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    • 专利摘要:
    The present invention describes a method and an implementation device for determining the state of the neutral conductor in an electrical distribution system of b.t. By means of the indirect determination of the real value of the resistance of the neutral conductor, as well as other parameters that inform on the state of said conductor, such as its real section and the energy losses in it, using for this the value of the component of the neutral power of the system measured in the loads at the fundamental frequency. (Machine-translation by Google Translate, not legally binding)
    公开号:ES2588260A1
    申请号:ES201630767
    申请日:2016-06-07
    公开日:2016-10-31
    发明作者:Vicente LEÓN MARTÍNEZ；Joaquín MONTAÑANA ROMEU
    申请人:Universidad Politecnica de Valencia；
    IPC主号:
    专利说明:

    DESCRIPTION

    PROCEDURE AND DEVICE FOR THE DETERMINATION OF THE STATE OF THE NEUTRAL DRIVER IN AN ELECTRICAL INSTALLATION
     5
    Field of the Invention
    The present invention relates generally to the determination of the conservation state of the neutral conductor in the low voltage electrical distribution (BT) installations and to the indirect measurement of the resistance, section and losses in said conductor, based on the analysis of the energetic effects that the neutral conductor produces on the electrical receivers and, more specifically, to the measure of the neutral power of the loads, as well as its application in instruments of 15 measurement dedicated to the preventive surveillance of the neutral conductor and in the realization of load protection devices and electrical installations, in general.

    Background of the invention
    The neutral conductor in the electrical distribution installations of B.T. It has the mission of maintaining balanced the voltages of the phases of the receivers, with effective values equal or approximate to the nominal value of the voltage of the mains, as well as facilitating the evacuation of a part of the effects of the imbalances (and also of harmonic distortions), through the neutral current. The breakage or the decrease in the effective section of the neutral conductor in the electrical networks give rise to effects well known in industrial practice. In general, the receivers of the electrical installations are subjected to permanent surges (F. Redondo Quintela and others, “Overvoltages
    by neutral cut ”. University of Salamanca), which usually lead to the deterioration of these receivers and their subsequent decommissioning. The presence of overvoltages in the loads due, in this case, to the increase in the value of the third harmonics of voltage 5 are studied in the publications “The Effect of Neutral Path Impedance on Voltage and Current Distortion. Parts I and II ”, presented by A.E. Emanuel and J.A. Orr at the 2004 11th Conference on Harmonics and Quality of Power. These effects on the load voltages show the importance of knowing the state of the neutral conductor at all times and the need to have protection devices for electrical installations against untimely failures of the neutral conductor.
    The deterioration of the neutral conductor can be known by direct and indirect procedures. The former consist of the measurement on the neutral conductor itself, applying techniques such as signal reflectometry (in time or frequency), to know its continuity. The indirect procedures mainly used until the present moment are two. The first is based on the monitoring of the voltages in the phases of the receivers and their protection, by means of maximum and minimum voltage relays, against overvoltages and undervoltages that occur as a result of the deterioration of the neutral conductor 25. However, this procedure does not allow for real preventive maintenance, since the relays act when the fault in the neutral conductor is very important and, sometimes, when the lines work in conditions much lower than their nominal operation, 30 this system of protection is inoperative, since, in these cases, significant decreases in the neutral conductor section may occur, without the tensions in
    the phases of the receptors increase significantly.
    The second indirect procedure consists in the measurement of the circulating currents through the neutral conductor. The vast majority of systems based on this procedure have been applied to the monitoring of the neutral grounding conductor, rather than to the detection of the neutral conductor state itself. However, in US Patent 4012668A ("Ground fault and neutral fault detection circuit"), published on March 15, 1977, a system of protection of 10 installations against earth faults is described, consisting of measuring the difference of the currents in the lines and in the neutral, which could also be used to detect faults in the neutral conductor. Its main drawback is that when the differences between the currents of the 15 phases and the neutral are very small, the error can become important.
    Therefore, there is still a need in the art for an alternative procedure that allows determining the state of conservation of the neutral conductor in an electrical installation in order to provide preventive maintenance and protection of the electrical network.

    Summary of the invention
    In order to solve the problems of the prior art, 25 a new indirect procedure is described herein which, unlike those indicated above, is able to measure with real accuracy the actual resistance and, therefore, the actual physical section of the conductor neutral at any time, ensuring, in this way, a true preventive maintenance and effective protection of the electrical networks against deterioration or cutting of the neutral conductor. This procedure is based on
    the measurement of the energy impact of the neutral conductor on the loads.
    The energy effects of the neutral conductor in electrical installations are determined by a new magnitude, developed by the authors of the present invention, which has been termed "system neutral power" (Sn). Its formulation and some of its properties are described for the first time in this document, applied to the detection of the conservation state of the neutral conductor and to the protection of electrical installations.
