CN106873461A - A kind of control method of remanence of current transformer degaussing gear - Google Patents

Abstract

The invention discloses a kind of control method of remanence of current transformer degaussing gear, belong to Deperming Facility field, the remanence of current transformer degaussing gear includes the incoming end electrically connected for summation current transformer, analogue collection module, central control module, safety control module, power module and the short circuit contact, adjustable resistance and the controllable impedance that are controlled by peripheral drive circuit, and central control module is connected with a human-computer interaction interface；The control method includes the decision algorithm of the Row control included in self-inspection and setup parameter stage and degaussing phase, and two stages and correlation.The remanent magnetism that the present invention realizes under conditions of current transformer does not have a power failure to current transformer carries out demagnetization, and, motion flow safer relative to traditional Deperming Facility is more reasonable.

Description

A control method for a current transformer residual magnetization degaussing device

technical field

The invention relates to the field of degaussing equipment, in particular to a control method of a circuit transformer residual magnetization demagnetization device, which is used for eliminating the residual magnetism of the circuit transformer iron core.

Background technique

Due to the inherent hysteresis of ferromagnetic materials, when the EHV system fails, the strong primary short-circuit current contains a relatively high non-periodic component. When the primary short-circuit current is transmitted to the secondary side through the current transformer, Because the transfer characteristic is different from the AC periodic component, the magnetic flux generated in the iron core cannot be completely balanced by the secondary current. When the fault is eliminated, part of the magnetic flux generated by the non-periodic component will exist in the iron core of the circuit transformer for a long time in the form of residual magnetism. Secondly, there will be high non-periodic components in the excitation inrush current and inrush current when the transformer is air-dropped, and the final result will generate residual magnetism in the iron core of the current transformer. Thirdly, after the current transformer is tested for direct resistance measurement and transformation ratio, if a good degaussing test is not carried out, residual magnetism may also exist in the iron core of the current transformer.

The existence of residual magnetism will cause the hysteresis loop during the operation of the current transformer core to no longer surround the origin, but to shift. Due to the deviation of the hysteresis loop, its anti-saturation performance will be greatly affected. If multiple short-circuits occur, its operating characteristics will change greatly. Even if a small short-circuit current occurs in the primary system, the current transformer may be deeply saturated. Therefore, the demagnetization of the residual magnetism of the core of the current transformer is an indispensable work.

Traditional current transformer degaussing methods include primary open circuit degaussing method and secondary open circuit degaussing method. Both methods require a device power outage. However, the reality is that when a transient fault occurs in the system, the system has resumed normal operation after re-closing to remove the fault. If the equipment is powered off to deal with the residual magnetism of the current transformer, it is not allowed by the condition-based maintenance of the current power grid operation. of. Therefore, there is an urgent need in the prior art for a device capable of demagnetizing the residual magnetism of the iron core of the current transformer without power failure of the equipment.

Contents of the invention

The technical problem to be solved by the present invention is to provide a control method capable of realizing the residual magnetism degaussing device of the iron core of the current transformer under the condition that the equipment is not powered off.

In order to solve the problems of the technologies described above, the technical solution adopted in the present invention is:

A control method for a current transformer residual magnetization demagnetization device, the current transformer residual magnetization degaussing device includes an access terminal for electrical connection with the current transformer, an analog quantity acquisition module, a central control module, a safety control module, a power supply The module and the short contact point, adjustable resistance and adjustable inductance controlled by the peripheral drive circuit, the central control module is connected with a man-machine interface;

The control method includes self-inspection and parameter setting phases and degaussing phases;

In the stage of self-inspection and parameter setting, follow the steps below:

Step 1, the central control module first sets a program infinite loop variable A, and sets the initial value of A to zero;

Step 2. The central control module reads the status information of the adjustable resistance, adjustable inductance and short contact point from the peripheral control circuit, and sends an instruction when the value of the adjustable resistance and adjustable inductance is zero and the state of the short contact point is closed To the human-computer interaction interface prompts to input the number of degaussing cycles, the saturation voltage limit and the load impedance angle connected in series with the device;

