KR20000031658A - Apparatus for restraining transformer from generating exciting inrush current and method thereof - Google Patents

Abstract

PURPOSE: An apparatus for restrain a transformer from generating the exciting inrush current and the method thereof are provided to suppress the exciting inrush current generated by characteristics in the magnetizing current of a transformer when power is supplied. CONSTITUTION: A demagnetization coil(14) demagnetizes residual magnetic flux causing the exciting inrush current of a transformer. Circuit breakers(12,13) connected to the primary and secondary of the transformer in series interrupt driving power. A variable voltage power supply part(50) supplies the voltage signal of a hysterisis loop reduced by the demagnetization coil(14) at the time that a power trip signal from the circuit breaker(12,13) is inputted. A current detector(20) detects the variation of a current magnitude supplied to the demagnetization coil(14). A ROM(60) stores data to generate the voltage signal waveform of the hysterisis loop. An address decorder appoints the write and read address of data according to the control signal of a microprocessor(30). A first A/D converter(80) converts the magnitude of a demagnetization current into a digital value. A second A/D converter(90) converts the actual supply current of the demagnetization current into a digital value.

Description

Excited inrush current generation suppression device and method of transformer

The present invention relates to an apparatus and method for suppressing the excitation inrush current generation of a transformer, and more particularly, to suppress the occurrence of the transient inrush current (excited inrush current) generated by the characteristics of the magnetizing current of the transformer when the power is turned on in the transformer. The present invention relates to an apparatus and a method for suppressing excitation inrush current generation of a transformer.

1 is a waveform diagram showing generation of an exciting inrush current of a general transformer. As shown in FIG. 1, the excitation inrush current of a transformer, which is widely used in industrial and home appliances, as a core device of electric equipment, is greatly influenced by the residual magnetic flux density remaining in the iron core when the transformer is turned off, and the amount of residual magnetic flux is increased. According to this, a large value of several times to several tens of the normal current is shown.

2 is a conceptual diagram illustrating residual magnetic flux generation in an iron core of a general transformer. As shown in FIG. 2, when the power supply of the transformer is turned off, the magnetic flux density inside the iron core is different depending on the current phase at the time of turning off the power. When the power is turned on again in this state, an alternating magnetic flux with the initial value of residual magnetic flux is generated. Depending on the amount of residual magnetic flux, the iron core may be saturated.

Inductance, a circuit element that suppresses the flow of current in an AC circuit, is the ratio of the generation of magnetic flux to the applied current. Therefore, inductance is high in the condition that can generate a large amount of magnetic flux even at the same current, and inductance is the condition that can generate small magnetic flux. The value becomes smaller. Therefore, the value of inductance is small because the magnetic space that can generate magnetic flux becomes narrow even with the same current in the core where many residual magnetic fluxes remain. For this reason, a large exciting inrush current occurs when the power is turned on in a transformer with residual magnetic flux. If we actually measure the waveform of this excitation inrush current, the effect of the excitation can never be neglected because it often occurs for several tens of cycles.

On the other hand, conventionally, as a method for suppressing the generation of the excitation inrush current, when the power is turned on, the switch has two stages, and in the first step, the voltage is lowered in half with a series resistor, and the method is reduced in the second step. A method of demagnetizing the magnetic flux in an iron core by using a capacitor or a capacitor having a charge current equal to the magnetization current and applying attenuation vibration of the LC circuit when the power is cut off has been proposed. However, this method did not have a great effect on the reduction of the transformer inrush current and was not put to practical use because the demagnetization using the residual energy remaining in the coil after the transformer was cut off did not apply enough energy. .

Thus, up to now, the excitation of the transformer has been taken for granted, and a method for preventing the malfunction of the relay has been devised as a workaround, and in such a method, it is necessary to lock the temporary circuit during power-on or to turn off the power for a certain time after the power is turned on. In order to reduce the sensitivity of the relay, a resistor is installed in parallel to the working coil and a current flows through the resistor for a short time when the power is applied.

