Current sensor according to the compensation principle and method for operating such a current sensor

Abstract

Current sensor based on the compensation principle with a primary winding (11) for generating a magnetic field as a result of a primary current (I P ), a secondary winding (12) for generating a magnetic field as a result of a compensation current (I K ), a magnetic core (13) which magnetically couples the primary winding (11) and secondary winding (12), a magnetic field probe (14) magnetically coupled to the magnetic core (13) and designed to provide a quantity representing the strength of the resulting magnetic field in the magnetic core, an evaluation unit (15) connected downstream of the magnetic field probe (14) and upstream of the secondary winding (12), which is designed to generate a compensation current (I K ) depending on the quantity representing the strength of the resulting magnetic field in the magnetic core, where the evaluation unit (15) is designed to, in the event of overdriving of the magnetic field probe (14), by means of an excitation current (I A ) to find a compensation point (31) of the current sensor (10) and to determine from the compensation point (31) the corresponding value for the compensation current (I K ) and the excitation current (I A ) in the event of overdriving of the magnetic field probe (14), passes through a current range lying between a minimum and a maximum current intensity at least until the compensation point is reached.

Description

[0001] The invention relates to a current sensor based on the compensation principle and a method for operating such a current sensor.

[0002] Current sensor assemblies are used to determine the electrical current strength of a current to be measured and are special measuring transducers that operate according to different principles. Current sensor assemblies that operate according to the compensation principle, also called compensation current sensors, usually have a magnetic core made of soft magnetic material that encloses a primary conductor carrying the current to be measured. The current to be measured flows through the primary conductor and generates a magnetic field in the magnetic core, which is compensated by a compensation current in a secondary winding wound around the core. For this purpose, the magnetic flux in the magnetic core is measured using a magnetic field sensor and regulated towards zero with the help of an evaluation circuit by feeding a suitable compensation current into the compensation winding.Finally, if the resulting magnetic flux in the magnetic core is essentially zero, then the compensation current is proportional to the primary current to be measured.

[0003] However, situations in which the current sensor is overloaded can occur during operation of such compensation current sensors. This occurs, for example, when the compensation current is too low to compensate for the magnetic field caused by the primary current. In such a case, for example, a core of a field-detecting magnetic probe becomes saturated. If the probe is in an overloaded state, it may no longer be able to provide information about the magnitude and direction of the primary current to be compensated. Therefore, in this state, the compensation current would be switched off due to the information-free probe signal.

[0004] As a result, the primary current would keep the probe in saturation even when it returns to the normal measuring range due to the lack of compensation. The consequence would be that if the sensor were to be overloaded once, it would no longer provide an output signal as long as the primary current continues to overload the probe without compensation measures.

[0005] To prevent such overload situations during operation of a current sensor, an overcurrent latch control is used. A so-called latch-up is an uncontrolled state of the current sensor, which is to be avoided by an overcurrent latch control, also called latch-up control or latch control for short. The overcurrent latch control ensures that shortly before the primary current exceeds the measuring range limits, i.e. when the probe signal becomes higher frequency but still carries information about the current direction, the compensation winding is brought to full control and held in accordance with the last detected current direction. When the primary current returns to the compensable measuring range, the probe frequency drops, causing the sensor to return to normal operation. The probe now supplies a usable signal again.

[0006] However, situations can also arise that are undesirable when switching on such a current sensor based on the compensation principle. For example, if a primary current is already flowing before the current sensor's sensor electronics are switched on, the probe may already be saturated due to the lack of compensation current. If the current sensor is switched on in this state, the probe signal is already high-frequency and information about the magnitude and direction of the primary current is missing. In this case, the electronics or evaluation device is unable to provide a suitable compensation current with the correct sign. The consequence is that the compensation current and thus the sensor's output signal remains at zero and no compensation current is generated, even though a primary current is flowing.

[0007] European patent EP 0 742 440 B1 discloses, particularly in paragraphs

[0013] ,

[0029] , and

[0030] , that in a compensation current transformer, an excessively high compensation current can occur upon power-up due to different ramp-ups of the positive and negative supply voltages and uncontrolled overshoots of the regulator stage, which can potentially cause the electronics of the evaluation stage to enter the "latch-up" state. This is prevented by controlling the regulator and / or amplifier stages via a latch-up control, which, in particular, monitors the symmetry of the positive and negative supply voltages and the regulator summation point for irregular values ​​and prevents this condition by implementing a "soft start."

