ES2324568A1 - "amperimetrica clip of leaks with measure of harmonics and diagnosis of the cause of the leak". (Machine-translation by Google Translate, not legally binding) - Google Patents

Abstract

Leakage current clamp with measurement of harmonics and diagnosis of the cause of the leak, which has means of display (12) of the information, means of selection (11) through which the user selects the mode of operation, a first microcontroller (5) with adc digital analog converter (6), a second microcontroller (10) which controls the display (12) and selection means (11) and which is connected to the first microcontroller (5), two terminals of input (1) for voltage measurement, two input terminals (2) for maxillary current measurement, conversion and adaptation means (3, 4) of the current and the input voltage to the voltage levels compatible with the input of the adc (6), said means (3, 4) being controlled from the first microcontroller (5) by means of an analogue switch. The present invention also includes a method for measuring leakage current using said clamp meter. (Machine-translation by Google Translate, not legally binding)

Description

Ammeter leakage clamp with measurement of Harmonics and diagnosis of the cause of the leak.

Field of the Invention

The present invention relates to a clamp High resolution digital ammeter for measuring both the current flowing through a certain conductor as of the voltage difference between two points of an electrical circuit, as well as power measures associated with that current and voltage. Said invention allows measuring with sufficient precision the currents that leak to the ground, including the study of harmonics of the signal, in addition to giving an idea about the cause that produces it. Although applicable to the measure of any current alternate that circulates through a conductor, the instrument is designed especially to measure the leakage current of a installation, this is the difference between the outgoing current and incoming from said installation.

State of the art

A clamp meter is a device intended for current measurement in a circuit under test or measurement without interrupting said circuit. That's your main utility or advantage over the measure alternative of the voltage drop in shunts or resistances that are due interleave in series within the circuit itself and on the branch in the that you want to know the circulating current.

In a clamp meter, the measurement of the current is performed indirectly, by valuing the magnetic field that generates all current in its environment. For facilitate its assessment, the magnetic field lines generated are "concentrate" or circumscribe an element of the clamp that It consists of a material with ferromagnetic properties and which is usually called "jaw" or "maxillary". The geometry of that jaw must remain closed during the process measurement (to prevent magnetic field lines from jumping over the air) but its opening must be possible to surround and embrace the conductor through which the current to be measured circulates. On the other hand, should not be sensitive to external magnetic fields that They could distort the measurement.

If the current to be measured is only alternating, a winding is formed in the jaw that constitutes the secondary of a current transformer and on which it will circulate a current proportional to the current to be measured and that will be treated and processed by the rest of the measurement circuit and instrumentation. If the current is continuous, it must be included inside the magnetic circuit some Hall effect sensors that they generate a voltage proportional to the magnetic field that the crosses, proportional to the current to be measured.

Current clamps are instruments widely demanded within the electricity sector and are usually distinguish two categories or types. First, the tweezers Conventional ammeters, capable of measuring currents of up to thousands of amps in alternating or continuous and that are equipped of large diameter jaws as they must surround conductors through which currents of these orders of magnitude circulate. In second, the "leakage" clamps, which are simply current clamps that have a high resolution (of the order of microamps) to be able to measure the small current that can be "leak" by the ground conductor, equivalent to imbalance that may appear between the "incoming" current and "outgoing" in a single phase installation. In all the cases, the circulation of that current is due to defects of insulation present in electrical installations and can cause the trip of the differential protection switch of installation. The detection of this current is essential to correct potential problems in the facilities.

In clamp meters, the  maximum current value with jaw size: currents high supposes large jaws, low currents are measured with small jaws For this reason the leakage clamps always they have small jaws and cannot be used in centers transformation, substations, etc. that have drivers of big size.

The present invention is tailored of leakage currents but pretending to give capacities added to those of similar products present in the market. For the measure of magnitudes in most of the clamps Current digital ammeters and multimeters are used A / D converters with double or single ramp with high conversion that only have the ability to convert signals continuous from its analog value to a digital value. Therefore in these types of devices when trying to measure a signal alternate the use of analog circuits is necessary averages or converters of true effective value, used to convert an analog signal into a continuous signal whose value be the effective of the alternate. Through these types of techniques you don't know You can get additional information about the signal.