In addition, as a result of analyzing the waveform of the excitation inrush current, a method of preventing malfunction by using a second harmonic suppression ratio differential relay has been proposed and applied. Either way is not to suppress the generation of the excitation inrush current, but to prevent the malfunction of the relay caused by the excitation inrush current, there is a problem that the transformer and grid series connection equipment due to the excitation inrush current deteriorates or burns out.

Accordingly, the present invention has been made to solve the above-mentioned conventional problems, and its purpose is to demagnetize the residual magnetic flux inside the core of the transformer, which causes the excitation inrush current, before powering on the transformer, It is an object of the present invention to provide an apparatus and method for suppressing excitation inrush current generation of a transformer to prevent burnout of a transformer and grid equipment by applying power.

1 is a waveform diagram showing generation of an exciting inrush current of a general transformer.

2 is a conceptual diagram illustrating residual magnetic flux generation in an iron core of a general transformer.

3 is a schematic diagram of a transformer excitation inrush current generation suppression apparatus according to the present invention.

Figure 4 is a block diagram of a transformer excitation inrush current generation device for implementing the present invention.

5 is a diagram illustrating a demagnetizing current waveform applied to the demagnetizing coil in order to implement the present invention.

6 is a flowchart illustrating a method of suppressing transformer excitation inrush current generation according to the present invention.

Explanation of symbols on the main parts of the drawings

10: transformer enclosure 11: transformer coil

12, 13: circuit breaker 14: demagnetizing coil

15: ORGATE 20: Current detector

30: microprocessor 40: display unit

50: variable voltage power supply 60: ROM (ROM)

70: address decoder 80,90: first and second A / D converters

In order to achieve this purpose, the excitation inrush current generation suppression device of the transformer according to the present invention is wound in a predetermined number of turns in an enclosure of a transformer having primary and secondary transformer coils wound around an internal iron core to remove residual magnetic flux of the iron core when the power is cut off. Demagnetizing coil for generating a magnetic field for the purpose, a circuit breaker for generating a power off signal by detecting whether the power supply of the transformer is cut off, and to form a magnetic field with the magnetic stripe coil at the time when the power off signal is input from the circuit breaker The variable voltage power supply unit applies a demagnetizing current of a predetermined waveform, a ROM storing data for generating a waveform of a demagnetizing current signal applied to the system driving program and the demagnetizing coil, and a power cut-off of the transformer according to the output signal of the breaker. If it is determined, the demagnetizer on the demagnetizing coil is based on the data read from the ROM. Applying a voltage signal to form a so by a microprocessor for outputting the control signal to the variable voltage power source is characterized in that formed.

In addition, the method for suppressing the excitation inrush current generation of the transformer for implementing the present invention (A) receiving a demagnetizing current value (ld) for demagnetizing the residual magnetic flux of the transformer core to the demagnetizing coil wound in the transformer enclosure, (b Determining whether the power supply of the transformer is cut off; (c) when it is determined that the power of the transformer is cut off, the ROM table data pre-programmed in the ROM to generate a signal waveform of the demagnetizing current; Reading and multiplying with the demagnetizing current input in step (a) and applying it to the demagnetizing coil, (d) detecting the real demagnetizing current T applied to the demagnetizing coil, and detecting the detected demagnetizing current and the step ( (C) comparing the applied current applied in (c), (e) if the actual demagnetizing current is less than the applied current applied to the demagnetizing coil in step (c). Multiplied by the reduction of a predetermined value to the table data printing, if large, characterized in that formed by a step of multiplying the increase factor of a predetermined value, performing the step (C) or less until the demagnetisation of residual magnetic flux to close repeatedly.

Hereinafter, the configuration and operation of an excitation inrush current generation suppression apparatus and method of a transformer according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

3 is a view showing a schematic configuration of an excitation inrush current generation device of the transformer according to the present invention, Figure 4 shows a block diagram for implementing the present invention.