[0008] The invention is therefore based on the problem of developing current sensors according to the compensation principle in such a way that the problems described above are avoided or at least mitigated.

[0009] The object is achieved by a current sensor according to claim 1 and by a method according to claim 16.

[0010] The current sensor according to the invention has a primary winding for generating a magnetic field as a result of a primary current to be measured flowing through it, a secondary winding for generating a magnetic field as a result of a compensation current flowing through it, a magnetic core magnetically coupled to the primary winding and the secondary winding, a magnetic field probe magnetically coupled to the magnetic core for generating a variable representing the strength of the resulting magnetic field in the magnetic core and an evaluation unit connected downstream of the magnetic field probe and upstream of the secondary winding for generating the compensation current depending on the variable representing the strength of the resulting magnetic field in the magnetic core.In this case, the evaluation unit is designed to find a compensation point of the current sensor in the event of an overdrive of the magnetic field probe by means of an excitation current fed into the secondary winding and with a variable current intensity and to determine the corresponding value for the compensation current from the compensation point, wherein the excitation current with a variable current intensity in the event of an overdrive of the magnetic field probe passes through a current intensity range lying between a minimum and a maximum current intensity at least until the compensation point is reached.

[0011] The method according to the invention serves to operate a current sensor according to the compensation principle, which has a primary winding for a primary current to be measured, a secondary winding for a compensation current, a magnetic core magnetically coupling the primary winding and the secondary winding, and a magnetic field probe for measuring a quantity representing the strength of the resulting magnetic field in the magnetic core.The method includes the following steps: detecting an overload of the magnetic field probe, starting the first waiting time in the event of an overload, providing a time-varying compensation current to the secondary winding, finding a compensation point of the current sensor, determining a value of the compensation current associated with the found compensation point based on the found compensation point and setting the compensation current to the determined value, wherein the excitation current, which is variable in current intensity, in the event of an overload of the magnetic field probe passes through a current intensity range lying between a minimum and a maximum current intensity at least until the compensation point is reached.

[0012] The invention is explained in more detail below with reference to the drawings. However, the invention is not limited to the illustrated embodiments, so that further combinations of the individual features and other applications are also possible. It shows: Fig. 1 in a schematic sketch a current sensor according to the compensation principle; Fig. 2 shows a block diagram of an exemplary sequence of a method according to the invention for operating a current sensor working according to the compensation principle; Fig. 3 shows a schematic diagram of the voltage and current curves in a method according to the invention with a current sensor based on the compensation principle; and Fig. 4 in a diagram showing the course of two current sensors according to Fig. 1 usable magnetic field probes.

[0013] Fig. 1 schematically shows an exemplary structure of a current sensor 10 based on the compensation principle. The compensation principle is suitable for measuring alternating currents as well as direct currents, so that even higher-frequency alternating currents with complex waveforms and a direct current component contained therein can be easily measured. The current sensor 10 has a first winding as the primary winding 11 (in the example shown with a number of turns ≤ 1) and a second winding as the secondary winding 12, which are magnetically coupled to one another via a magnetic core 13, such as a slotted toroidal core, i.e. a toroidal core with an air gap 17 (hereinafter referred to simply as gap 17). The magnetic core 13 is, for example, an iron core or a core made of a suitable soft magnetic alloy.

[0014] A primary current I flows through the primary winding 11 Pand generates a first magnetic field. The secondary winding 12 is supplied with a compensation current I K , generating a second magnetic field. The compensation current I K is used to measure the primary current I P is now adjusted so that the two magnetic fields of the primary winding 11 and the secondary winding 12 cancel each other out in the magnetic core 13. The magnitude of the compensation current I K is then proportional to the current to be measured, ie the primary current I P in the primary winding 11. The two magnetic fields caused by primary current I P and the compensation current I K generated in the primary winding 11 and the secondary winding 12 are characterized in this case by their respective associated magnetic flux B1 and B2.