Step 3. The central control module detects whether the above three parameters have been input. After the above three parameters are input, the central control module sends an instruction to the peripheral drive circuit to close the short contact point, and sets the adjustable resistance and adjustable inductance to Zero, and finally the central control module sends instructions to the human-computer interaction interface to prompt to enter the next stage;

After removing the current connecting piece on the terminal block of the secondary line of the current transformer, the degaussing stage can be started after confirmation on the man-machine interface. In the degaussing stage, follow the steps below:

Step A, the central control module first reads the values of the number of demagnetization cycles, the saturation voltage limit and the load impedance angle from the man-machine interface;

Step B, the central control module sends the saturation voltage limit to the safety control module, and the safety module returns a confirmation message to the central control module after receiving the saturation voltage limit;

Step C. After receiving the confirmation message, the central control module sends a message to the peripheral control circuit to open the short contact point, and then sets the initial value of the number of degaussing cycles to 0;

Step D, the central control module sends instructions to the peripheral drive circuit to make the adjustable resistance and adjustable inductance increase linearly in steps of 0.1 ohms according to the set load impedance angle;

Step E. The analog quantity acquisition module collects current information and sends it to the central control module. The central control module judges whether the current transformer has reached a critical saturation state according to a preset algorithm, and sends information to the peripheral control circuit when the current transformer reaches a critical saturation state. Make the adjustable resistance and the adjustable inductance linearly decrease in the range of 0.1 ohms according to the set load impedance angle;

Step F, when both the adjustable resistance and the adjustable inductance are reduced to zero, the peripheral drive circuit returns information to the central control module, and the central control module increases the value of the number of degaussing cycles by 1 and then returns to step D to continue the cycle;

Step G. When the central control module detects that the number of degaussing cycles is greater than or equal to the preset number of degaussing cycles, it delays for 10 seconds to send a message to the peripheral drive circuit to close the short contact, and then executes the interrupt program.

The further improvement of the technical solution of the present invention lies in: when the central control module detects that the value of the adjustable inductance and the adjustable resistance is not zero or the short contact point is not in the closed state in the step 2 of the self-inspection and parameter setting stage, it will send a corresponding Instruct the peripheral drive circuit to set the value of the adjustable inductance or adjustable resistance to zero or set the short contact point to the closed state, and at the same time increase the value of the variable A of the program dead loop by 1 before continuing.

The further improvement of the technical solution of the present invention is: in the step B of the degaussing stage, when the safety control module does not receive the saturation voltage limit, it sends feedback information to the central control module, and the central control module increases the value of the program dead-loop variable A by 1 to continue.

The further improvement of the technical solution of the present invention lies in that: when the value of the program infinite loop variable A is greater than or equal to 100, the interrupt program is executed.

The further improvement of the technical solution of the present invention lies in: the central control module simultaneously sends an instruction to close the short contact point to the peripheral control circuit and the safety control module in the interrupt program, and then sends an instruction to the human-computer interaction interface to prompt interruption.

The further improvement of the technical solution of the present invention is that: the safety control module operates according to the following program, first reads the saturation voltage limit value from the central control module, then transmits the return information to the central control module, and then the safety control module reads the analog quantity acquisition Module information and judge whether the secondary voltage of the current transformer exceeds the saturation voltage limit. When the secondary voltage of the power transformer exceeds the saturation voltage limit, an instruction is sent to the peripheral control circuit to close the short contact point. When the secondary voltage of the current transformer When the voltage does not exceed the saturation voltage limit, the safety module does not act; when the safety control module does not receive the saturation voltage limit from the central control module, it first detects whether the short contact is in the closed state, otherwise it sends an instruction to close the short contact.

