the wave amplitude value is obtained by taking the arithmetic mean of the sampled values, being able to also obtain its effective value;
    [0098] N: is the number of samples per wave period;
    [0100] n: is the number of sample to be evaluated between 0 and the number of samples per wave period;
    [0102] ugnd.j: is the instantaneous value of the voltage between terminals of at least one earthing device originating from a fault in zone j;
    [0104] AUkj: is the value of the cosine filter applied for the fast Fourier transform in the voltage wave for the harmonic k of zone j;
    [0106] BUkj: is the value of the sine filter applied for the fast Fourier transform in the voltage wave for the harmonic k of zone j;
    [0108] Ukj: is the amplitude value, or effective value if it is attenuated by a factor of 1.4142, of the voltage wave recorded at the terminals of at least one grounding device for harmonic k of zone j in the case of direct current the value will be obtained as the arithmetic mean of the recorded instantaneous voltage values.
    [0110] In case the measured signal is a current signal, the stage of calculating the harmonics is carried out by means of the Fast Fourier Transform FFT to the measured current signal as follows:
    [0112] where:
    [0114] j: is the system's operating zone according to the wave frequency;
    [0116] k: is the harmonic to be evaluated according to the operating zone, these being multiples and submultiples of the fundamental frequency of the zone in question; in the case of direct current, this value is 0 and the wave amplitude value is obtained by taking the arithmetic mean of the sampled values, being able to also obtain its effective value;
    [0118] N: is the number of samples per wave period;
    [0120] n: is the number of sample to be evaluated between 0 and the number of samples per wave period;
    [0122] ij: is the instantaneous value of the current flowing between terminals of at least one grounding device from a fault in zone j;
    [0124] AIkj: is the value of the cosine filter applied for the fast Fourier transform in the current wave for the harmonic k of zone j;
    [0126] BIkj: is the value of the sine filter applied for the fast Fourier transform in the current wave for the harmonic k of zone j;
    [0128] Ik.j: is the amplitude value, or effective value if it is attenuated by a factor of 1.4142, of the recorded current wave flowing through the grounding device for harmonic k of zone j in case of current The continuous value will be obtained as the arithmetic mean of the recorded instantaneous current values.
    [0129] For its part, the comparison stage evaluates the amplitudes of the fundamental frequency of each zone with its adjustment value, of which if it is exceeded, a fault signal is emitted with at least information on where the fault has occurred, which can be:
    [0130] - The alternating current side of the network between the neutral of the transformer or, failing that, an artificial neutral and the terminals of the converter-rectifier if the fundamental frequency is that of the network.
    [0131] - Positive pole on the direct current side if a direct current component of opposite sign (negative) is detected.
    [0132] - Positive pole on the direct current side if a direct current component of opposite sign (negative) is detected.
    [0133] - AC side of the controlled drive if the recorded current wave shows a fundamental frequency different from that of the mains.
    [0135] In case the comparison is made with voltage signals, the comparison stage and the default values can be represented as follows:
    [0137] ^ 1.7 U shotgun AC
    [0141] where:
    [0143] U1, j: is the value of the voltage at the terminals of at least one grounding device at fundamental frequency of a zone j;
    [0145] U0j: is the value of the voltage at terminals of at least one grounding device in a direct current component of a direct current zone j;
    [0147] UtripAC: is the voltage adjustment value previously defined for the detection system to emit a fault signal in alternating current areas;
    [0148] UdisparoDC: is the previously defined voltage adjustment value for the detection system to emit a fault signal in direct current areas.
    [0149] In case the comparison is made with current signals, the comparison stage and the default values can be represented as follows:
    [0151] ^ 1.7 Idisparo.AC
    [0153] Oh' Idisparo.D C
    [0155] where:
    [0157] I1, j: is the value of the current flowing through at least one grounding device at fundamental frequency of a zone j;
    [0159] I0J: is the value of the current circulating through at least one grounding device in a direct current component of a direct current zone j;
    [0161] IdisparoAC: it is the setting value in current previously defined so that the detection system emits a fault signal in alternating current areas;
    [0162] IdisparoDC: is the current setting value previously defined for the detection system to emit a fault signal in direct current areas.