[0015] In the present example, a magnetic field probe 14 (hereinafter referred to as probe 14) is provided to measure the magnetic field resulting from the superposition of the first and second magnetic fields in the magnetic core 13. However, it is also possible to use a plurality of magnetic field probes which are then suitably connected to the evaluation circuit 15 and which can be arranged within one or more gaps or recesses in the magnetic core 13 or on the magnetic core 13 itself. For this purpose, the probe 14 has, for example, a field-sensing soft magnetic core 19 with a winding 21 applied thereto and can be arranged, for example, in the gap 17 or within a recess (not shown) in the region of the gap 17 of the magnetic core 13 or on the gap 17 (not shown). During operation, the probe 14 outputs the field strength orFlux density representing measurement signals to an evaluation unit 15, which allows, according to the detected resulting magnetic field and thus as a function of the primary current I. P the compensation current I K in the compensation winding so that the resulting magnetic field becomes zero. The evaluation unit 15 evaluates, for example, a current probe frequency f S of the measuring signal and then sets the compensation current I K a.

[0016] Furthermore, it compares the current probe frequency f S with a probe frequency at overload f krit This comparison can take place both during normal sensor operation and during the switch-on process of the current sensor 10. In both cases, a compensation of the primary current I P by the compensation current I to be generated K Instead of the current probe frequency f Scan also be an instantaneous pulse width t p of the measuring signal and with a critical pulse width t characteristic of an overload pkrit For the sake of simplicity, only the procedure using the probe frequency will be described in more detail below; however, the pulse width can be used accordingly.

[0017] Now assume that the probe 14 is already in saturation state when operation begins and thus a current probe frequency f S which is equal to or greater than the probe frequency f characteristic of an overload krit For example, a compensation current I K generating, acting as a current or voltage source, control circuit 16 is provided, with which an excitation current I Acan be generated in the secondary winding 12. The secondary winding 12 is connected in series with a resistor 18, across which a compensation current I K proportional voltage U M can be tapped.

[0018] When the current sensor 10 is switched on, a suitable value of the compensation current I K determined, so that the probe 14 can start operating even in the presence of a saturation condition, ie in the case of overload. In this case, the actual normal operation of the probe is preceded by a scanning process in order to find a compensation point 31 (shown in Fig. 3) where the magnetic field generated by the primary current (flux B1) and the magnetic field generated by the compensation current I Kgenerated magnetic field (flux B2) in the magnetic core 13. The compensation point is therefore considered to be the point at which the product of the current flowing in the primary winding and the number of turns of the primary winding is equal to the product of the current in the secondary winding and the number of turns of the secondary winding. This compensation point 31 is now to be found, although the probe 14 is in an overload state, i.e. the probe is saturated, when the current sensor 10 is switched on. In this case, the probe only acts like an air coil, whereby its magnetization reversal frequency is much higher than in normal operation. An increase in frequency is therefore an indication of sensor overload.

[0019] To locate the compensation point 31 during a switch-on process of the current sensor 10, the evaluation unit 15 controls the control circuit 16 accordingly, so that it acts as a (controlled) current or voltage source. For this purpose, a switchable constant voltage source 21 can be provided in the evaluation circuit 15, which, when switched on, outputs a constant voltage to the control circuit 16. The control circuit 16 is designed, for example, as a (push-pull) output stage, which amplifies this constant voltage and thus feeds the secondary winding 12, in which the excitation current I passing through a specific current range is then determined by the inductance of the secondary winding 12 and the ohmic resistance values ​​of the secondary winding 12 and the measuring resistor 18 (corresponding to an RL element). AThe control circuit 16 consequently generates a DC voltage of a predetermined magnitude, so that the correspondingly increasing and thus temporally varying excitation current I A This excitation current I A can be used to locate a compensation point 31 as described in more detail below in connection with Fig. 2. After finding the compensation point 31 during the switch-on process of the current sensor 10, it can be transferred to normal operation, so that the compensation point 31 determined during the switch-on process is maintained in normal operation until further adjustment by the active control loop occurs in normal operation. In normal operation, this current or voltage impression controlled by the search mode is ineffective, and the usual control principle applies, in which the controlled compensation current IK The control circuit 16 can alternatively have a controllable voltage or current source that can be directly connected or hard-wired to the secondary winding 12 in the search mode, as is the case with a controllable current source 22, for example, supplying a triangular current waveform in Fig. 1 is indicated.