The further improvement of the technical solution of the present invention is that: the preset algorithm described in the step E of the degaussing stage includes the following two criteria:

Criterion one:

Δi _k =i _kN -i _k

Δi _k ＞ΔI _zd

Among them: Δi _k - the calculated value of the secondary circuit current of the current transformer at the k sampling time (t=kT _s ) (T _s is the sampling interval, the device samples at 24 points, so T _s =1ms);

i _k ——the measured current sampling value of the secondary circuit current of the current transformer at the k sampling moment;

i _kN ——the current sampling value of a cycle before k sampling time (N is the number of sampling points of a power frequency, the device N=24);

ΔI _{zd ——a} fixed threshold value set by the programmer. According to the debugging experience, the device is set to 0.025A;

Judgment 2:

i _k <ΔI _zd1

|i _k -i _k-1 |<ΔI _zd2

|i _k -i _k+1 |<ΔI _zd2

Among them, i _k ----- the measured current sampling value of the secondary circuit current of the current transformer at the k sampling time;

i _k-1 ------ the measured current sampling value of the secondary circuit current of the current transformer at the k-1 sampling time;

i _k+1 ------ the measured current sampling value of the secondary circuit current of the current transformer at the k+1 sampling moment;

ΔI _zd1 ------ zero threshold limit value, the reference data and experience of this device is set to 2mA;

ΔI _zd2 ------ Judging the threshold limit of linear transmission, the reference data and experience of this device are set to 5mA;

After the above two criteria are satisfied at the same time, it can be determined that the current transformer is in a critical saturation state.

Owing to having adopted above-mentioned technical scheme, the technical progress that the present invention obtains is:

The present invention realizes the automatic degaussing of the residual magnetism in the iron core of the current transformer under the condition of no power failure. According to the artificial parameter setting, through the internal software program and related algorithms, the adjustable resistance and adjustable inductance are automatically increased step by step, so that the load impedance of the secondary circuit of the current transformer is continuously increased until it reaches the critical saturation point , At this time, the primary current of the current transformer will be completely converted into the excitation current of the current transformer, and the strong magnetic flux generated by the current will spontaneously weaken the effect of the residual magnetism. Then, the secondary load impedance is reduced to the load state (short circuit state) during normal operation by adjusting the adjustable resistance and adjustable inductance step by step. By repeating several processes, the residual magnetism of the iron core will be greatly weakened until completely eliminated. In addition, this device is also equipped with a safety control module and an analog quantity acquisition module, which can detect that if the secondary saturation voltage of the current transformer exceeds the artificially set safety saturation voltage limit, it will quickly close the short contact point to restore the current transformer. To the normal operation state and send an alarm, which greatly guarantees the safety of personal and equipment.

Different from the traditional central control module single-control drive output peripheral drive circuit mode, this patent specifically designs the dual drive design idea that the peripheral drive can receive the central control module and the safety control module at the same time. The main purpose of adopting this design idea is to ensure that the central After the main program of the single-chip microcomputer of the control module is abnormal, the safety module can still drive the peripheral circuit. Even if the central processing module is abnormal, the safety module can still play the role of safety monitoring, thus avoiding the risk of open circuit in the secondary circuit of the current transformer. Secondly, in special circumstances, the central control module can issue another command through the safety module after issuing the drive command to ensure safety, thereby avoiding the risk of an open circuit in the secondary circuit of the current transformer under special circumstances.

Description of drawings

Fig. 1 is the functional block diagram of power transformer residual magnetism degaussing device among the present invention;

Fig. 2 is the wiring diagram of self-inspection and setting parameter stage of power transformer residual magnetism degaussing device among the present invention;

Fig. 3 is the flow chart of self-inspection and setting parameter stage among the present invention;

Fig. 4 is the flowchart of degaussing phase among the present invention;

Fig. 5 is the flow chart of interrupt program among the present invention;

Fig. 6 is an action flowchart of the security control module in the present invention.

detailed description

Below in conjunction with embodiment the present invention is described in further detail:

As shown in Fig. 1, the present invention is a device for demagnetizing the residual magnetism of a current transformer, which can demagnetize the iron core of the current transformer without power failure of the equipment. The invention mainly includes an analog quantity acquisition module, a central control module and peripheral drive circuits. The analog quantity acquisition module is powered on and connected with an access terminal, which is used to connect with the current transformer and other related loads. The analog quantity acquisition module can collect the current and voltage information in the circuit in real time, and the collected information sent to the central control module. The central control module converts and compares the received information before sending information to the peripheral drive circuit, and the peripheral drive circuit then drives the short contact point, adjustable resistance and adjustable inductance controlled by it to take action.

In order to ensure the normal operation of the whole set of equipment, the present invention is also equipped with a safety control module. The safety control module can read the information collected by the analog quantity acquisition module, and then compare it with the information cached in the central control module, and then find that the current transformer Whether the secondary voltage in the current transformer exceeds the saturation voltage limit cached in the central control module. When the secondary voltage in the current transformer exceeds the saturation voltage limit, the safety control module will send an alarm to the peripheral drive circuit and close the short contact to avoid There is a risk of an open circuit in the secondary circuit of the circuit transformer.

Different from the traditional central control module single-control drive output peripheral drive circuit, the safety module only communicates with the central control module for data communication, the peripheral drive in the present invention can simultaneously receive the dual drive of the central control module and the safety control module. The main purpose of the design idea is to ensure that after the main program of the single-chip microcomputer of the central control module is abnormal, the safety module can still drive the peripheral circuit, which has a double protection effect on the operation of the equipment.

In order to conveniently input relevant parameters into the central control module, the present invention also includes a human-computer interaction interface connected with the central control module. In the human-computer interaction interface, the operator can input information such as the saturation voltage limit, the number of degaussing cycles, and the impedance angle of the load, and can also receive incomplete parameter input, the secondary voltage of the current transformer exceeds the saturation voltage limit, and the equipment is interrupted. Wait for security tips.

The invention also includes a power supply module that provides power for the central control module, the man-machine interface, the analog quantity acquisition module and the peripheral drive circuit.

The control method of the residual magnetism degaussing device of the current transformer is as follows:

Before starting to use this device, all protective devices, measuring devices and other devices connected to the secondary circuit of the current transformer must be out of operation.

The control method includes a self-inspection and parameter setting stage and a degaussing stage;

In the stage of self-inspection and parameter setting, follow the steps below:

Step 1, the central control module first sets a program infinite loop variable A, and sets the initial value of A to zero;

Step 2. The central control module reads the status information of the adjustable resistance, adjustable inductance and short contact point from the peripheral control circuit, and sends an instruction when the value of the adjustable resistance and adjustable inductance is zero and the state of the short contact point is closed To the human-computer interaction interface prompts to input the number of degaussing cycles, saturation voltage limit and load impedance angle.

When the central control module detects that the value of the adjustable inductance and the adjustable resistance is not zero or the short contact point is not closed, it sends a corresponding instruction to the peripheral drive circuit to set the value of the adjustable inductance or the adjustable resistance to zero or set The short contact point is set to the closed state, and at the same time, the value of the program infinite loop variable A is increased by 1 before continuing. When the value of A is greater than or equal to 100, the interrupt program is executed. When it is determined that the value of the adjustable resistance and adjustable inductance is zero and the state of the short contact point is closed, the value of A is reset to 0 to continue to the next stage.

Step 3. The central control module detects whether the above three parameters have been input. After the above three parameters are input, the central control module sends an instruction to the peripheral drive circuit to close the short contact point, and sets the adjustable resistance and adjustable inductance to Zero, and finally the central control module sends instructions to the human-computer interaction interface to prompt to enter the next stage;

After removing the current connecting piece on the terminal block of the secondary line of the current transformer, the degaussing stage can be started after confirmation on the man-machine interface. In the degaussing stage, follow the steps below:

Step A, the central control module first reads the values of the number of demagnetization cycles, saturation voltage limit and load impedance angle from the man-machine interface;

Step B. The central control module sends the saturation voltage limit to the safety control module, and the safety module returns a confirmation message to the central control module after receiving the saturation voltage limit; when the safety control module does not receive the saturation voltage limit, it sends the central The control module sends feedback information, and the central control module increases the value of the program dead-loop variable A by 1 before continuing. When the value of A is greater than or equal to 100, the interrupt program is executed.