Leakage currents may be caused for various reasons but in broad strokes they can be divided into two sets

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Leakage currents due to Insulation defects: This type of leakage is due to the current circulation between voltage terminals and parts grounded These currents are of the same frequency fundamental of the network (50 or 60 Hz) and have a low distortion harmonica

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Leakage currents due to non-linear loads: This other type of leakage is not due to failures of isolation but are currents derived to earth by the capacitors that incorporate the power supplies of the electronic equipment such as computers, televisions, etc. Due to the non-linearity of this type of loads, the currents consumed by them usually present a great distortion harmonica, which in turn implies a greater current drift in the upper harmonics through said capacitors

With the present invention it is intended not only be able to measure with sufficient precision the leaking currents at land but also intended to have an idea of the cause that It produces it. For this it is not enough to know the effective value of current leaks, you should have information about your harmonic content. Said harmonic content can be obtained by using the fast transform of Fourier (FFT) or through the use of analog filters. The 1 First method is the one used in the present invention and requires the realization of a sampling and a subsequent mathematical processing of the signal while the second method is fully analog and requires the use of a very large number of filters per which would not be applicable for a portable instrument and of small dimensions like this, in addition to that on the other hand it would imply a much higher final cost of the equipment.

Digital signal processing is a technique relatively recent that has been increasingly used in everyday equipment because the size and cost of microprocessors, A / D converters and DSPs (digital processors signal) has been reduced over recent years. Initially this type of 1 techniques were only used in equipment highly expensive and sophisticated due to the cost of its components. Through proper digital processing you can obtain parameters of the sampled signals using the mathematical calculation capacity of the referred circuits microelectronics, which translates into obtaining products with functionalities far superior to those of the equipment that they use conventional analog processing techniques, and where in addition the set of components of the circuit is seen noticeably reduced

In the market there are clamp meters of high range and high cost that use digital signal processing to get information about the harmonic content of a certain signal but none of them has the precision to measure leakage currents nor have the ability to give a diagnosis on the possible causes that produce a current of leak in a certain installation. With the present invention, you can get the harmonic decomposition as well as the THD (rate total harmonic distortion) and the CF (crest factor) of leakage currents of few milliamps. With these parameters you it can help determine the cause of the failure or leakage, but in addition, the team makes a diagnosis using a mathematical algorithm with the information obtained after harmonic decomposition.

Description of the invention

The present invention relates to a clamp ammeter of leaks with harmonic measurement and diagnosis of the cause of the leak and a procedure for measuring currents of leak according to claim 1 and claim 6, respectively. Preferred embodiments of the clamp meter and of the procedure are defined in the claims Dependents

The clamp meter, which works with the minus a battery, it has:

- display media where the user information, such as a glass screen LCD liquid;

- means of selection through which the user selects the operating mode of the clamp ammeter, such as a plurality of buttons and a rotary switch or selector;

- first means of data processing, especially a microcontroller (like a digital processor of signal (DSP)) with digital analog converter (ADC);

- two input terminals for jaw or jaw current measurement;

- means of conversion and adaptation of the input current at voltage levels compatible with the converter input, said conversion means being and adaptation controlled by at least one analog switch controlled in turn from the first means of processing data; Y

- second means of data processing, especially a microcontroller, which control the means of visualization and selection, said means being communicated with The first means of data processing.

The first means of data processing and the second means of data processing may be contained in a microprocessor or, conversely, the first data processing means may consist of a first microcontroller and the second means of data processing consist of a second microcontroller, which would be communicated with the first microcontroller via a bus communications, the second microcontroller being the device teacher. The communication that is established between the first microcontroller and the second microcontroller (10) can be, by example, bidirectional series.

The ammeter leakage clamp can have in addition to two input terminals for voltage measurement, in in which case the clamp meter also has means of adaptation of said input voltage to voltage levels compatible with the ADC input. These means of adaptation they can consist of a resistive divider, controlled from the first data processing means through a switch analogical.