    [0164] In an embodiment of the invention, the method comprises the stage in which the polarity of the fault is detected in direct current, this fault can be detected due to the sign of the mean value calculated in the previous step (see the steps described for the first aspect of the invention) as the arithmetic mean of the recorded instantaneous values. That is, the step of calculating the fault polarity in case the amplitude for zero frequency exceeds the predetermined value, is carried out by:
    [0165] Missing in the positive pole fulfills that:
    [0167] U0lj ~ U0J = 2 • U0J
    [0169] Missing in the negative pole fulfills that:
    [0171] U o j- U OJ = 0
    [0173] Adopting the voltage measurement criterion from neutral to ground. In case On the contrary (from ground to neutral) the conditions of equality raised above would be the opposite cases, clarifying it is:
    [0174] • fault in the positive pole fulfills that:
    [0175] Uoj ~ Uoj = 0
    [0177] • fault in the negative pole fulfills that:
    [0178] U0J - | U0 j | = 2 • U0ij
    [0180] In the case of current measurement, the conditions for polarity detection would be such that taking the direction of the circulating fault current from earth to neutral:
    [0181] • fault in the positive pole fulfills that:
    [0183] Io, j ~ Io, j = 0
    [0185] • fault in the negative pole fulfills that:
    [0187] hi ~ IA ), i I = 2 • I0J
    [0189] and from neutral to ground:
    [0191] • fault in the positive pole fulfills that:
    [0193] hi ~ IA ), i I = 2 • I0J
    [0195] • fault in the negative pole fulfills that:
    [0197] Ioj ~ I0j = 0
    [0199] In a second aspect of the invention, a ground fault detection system is disclosed in electrical installations with conversion between alternating current and direct current. The system of the present invention comprises:
    [0201] • an earthing device connectable between a neutral of an electrical installation and earth;
    [0202] • a frequency meter (optional) located on a controlled side where an inverter / variable frequency drive / controller is located and which generates an alternating current signal on the controlled side; and,
    [0203] • a processor.
    [0204] The processor is specially configured to:
    [0205] or measure a voltage / current signal between the ends of the grounding device;
    [0206] or calculate harmonics of the signal previously measured by applying the fast Fourier transform FFT; and to calculate amplitudes of the signal previously measured at the following fundamental frequencies for each of the harmonics: zero frequency for direct current; mains frequency for a power supply with alternating current; and, variable frequency of alternating current on a controlled side;
    [0207] or compare the amplitudes of each frequency with predetermined values of trigger settings for direct current, alternating current from the network and alternating current on the controlled side (the latter only if there is a frequency meter); and,
    [0208] or calculating a fault polarity in case the amplitude for zero frequency exceeds the predetermined value; and, emit a ground fault signal, when at least one of the following conditions is met: the amplitude for zero frequency (direct current) exceeds the predetermined value, the amplitude for mains frequency (alternating current) exceeds the predetermined value, and the amplitude for variable frequency (alternating current on controlled side and only if there is a frequency meter) exceeds the predetermined value.
    [0210] BRIEF DESCRIPITION OF THE FIGURES
    [0212] A series of figures, of non-limiting examples, that help to better understand the invention are briefly described here:
    [0214] Figure 1 shows a converter with a DC stage for controlling an electric drive supplied from the mains with the detection device implanted in the star center of the secondary of a three-phase transformer.
    [0216] Figure 2 shows the block diagram of the ground fault detection system of the present invention.
    [0217] Figure 3 shows the possible faults on the alternating current grid side, in the positive or negative poles of the direct current bus between rectifier and inverter and in the alternating current area of the electric drive shown in figure 1.
    [0219] Figure 4 shows an example of voltage records at the terminals of the grounding device obtained for each of the types of faults shown in figure 3.
    [0221] Figure 5 shows the flow chart for the method of the present invention.