Step C. After receiving the confirmation message, the central control module sends a message to the peripheral control circuit to open the short contact point, and then sets the initial value of the number of degaussing cycles to 0;

Step D, the central control module sends instructions to the peripheral drive circuit to make the adjustable resistance and adjustable inductance increase linearly in steps of 0.1 ohms according to the set load impedance angle;

Step E. The analog quantity acquisition module collects current information and sends it to the central control module. The central control module judges whether the current transformer has reached a critical saturation state according to a preset algorithm, and sends information to the peripheral control circuit when the current transformer reaches a critical saturation state. Make the adjustable resistance and the adjustable inductance linearly decrease in the range of 0.1 ohms according to the set load impedance angle;

Step F, when both the adjustable resistance and the adjustable inductance are reduced to zero, the peripheral drive circuit returns information to the central control module, and the central control module increases the value of the number of degaussing cycles by 1 and then returns to step D to continue the cycle;

Step G. When the central control module detects that the number of degaussing cycles is greater than or equal to the preset degaussing cycle, it delays for 10 seconds to send a message to the peripheral drive circuit to close the short contact, and then executes the interrupt program.

The interrupt program described in the above self-inspection and input parameter stage and the degaussing stage includes: the central control module sends an instruction to close the short contact point to the peripheral control circuit and the safety control module at the same time, and then sends an instruction to the human-computer interaction interface to prompt the interrupt command .

The safety control module in this control method operates according to the following steps: first read the saturation voltage limit value from the central control module, then transmit the return information to the central control module, and then the safety control module reads the information of the analog quantity acquisition module and judges Whether the secondary voltage of the current transformer exceeds the saturation voltage limit. When the secondary voltage of the power transformer exceeds the saturation voltage limit, an instruction is sent to the peripheral control circuit to close the short contact point. When the secondary voltage of the current transformer does not exceed the saturation voltage When the limit is reached, the safety module does not act; when the safety control module does not receive the saturation voltage limit sent by the central control module, it first detects whether the short contact is in the closed state, otherwise it sends an instruction to close the short contact.

The preset algorithm described in the step E of the degaussing phase includes the following two criteria:

Criterion one:

Under normal conditions, TA does not reach saturation, and its primary and secondary currents run in the linear region, but when it reaches critical saturation, its secondary current will instantly decrease to zero. Therefore, it can be judged whether it has reached the critical saturation state by comparing the current difference before a cycle and at the same moment of this cycle.

Δi _k =i _kN -i _k

Δi _k ＞ΔI _zd

Among them: Δi _k - the calculated value of the secondary circuit current of the current transformer at the k sampling time (t=kT _s ) (T _s is the sampling interval, the device samples at 24 points, so T _s =1ms);

i _k ——the measured current sampling value of the secondary circuit current of the current transformer at the k sampling moment;

i _kN ——the current sampling value of a cycle before k sampling time (N is the number of sampling points of a power frequency, the device N=24);

ΔI _{zd ——a} fixed threshold value set by the programmer. According to the debugging experience, the device is set to 0.025A;

analyse as below:

During the period when TA is not saturated, the calculated value of Δi _k is almost zero. When critical saturation is reached, the calculated value of Δi _k is no longer 0, and the calculated value of Δi _k satisfies the formula Δi _k > ΔI _zd , which satisfies the first criterion condition.

