KR20010111285A - Current meter - Google Patents

Abstract

The present invention relates to an ammeter based on the principle of measurement of the surface electric field. The Hall sensor 1 arranged in such a way as to be excited by a magnetic field proportional to the current is used. Two Hall sensors are arranged in a manner that detects an electric field with an opposite pole signal to be measured quantitatively in a uniform manner. By subtracting the output signal from the Hall sensor, the measurement of current is amplified, while external parasitic induction is eliminated.

Description

Current Detection Unit {CURRENT METER}

To date, current has been measured using a LEM transducer as well as a measuring device including a shunt isolation amplifier, a ferrite core and a Hall sensor. However, these known devices carry significant disadvantages.

For example, when measuring current by shunt resistant, the current to be measured passes through a precision resistor and the voltage drop caused by the current is measured. This kind of measurement consumes unnecessary energy which causes heating of the surrounding environment of the circuit breaker. In addition, since the current measuring device is necessarily integrated in the measured current circuit and affects the measured current itself, the measurement result is somewhat distorted depending on the size of the shunt resistor. Also in this way, potential isolation measurements are not possible at high voltages.

In the case of an LEM transducer, a ferrite core is arranged around the conductor whose current flow is to be measured. A second coil is arranged around the ferrite core, and the current is controlled by the second coil so that the resulting magnetic field is adjusted to zero. In this way, potential discrete measurements are possible, but the cost of this kind of measurement is high.

By the Hall sensor, the magnetic field can be measured relatively appropriately using the Hall effect. The hall sensor generates a voltage proportional to the magnetic field acting on the hall sensor. These Hall effects generated have varying strengths depending on the materials used, the most preferred of which are Hall sensors made of semiconductors. Therefore, by the Hall sensor, the magnetic field induced by the current flowing through the semiconductor can be measured. In this way, current is measured as a potential separation method.

However, since the voltage generated by the Hall sensor during the measurement is low, and in a steady state the magnetic field is externally influenced, amplification of the magnetic field is required and generally this is achieved by the ferrite core. However, in this device, non-linearity occurs due to the saturation action of the magnetic core used. Because of this, current can only be measured in a sufficiently limited manner in a specific limited range, but currents measured outside this range have the disadvantage that they deviate significantly from the actual current due to saturation. In addition, the cost of such a measuring device is relatively high due to the ferrite core.

In conclusion, the device according to the prior art is disadvantageous as long as non-linearity occurs due to the saturation action, the device has only a small electrical strength, the device is relatively expensive, and the consumption of the device itself is high.

Summary of the Invention

Accordingly, the present invention is based on the purpose of detecting current values by a potential separation method, and forming a current detection unit that is sufficiently accurate and has a high degree of immunity to interfering.

This problem is solved by the current detection unit disclosed in claim 1. This means that the current detection unit according to the invention comprises at least two Hall sensors arranged on the conductor. The Hall sensor not only uniformly detects the magnetic field generated by the current flowing through the conductor in an absolute amount, but also uniformly detects the interference field in an absolute amount, and detects the magnetic field or the disturbing electric field having different signals, respectively. Is placed.

Other embodiments are disclosed in the dependent claims of the claims.

Thus, the current measurement is amplified by addition or subtraction, but the disturbing field due to external interference is eliminated.

According to the current detection unit according to the present invention, since no additional ferrite core is required, it is achieved in a preferable way to carry out the detection of the current value at low cost. In addition, they are not affected by high insulation voltage as well as interference.

According to the present invention, it is possible to achieve a current detection unit for a simple electronic release trigger in the DC current range, which detects the current value as a potential isolation method for direct current up to 4 kV. do.

With reference to the accompanying drawings, the present invention will be described in more detail below through examples.

The present invention relates to a current detection unit for potential discrete measurement of high direct current in energy distribution facilities with a nominal voltage up to several kV.

1 is a schematic perspective view showing an overcurrent relay including a current detection unit fixed to a conductor according to a first embodiment;

2 is a partially enlarged perspective view showing in more detail the current detection unit according to FIG. 1, FIG.