    [0223] NUMERICAL REFERENCES OF THE FIGURES
    [0225] (1) Grid-side transformer;
    [0226] (2) Primary of the grid side transformer;
    [0227] (3) Secondary of the transformer on the grid side;
    [0228] (4) Grounding device;
    [0229] (5) Fault detection device;
    [0230] (6) Rectifier converter;
    [0231] (7) IGBTs of the rectifier converter;
    [0232] (8) Positive pole of the DC bus;
    [0233] (9) Negative pole of the DC bus;
    [0234] (10) DC bus capacitor;
    [0235] (11) Inverter converter;
    [0236] (12) IGBTs of the inverter converter;
    [0237] (13) Electric drive;
    [0238] (14) Frequency measuring device;
    [0239] (15) Frequency measurement of the controlled side of alternating current;
    [0240] (16) Measurement of voltage in the grounding device;
    [0241] (17) FFT realization stage;
    [0242] (18) DC component extraction stage;
    [0243] (19) Stage of extraction of fundamental frequency component from the network side;
    [0244] (20) Step of setting the value for tripping by direct current component;
    [0245] (21) Stage of setting the value for the trip by alternating current component;
    [0246] (22) Stage of extraction of fundamental frequency component from the controlled side of alternating current;
    [0247] (23) Step of comparing direct current extraction with the control variable for direct current tripping;
    [0248] (24) Step of comparing the AC power draw from the mains side with the control variable for AC tripping;
    [0249] (25) Step of comparing alternating current draw of the controlled alternating current side with the control variable for alternating current tripping;
    [0250] (26) DC fault polarity discrimination stage;
    [0251] (27) Stage of sending information about the ground fault;
    [0252] (28) Information signal about the earth fault;
    [0253] (29) Earth fault with fault resistance on the AC mains side; (30) Ground fault with fault resistance on the positive pole of the DC bus;
    [0254] (31) Earth fault with fault resistance in the negative pole of the DC bus;
    [0255] (32) Ground fault with fault resistance on the controlled AC side;
    [0256] (33) Sampling time of the voltage measurement in the earthing device.
    [0258] FORMS OF EMBODIMENT OF THE INVENTION
    [0260] A description is now made of a preferred embodiment in a variable speed drive with a direct current stage, in a non-limiting manner to said embodiment.
    [0261] Figure 1 uses a design of an electrical power system to drive an electrical machine in a controlled manner. In it, a ground fault detection system has been installed in electrical systems in the secondary of the mains side transformer (3) consisting of a grounding device (4) in conjunction with a fault detection device (5 ).
    [0263] The system has two steps of current conversion. The first is through a rectifier converter (6) that from the commutation of IGBTs (Insulated Gate Bipolar Transistors, (7)), or other possible switching elements or semiconductors, create a voltage with a direct current component and high frequency ripple (switching frequency of the IGBTs).
    [0265] Once the wave has been rectified, the system has a direct current stage with a positive pole of the direct current bus (8), a negative pole of the direct current bus (9) and a capacitor of the direct current bus (10) that maintains the voltage on said bus.
    [0267] Then, by means of an inverter converter (11), a wave is created by means of the PWM (Pulse Width Modulated Wave) type switching of IGBTs of the inverter that allows the control of an electric drive, generally with a variable speed motor or generator.
    [0269] Figure 2 shows a signal processor (5) configured to detect earth faults in electrical installations with conversion between alternating current and direct current according to the present invention. The processor (5) is connected to the ends of the grounding device (4), which is connected between the neutral on the mains side and ground. Optionally, the processor (5) can receive a measured frequency signal at the input of an inverter / variator from the frequency meter (14). First, the voltage and / or current are measured in the grounding device (16).
    [0271] Once the measurements in the time domain have been obtained, this signal is introduced in an algorithm for obtaining the different harmonics, for example by means of an FFT realization stage (17) where the values for the direct current component, the fundamental frequency of the network and the fundamental frequency of the alternating current side of the electric drive are extracted, if Any (this changes according to the speed of the drive, so the frequency measurement of the controlled side of alternating current is required, 15). These are obtained by means of a direct current component extraction stage (18), a fundamental frequency component extraction stage from the network side (19), a fundamental frequency component extraction stage from the alternating current controlled side ( 22).
    [0273] After extracting the aforementioned frequency values, these values are compared with the settings for direct and alternating current, the setting stage of the value for tripping by direct current component (20) and the stage of setting the value for tripping by alternating current component (21). The comparison stages in turn are three:
    [0274] - (23) Step of comparing direct current extraction with the control variable for direct current tripping;
    [0275] - (24) Step of comparing the AC power draw from the mains side with the control variable for AC tripping; - (25) Step of comparing the extraction of alternating current from the controlled alternating current side with the control variable for tripping by alternating current, if any.