An object of the present invention is also a procedure for measuring leakage currents, with measurement of harmonics and diagnosis of the cause of the leak, which uses the commented leakage clamp meter. The procedure includes the following stages:

a) user selection of the measure to be performed by the clamp meter;

b) request for measurement of the second means of data processing to the first means of processing data;

c) scale selection, carried out by first means of data processing, which is appropriate for measure;

d) sample capture, performed by first means of data processing prior conversion ADC analog-digital included in such media, of the voltage, current or both signal simultaneously, depending on the measurement request of the second means of data processing;

e) mathematical calculations to obtain the requested measure, made by the first means of processing of data;

f) sending the first means of data processing to the second processing means of data of the value of the calculated measure (shipment made through of the serial communication bus in case the first and second means of data processing are each a microcontroller); Y

g) presentation, made by the seconds means of data processing, of measurement in the means of display.

In the event that a measurement of the current signal or voltage signal, in step a) the selection is made from the following measures: effective value, maximum and minimum value, total harmonic distortion (THD), value Effective of the different harmonics, crest factor and value of peak. In the case that the measure of value has been selected effective or the measure of THD, in step g) can be shown in the simultaneously display the effective value and the THD

For when a measurement is made so simultaneous both of the current that crosses a certain device as the tension between the ends of it for any type of temporary periodic evolution in regime permanent, in stage a) the selection is made from among the following measures: active power, reactive power, power apparent, power factor and total offset angle. If it has selected the measure of active or reactive or apparent power, in step g) can be displayed on the display media of simultaneously the value of the selected power and the factor of power, also showing if this power factor is capacitive or inductive.

In the event that a measurement of the leakage current signal, in step e) it can be analyzed also the cause that causes the leak, by studying the value effective of the different harmonics of the measured leakage current and its comparison with the effective value of said leakage current. The The cause of the leak is studied from among the following: caused by accumulation of non-linear loads or caused by defects in isolation. In step g) it can be shown additionally in the display means a warning signal that indicates to the user the cause of leakage.

Brief description of the drawings

For a better understanding of the invention, to Then we briefly describe a mode of embodiment of the invention, as an illustrative example and not limiting it. For this reference is made to the drawings attachments, in which:

A general scheme of the clamp meter with its different components, in the form of blocks diagram.

Figure 2 shows a diagram of the means of conversion and adaptation of the input current in the levels voltage compatible with the ADC input.

Figure 3 shows a diagram of the means of adaptation of the input voltage to the voltage levels compatible with the ADC input.

Figure 4 shows the stage where a virtual mass

Figure 5 shows another embodiment of the present invention, where the first means of processing data (5) and the second means of data processing (10) they are contained in a single microprocessor (31).

Detailed description of the invention

The present invention consists of a clamp High resolution digital ammeter for measuring both the current flowing through a certain conductor as of the voltage difference between two points of an electrical circuit. He team has the ability to break down the corresponding magnitude periodic in its content in frequency sinusoidal harmonics multiples of the fundamental frequency of the starting signal. He equipment has a liquid crystal display (LCD) where they can show diverse values that quantify the quality of the electrical signal and its approach to a pure sine wave as well it is possible to show the true total effective value together with the harmonic distortion rate (THD), the effective value of each of harmonics, the relative value of a harmonic with respect to the fundamental component, the crest factor and the peak value. As an additional feature and oriented to the measurement of currents of leaks, the equipment incorporates an algorithm for the analysis of the cause of a leakage current, so that it indicates if the cause of this defect is due to a high accumulation of loads nonlinear, such as switched sources used in equipment computer and electronic equipment, or due to defects in isolation.

The external appearance of the equipment is similar to that of A clamp meter for current measurement without the need for opening in the measuring circuit, you can also have two additional input terminals for voltage measurement, being able to simultaneously measure both quantities and process them to show the active, reactive and apparent powers resulting, in addition to the power factor and offset angle Between both magnitudes.

Internally, the team has about first means of data processing, usually a digital signal processor (DSP), which performs both the conversion analog-digital of the real magnitude, such as mathematical calculations necessary to obtain the result of the As required. The equipment is powered by batteries small size

In Figure 1 you can see the general scheme of the clamp in the form of a block diagram. Input signal it can be both current and voltage and therefore it can come from the test leads to measure the voltage, connected to the input terminals (1) for voltage measurement, such as the coil housed in the jaw or jaw, which connects to the clamp a through the input terminals (2) for maxillary measuring of stream.