    The neutral power of the system (Sn) is not one of the well-known active, reactive and apparent powers of the neutral, which are determined by the neutral current. This is a new power, obtained from 15 of the methodology proposed in this document, whose expression implicitly includes the previous powers, in addition to the products of voltages and currents that represent the imbalance and distortion energies, which are manifest in the electrical networks 20 as a result of the operation of the neutral conductor.
    Therefore, the present invention discloses a method and an implementation device for indirect determination of the real value of the neutral conductor resistance in electrical installations of BT distribution, as well as other parameters that inform on the state of said conductor, such as its real section and the energy losses in it, using the value of the neutral power component of the system measured in the loads at the fundamental frequency.
    Specifically, the present invention discloses a method for determining the state of the
    neutral conductor in an electrical installation comprising:
    i) calculate the theoretical resistance of the neutral () at the initial moment, based on the following characteristics of the line: initial nominal conductor section (A0), generally known, 5 estimated or measured cable length (10) and conductivity ( 0) of the conductor used (usually of copper or aluminum), at the nominal working temperature of the cable, determined by current regulations, 10 depending on the type of line (underground, aerial or indoor), 0nr
      [one]
    ii) acquire the instantaneous values of voltage (vA, vB, vC) and intensity (iA, iB, iC) of the phases (A, B, 15 C) at the point of connection of the loads with the mains, separating their components at the fundamental frequency (vA1, vB1, vC1) and (iA1, iB1, iC1), of the non-fundamental frequency currents (iAh, iBh, iCh); twenty
    ii-a) determine, from the components at the fundamental frequency, the homopolar sequence components at the fundamental frequency of the voltages (v01l) and currents (i01); 25
    iii) obtain the offset angle between the voltages and currents of homopolar sequence in the load, at the fundamental frequency (01l), as the difference between the initial phase of said voltages and currents (01l, 01): 30
     [2]
    iv) calculate the neutral power of the load at the fundamental frequency (Sn1l) according to the following expression:
     [3]
    v) determine the value of the relative difference c 5 between the neutral power of the load and the neutral power of the system, beginning by substituting the value = in the following potential function cnr
     [4] 10
    in which the values of k and a are known from tables shown hereinafter;
    vi) calculate the neutral power of the system at the fundamental frequency (), such as: 15 cns1
     [5]
    vii) determine the neutral power of the source at the fundamental frequency () based on the following expression: csnS1
     [6] 20
    viii) obtain the effective value of the homopolar sequence voltage at the source, at the fundamental frequency (), according to the expression: csV01
     [7]
    ix) calculate the offset angle () between the 25 cs01
    voltages and currents of homopolar sequence at the source, at the fundamental frequency, according to the expression:
     [8]
    x) determine the active powers of the homopolar sequence 5 of the source () and the load (P01l), at the fundamental frequency, based on the following expressions: csP01
     [9]
    in which the first is calculated, while the second is obtained from voltages and currents measured in the load;
    xi) calculate the losses in the neutral conductor at the fundamental frequency such as:
     [10] 15
    xii) obtain the calculated resistance of the neutral () from the following relation: cnr
     [eleven]
    xiii) in the event that the value of is very close to, the real resistance of the neutral conductor is determined and coincides with the theoretical value obtained at the initial moment of the procedure, 0nr
     [12]
    xiv) in case the values of y differ, repeat steps v) to xii), using the value 25 obtained each time in stage xii) until reaching a convergence value (), which will be cnr0nrconvnr
    the actual value of the neutral resistance,
     [13]
    xv) obtain the actual neutral conductor section as:
     [fifteen]
    If the actual section of the neutral conductor 5 decreases below a certain threshold with respect to the initial section of the neutral conductor, the procedure may include the step of issuing an alarm and / or opening the installation for protection.
    The present invention also discloses a device for determining the condition of the neutral conductor in an electrical installation. The device comprises:
    - means of entry for the introduction of data by a user; fifteen
    - physical means of measurement and acquisition of electrical signals; Y
    - programmable calculation means for carrying out the calculations of the process according to the present invention. twenty
    Preferred embodiments of the method and device of the present invention are defined in the dependent claims.

    Brief description of figures 25
    To complement the description of the procedure and device for the indirect determination of the resistance of the neutral conductor and of other magnitudes, such as the section and the energy losses, which inform the state of conservation and operation of said conductor, and in order to help to a better understanding
    of the features of the invention, according to preferred examples of practical implementation thereof, an assembly of drawings is attached as an integral part of said description, where, as an illustration and not limitation, the following has been represented:
    Figure 1 is a graph representing the variation of the relative difference () between the neutral power of the load and the neutral power of the system as a function of the increase in neutral resistance.
    Figure 2 shows the trend line of the relative difference between the neutral power of the load and the system as a function of the increase in neutral resistance, for a 30 m, 25 mm2 section cable and temperatures of 30ºC and 70 ° C, and its adjustment to a potential function. fifteen
    Figure 3 is a diagram showing the operational sequence of the process according to a preferred embodiment of the invention, applicable to measuring and monitoring instruments of the neutral conductor state.