[0020] Fig. 2 shows an exemplary sequence of a method for switching on a current sensor according to the compensation principle using the current sensor 10 according to Fig. 1. After switching on the current sensor 10 (S100), the probe 14, where the frequency of the measuring signal (probe frequency) represents the detected magnetic field, which is generated by the compensation current I K magnetic field generated in the primary winding 11 is determined. The evaluation unit 15 then checks whether the current probe frequency f S greater than or equal to a critical probe frequency fkrit is, ie it is checked whether there is an overload of the current sensor 10 and thus a saturation of the probe 14 (S101).

[0021] In case the probe frequency f S is not critical, normal sensor operation (normal operation) with corresponding control behavior is started (S200) without the need for a latch-up control. This means that in this case, finding a compensation point 31 (in Fig. 3) is not necessary.

[0022] If the current probe frequency f S However, it can be critical, ie the instantaneous probe frequency f S is greater than or equal to the critical probe frequency f krit , the control circuit 16 is controlled (S102) in such a way that a unipolar, for example positive, full control of the compensation winding 12 is achieved (S103), such as by a positive square wave signal (cf. Fig. 3), whereby the excitation current IA is generated.

[0023] In step S102, a first waiting time W1 is started. This first waiting time W1 is monitored for its end (S104). During the first waiting time W1, a continuous check is carried out to determine whether the current probe frequency f S greater than or equal to the critical probe frequency f krit (S105). If this is the case, a new check of the current probe frequency f S This continues until either the first waiting time W1 has elapsed or the current probe frequency f S has become uncritical. If the uncritical case is reached, ie the current probe frequency f S is below the critical probe frequency f krit , normal sensor operation or normal operation (S200) is started, since a compensation point 31 (see Fig. 3) was found.

[0024] In the event that the first waiting time W1 has expired without the current probe frequency f S below the critical probe frequency f krit has dropped, the control circuit 16 is set to a state of negative full control (S112), whereby the excitation current I A is generated. A second waiting period W2 is then started (S112). The output stage 17 then generates, for example, a negative square-wave voltage (S113), which directly follows the previously generated positive square-wave voltage. The second waiting period W2 is also monitored (S114). During the second waiting period W2, it is also continuously checked whether the current probe frequency f S greater than or equal to the critical probe frequency f krit (S115). If the second waiting time W2 expires without the current probe frequency f S below the critical probe frequency f krithas fallen, an error message is generated (S210), since in such a case no compensation point 31 (see Fig. 3) was found.

[0025] However, if during the second waiting time W2 (or one of the further waiting times) it is determined that the current probe frequency f S below a value of the critical probe frequency f krit has fallen (S115), a compensation point 31 (see Fig. 3) has been found and normal sensor operation (S200) can be continued. Checking whether the current sensor frequency f S greater than or equal to the critical sensor frequency f krit (S115), continues until the waiting time W2 (or further waiting times) has (have) expired or until a compensation point 31 (see Fig. 3) was found.

[0026] Alternatively, as already explained, the period t p instead of the special frequency tS be monitored. Alternatively, further waiting times with the procedures running there may follow before a compensation point is found or an error message is output. In any case, the switch-on process (S100) of the current sensor 10 ends according to the compensation principle with a transition to normal sensor operation (S200) or with an error message (S210).

[0027] In the Fig. 3, a constant negative primary current I flows in the primary winding 11 of the current sensor 10. pos = I neg , which is determined by means of the compensation current I K in the secondary winding. After switching on the current sensor at time t = 0, it is determined that the instantaneous probe frequency f S greater than or equal to the critical probe frequency f kritThen a direct voltage U A with a value U pos and positive polarity, which can be achieved, for example, by the control circuit Fig. 1 is generated and which has a positive excitation current I A with an initially increasing curve. Alternatively, the excitation current I A with an initially essentially increasing curve. The excitation current I A is fed in until a compensation point 31 is found or until the first waiting time W1 has elapsed. In the example according to Fig. 3, no compensation point 31 is found during the first waiting time W1, since the primary current I P has a negative polarity.