The voltage waveform proportional to the Measurement is sampled by Analog to Digital ADC converter (6) integrated into first data processing means (5), in this case a microcontroller, this being normally a digital signal processor (DSP). Sampling is done at a sampling rate proportional to the fundamental frequency of the network, so that the same number of samples per period (with a network frequency of 50 Hz or of 60 Hz which are the two fundamental frequencies considered).

Before it can be sampled by the ADC (6) that  incorporates the first microcontroller (5), an adaptation is made to the voltage levels compatible with the input of said converter In the case of a current measurement, the Maxillary coil generates a current in its secondary, proportional to the current flowing through the conductor that is hugged by the maxilla; said current becomes voltage by means of conversion and adaptation (4) based on analog switches, controlled in turn from the first microcontroller (5), so that it can be sampled by the ADC (6). There are several current scales that are controlled by automatically using said analog switches digitally controlled from the first microcontroller itself (5).

When it comes to voltage measurement, the scales available for this are always higher than ADC margins of entry (6). For this reason the tension of entry is reduced by means of adaptation (3) of said input voltage at voltage levels compatible with the ADC input (6), such as using a splitter configurable resistive. There are also several scales of voltage and therefore several resistive dividers that are controlled also digitally, by analog switches controlled from the first microcontroller (5).

In this design the first microcontroller (5) acts as a slave device for a few seconds means of data processing (10), in this case a microcontroller, which acts as a master device, communicating both circuits integrated via a communications bus (9), usually a bidirectional serial communication. The second microcontroller (10) is responsible for managing the interface between the user and the equipment, that is, both the display means (12), by for example an LCD screen, such as the selection means (11) a through which the user selects the mode of operation of the clamp meter, such as some push buttons and a rotary switch / selector; for this reason, it it is a specific microcontroller that has the hardware internal required for direct handling of the electrodes present in liquid quartz displays (LCD) and for generation of the corresponding polarity voltage signals alternate

Taking into account the measure you want perform, the master integrated circuit, the second microcontroller (10), makes a request for measurement and processing to the slave integrated circuit, the first microcontroller (5). The communication between the two can be Perform via a synchronous serial communication interface. He first microcontroller (5) can capture the signs of the voltage, current, or both signal simultaneously. Depending on the value of the samples captured on device itself is responsible for selecting the appropriate scale for the measurement and repeat it if the Current margin selected.

Equipment power is obtained from of batteries, specifically two 1.5V batteries. Said voltage of 3V it can be variable throughout the cycle of use of those batteries, for this reason the voltage rises and stabilizes by a continuous-continuous converter switched to 3.3 V, that voltage value will remain constant while the input voltage is maintained above 1V, which guarantees correct operation until the batteries are completely sold out

In order for the measures to be the most precise possible it is necessary to have a stable reference in the ADC (6), so that the measure is little affected by factors external and environmental such as temperature and humidity. For such reason, from the voltage of 3.3 V a voltage is generated 3V stable by using a stable voltage reference (integrated circuit), which will provide the reference for the ADC (6) integrated in the first microcontroller (5). Since the Measured quantities are alternate, it is necessary to create a reference virtual voltage so that the ADC (6) can also read the negative parts of the waves. This virtual mass is generated at from the stable voltage reference and set to a value of 1.5 V, right in the center of the total signal variation range input to the A / D converter.

Figure 2 shows a diagram of the media of conversion and adaptation (4) of the input current in the voltage levels compatible with the ADC input (6), where the current (13) coming from the jaw of the clamp becomes tension by passing it through resistance (14). That tension, which has a reduced value, is amplified using a stage amplifier based on the use of an operational amplifier (fifteen). The gain of the stage is adjustable through the network of resistors (17) present in the amplifier feedback operational (15). The analog switch (16) is controlled by the first microcontroller (5) digitally via connection (18) and fulfills the function of selecting the amplifier gain appropriate for the input current level by connecting one of the resistors of the resistor network (17). The exit (19) of operational amplifier (15), which is an already amplified signal and normalized, it is connected to the ADC input (6) of the first microcontroller (5).