    Figure 4 is a diagram showing an embodiment of a device for measuring resistance, section and losses in the neutral conductor.
    Figure 5 is a diagram showing the programming modules for the instrument for measuring and monitoring the condition of the neutral conductor according to a preferred embodiment of the present invention.
    Figure 6 shows a possible arrangement of the display of the measuring instrument and monitoring the condition of the neutral conductor.
    Figure 7 is a diagram showing the operational sequence 30 of the process according to an embodiment of the invention applied to the protection of electrical installations against deterioration of the neutral conductor.
    Figure 8 is a diagram showing an embodiment of a relay for protection of electrical installations against deterioration of the neutral conductor.
    Figure 9 is a diagram showing the programming modules for the protection relay of electrical installations 5 against the deterioration of the neutral conductor.
    Figure 10 is a diagram depicting the increase in load voltage as a function of the increase in neutral conductor resistance.
     10
    Detailed description of the preferred embodiments
    The "neutral power of the system" (Sn) is a magnitude that measures the combined effect of the energies that are manifested in electrical installations as a result of the operation of the neutral conductor, which can be noticed by the different value of the apparent powers of directly connected sources and loads. The existence of the neutral power of the system is necessary to verify the principle of conservation of energy in the whole of the electrical system. The module of the neutral power of the system at the fundamental frequency (50-60 Hz) responds to the following expression:

    in which V01l and V01s are the effective values of the 25 components of the homopolar sequence of the voltages in the phases of the load and of the source, respectively, measured at the fundamental frequency at the point of connection of the loads with the mains , and Ia1, Ib1, Ic1 are the effective values of the fundamental frequency currents measured in the phases of the load. The neutral power of the system has apparent power units. In its
    expression implicitly includes Joule losses in the neutral conductor (as well as the reactive power of the neutral); for this reason, the system's neutral power (Sn1) and the neutral conductor resistance (rn) are related. 5
    From the point of view of its practical utility, two components of the neutral power of the system are distinguished in the first instance. The first component, Sn1s, is the neutral power of the source, a quantity that quantifies the effects of the neutral on the transformer and 10 lines. The second component, Sn1l, is the neutral power of the charges, which measures the energy impact of the neutral conductor on the receivers; its value is generally greater than Sn1s and increases significantly as the neutral resistance increases. This component of the neutral power of the system makes it possible to explain, from an energy point of view, the existence of overvoltages in the loads and the greater value of the apparent power of the unbalanced and distorted loads, above the apparent power of the 20 sources, as a consequence of the deterioration of the neutral conductor.
    The value of the neutral power of the loads (Sn1l) depends, logically, on the electrical installation where this magnitude is measured. However, based on previous analyzes performed, it has been found that its relative difference () with the neutral power of the system (Sn1),

    It is completely independent of the loads and, for a given line, it only depends on the value of the neutral resistance (rn). This fact has great practical importance in
    The present invention, therefore considerably simplifies the method and the device for obtaining the neutral resistance, avoiding the need to simultaneously measure the source (which is generally very restricted access) and the loads. According to the present invention, the value of the neutral resistance can be determined with great accuracy by measuring only at the point of connection of the loads with the mains.
    The relative difference, , between the neutral power of the loads (Sn1l) and the neutral power of the system 10 (Sn1) is equal to 1 in the ideal case of neutral resistance equal to zero (rn = 0) and, for each line of characteristics (length, section, working temperature, etc.) determined, it evolves towards zero according to a potential function, as the resistance value of the neutral (rn) increases, which responds to the following general expression:

    in which the coefficients k and a are independent of the load; and they have been tabulated and are available for the different standardized sections and cable lengths, 20 at the normal working temperatures of the conductor, set by current regulations. The following tables show values of the coefficients k and a for different sections and cable lengths, at temperatures of 30ºC and 70ºC: 25