First, as shown in FIG. 3 and FIG. 4, the excitation inrush current generation suppression device of the transformer for implementing the present invention is a demagnetizing coil 14 for demagnetizing (or device) the residual magnetic flux causing the excitation inrush current of the transformer And a hysteresis that decreases to the demagnetizing coil 14 at the point of time when a power off signal is input from the breaker 12, 13 which is connected in series with the primary and secondary sides of the transformer to block the driving power. A variable voltage power supply unit 50 for applying a voltage signal of the loop is provided.

In addition, the operation of the current detector 20 for detecting a change in the magnitude of the current applied to the demagnetizing coil 14 and the drive signals of the primary and secondary breakers 12 and 13 of the transformer is calculated by OR. Determining the drive off time of the transformer in accordance with the or gate 15 to determine and the output signal of the or gate 15 to control the variable voltage power supply unit 50 to apply a decreasing voltage signal to the demagnetizing coil 14 A microprocessor 30, a ROM 60 for storing data for generating a voltage signal waveform of a hysteresis loop applied to the operation program and demagnetizing coil 14 for implementing the present invention, and a microprocessor 50 The address decoder 70 designates the address of writing and reading the data according to the control signal outputted from the C1), and the magnitude of the demagnetizing current to be applied to the demagnetizing coil for the first time by the user through the variable resistor. After the analog-to-digital conversion, the first A / D converter 80 input to the microprocessor 50 and the actual applied current of the demagnetizing current detected by the current detector 20 are received and converted into digital values. Screen display unit for displaying the change value of the initial demagnetizing current and the demagnetizing current applied to the second A / D converter 90 and the demagnetizing coil 14 input to the corresponding input terminal of the processor 30 so as to be easily identified by the user. 40 is provided.

In this configuration, the demagnetizing coil 14 is preferably wound in the enclosure 10 of the transformer case and is made of a square coil having a sufficient number of turns to reduce the residual magnetic flux of the transformer core. In addition, the transformer case portion in which the transformer coil 11 is installed in order for the magnetic flux generated from the demagnetizing coil 14 to be effectively applied to the transformer core is made of a nonmagnetic material (for example, SUS 304) instead of steel. Produce using

It is preferable to use a low frequency so that the frequency of the alternating magnetic field produced by the demagnetizing coil 14 is not affected by the induced current generated in the transformer winding. That is, when an alternating current with a high frequency flows, an induced current is generated in the coil 11 inside the existing transformer to generate a magnetic flux in a direction opposite to the removal of the residual magnetic flux. Thus, a low frequency of 10 [Hz] or less is used. It is effective to perform deprivation.

The demagnetizing field is reduced to an appropriate width by inverting the proper number of times, thereby inducing a gradually decreasing residual magnetic flux to the iron core.

The variable voltage power supply unit 50 is a single-phase inverter device using a semiconductor for power, and the variable voltage power supply unit 50 applies an alternating alternating current to the demagnetizing coil 14 to provide proper demagnetization required by the demagnetizing coil 14. Create a magnetic field

In addition, the or gate 15 is the primary and secondary circuit breaker 12 to detect the power cut signal of the primary and secondary circuit breakers 12 and 13 of the transformer to automatically perform the demagnetization process after the power is cut off from the transformer. When a power off signal is applied from any one of the circuit breakers 13), a control signal for performing the demagnetization work is output to the microprocessor 30.

The ROM 60 stores, as a unit value, data for a waveform of an optimally reduced hysteresis current required for demagnetization at the time when an operating program of the system and a power off signal of the breaker are applied.

Figure 5 shows the waveform and hysteresis loop of the current applied to the demagnetizing coil for implementing the present invention. As shown in FIG. 5, the waveform of the reduced hysteresis current for realizing the present invention is a waveform having a constant decrease width every half cycle, and at the time of setting the waveform, optimum efficiency within a desired frequency according to various types of waveforms. The rate of demagnetization is reduced.

Hereinafter, with reference to the accompanying drawings the operation and effect of the excitation inrush current generation device of the transformer according to the present invention will be described in detail.