Figure 3 shows a diagram of the means of adaptation (3) of the input voltage to the voltage levels compatible with the ADC input (6). The voltage measured through of the terminals (1) of the device is represented by the source (20). Said voltage is attenuated by a resistive divider composed of the resistance (24) and the resistance network (25). The selection of  proper level of attenuation is done by the switch or analog switch (21), directly controlled by the first microcontroller (5) through the connection (22). The exit (23) of the dimmer goes directly to the ADC input (6).

For both the stage shown in Figure 2 and  for that of Figure 3, the voltage reference used is not corresponds to the negative terminal voltage of the batteries feeding, but the so-called virtual mass (30) is used. It is therefore a level of tension located at the midpoint between the maximum ADC voltage (6), 3 volts, and the most voltage low of all equipment (negative battery terminal of feeding). Figure 4 shows the stage where this mass is created virtual (30). From the stable voltage reference (26) provided by the integrated circuit called reference of tension, a voltage with half value is created using a resistive divider (27) with both equal resistors. So that the voltage of this virtual mass is stable, a follower of transmitter based on the use of an operational amplifier (28) with two additional stabilization capacitors (29). The exit of this stage is the virtual mass (30) that connects to the rest of circuits that need it.

To calculate the required measure from the second microcontroller (10), the first microcontroller (5) takes signal samples at a given sampling frequency, the which varies depending on the fundamental frequency of the network, 50 Hz or 60 Hz, so that the same is always obtained number of samples in a fundamental period of network frequency. By default the number of samples is 256 per period, value that It is sufficient for the precision required by the equipment. A Once the data capture is done, the calculations are performed mathematicians needed to obtain the results required, which may be the following:

- For current or voltage measurements: Effective value, THD, harmonic effective value, crest factor and peak value

- For current and voltage measurements simultaneously: active power, reactive power, power apparent, power factor and total offset angle.

Once the measurement result is obtained, the value of that magnitude is sent through the bus communications (9) back to the master microcontroller (10) which is responsible for displaying the measurement on the glass screen liquid (12). The first microcontroller (5) has the ability to perform any of the measures mentioned above in a time less than 100 ms, so that up to 10 measurements can be made of a certain magnitude every second which means a soda of information on the raised screen. To obtain some types of measures, such as THD and effective values are necessary  perform a processing and calculation of the Fast Transform Fourier (FFT), for this reason the number of samples taken is 256 since a requirement for the realization of the FFT is to have 2 N number of samples, N being a natural number (in this case 8).

The design can be done in the same cycle of 100 ms several joint operations being able to perform the calculation simultaneous of both the THD rate and the effective value of the magnitude, which allows you to display both measurements on the screen LCD simultaneously.

An algorithm has been added to the team for application in the measurement of leakage currents. With said algorithm it is intended to have additional information on what is the cause that causes such leakage, differentiating between two types of failures:

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Failures caused by accumulation of non-linear loads, as sources Switched electronic equipment. These types of charges include filters to reduce electromagnetic interference (filters EMI). Due to the high harmonic distortion they generate in the current consumed by this type of non-linear loads derives from running earth with a high harmonic component.

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Failures caused by insulation defects, which leak currents Mainly at the network frequency.

The algorithm used is based on the study of  harmonic content of the measured leakage current. Saying algorithm conducts a study of the effective value of the current at higher harmonics and compares it to the effective current value. Depending on the result obtained by said operation, a Judgment on the cause of the failure. To show the judgment in the Two icons are available, an icon that indicates the leak it is due to insulation failure and another icon that indicates that the leakage is due to accumulation of non-linear loads.

Another embodiment of the present invention is shown in Figure 5, where the first means of processing of data (5) and the second means of data processing (10) they are contained in a single microprocessor (31). He operation for this particular embodiment would be similar to the explained for figure 1, with the peculiarity that now the first (5) and second (10) data processing means they communicate internally and not using a bus external communications, being contained in the same encapsulated

Claims (18)