        A0 mm2  Insulated copper cable lengths at 30 ° C, 10 (m)
     10  20 30 40 50 75 100
     K 10-2  a K 10-2 a K 10-2 a K 10-2 a K 10-2 a K 10-2 a K 10-2 a
     10  6.36 1.59 4.35 1,637 3.86 1.65 3.65 1,657 3.52 1,662 3.4 1.67 3.34 1.67
     16  9.22 1,532 5.35 1,612 4.39 1,635 4.00 1,646 3.79 1,653 3.55 1.66 3.45 1,664
     25  15.15 1,421 7.61 1,563 5.61 1,606 4.78 1,626 4.35 1,637 3.86 1.65 3.65 1,657
     35  21.5 1,305 10.42 1,509 7.17 1,573 5.78 1,602 5,06 1,619 4.24 1.64 3.9 1,649
     fifty  30.3 1,144 15.15 1,421 9.95 1,517 7.61 1,563 6.36 1,589 4.94 1.62 4.35 1,637
     70  39.6 0.968 21.5 1.305 14.04 1.44 10.42 1.509 8.4 1.548 6.04 1.60 5.06 1,619
     95  46.16 0.841 27 1.205 17.97 1.369 13.25 1.456 10.52 1.507 7.22 1.57 5.82 1.601
     120  54.41 0.676 35.34 1.05 24.65 1,248 18.4 1,362 14.53 1,432 9.57 1.53 7.36 1,569

        A0 mm2  Insulated copper cable lengths at 70 ° C, 10 (m)
     10  20 30 40 50 75 100
     K 10-2  a K 10-2 a K 10-2 a K 10-2 a K 10-2 a K 10-2 a K 10-2 a
     10  5.76 1.603 4.14 1,642 3.74 1.65 3.58 1.66 3.47 1,663 3.37 1,667 3.32 1,669
     16  8.38 1,552 5.05 1,523 4.23 1.64 3.91 1,658 3.72 1,659 3.51 1,652 3.42 1,659
     25  13.08 1.459 6.79 1.58 5.17 1.62 4.49 1,633 4.15 1,642 3.75 1,654 3.58 1.66
     35  18.59 1,358 9.08 1,354 6.41 1.59 5.3 1.613 4.71 1,627 4.05 1,645 3.78 1,653
     fifty  26.7 1.21 13.08 1,459 8.71 1.54 6.79 1.58 5.77 1.602 4.62 1.63 4.15 1,642
     70  36.08 1,036 18.91 1,352 12.32 1.47 9.22 1,532 7.53 1,565 5.56 1,607 4.75 1,626
     95  44.35 0.876 25.39 1,234 16.79 1.39 12.38 1,472 9.86 1,519 6.85 1,579 5.58 1,607
     120  50.81 0.748 31.49 1,122 21.46 1.31 15.88 1.41 12.54 1,649 8.39 1,548 6.58 1,585

    Values of k and a can be obtained for intermediate lengths and temperatures to those of the previous tables by interpolation. 5
    Figure 1 shows the evolution of the relative difference between the neutral power of the load and the neutral power of the system as a function of the increase in neutral resistance, for different cable lengths, with a section of 10 mm2 and a temperature of 70 ° C.
    Figure 2 shows the trend line of the relative difference () between the neutral power of the load and the system as a function of the increase in neutral resistance, for a 30 m, 25 mm2 cable with a 15 section and at temperatures of 30ºC and 70ºC, as well as its adjustment to a potential function.
    These two figures 1 and 2 thus illustrate how the relative difference () evolves towards zero according to a potential function, as the value of the
    neutral resistance (rn), for different values of cable length, cable section and working temperature.
    As mentioned above, the present invention discloses according to a first aspect a method for determining the state of the neutral conductor in an electrical installation by indirect measurement of the resistance, section and energy losses in the neutral conductor of the electrical installations BT distribution According to a preferred embodiment 10, the process of the invention comprises:
    i) calculate the theoretical resistance of the neutral () at the initial moment of the procedure, from the following characteristics of the line: conductor nominal section (A0), generally known, estimated or measured length of the cable (10) and conductivity (0) of the conductor used (usually copper or aluminum), at the nominal working temperature of the cable, determined by current regulations, depending on the type of line 20 (underground, aerial or indoor),
      [one]
    ii) acquire the instantaneous values of voltage (vA, vB, vC) and intensity (iA, iB, iC) of the phases (A, B, C) at the point of connection of the loads with the electrical network 25, separating their components at the fundamental frequency (vA1, vB1, vC1) and (iA1, iB1, iC1), of the non-fundamental frequency currents (iAh, iBh, iCh);
    ii-a) determine, from the components at the fundamental frequency, the components of
    homopolar sequence at the fundamental frequency of the voltages (v01l) and currents (i01),
    ii-b) optionally, determine, from the non-fundamental frequency currents, the 5 harmonic third-party currents (i0h);
    iii) obtain the offset angle between the voltages and currents of homopolar sequence in the load, at the fundamental frequency (01l), as the difference between the initial phase of said voltages and 10 currents (01l, 01):
     [2]
    iv) calculate the neutral power of the load at the fundamental frequency (Sn1l) according to the following expression:
     [3]
    v) determine the value of the relative difference c between the neutral power of the load and the neutral power of the system, beginning by replacing the value = in the following potential function 20
     [4]
    in which the values of k and a are those shown in the previous tables for different sections (A0) and lengths (10) of the cables, for two 25 working temperatures thereof: 30ºC and 70ºC.