    [0277] If the voltage value obtained from the FFT is less than the preset magnitude for the trip, the sensor does not issue a fault warning. However, if the comparisons are positive (the value obtained is greater than the adjustment value), an information signal about the earth fault (28) is emitted in the event of an alternating current fault through a stage of sending information about the fault. to ground (27) where it is transmitted at least if the fault exists and in which section it is. In the case of direct current, a direct current fault polarity discrimination step (26) must first pass, taking into account the value previously obtained in the FFT in the direct current section.
    [0279] Figure 3 refers to Figure 1 but with faults in each section of the system, that is, an earth fault with fault resistance on the AC mains side (29), or an earth fault with fault resistance on the positive pole of the DC bus (30), or an earth fault with fault resistance on the negative pole of the DC bus (31), or an earth fault with fault resistance on the current controlled side alternate (32).
    [0281] Figure 4 refers to the records of the voltage measurements in the earthing device (16) for an earth fault with fault resistance on the alternating current network side (29), an earth fault with resistance fault on the positive pole of the DC bus (30), an earth fault with fault resistance on the negative pole of the DC bus (31), an earth fault with fault resistance on the current controlled side toggles (32) respectively with respect to the sampling time of the voltage measurement at the grounding device (33). It is observed that the measurements of alternating current on the grid side have a main component of 50 Hz, as well as the predominant in those of direct current are those of zero harmonic. On the variable drive side, the noise increases considerably and the frequency is different from that of the mains.
    [0283] This system configuration occurs mainly in distributed generation systems where the presence of converters is essential for the adaptation of the generation frequency to that of the network. For example in wind turbines type of wound rotor technology, DFIG, or with type of permanent magnet technology, PMSG. In the case of alternating current of variable frequency, the fault detection device (5) will be supported by the frequency measurement on the controlled side of alternating current (15) by means of a frequency measuring device (14).
    [0285] Finally, figure 5 refers to the flow diagram carried out in the method of the invention. Where variables and trigger settings are collected to be compared and proceed to the detection of the faulty section (direct current side, and if so negative pole or positive pole according to the sign of the direct current component of the FFT, alternating current side of the network or side of controlled alternating current according to the frequency of the calculated component).
    [0287] The system can also be configured to detect ground faults in photovoltaic generation systems where only one DC stage is required.
    权利要求:
    Claims (10)
    [1]
    1. - Ground fault detection method in electrical installations with conversion between alternating current and direct current, characterized in that it comprises the following stages:
    a) measuring (16) a signal selected between a voltage between terminals of a grounding device (4) connectable between a neutral and a ground, and a current flowing through the grounding device;
    b) calculating harmonics (17) of the previously measured signal;
    c) calculate some amplitudes of the signal previously measured at the following fundamental frequencies for each of the harmonics:
    or zero frequency, f0, (18) for direct current;
    or network frequency, f1, (19) for a supply with alternating current;
    or variable frequency, f1 ', (22) of alternating current on a controlled side;
    d) comparing the amplitudes of each frequency with predetermined values (20, 21) of trigger settings for direct current (23), alternating current from the network (24) and alternating current on the controlled side (25);
    e) calculating a fault polarity (26) in case the amplitude for zero frequency exceeds the predetermined value (23); and
    f) issue (27) a ground fault signal (28), when at least one of the following conditions is met:
    or the amplitude for zero frequency the predetermined value (23);
    or the amplitude for network frequency exceeds the predetermined value (24); and,
    or the amplitude for variable frequency exceeds the predetermined value (25).
    [2]
    2. - Ground fault detection method in electrical installations with conversion between alternating current and direct current, according to claim 1, characterized in that the stage of calculating harmonics is carried out by means of the Fast Fourier Transform FFT to the voltage signal measured as follows:

    [3]
    3.- Ground fault detection method in electrical installations with conversion between alternating current and direct current, according to claim 1, characterized in that the step of calculating harmonics is carried out by means of the Fast Fourier Transform FFT to the signal of current measured as follows:

    [4]
    4.- Ground fault detection method in electrical installations with conversion between alternating current and direct current, according to claim 1, characterized in that the comparison stage evaluates the amplitudes of the fundamental frequency of each zone with its adjustment value, from that if it is exceeded, a fault signal is emitted with at least information on where the fault has occurred.