Judgment 2:

During the saturation period of TA, its primary current is all converted into excitation current, but when the primary current crosses zero, because the current value is very small, the iron core is not saturated within a period of time at this moment, and its secondary Current also has a linear transmission process. Taking into account the influence of remanence and referring to relevant scientific data and debugging experience, the positive and negative half-waves at the zero-crossing point of the zero-crossing linear transmission process will not exceed the electrical angle of 30°, and the time is 1.67ms. That is, no more than one sampling interval, that is, two sampling points before and after the zero-crossing time.

i _k <ΔI _zd1

|i _k -i _k-1 |<ΔI _zd2

|i _k -i _k+1 |<ΔI _zd2

Among them, i _k ----- the measured current sampling value of the secondary circuit current of the current transformer at the k sampling time;

i _k-1 ------ the measured current sampling value of the secondary circuit current of the current transformer at the k-1 sampling time;

i _k+1 ------ the measured current sampling value of the secondary circuit current of the current transformer at the k+1 sampling moment;

ΔI _zd1 ------ zero threshold limit value, the reference data and experience of this device is set to 2mA;

ΔI _zd2 ------ Judging the threshold limit of linear transmission, the reference data and experience of this device are set to 5mA;

After the above two criteria are satisfied at the same time, it can be determined that the current transformer is in a critical saturation state.

Claims (7)

1. a kind of control method of remanence of current transformer degaussing gear, it is characterised in that：The remanence of current transformer demagnetization Device includes incoming end, analogue collection module, central control module, the security control mould for summation current transformer electrical connection Block, power module and the short circuit contact, adjustable resistance and the controllable impedance that are controlled by peripheral drive circuit, central control module with One personal-machine interactive interface is connected；

The control method includes self-inspection and setup parameter stage and degaussing phase；

In self-inspection and setup parameter stage, carry out in accordance with the following steps：

Step 1, central control module set a program endless loop variables A first, and the initial value of A is set as into zero；

Step 2, central control module read the state letter of adjustable resistance, controllable impedance and short circuit contact from peripheral control circuits Breath, human-computer interaction interface is just sent a command to when the value of adjustable resistance and controllable impedance is zero and short circuit contacts status are and close Prompting input demagnetization cycle-index, saturation voltage limit value and load impedance angle；

Whether step 3, central control module detection above three parameter are input into and finish, after the input of above three parameter is finished in Centre control module sends a command to peripheral drive circuit and closes short circuit contact, and adjustable resistance and adjustable electric inductance value are set as Zero, last central control module sends command prompt and enters next stage to human-computer interaction interface；

After removing the electric current connection sheet on Current Transformer Secondary line terminal row, after human-computer interaction interface is confirmed Start degaussing phase, carried out in accordance with the following steps in degaussing phase：

Step A, central control module read demagnetization cycle-index, saturation voltage limit value and load resistance from human-computer interaction interface first The value at anti-angle；

Step B, central control module send to safety control module saturation voltage limit value, and security module receives saturation voltage After limit value confirmation is returned to central control module；

Step C, central control module send information unlatching short circuit contact after being connected to confirmation to peripheral control circuits, then will Demagnetization cycle-index initial value is set as 0；

The instruction of drive circuit transmission to the periphery of step D, central control module makes adjustable resistance and controllable impedance according to the negative of setting Carrying impedance angle allows the adjustable resistance to carry out linear increase according to 0.1 ohm of stepping amplitude；

Step E, analogue collection module collected current information are simultaneously sent to central control module, and central control module is according to default Algorithm judges whether current transformer reaches critical saturation state, after current transformer reaches critical saturation state just to the periphery Control circuit sends information makes adjustable resistance and controllable impedance allow adjustable resistance according to 0.1 Europe according to the load impedance angle of setting The amplitude of nurse is linearly reduced；

Step F, after adjustable resistance and controllable impedance are decreased to zero, peripheral drive circuit to central control module return believe Breath, central control module is back to step D and continues cycling through after the value of demagnetization cycle-index is increased into 1；

Step G, when central control module detect demagnetization cycle-index value be more than or equal to demagnetization cycle-index set in advance When, then postpone the 10 seconds information of drive circuit transmission to the periphery and close short circuit contact, then perform interrupt routine.