    vi) calculate the neutral power of the system at the fundamental frequency (), such as:
     [5]
    vii) determine the neutral power of the source at the fundamental frequency () based on the following expression:
     [6]
    viii) obtain the effective value of the homopolar sequence voltage 5 at the source, at the fundamental frequency (), according to the expression:
     [7]
    ix) calculate the offset angle () between the voltages and currents of the homopolar sequence at the source, at the fundamental frequency, according to the expression:
     [8]
    x) determine the active powers of the homopolar sequence of the source () and the load (P01l), at 15 the fundamental frequency, based on the following expressions:
     [9]
    in which the first one is calculated, while the second one is obtained from voltages and 20 currents measured in the load;
    xi) calculate the losses in the neutral conductor at the fundamental frequency such as:
     [10]
    xii) obtain the calculated resistance of the neutral () from the following relation:
     [eleven]
    xiii) in the event that the value of is very close to (the acceptable difference between both values can be set by the user, depending on the maximum permissible error), the actual resistance 5 of the neutral conductor is determined and coincides with the theoretical value obtained at the initial moment of the procedure,
     [12]
    xiv) in case the values of y differ, repeat steps v) to xii), using the value obtained each time in stage xii) until a convergence value () is reached, which will be the value real neutral resistance,
     [13] 15
    xiv ’) optionally, determine the actual losses in the neutral conductor, based on the following expression:
     [14]
    in which I0h is the effective value of the third harmonics; Y
    xv) obtain the actual neutral conductor section as:
     [fifteen]
    The length of the cable (10) can be estimated quite closely with the naked eye, mainly in 25 low voltage installations, in which the lengths are usually not large. It can also be measured using any of several procedures known to the
    skilled in the art, such as based on the plans of the installation, by the use of meters or by devices such as reflectometers.
    According to a preferred embodiment of the present invention, the method further includes the step of issuing an alarm to notify a user of a hazardous situation in case the actual section of the neutral conductor decreases below a certain threshold with respect to the initial section of the neutral conductor.
    The amount of decrease in the section of the conductor 10 that results in a hazardous situation depends on each application and can be easily determined by one skilled in the art. Specifically, it depends on whether the line being analyzed is heavily loaded or underloaded. In a low-charged line, reductions of up to 5 times, 15 or even higher, can occur in the neutral section without any overvoltages in the load phases being noticeable. However, in a heavily charged line, neutral reductions of only 25% are sufficient for overvoltages in the installation to be dangerous. According to a preferred embodiment 20, a hazard threshold is defined for decreases in the neutral section between 25% and 50% of its nominal value.
    Figure 10 shows a diagram that represents the increase in the load voltage as a function of the resistance of the neutral conductor, related to the decrease in the section of the same. In this case it is a copper line, 50 m long and 50 mm2 in section, with PVC insulation, working in two situations: unloaded and heavily charged. An increase of 5 30 times the resistance of the neutral conductor means that said conductor is very damaged; about to cut. As can be seen in the figure, if the line that
    Connects to the transformer with the electrical installation working poorly charged, increases of up to 5 times in the resistance of said conductor can occur (which is equivalent to decreases of the same value in its section) without the voltage in the load being dangerous (236,82 V). However, in a very charged line, increases in neutral resistance of just 2 times are sufficient to reach dangerous voltage values (close to 240 V).
    According to another preferred embodiment of the present invention, the method further includes the step of opening the installation to protect it in case the actual section of the neutral conductor decreases below a certain threshold with respect to the initial section of the neutral conductor.
    According to a preferred embodiment of the present invention, a device for determining the neutral conductor status of an electrical installation is disclosed, comprising:
    - means of entry for the introduction of data by a user; twenty
    - physical means of measurement and acquisition of electrical signals; Y
    - programmable calculation means for carrying out the calculations of the process according to the present invention. 25
    According to a preferred embodiment, the device further comprises display means to present to the user the result of at least one of the values obtained by the programmable calculation means.
    According to another preferred embodiment, the input means 30 and the display means are combined forming a touch screen. According to other embodiments of the invention, the input means may be constituted by a
    keyboard, push buttons, rotary buttons, etc., while the display means consist of a screen, light media (lights, LEDs, etc.) and the like.
    Figure 3 shows a preferred embodiment of the method for indirect determination of the neutral resistance according to the present invention and its application to network analyzers and instruments for monitoring the conservation status of the neutral conductor in electrical installations. The procedure comprises the following 10 stages:
    - Digital processing (1) of sampled signals obtained by physical means (see Figure 4) for measuring and acquiring electrical signals from the device, obtaining (in 3) the effective values and the initial phases of the third harmonics of current, and also obtaining (in 4) the matrices of effective values and initial phases of voltage and intensity at fundamental frequency for each phase, in total six matrices for each phase of voltage and intensity. twenty
    - With these matrices the effective values and initial phases of the homopolar sequence components of the voltages and currents of the load at the fundamental frequency are obtained (in 5).
    - From the arrays of effective values of 25 intensity for the fundamental frequency (in 4) and the homopolar sequence voltage (in 5), the neutral powers of the load at the fundamental frequency (in 6) are obtained, according to the expression [3] shown above.
    - From the initial characteristics of the line (section, length, conductivity of the conductor, according to its working temperature), the initial (theoretical) resistance of the line is obtained (in 2), according to the
    expression [1], indicated above.