[0028] After applying the positive DC voltage U pos the excitation current I increases Ai.e. continuously (for example, with a nearly constant gradient) until it reaches a constant final value 30 (maximum value of the range traversed). The excitation current I A maintains the final value of 30 until the first waiting time W1 has elapsed and the control circuit 16 transitions from positive to negative control. Thus, during the first waiting time W1, a current range between zero (minimum value) and the final value of 30 (maximum positive value) is traversed, whereby the curve can be arbitrarily shaped.

[0029] With negative modulation, there is a negative DC voltage U neg The negative modulation is maintained over a second waiting time W2 until a compensation point 31 is reached at a compensation time t kompis found or until the second waiting time W2 has elapsed (at the maximum negative value). Thus, a scan cycle (scanning process) with positive and negative polarity of the DC voltage U is performed to locate the compensation point 31. The maximum current intensity of the excitation current generated is the voltage divided by the sum of the ohmic resistances of the compensation coil and the measuring resistor, or the primary maximum measuring range divided by the number of compensation windings. For example, for a 1000A sensor with a maximum measuring range of + / -2000A and a transformation ratio of 1:5000, the maximum compensation current Imax = 0.4A results. The magnetization reversal time t is as follows: t≥Nkomp⋅ΔBs⋅AFe / (U−ikomp⋅(Rcu_komp+Rmess)), with N komp is the number of compensation turns, ΔB S is the magnetic flux displacement, A Feis the core cross-section, U is the voltage at the compensation winding, i komp is the compensation current, R cu_komp is the resistance of the compensation winding and R mess is the measuring resistor in series with the compensation winding.

[0030] The second waiting time W2 follows the first waiting time W1. In the example after Fig. 3, the first waiting time W1 is longer than the second waiting time W2. This is used, for example, when a search for a compensation point 31 with a positive DC voltage U pos begins as in Fig. 3. There is then sufficient time available during the second waiting time W2 for the excitation current I A from the positive final value 30 (positive maximum value of the range traversed) into a current range with negative polarity.

[0031] It may also be provided that, as an alternative to the procedure according to Fig. 3, initially a negative DC voltage U neg and then a positive DC voltage U pos In this case, a compensation point 31 would already be created during the first waiting time W1 in the example according to Fig. 3, provided that the primary current I P again has a negative polarity as in Fig. 3. Other configurations with different waiting times, including additional waiting times, modified scanning processes taking place during the waiting times, and any desired characteristics of the primary current are readily possible.

[0032] Furthermore, it can be provided that a magnetic field probe 14 is used that can be brought into mutual saturation. This has the advantage that the operation of the current sensor is particularly reliable in an overload state. For example, the pulse width, which is proportional to the measured magnetic field, can be evaluated. Furthermore, it can be provided that the evaluation unit 15 is part of a computer-implemented application. It can also be provided that the evaluation unit 15 is part of an integrated circuit. This can, for example, be an application-specific integrated circuit, such as an ASIC circuit (ASIC = Application Specific Integrated Circuit). Because the architecture can be adapted to a specific measuring task, such a circuit can be very efficient and also faster than a functionally equivalent implementation using a microcontroller.

[0033] Fig. Figure 4 shows a diagram comparing two different probes S1 and S2, each of which shows the curve of the output voltage U as a function of the flux density B. The regular working range of the two probes S1 and S2 extends around the origin of the shown coordinate system of the Fig. 4. The two curves shown for probes S1 and S2 exhibit point symmetry with respect to the origin of the coordinate system. Around the origin, both the first probe S1 and the second probe S2 exhibit steep curves, each reaching a maximum. In this first region, the behavior of the parameters U and B is almost proportional to each other, resulting in a nearly linear curve.

[0034] With further increase of the flux density B in Fig.4, the first probe S1 delivers a slightly decreasing signal, so that voltage values ​​U gradually decrease with increasing flux density B. The second probe S2, on the other hand, has a steeply decreasing range after reaching its maximum and delivers above a flux density B x and correspondingly below a flux density -B x no more information about the magnetic field and therefore no information about the current I to be measured p . A control of the compensation current I K In this case, this is no longer possible with probe S2. However, the invention also allows the use of probes with smaller control ranges (such as probe 2).