Figure 6 shows a flowchart for explaining the operation of the excitation inrush current generation device of the transformer for implementing the present invention. As shown in FIG. 6, the excitation inrush current generation suppression apparatus of a transformer for implementing the present invention is first supplied with power to the microprocessor 30 when system power is applied to prepare the system for operation. It enters the standby state to receive the appropriate magnitude of demagnetizing current. In this case, when the user sets and inputs a demagnetizing current of an appropriate magnitude to be applied to the transformer through the variable resistor VR in step S10, the user demagnetizing current is passed through the first A / D converter 80 to the microprocessor 30. Will be input to the corresponding input terminal. The microprocessor 30 stores the user-set demagnetization current input through the first A / D converter 80 as a variable value of ld (demagnetization current).

In the next step (s12), it is determined whether the power cutoff signal is applied from the first breaker 12 or the second breaker 13 while the transformer is being driven, and at this time, the first or second breaker through the or gate 15 If it is determined that the power-off signal is applied from at least one of (12) and (13), the process proceeds to step s14 to operate the counter i to count the number of repetitions of the removal process.

Further, in step S16, the microprocessor 30 receiving the power off signal starts the demagnetization operation by a program previously inputted into the ROM 60, and demagnetization stored as a unit value in the ROM 60. The waveform data (hereinafter referred to as ROM table data) is read out and multiplied by the user-set demagnetizing current value ld input in the step S10, and this current value is applied to the demagnetizing coil 14 of the actual transformer. It becomes the demagnetizing current value.

The microprocessor 30 calculates the gate pulse time point of the variable voltage power supply unit 50 to generate the current value based on the demagnetizing current value calculated in the step s16, and then applies it to each switching element of the variable voltage power supply unit 50. To generate a gate pulse. As with the single-phase inverter control, the gate signal applies a driving pulse to G1 and G4 when generating a positive current, and generates a driving pulse to G2 and G3 when generating a reverse current to control a current waveform applied to the demagnetizing coil.

On the other hand, in step s18, since the calculated value of the microprocessor 30 and the output of the variable voltage power supply unit 50 cannot exactly match the intention of the designer, it is applied to the actual transformer demagnetizing coil 14 through the current detector 20. By detecting the current (T) is to monitor whether the intended demagnetizing current is properly applied, if the difference is corrected. That is, since the actual demagnetizing current T detected through the current detector 20 in step S20 is converted into a digital value through the second A / D converter 90 and then applied to the microprocessor 30, The processor 30 compares the demagnetizing current calculated in step S16 with the actual demagnetizing current T. As a result of the comparison, when the actual current T is larger than the set value, as shown in step s24, the current value detected through the current detector 20 is multiplied by a decreasing factor, and in the next step, a smaller current is applied to the demagnetizing coil. Is authorized. In addition, when the actual current is smaller than the set value as a result of the comparison, the demagnetizing current value detected by the current detector 20 in the step s26 is multiplied by an increase factor, and a larger current is applied to the demagnetizing coil 14 in the next step. . At this time, in one embodiment of the present invention, the decreasing factor and the increasing factor are respectively designated as 0.98, which is a value less than 1, and 1.02, which is a value of 1 or more, respectively.

Meanwhile, when the feedback correction of the current applied to the demagnetizing current is completed as in the above step, in step S28, the current value applied to the demagnetizing coil 14 is displayed through the screen display unit 40 to easily identify the external user. Do it.

In the next step s30, it is determined whether or not the removal process is finished by comparing whether or not the value of the counter matches a preset number of times of removal. At this time, the most suitable frequency for demagnetization is set as the demagnetization termination number N, which is input to the ROM as a demagnetization profile in the form of a reduced hysteresis waveform. The optimum demagnetization waveform is a reduced sine wave within several cycles, and every half cycle is repeated in consideration of the number of switching pulses per unit cycle of the switching element (eg, IGBT) of the microprocessor 30 and the variable voltage power supply 50. The number N is determined. In this case, when IGBT is used as the switching element, the number of switching pulses per unit cycle is 200 times / cycle.