2. the control method of a kind of remanence of current transformer degaussing gear according to claim 1, it is characterised in that：Self-inspection And when the value that central control module detects controllable impedance and adjustable resistance is not zero or short circuit in the step of setup parameter stage 2 When contact is not closed mode, just sends command adapted thereto to peripheral drive circuit and the value of controllable impedance or adjustable resistance is set to zero Or short circuit contact is set to off closed state, and will continue after the value increase by 1 of program endless loop variables A simultaneously.

3. the control method of a kind of remanence of current transformer degaussing gear according to claim 1, it is characterised in that：Demagnetization In the step of stage B when safety control module does not receive saturation voltage limit value, just sent to central control module and fed back Information, central control module continues after the value of program endless loop variables A is increased into 1.

4. the control method of a kind of remanence of current transformer degaussing gear according to Claims 2 or 3, it is characterised in that： Interrupt routine is performed when the value of program endless loop variables A is more than or equal to 100.

5. the control method of a kind of remanence of current transformer degaussing gear according to claim 4, it is characterised in that：It is described By central control module, control circuit and safety control module send the instruction for closing short circuit contact to interrupt routine to the periphery simultaneously, Then command prompt is sent to human-computer interaction interface again to interrupt.

6. the control of a kind of remanence of current transformer degaussing gear according to any one in claim 1 or 2 or 3 or 5 Method, it is characterised in that the safety control module runs according to following programs：First saturation electricity is read from central control module Pressure limit value, then transmits return information to central control module, and subsequent safety control module reads the letter of analogue collection module Cease and judge whether Current Transformer Secondary voltage exceedes saturation voltage limit value, when the secondary voltage of electric power mutual-inductor exceedes saturation Just peripheral control circuits are sent a command to during voltage limits and closes short circuit contact, when Current Transformer Secondary voltage is not less than saturation Security module is failure to actuate during voltage limits；When safety control module does not receive the saturation voltage limit value that central control module is sent Whether Shi Shouxian detection short circuits contact is closed, and otherwise sends instruction and closes short circuit contact.

7. a kind of control method of remanence of current transformer degaussing gear according to claim 1, it is characterised in that demagnetization Preset algorithm includes following two criterions described in the step of stage E：

Criterion one：

Δi_k=i_k-N-i_k

Δi_k＞ Δs I_zd

Wherein：Δi_k--- secondary loop of mutual inductor electric current is in k sample moment (t=kT_s) calculated value (T_sFor between sampling Every, the point sampling of the present apparatus 24, therefore T_s=1ms)；

i_k--- measurement current sampling data of the secondary loop of mutual inductor electric current at the k sample moment；

i_k-N--- (N is a sampling number for power frequency, present apparatus N=to the current sampling data in the previous cycle at k sample moment 24)；

ΔI_zd--- the fixed threshold value set by programmer.According to commissioning experience, the present apparatus is set as 0.025A；

Criterion two：

i_k＜ Δs I_zd1

|i_k-i_k-1| ＜ Δs I_zd2

|i_k-i_k+1| ＜ Δs I_zd2

Wherein, i_kMeasurement current sampling data of --- -- the secondary loop of mutual inductor electric current at the k sample moment；

i_k-1Measurement current sampling data of --- --- the secondary loop of mutual inductor electric current in k-1 sampling instants；

i_k+1Measurement current sampling data of --- --- the secondary loop of mutual inductor electric current in k+1 sampling instants；

ΔI_zd1--- --- sentences zero gate sill limit value, and present apparatus reference and experience are set as 2mA；

ΔI_zd2--- --- sentences linear transform threshold limit value, and present apparatus reference and experience are set as 5mA；Above-mentioned two criterion Cutoff current transformer has been in critical saturation state by meet simultaneously after.