3 is an enlarged perspective view of the current detection unit according to the second embodiment,

4 is a block diagram of an evaluation circuit for the current detection unit according to the first or second embodiment,

Fig. 5 is a block diagram of the evaluation circuit for the current detection unit including four Hall sensors according to the third embodiment.

1 is a schematic perspective view showing an over-current relay according to a first embodiment of the present invention. This overcurrent relay includes a basic switch (BS) and an arc quenching system (LS), and the exact function of this arc quenching system is not important in this embodiment and a detailed description thereof will be omitted.

The current detection unit SMA is fixed to the conductor 2. This current detection unit SMA is based on the principle of surface electric field measurement or Hall effect, respectively.

The current detection unit SMA according to the first embodiment is shown in more detail in FIG. 2. Here, two Hall sensors 1a and 1b are arrange | positioned at the part of conductor 2 so that they may oppose each other.

The reason for using two Hall sensors 1a and 1b is that the magnetic field is relatively weak and is disturbed by the interference from the surrounding environment, i.e., the disturbing electric field. In order to avoid such external interference, the two Hall sensors uniformly measure the absolute amount of the magnetic field generated by the flow of current, but are arranged to measure the magnetic field respectively by signals facing each other. If the absolute amount of current flowing through the conductor 2 is B, the Hall sensor 1a measures the magnetic field + B, for example, while the other Hall sensor 1a measures the magnetic field -B.

The output signals from the two Hall sensors 1a and 1b are subtracted. In this way, the disturbing field is removed from the output signal and the measured value of the magnetic field is increased. Thus, there is no need to reinforce the magnetic field itself, for example, by a ferrite core according to the prior art. This is because the subtraction of the signal eliminates the maximum possible disturbance and generates a strong measurement signal of the magnetic field to be measured.

The measurement signal of the hall sensor 1a will be denoted by MW1a, and the measured value of the hall sensor 1b will be denoted by MW1b. If the two Hall sensors are placed close enough to each other, it can be assumed that the disturbing electric fields in the two Hall sensors are the same. Therefore, the result of the measured value is as follows.

MW1a = + B + S

MW1b = -B + S

Here, S serves to represent the disturbing electric field. Therefore, the total measured value MW by subtraction of two measured values is as follows.

MW = MW1a-MW1b = + B-(-B) + S-S = 2B

Thus, the disturbing electric field disappears and the effective measured value is doubled.

As a variant, the two Hall sensors can be arranged to measure the entire measured magnetic field (ie, the effective magnetic field B has the same signal and the disturbing electric field S has a different signal) each having a different signal. have. In this case, the disturbing electric field is destroyed by the addition.

MW1a = B + S

MW1b = B-S

MW = MW1a + MW1b = 2B

As mentioned above, since the distance between the probes is as short as possible in the arrangement of the hall sensors, it should be noted that the disturbing electric field is the same for each position of the hall sensor if possible. It is also important that the magnetic field strength is not affected by current displacement. In this regard, it is advantageous to place the Hall sensor on a circular conductor. According to FIG. 2, for example, the conductor 2 is composed of a circular conductor in a hall sensor.

The two Hall sensors must be arranged at the same distance from the conductor 2 so that the two Hall sensors equally measure the absolute amount of magnetic field generated by the current flowing in the conductor.

In addition, the Hall sensor 1 may be arranged such that the conductor 2 extends between the two Hall sensors 1 as shown in FIG. 2. This arrangement is one possible arrangement of the Hall sensor to uniformly detect the absolute amount of the magnetic field by the opposite signal. Of course, other arrangements can also be expected, such as the arrangement in which the two Hall sensors 1 are arranged next to each other directly on one side of the conductor 2.