    [5]
    5. - Ground fault detection method in electrical installations with conversion between alternating current and direct current, according to claim 1, characterized in that the comparison stage and the predetermined values are represented as follows:
    ^ 1.7
    [6]
    6. - Ground fault detection method in electrical installations with conversion between alternating current and direct current, according to claim 1, characterized in that the comparison stage and the predetermined values are represented as follows:
    ^ 1.7 I shot.A C
    A), 7 Idisparo.D C
    where:
    l1j: is the value of the current circulating through at least one grounding device at the fundamental frequency of a zone j;
    I0j: is the value of the current flowing through at least one grounding device in a direct current component of a direct current zone j;
    IdisparoAC: it is the current adjustment value previously defined for the detection system to emit a fault signal in alternating current areas; IdisparoDC: is the current setting value previously defined for the detection system to emit a fault signal in direct current areas.
    [7]
    7. - Ground fault detection method in electrical installations with conversion between alternating current and direct current, according to claim 1, characterized in that the step of calculating the fault polarity (26) in the event that the amplitude for zero frequency exceeds the default value (23), is carried out by calculating:
    U0J - | U0 j | = 2 • U0ij
    which determines a fault in the positive pole; and alternatively:
    Uoj ~ Uoj = 0
    which determines fault in the negative pole.
    [8]
    8. - Ground fault detection method in electrical installations with conversion between alternating current and direct current, according to claim 1, characterized in that the step of calculating the fault polarity (26) in case the amplitude for zero frequency exceeds the default value (23), is carried out by calculating:
    Io, j ~ Io, j = 0
    which determines a fault in the positive pole; and alternatively:
    A), y - IA) j I = 2 • i 0J
    which determines fault in the negative pole.
    [9]
    9. - Ground fault detection method in electrical installations with conversion between alternating current and direct current, according to one of claims 1 to 8, in which the ground fault signal (28) comprises at least at least information from where the fault has occurred selected between:
    - side of the alternating current of the network between the neutral of the transformer and the terminals of a converter-rectifier if the fundamental frequency is the network frequency;
    - positive pole on the direct current side if a direct current component of opposite sign is detected;
    - positive pole on the direct current side if a direct current component of opposite sign is detected;
    - AC side of the controlled drive if the recorded current wave shows a fundamental frequency different from the mains frequency.
    [10]
    10.- Ground fault detection system in electrical installations with conversion between alternating current and direct current, characterized in that it comprises:
    • an earthing device (4) connectable between a neutral of an electrical installation and earth;
    • a frequency meter (14) located on a controlled side where a variator / variable frequency controller / inverter is located and which generates an alternating current signal on the controlled side;
    • a processor (5) configured to:
    or measure a voltage / current signal between the ends of the grounding device (4);
    or calculate harmonics of the signal previously measured by applying the fast Fourier transform FFT; and to calculate amplitudes of the signal previously measured at the following fundamental frequencies for each of the harmonics: zero frequency for direct current; mains frequency for a power supply with alternating current; and, variable frequency of alternating current on a controlled side;
    or comparing the amplitudes of each frequency with predetermined values of trigger settings for direct current, mains alternating current and alternating current on the controlled side; and,
    or calculating a fault polarity in case the amplitude for zero frequency exceeds the predetermined value; and, emitting a ground fault signal, when at least one of the following conditions is met: the amplitude for zero frequency exceeds the predetermined value, the amplitude for network frequency exceeds the predetermined value, and the amplitude for variable frequency exceeds the default value.
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    同族专利:
    公开号 | 公开日
    ES2798348B2|2021-08-05|
    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    US20130322133A1|2012-06-04|2013-12-05|Huaqiang Li|System and method for high resistance ground fault detection and protection in power distribution systems|
    US20200166558A1|2017-07-27|2020-05-28|Siemens Aktiengesellschaft|Location of a ground fault in an it network|
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