    - From the tables containing the values of the coefficients kya, shown above, and the initial value of the neutral resistance [1], the relative difference between the neutral power of the load and the neutral power is obtained of the system according to the expression [4], where this last power is determined, as indicated in the expression [5] shown above, as well as the neutral power of the source, applying the expression [6], shown previously. 10
    - From the neutral power of the source and the effective values of the line currents, the effective value of the homopolar voltage of the source is obtained, according to the expression [7] shown above, as well as the angle is calculated of offset between said voltage and the homopolar current of the source according to the expression [8], in which the offset angle between the voltages and homopolar sequence currents in the load have been determined according to the expression [2], indicated above. twenty
    - From the voltages and currents of the homopolar sequence in the phases of the source and the load, and of their respective offset angles, the active powers of the homopolar sequence in the source (subscript s) and in the load are obtained ( subscript l), according to the 25 expressions [9] shown above.
    - From the active powers of the homopolar sequence of the source and the load, the losses in the neutral conductor are obtained, according to the expression [10], as well as the calculated resistance of the neutral, according to the expression [11 ], indicated above.
    - From the actual neutral resistance, defined by the expression [12] or the expression [13],
    indicated above, the real losses of the neutral are obtained (in 8), according to the expression [14], and the real section of the neutral conductor (in 8), according to the expression [15], both indicated above.
    - The graphical and numerical information of the neutral resistance, its section and the losses in the neutral conductor, as well as certain values of the physical quantities used during the procedure, are displayed (in 9) on display means, for example on a screen 10
    Figure 4 shows a device for the implementation of the procedure described above shown in Figure 3. In this case, the device comprises physical means for measuring and acquiring electrical signals (A) (hardware) and a processor ( B), as well as a measurement program (calculation means) of the neutral resistance (C) and display means (D).
    The physical means (A) comprise signal conditioners and a data acquisition card; the former adapt the instantaneous values of the secondary voltages and currents of a voltage and intensity measurement sensors (E), so that the voltages at their outputs may be applicable to the analog inputs of the acquisition card or media 25 equivalent, which converts the analog voltage and intensity signals into a series of discrete samples that are used as input in the measurement program. There is also a processor (B) with a motherboard on which the acquisition card is placed so that discrete samples of the voltage and intensity signals can be exchanged with the measurement program (C), into which they can be inserted the initial specifications of
    the line and the neutral (section, length and conductor). In addition there is a touch screen or other display means (D) in which all the information about the waveforms and the value of all the electrical quantities related to the measurement of the neutral conductor resistance, of its section and losses, namely: voltages, intensities, neutral powers of the system and its components at the source and in the load.
    The measurement program (C) comprises the following modules (figure 5): 10
    - Digital signal processing module (11), which acquires voltage and intensity samples, and saves them in a vector for each of them.
    - Theoretical neutral resistance module (13), which calculates the initial neutral resistance, according to the expression [1], based on the section, length and conductivity data of the conductor entered in the user data input ( 12).
    - Analysis module (14), in which the effective values and the initial phase of the tensions and 20 fundamental frequency currents, as well as the harmonic third-party currents, are obtained from the samples acquired in the digital processing module signal (11).
    - Symmetric module (15), which obtains the matrices of the homopolar sequence components, in effective value 25 and in phase, of the voltages and currents of the load at the fundamental frequency, from the matrices obtained in the previous module .
    - Neutral powers module (16), in charge of obtaining the values of the neutral powers of the system 30 and its components at the source and in the load, as well as the homopolar sequence powers at the source and in the load and energy losses in the neutral conductor,
    according to the expressions [2] to [10], based on the voltage and current matrices of the two previous modules, as well as the relative difference value matrices of the neutral powers of the load and the system, corresponding to each value of the theoretical resistance of the neutral 5, obtained in the module (13).
    - Neutral and loss resistance module (17), in which the resistance and the actual section of the neutral conductor are obtained, as well as the losses in said conductor, based on the data obtained in the neutral power module 10 (16 ), according to the expressions [11] to [15].
    - Visualization module (18), responsible for displaying on a screen the graphic and numerical information of the resistance, section and losses in the neutral conductor, as well as the information on the state of conservation of said conductor in a bar with three colors (green, yellow or orange and red), as shown in figure 6.
    Although not shown in the figures, according to a preferred embodiment of the invention, the device 20 further comprises alarm means for issuing an alarm to notify a user of a dangerous situation in case the actual section of the neutral conductor decreases by below a certain threshold with respect to the initial section of the neutral conductor. The alarm 25 emitted by said alarm means can be, for example, an acoustic alarm, a visual alarm or a combination of both.
    Figure 7 shows another possible embodiment of the procedure for indirect determination of the neutral resistance and its application to protection devices of electrical installations against the deterioration of the neutral conductor (protection relays), object of the
    present invention It includes the same operations (1), (2), (4), (5) and (6) of the previous procedure, applied to the performance of network analyzers and instruments for monitoring the neutral status, although in this case it is not Necessary calculation of the third harmonics (3), or 5 losses in the neutral conductor (8). As a difference, the present procedure integrates the calculation of the neutral conductor section within step 7. Specifically, from the active powers of the homopolar sequence of the source and the load, according to the expressions [9], it obtains (in 7) the real resistance of the neutral, according to the expressions [10] to [13], as well as the real section of the neutral conductor (in 7), according to the expression [15], indicated above.