1. Leakage clamp meter with harmonic measurement and diagnosis of the cause of the leakage, that works with at least one battery and that has visualization means (12) where the information is shown to the user, selection means (11) through which the user selects the operating mode of the clamp meter, first data processing means (5) with ADC digital analog converter (6) and two input terminals (2) for maxillary current measurement, characterized because it has conversion and adaptation means (4) of said input current at the voltage levels compatible with the ADC input (6), said conversion and adaptation means (4) being controlled by at least one analog switch (16 ) controlled in turn from the first data processing means (5), and because it has second data processing means (10) that control the display (12) and selection means (11) , said means (10) being communicated with the first data processing means (5). 2. Ammeter leakage clamp according to claim 1, which additionally has two input terminals (1) for voltage measurement, characterized in that it has means for adapting (3) said input voltage to the voltage levels compatible with the voltage ADC entry (6). 3. Leakage clamp meter according to the preceding claim, characterized in that the adaptation means (3) consist of a resistive divider, controlled from the first data processing means (5) by means of an analog switch (21). 4. Ammeter leakage clamp according to any of the preceding claims, characterized in that the display means (12) is an LCD liquid crystal display. 5. Ammeter leakage clamp according to any of the preceding claims, characterized in that the selection means (11) are a plurality of pushbuttons and a rotary selector. 6. Ammeter leakage clamp according to any one of claims 1 to 5, characterized in that the first data processing means (5) and the second data processing means (10) are contained in a microprocessor (31). 7. Ammeter leakage clamp according to any one of claims 1 to 5, characterized in that the first data processing means (5) consist of a first microcontroller and the second data processing means (6) consist of a second microcontroller, the which is communicated with the first microcontroller (5) via a communications bus (9), the second microcontroller (10) being the master device. 8. Ammeter leakage clamp according to the preceding claim, characterized in that the communication established between the first microcontroller (5) and the second microcontroller (10) is bidirectional series. 9. Ammeter leakage clamp according to any of claims 7 to 8, characterized in that the first microcontroller (5) is a digital DSP signal processor. 10. Procedure for measuring leakage currents, with harmonic measurement and diagnosis of the cause of the leakage, which uses the ammeter leakage clamp according to any of claims 1 to 9, characterized in that it comprises the following steps: a- selection by the user of the measure to be performed by the clamp meter; b- request for measurement of the second means of data processing (10) to the first processing means data (5); c- selection of the scale, made by the first means of data processing (5), as appropriate for the measure; d- sample capture, performed by first means of data processing (5) after conversion ADC analog-digital (6) included in said means (5) of the voltage, current or both signal simultaneously, depending on the measurement request. (20) of the second means of data processing (10); e- mathematical calculations to obtain the requested measure, made by the first means of processing data (5); f- sending, of the first means of data processing (5) to the second processing means of data (10) of the value of the calculated measure; Y g- presentation, made by the seconds data processing means (10), of the measurement in the media of display (12). Method according to claim 10, in which a measurement of the current or voltage signal is made, characterized in that in step a) the selection is made from the following measures: effective value, maximum and minimum value, distortion Total harmonic (THD), effective value of the different harmonics, crest factor and peak value. 12. Method according to the preceding claim, in which the effective value measurement or the THD measurement has been selected, characterized in that in step g) the effective value and the value are simultaneously shown in the display means (12). THD 13. The method according to claim 10, in which a measurement is made simultaneously of both the current through a certain device and the voltage between the ends thereof for any type of temporary periodic evolution in permanent regime, characterized in that in the step a) the selection is made from the following measures: active power, reactive power, apparent power, power factor and total offset angle. 14. Method according to the preceding claim, in which the measure of active or reactive or apparent power has been selected, characterized in that in step g) the value of the selected power is displayed simultaneously in the display means (12) and the power factor, also showing whether this power factor is capacitive or inductive. 15. Method according to claim 10, in which a measurement of the leakage current signal is carried out, characterized in that in step e) the cause causing the leakage is also analyzed, by studying the effective value of the different harmonics of the measured leakage current and its comparison with the effective value of said leakage current. 16. Method according to the preceding claim, characterized in that the cause of the leak is studied from among the following: caused by accumulation of non-linear loads or caused by insulation defects. 17. Method according to any of claims 15 to 16, characterized in that in step g) a warning signal is further shown in the display means (12) indicating to the user the cause of the leak. 18. A method according to any of claims 10 to 17, wherein the first data processing means (5) of the clamp meter consist of a first microcontroller and the second data processing means (10) consist of a second microcontroller , both communicated by means of a communications bus (9), characterized in that in step f) the sending of the value of the calculated measurement of the first data processing means (5) to the second data processing means (10) is performed through the serial communication bus (9).