According to FIG. 1, a current detection unit consisting of two Hall sensors 1 is installed in a predetermined conductor arrangement, for example according to FIG. 1, in an overcurrent relay comprising a conductor 2 and a return conductor 4. Thus, in consideration of the influence of the return conductor 4, it is possible to arrange and adjust the hall sensors 1a and 1b such that at least the known interference is reduced by the configuration of the conductor. Thus, the current detection unit according to the first embodiment can be preferably used for the arrangement of known rigid conductors.

Next, a current detection unit according to the second embodiment, which may be used for disposing an unknown conductor, will be described.

This current detection unit is shown in FIG. According to FIG. 3, two Hall sensors are surrounded by a tubular shield 3. By this measurement, external interference is shielded and more accurate measurement becomes possible.

According to the embodiment described above, two Hall sensors, i.e., a pair of Hall sensors, are used. However, any number of Hall sensor pairs can be used as long as the pair of these Hall sensors is changed to remove the disturbing field and the measured signal is added.

By increasing the number of Hall sensors, the spacing of the resulting measurement MW for the disturbing field can be increased. This is because the disturbing electric field of each pair of Hall sensors is eliminated while the measurement signal is doubled. This means that 2n times the magnetic field is measured by n pairs of Hall sensors.

Next, an evaluation circuit of the current detection unit according to the first or second embodiment including two Hall sensors will be described with reference to FIG.

Two Hall sensors 11 and 21 are disposed at positions facing each other on the tubular conductor L. These Hall sensors are disposed opposite each other such that the disturbing electric field is eliminated by subtraction of the output signals from the two Hall sensors.

The output signal from the hall sensor 11 is first sent to the temperature compensation sensor 12. The influence of temperature on the measurement result is eliminated by the temperature compensation sensor 12. The compensated signal is amplified by the amplifier 13 and the amplified signal is sent to an offset balancing arrangement 14 in which the deviation of the signal is balanced.

In the same way, the output signal from the hall sensor 21 is transmitted to the temperature compensation sensor 22, the amplifier 23, and the offset balancer 24. The signals are supplied to the subtractor 5 in balance with each other by the offset balancers 14, 24.

The subtractor 5 subtracts the two measurement signals from each other and outputs the resulting signal, which is the signal from which the disturbing field has been removed as described above. The output signal from the subtractor 5 is amplified by the amplifier 6 and output to an appropriate additional processing unit. In one example, an over-current release 8 and a signal conversion interface 7 are shown in FIG. 4. The overcurrent release may be a release as described in the first embodiment. The signal conversion interface 7 outputs a current proportional to the measurement signal, for example, and the current range is, for example, 4 to 20 mA. In addition, additional interfaces may be connected as indicated by the dashed lines leading to the reference 9.

As described above, the number of Hall sensors of the current detection unit is not limited to two, and any number of pairs of Hall sensors can be used.

Next, an evaluation circuit of the current detection unit including the four Hall sensors according to the third embodiment will be described with reference to FIG.

In the drawings, the same reference numerals correspond to the same components as in FIG. This is shown in the upper half of the figure and there are two branches according to FIG. 4 comprising a temperature compensation sensor 12, 22, an amplifier 13, 23, and an offset balancer 14, 24. Means that The output signals of these two branches are subtracted from each other by a subtractor 51 which serves to extinguish the disturbing electric field. The output signal from the extractor 51 is amplified by the amplifier 61 before being supplied to the adder 15.

In addition to this arrangement, two further Hall sensors 31 and 41 are arranged on the conductor, which are spatially displaced, for example by 90 °, with respect to the arrangement of the Hall sensors 11 and 21. As described above, the output signal from the Hall sensor 31 is transmitted to the temperature compensation sensor 32, the temperature compensated signal is amplified by the amplifier 33, the offset balancer 34 is offset balanced by Is executed. The output signal from the hall sensor 41 is transmitted to the temperature compensation sensor 42, the temperature compensated signal is amplified by the amplifier 43, and the offset balancer is executed by the offset balancer 44. The output signals of the offset balancers 34, 44 are then subtracted from each other by the subtractor 52, and the output signals from the subtractor 52 are amplified by the amplifier 62 before being sent to the adder 15.