[0035] In situations during the switch-on of a current sensor, it is therefore possible that the magnetic field probe does not provide any information about the direction and magnitude of the primary current in the primary winding, causing the compensation current to remain at zero. In order for the probe to provide a signal to regulate the compensation current, a sufficiently high voltage is initially applied to the compensation winding, for example. Due to the inductance of the compensation winding, the current can increase according to a given time constant (of the RL element) and can reach a steady-state final value after a certain time. If, for example, the polarity of the voltage is reversed, the current increases in the opposite direction until the corresponding steady-state final value is reached again. In these two cycles, the compensation current, for example, passes through the entire measuring range of the current sensor.The measuring range is therefore searched or scanned for the correct operating point using the proposed method.

[0036] If the operating point at which the magnetic field of the primary current and the magnetic field of the compensation current compensate each other lies within the scanned range, the probe will exit saturation near this operating point and thus, for example, deliver a suitable probe signal. The scan cycle can then be aborted, and the sensor can return to normal operation. However, if no compensation point is found within a specified time, a suitable circuit generates an error signal indicating a fault.

Claims

[1] Current sensor based on the compensation principle with a primary winding (11) for generating a magnetic field as a result of a primary current (I P ), a secondary winding (12) for generating a magnetic field as a result of a compensation current (I K ), a magnetic core (13) which magnetically couples the primary winding (11) and secondary winding (12), a magnetic field probe (14) magnetically coupled to the magnetic core (13) and designed to provide a quantity representing the strength of the resulting magnetic field in the magnetic core, an evaluation unit (15) connected downstream of the magnetic field probe (14) and upstream of the secondary winding (12), which is designed to generate a compensation current (I K ) depending on the quantity representing the strength of the resulting magnetic field in the magnetic core, where the evaluation unit (15) is designed to, in the event of overdriving of the magnetic field probe (14), by means of an excitation current (I A ) to find a compensation point (31) of the current sensor (10) and to determine from the compensation point (31) the corresponding value for the compensation current (I K ) and the excitation current (I A ) in the event of overdriving of the magnetic field probe (14), passes through a current range lying between a minimum and a maximum current intensity at least until the compensation point is reached. [2] Current sensor according to claim 1, wherein the case of overdriving of the magnetic field probe (14) is determined by a comparison of an instantaneous probe frequency (f S ) with a critical probe frequency (f krit ) is detected. [3] Current sensor according to claim 1, wherein the case of overdriving of the magnetic field probe (14) is detected by a comparison of an instantaneous pulse width (t S ) with a critical pulse width (t krit ) is detected. [4] Current sensor according to claim 1, 2 or 3, wherein the evaluation unit (15) is designed to find the compensation point (31) of the current sensor (10) when the current sensor (14) is switched on and to determine the compensation current (I K ) in the event of overdriving of the magnetic field probe (14). [5] Current sensor according to one of claims 1 to 4, wherein the evaluation unit (15) is designed to provide compensation currents with different polarities. [6] Current sensor according to one of claims 1 to 5, in which a first positive or negative compensation current can be generated during a first waiting time (W1) in a first time interval and a second negative or positive voltage can be generated during a second waiting time (W2) in a second time interval, the second waiting time (W2) beginning after the expiry of the first waiting time (W1). [7] Current sensor according to one of claims 1 to 6, wherein the first waiting time (W1) and the second waiting time (W2) are of different lengths. [8] Current sensor according to one of claims 1 to 7, wherein the magnetic field probe (14) is designed to be brought into saturation. [9] Current sensor according to one of claims 1 to 8, wherein at least one further magnetic field probe is magnetically coupled to the magnetic core (13) and is connected upstream of the evaluation unit. [10] Current sensor according to one of claims 1 to 9, wherein the excitation current is provided by a correspondingly controlled current or voltage source which is arranged inside or outside the evaluation unit and is controlled by it. [11] Current sensor according to claim 10, wherein the excitation current is provided by a current source which, when appropriately controlled, generates a continuously increasing current in the secondary winding. [12] Current sensor according to claim 10, wherein the excitation current is provided by a voltage source which, when appropriately controlled, provides