Therefore, when the demagnetization work is not repeated as many times as the end of the demagnetization operation as a result of the determination in step S30, the value of the counter is increased by 1 and the step S16 or less is repeated. As a result of repeating the demagnetization work, when the residual magnetic flux inside the transformer core is reduced to the range (100 [Gauss]) or less which does not affect the excitation inrush current, the microprocessor 30 proceeds to step S32. In 40, the completion of the removal process is displayed and the removal process is terminated.

As described above, when the demagnetizing current is applied to the demagnetizing coil to remove the residual magnetic flux, most (almost all) magnetic flux generated from the transformer coil flows through the transformer core even if the transformer is turned on again. There is almost no induced current generated, and there is no influence on the operation of the transformer by the demagnetizing coil.

The excitation inrush current generation suppression apparatus and method of the transformer according to the present invention can be implemented in various modifications within the range allowed by the technical idea of the present invention without being limited to the above-described embodiment.

As described above, the excitation inrush current generation device and method of the transformer according to the present invention is demagnetizing current for removing the residual magnetic flux of the transformer core in the demagnetizing coil wound around the transformer when it is detected that the driving power of the transformer is cut off That is, by applying a decreasing hysteresis voltage to bridge the residual magnetic flux, when the driving power is applied to the transformer again, generation of an excitation inrush current due to the residual magnetic flux can be minimized.

Therefore, by minimizing the generation of excitation inrush current generated in the transformer by the apparatus and method for suppressing the excitation inrush current generation of the transformer according to the present invention to prevent the malfunction of the relay, and also to prevent excessive shock current applied to the series-linked system equipment Can be. In addition, it is possible to solve the problem of the burnout of the transformer and the shortening of life due to the generation of the excitation inrush current.

Claims (4)

A demagnetizing coil wound around a predetermined number of turns in an enclosure of a transformer having primary and secondary transformer coils wound around an inner core and generating a demagnetizing magnetic field for removing residual magnetic flux of the iron core when the power is cut off; A breaker that detects whether the power supply of the transformer is cut off and generates a power cutoff signal; A variable voltage power supply unit for applying a demagnetizing current of a predetermined waveform to form a demagnetizing magnetic field with the demagnetizing coil at a point in time when a power cutoff signal is input from the breaker; A ROM storing a system driving program and data for generating a waveform of a demagnetizing current signal applied to the demagnetizing coil; A microprocessor outputting a control signal to the variable voltage power supply so that a voltage signal for forming a demagnetizing magnetic field is applied to the demagnetizing coil based on data read from the ROM when the power supply of the transformer is determined according to the output signal of the breaker. Excitation inrush current generation suppression device of a transformer, characterized in that comprises a. 2. The excitation inrush current generating device of claim 1, wherein the signal waveform of the demagnetizing current applied from the variable voltage power supply unit to the demagnetizing coil is a low frequency alternating current having a decreasing hysteresis loop. The method according to claim 1 or 2, Further provided with a current detector for detecting a change in the magnitude of the current applied to the demagnetizing coil, The microprocessor compares a demagnetizing current value output to the variable voltage power supply unit with an actual demagnetizing current detected from the current detector and controls driving of the variable voltage power supply unit to compensate for the difference. Generation suppression device. (A) receiving a demagnetizing current value ld for demagnetizing the residual magnetic flux of the transformer core in a demagnetizing coil wound in the transformer enclosure, (B) determining whether to shut off the driving power of the transformer, (C) If it is determined that the power of the transformer is cut off as a result of the step (b), the ROM table data pre-programmed in the ROM is read in order to generate a signal waveform of the magnetizing current, and the demagnetization input in the step (a) is performed. Multiplying by current to apply to the demagnetizing coil, (D) detecting the actual demagnetizing current T applied to the demagnetizing coil and comparing the detected real demagnetizing current with the applied current applied in the step (c), (E) If the actual demagnetizing current is smaller than the applied current applied to the demagnetizing coil in step (c) as a result of the comparison of step (d), the reduction table data is multiplied by a predetermined value; And multiplying the increasing factor and repeating the above step (c) until the demagnetization of the residual magnetic flux is completed.