    Additionally, the procedure comprises the following new stage:
    - Depending on the values of the resistance and the actual section of the neutral conductor and its comparison with a set value as a reference (between 1.25 and 1.5 times the nominal resistance of the neutral conductor), means will be activated. of protection (in 10), which can be the activation coil of a mechanical switch or the trip circuit for a static switch.
    The device for implementing the protection procedure, as shown in Figure 25 8, comprises physical means for measuring and acquiring electrical signals (A) (hardware) and a processor (B), as well as a program of measurement (calculation means) of the neutral resistance (F) and protection means (G) formed by activation means (H) and a switch 30 (I).
    The output signals of the internal voltage and intensity measurement sensors (E) are adapted by
    signal conditioners and are applied to the analog inputs of a data acquisition card or equivalent means, elements, all of them, which integrate the physical data acquisition means (A), shown in Figure 8. The acquisition card of data is arranged on a motherboard of a processor (B), which exchanges with the program (F) discrete samples of voltage and intensity signals, coming from the data acquisition card; the program (F) supports the introduction of the initial specifications of the line 10 and the neutral (section, length and conductivity of the conductor), by the user, and exchanges information with the activation means (H) of the protection means (G), managing the application or not of an activation signal of a switch (I), obtained through physical means (A), depending on the conditions in which the neutral conductor is.
    Program (F) consists of the same modules (11) through (15), with similar functions as in the application for network analyzers and monitoring instruments of the neutral conductor state described above, and additionally comprises the following modules (figure 9):
    - Neutral power module (19), responsible for obtaining the values of the neutral powers of the system 25 and its components at the source and in the load, according to the expressions [2] to [10], from the voltage and current matrices of the modules (14) and (15), as well as the matrices of relative difference values of the neutral powers of the load and of the system, 30 corresponding to each value of the theoretical neutral resistance, obtained in module (13); this module also integrates the calculation of the resistance and the actual section
    of the neutral conductor, according to the expressions [11], [12], [13] and [15], it is not strictly necessary to determine the losses in the neutral for this application.
    - Protection module (20), responsible for deciding the application of the switch activation signal (I) based on the resistance value (or section) of the neutral conductor, obtained from the previous module.
    The invention has been described according to preferred embodiments thereof, but it will be apparent to the person skilled in the art 10 that multiple variations can be introduced into said preferred embodiments without departing from the object of the claimed invention.
    权利要求:
    Claims (18)
    [1]
    1. Procedure for determining the condition of the neutral conductor in an electrical installation comprising the steps of:
    i) calculate the theoretical resistance of the neutral () 5 at the initial moment, based on the following characteristics of the line: initial nominal conductor section (A0), generally known, estimated or measured cable length (10) and conductivity ( 0) of the conductor used 10 (usually of copper or aluminum), at the nominal working temperature of the cable, determined by the regulations in force, depending on the type of line (underground, aerial or indoor), 15
      [one]
    ii) acquire the instantaneous values of voltage (vA, vB, vC) and intensity (iA, iB, iC) of the phases (A, B, C) at the point of connection of the loads with the mains, separating their components at the fundamental frequency, (vA1, vB1, vC1) and (iA1, iB1, iC1), of the non-fundamental frequency currents (iAh, iBh, iCh);
    ii-a) determine, from the components at the fundamental frequency, the 25 components of the homopolar sequence at the fundamental frequency of the voltages (v01l) and currents (i01);
    iii) obtain the offset angle between the voltages and currents of homopolar sequence in the load, 30 at the fundamental frequency (01l), such as the
    difference between the initial phase of these voltages and currents (01l, 01):
     [2]
    iv) calculate the neutral power of the load at the fundamental frequency (Sn1l) according to the following expression:
     [3]
    v) determine the value of the relative difference c between the neutral power of the load and the neutral power of the system, starting with 10 replace the value = in the following potential function
     [4]
    in which the values of k and a are known from tables shown below in this document;
    vi) calculate the neutral power of the system at the fundamental frequency (), such as:
     [5]
    vii) determine the neutral power of the source at 20 the fundamental frequency () based on the following expression:
     [6]
    viii) obtain the effective value of the homopolar sequence voltage at the source, at the fundamental frequency (), according to the expression:
     [7]
    ix) calculate the offset angle () between the voltages and currents of homopolar sequence at the source, at the fundamental frequency, according to the expression:
     [8]
    x) determine the active powers of the homopolar sequence of the source () and the load (P01l), at the fundamental frequency, based on the following expressions:
     [9]
    in which the first one is calculated, while the second one is obtained from voltages and currents measured in the load;
    xi) calculate the losses in the neutral conductor at 15 the fundamental frequency as:
     [10]
    xii) obtain the calculated resistance of the neutral () from the following relation:
     [11] 20
    xiii) in the event that the value of is very close to, the actual resistance of the neutral conductor is determined and coincides with the theoretical value obtained at the initial moment of the procedure, 25
     [12]
    xiv) in case the values of y differ, repeat steps v) to xii), using the value obtained each time in stage xii) until reaching a convergence value (), which will be the real value of the 5 neutral resistance,
     [13]
    xv) obtain the actual neutral conductor section as:
     [15] 10
    [2]
    2. The method according to claim 1, further comprising step ii-b) of determining, from the non-fundamental frequency currents, the harmonic third-party currents (i0h).