a constant voltage at the secondary winding so that a continuously increasing current is generated in the secondary winding. [13] Current sensor according to one of claims 1 to 12, in which the excitation current passes through the current intensity range in a time period which is at least sufficient for the complete saturation of the magnetic core. [14] Current sensor according to one of claims 1 to 13, wherein the magnitude of the minimum current intensity of the excitation current is zero. [15] Current sensor according to one of claims 1 to 14, wherein the maximum current intensity of the excitation current corresponds to the maximum measuring range. [16] Method for operating a current sensor according to the compensation principle, in which the current sensor (10) has a primary winding (11) for a primary current (I P ), a secondary winding (12) for a compensation current (I K ), a magnetic core (13) magnetically coupling the primary winding (11) and the secondary winding (12) and a magnetic field probe (14) for measuring a quantity representing the strength of the resulting magnetic field in the magnetic core (13) in order to measure a magnetic field of the magnetic core (13), the method comprising a first scanning process with the steps: Detecting an overload of the magnetic field probe (14), In case of overload, start the first waiting time (W1) Provide a time-varying compensation current (I K ) to the secondary winding (12), Finding a compensation point (31) of the current sensor (10) by means of an excitation current (I A ), Determining a value of the compensation current (I K ) based on the found compensation point (31) and Setting the compensation current (I K ) to the determined value, where the excitation current (I A) in the event of overdriving of the magnetic field probe (14), passes through a current range lying between a minimum and a maximum current intensity at least until the compensation point is reached. [17] Method according to claim 16, wherein the case of overdriving of the magnetic field probe (14) is determined by comparing an instantaneous probe frequency (f S ) with a critical probe frequency (f krit ) is detected. [18] Method according to claim 17, wherein the compensation point (31) is found by: Providing the excitation current (I A ), Starting a first waiting time (W1) in a first time interval, During the first waiting time (W1), check whether the current probe frequency (f S ) is smaller than the probe frequency at overload (f krit ) is, in case the current probe frequency (fS ) smaller than the probe frequency (f krit ) in case of overload, determining a compensation point (31) and determining a value of a compensation current (I K ) at the compensation point (31). [19] Method according to claim 16, wherein the case of overdriving of the magnetic field probe (14) is determined by a comparison of an instantaneous pulse width (t S ) with a critical pulse width (t krit ) is detected. [20] Method according to claim 19, wherein the compensation point (31) is found by: Providing the excitation current (I A ), Starting a first waiting time (W1) in a first time interval, Check during the first waiting time (W1) whether the current pulse width (t S ) is smaller than the pulse width at overload (t krit ) is, in case the instantaneous pulse width (tS ) smaller than the pulse width (t krit ) in case of overload, determining a compensation point (31) and determining a value of a compensation current (I K ) at the compensation point (31). [21] Method according to one of claims 16, 17 or 18, in which, in the event that no compensation point (31) was found in the first time range, a second scanning process is carried out with the following steps: Providing the excitation current (I A ) to the secondary winding (12) in a second time interval, Starting a second waiting time (W2), During the second waiting time (W2), check whether the current probe frequency (f S ) is smaller than a critical probe frequency in case of overload (f Pkrit ) is, in case the current probe frequency (f S ) smaller than the critical probe frequency (f krit), finding a compensation point (31) and determining a value of a compensation current (I K ) at the compensation point (31). [22] Method according to one of claims 16, 17 or 18, in which, in the event that no compensation point was found in the first time range, the following steps are carried out: Providing the excitation current (I A ) to the secondary winding (12) in a second time interval, Starting a second waiting time (W2), During the second waiting time (W2), check whether the current pulse width ( P ) smaller than a critical pulse width in case of overload (f Pkrit ) is, in case the instantaneous pulse width (t P ) smaller than the critical pulse width (t pkrit ), finding a compensation point (31) and determining a value of a compensation current (I K ) at the compensation point (31). [23] Method according to claim 21 or 22, wherein the two time intervals follow one another directly in time. [24] Method according to claim 21, 22 or 23, wherein further scanning operations are carried out after the first and second scanning operations. [25] A method according to any one of claims 16 to 24, wherein an error signal is generated if no compensation point is found within a certain time interval.

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