The adder 15 adds the resulting measurement signals from the two pairs of Hall sensors 11, 21 and 31, 41. The entire signal is amplified by the amplifier 16 and then sent to additional units 7, 8, 9 as in the evaluation circuit according to FIG. 4.

According to the third embodiment, two pairs of hall sensors were used. As mentioned above, the number of pairs of hall sensors may be used more. The evaluation circuit of such a device is configured in a manner similar to that according to FIG. 5, and then various signals may be supplied to the adder 15.

If the evaluation circuit according to Figs. 4 and 5 is modified, the arrangement in which the disturbing electric field is removed by addition of the output signal can be selected for the hall sensor as mentioned in the description of the first embodiment. In other words, in this case the Hall sensors must be arranged to detect the magnetic field generated by the conductor by the same signal, but to detect the disturbing electric field by the different signals, respectively. In the evaluation circuit, the subtractor 5 according to the third embodiment should then be replaced with an adder. In a variant of the evaluation circuit with two pairs of Hall sensors, the subtractors 51, 52 must each be replaced with an adder according to the fourth embodiment.

In the above, the current detection unit based on the principle of surface magnetic field measurement was demonstrated. The current detection unit comprises at least two Hall sensors 1a, 1b arranged on the conductor 2. The hall sensor is arranged not only to uniformly detect the absolute amount of the magnetic field generated by the current flowing through the conductor, but also to uniformly detect the absolute amount of the disturbing electric field, and to detect the magnetic field or the disturbing electric field by different signals, respectively. Therefore, the current measurement is amplified by addition or subtraction, but external interference caused by the disturbing electric field is eliminated.

Claims (11)

In the current detection unit, At least two Hall sensors 1a, 1b disposed on the conductor 2, The Hall sensors 1a and 1b not only detect the same amount of magnetic field generated by the current flowing through the conductor 2 in an absolute amount, but also detect the same amount of disturbing electric field in an absolute amount and detect the magnetic field or disturbing electric field in different signals. Arranged for detection by Current detection unit. The method of claim 1, The Hall sensors 1a and 1b are arranged so that the magnetic field generated by the current flowing through the conductor 2 is respectively detected by two Hall sensors having different signals, Output signals of the hall sensors 1a and 1b are subtracted from each other Current detection unit. The method of claim 1, The Hall sensors 1a and 1b are arranged so that the magnetic field generated by the current flowing through the conductor 2 is detected by two Hall sensors having the same signal, The output signals of the Hall sensors 1a and 1b are added up Current detection unit. The method according to any one of claims 1 to 3, The two Hall sensors 1a, 1b are arranged such that the conductor 2 extends between the two Hall sensors. Current detection unit. The method according to any one of claims 1 to 4, A shield 3 mounted around the Hall sensors 1a, 1b and the conductor 2; Current detection unit. The method according to any one of claims 1 to 5, The conductor 2 is a circular conductor Current detection unit. The method according to any one of claims 1 to 6, The Hall sensors 1a and 1b have a minimum possible distance from each other. Current detection unit. The method according to any one of claims 1 to 7, The Hall sensors 1a and 1b have equal distances with respect to the conductor 2, respectively. Current detection unit. The method of claim 2, Several pairs of Hall sensors 11, 21 and 31, 41 are provided, and the output signals of each pair of Hall sensors are subtracted from each other by subtractors 5, 51, 52, from each pair of Hall sensors The resulting output signal is added by adder 15 Current detection unit. The method of claim 3, wherein Several pairs of Hall sensors 11, 21 and 31, 41 are provided, the output signals from each pair of Hall sensors are added by an adder and the resulting output signals from each pair of Hall sensors are added to adder 15 Added by) Current detection unit. The method according to any one of claims 1 to 10, The output signal of the hall sensors 11, 21, 31, 41 is supplied to the temperature compensation sensors 12, 22, 32, 42. Current detection unit.