    [3]
    3. Method according to claim 2, characterized in that it further comprises step xiv ’) of determining the real losses in the neutral conductor, based on the following expression:
     [14] [4]
    4. Method according to any of the preceding claims 20, characterized in that it further comprises the step of issuing an alarm to notify a user of a dangerous situation in case the actual section of the neutral conductor decreases below a certain threshold with with respect to the initial section 25 of the neutral conductor.
    [5]
    5. Method according to any of the preceding claims, characterized in that it further comprises the step of opening the installation to protect it in case the actual section of the neutral conductor decreases.
    below a certain threshold with respect to the initial section of the neutral conductor.
    [6]
    6. Device for determining the condition of the neutral conductor in an electrical installation, said device comprising:
    - means of entry for the introduction of data by a user;
    - physical means of measurement and acquisition of electrical signals; Y
    - programmable calculation means for carrying out the calculations of the method according to any one of claims 1 to 5.
    [7]
    7. Device according to claim 6, characterized in that it further comprises:
    - voltage and intensity measurement sensors; and 15
    - a processor.
    [8]
    Device according to claim 7, characterized in that the physical means for measuring and acquiring electrical signals comprise:
    - signal conditioners to adapt the values 20 provided by the voltage and intensity measurement sensors; Y
    - a data acquisition card that receives signals adapted from the signal conditioners and communicates them to the programmable calculation means 25 through the processor.
    [9]
    9. Device according to any of claims 6 to 8, characterized in that it further comprises display means for presenting to the user the result of at least one of the values obtained by the programmable calculation means.
    [10]
    10. Device according to claim 9, characterized in that the input means and the
    Visualization combine to form a touch screen.
    [11]
    Device according to any one of claims 6 to 10, characterized in that it further comprises alarm means for issuing an alarm to notify a user of a dangerous situation in case the actual section of the neutral conductor decreases below a certain threshold with respect to the initial section of the neutral conductor.
    [12]
    12. Device according to claim 11, characterized in that the alarm means emit an acoustic alarm.
    [13]
    13. Device according to any of claims 11 and 12, characterized in that the alarm means emits a visual alarm. fifteen
    [14]
    14. Device according to any of claims 6 to 13, characterized in that the calculation means comprise:
    - a digital signal processing module;
    - a theoretical neutral resistance module; twenty
    - an analysis module;
    - a symmetric module;
    - a neutral power module;
    - a module of neutral resistance and losses; Y
    - a display module. 25
    [15]
    15. Device according to any of claims 6 to 8 and 11 to 13, characterized in that it further comprises protection means for opening the installation to protect it in case the actual section of the neutral conductor decreases below a threshold 30 determined with with respect to the initial section of the neutral conductor.
    [16]
    16. Device according to claim 15, characterized
    because the protection means comprise activation means and a switch activated by the activation means.
    [17]
    17. Device according to claim 16, characterized in that the activation means is an activation coil.
    [18]
    18. Device according to any of claims 15 to 17, characterized in that the calculation means comprise:
    - a digital signal processing module; 10
    - a theoretical neutral resistance module;
    - an analysis module;
    - a symmetric module;
    - a neutral power module; Y
    - a protection module. fifteen
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    同族专利:
    公开号 | 公开日
    WO2017212088A1|2017-12-14|
    ES2588260B2|2017-05-09|
    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    US4012668A|1973-06-11|1977-03-15|Rca Corporation|Ground fault and neutral fault detection circuit|
    US20100102826A1|2006-11-24|2010-04-29|Karl Nathan Edwards|Power supply monitoring system|
    US8310370B1|2009-12-23|2012-11-13|Southern Company Services, Inc.|Smart circuit breaker with integrated energy management interface|
    EP2693227A2|2012-07-31|2014-02-05|Schneider Electric Industries SAS|System for detecting an impedance variation in a neutral conductor, transformer station including such a system and method for detecting an impedance variation in a neutral conductor with such a system|
    ES2712350B2|2018-11-14|2019-09-12|Univ Valencia Politecnica|PROCEDURE AND SYSTEM OF MEASUREMENT OF LACK OF SYMMETRY IN THREE-PHASE INDUCTION MOTORS|
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    PCT/ES2017/070185| WO2017212088A1|2016-06-07|2017-03-30|Method and device for determining the state of the neutral conductor in an electrical installation|
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