KR20220163001A - High surge current measuring method using low-current transformer - Google Patents

Abstract

The present invention relates to a high surge current measurement method using a low current transformer. The surge current is divided into a main current flow unit (200) and a detection current flow unit (201) according to a resistance value, and the surge current is detected using the low current transformer (202). The method of the present invention can measure up to the high surge current area simply and easily with the low-cost low current transformer, so that it is convenient to use and has significant economical effects.

Description

High surge current measuring method using low-current transformer

The present invention relates to a method for measuring high surge current using a low current current transformer, and more particularly, the surge current is divided into a main current flow part and a detection current flow part according to resistance values, and the high surge current is detected using a low current current transformer. It relates to a high surge current measurement method using a low current current transformer.

The current transformer must have a high current measurement range, such as 100 kA, to measure the surge current. As an example, in Registered Patent Publication No. 10-0508893, which is a prior art, a detection unit for detecting the occurrence of a surge current as a surge voltage;

a display unit for displaying detection of a surge voltage;

A driving circuit and a driving unit for operating the display unit when a surge voltage is detected by the detection unit,

The driving circuit and the driving unit include a plurality of fixed resistors having different values and a fixed resistance changeover switch as a means for adjusting the sensitivity of whether to operate the display unit when a surge voltage of a certain magnitude is detected, and the driving circuit and the driving unit A rectification circuit for rectifying the surge voltage detected by the detection unit;

a sensitivity adjustment circuit connected to the output of the rectifier circuit and configured to switch a plurality of fixed resistors having different values with a switch;

a switching circuit connected to the output of the sensitivity adjustment circuit, integrating the input voltage, and operating the switching element when the integrated voltage reaches a predetermined voltage;

A surge current detection and display device characterized by comprising a drive unit for operating the display unit when the switching element of the switching circuit operates is disclosed.

In addition, Registered Patent Publication No. 10-1406902 discloses a surge equipped with a first varistor and a second varistor that are connected in parallel to the signal line between the hot line and the neutral line and conduct when the input voltage is higher than the withstand voltage. voltage sensing unit;

A first gas discharge tube that is connected in parallel to the signal line between the neutral line and the frame ground line and absorbs the transient voltage passing through when the first varistor of the surge voltage detection unit conducts and converts it into light energy, and the surge voltage detection unit 2. A gas discharge unit equipped with a second gas discharge tube that absorbs the transient voltage passing through when the varistor is conducting and converts it into light energy;

a first current sensor outputting a surge current detection signal when a potential difference is generated between the neutral line and the frame ground line due to the surge current output when the first varistor and the second varistor of the surge voltage detector are connected;

A surge occurrence count counter counting the number of surge occurrences by increasing the number of surge occurrence counts once when a surge current detection signal is input from the first current sensor is included,

Surge current monitoring characterized in that it comprises a switch connected to the inlet terminal of the hot line and one end of the hot line between the first varistor and the second varistor to melt when heat is generated in the varistor so that an alarm signal is output. A surge protector having a counter function has been disclosed.

However, such current transformers are very expensive, and current transformers costing hundreds of thousands of won such as Rogowski coils are sometimes used.

The transient surge current flowing through the SPD is generally measured using an expensive current transformer (CT) or Rogowski coil. This is because it must have a high current detection range and high frequency characteristics in order to measure the transient surge current. Such expensive current transformers are expensive, costing thousands of dollars. In the conventional measurement method, when a current is passed through a current transformer, a voltage proportional to the amount of time change in flux linkage is induced on the secondary side.

Schematically, this is as follows.

In this configuration, there is a problem in that an expensive current transformer that does not become magnetically saturated at a high surge current must be used.

Therefore, the present invention has been made to solve the above problems, and the present invention is a low-cost, low-current current transformer that can easily and easily measure up to a high surge current area, so it is convenient to use and economical using a low-current current transformer. It is intended to provide a surge current measurement method.

The present invention relates to a high surge current measurement method using a low current current transformer, wherein the surge current is divided into a main current flow unit 200 and a detection current flow unit 201 according to resistance values, and a low current current transformer 202 is used. It is characterized in that it detects the surge current.

Therefore, the present invention is a low-cost, low-current current transformer, which can simply and easily measure up to a high surge current range, so it is convenient to use and has a remarkable economical effect.

1 is a circuit diagram for measuring high surge current using the low current current transformer of the present invention.
Figure 2 is a conventional high surge current measuring circuit diagram
Figure 3a toroidal core shape, Figure 3b is the appearance of the current detector
Figure 4 is a circuit diagram for the maximum surge current that can flow through the PE conductor
Figure 5a is a surge current detection sensor, Figure 5b is a photograph of the surge current detection sensor combined with the SPD
6 is an external view of the SCDS PCB

The present invention relates to a high surge current measurement method using a low current current transformer, wherein the surge current is divided into a main current flow unit 200 and a detection current flow unit 201 according to resistance values, and a low current current transformer 202 is used. It is characterized in that it detects the surge current.

In addition, the detection current flow unit 201 is characterized by using a wire thinner than the lead wire of the main current flow unit or ultra-low resistance.

In addition, when the surge current detected by the detection current flow unit 201 passes through the low current current transformer 202, a voltage proportional to the surge current is generated, which is generated in the microcontroller 204 through the signal conditioning circuit 203. It is characterized in that the surge current is detected, the classified ratio is calculated, multiplied, and transmitted to the display unit 205 or the communication unit 206.

The present invention will be described in detail with reference to the accompanying drawings.

1 is a high surge current measurement circuit diagram using the low current current transformer of the present invention, and FIG. 2 is a conventional high surge current measurement circuit diagram.

The present invention relates to a method capable of measuring a high current such as 100 kA using a low current current transformer having a measurement range of 1 kA, for example.

The present invention is a method of distributing current by using a thinner wire or ultra-low resistance so that the current can be distributed without directly passing through a current transformer to the conducting wire for measuring the current. For example, if the distribution is 99:1 using a current transformer that can measure up to 1kA, it is possible to measure up to 100kA. 99kA flows in the main current flow unit 200, and is classified as the detection current flow unit 201. This may use a wire thinner than the main current flow part or use ultra-low resistance. After that, the current transformer 202 shows a flux linkage proportional to the current, and consequently, a voltage proportional to the amount of time change of the flux linkage is induced on the secondary side. Then, in the signal conditioning circuit 203, it is transmitted to the microcontroller 204 through an integrator or attenuator so that the microcontroller can process it, and the microcontroller 204 measures the corresponding current of 1 kA and multiplies it by 100. The calculated value is displayed through the display unit 205 . The display unit may be an LCD or audio or monitor. Also, the calculated current value may be communicated over a short distance or a long distance through the communication unit 206, and may be wired or wireless.

In the present invention, low surge current means 1 kA or less, and high surge current means 100 kA or more for convenience.

The design and configuration of the toroidal coil type current detector of the present invention are as follows.

In general, in order to measure a large surge current, a Rogowski coil that is not saturated even with a large current or a current transformer for high frequency with excellent frequency characteristics is used. However, since all of these current detectors are expensive, their market competitiveness is weak. In order to solve such a cost problem, a current sensor using three toroidal cores (part name: C27-B11) from Core Electronics made of inexpensive general iron powder was designed. A toroidal current sensor in which a winding wire having a diameter of 1.2 mm is wound 11 times around a toroidal core is shown in FIG. 3, and the material and size of the core are shown in Table 2.2.

Part no. inner diameter
(mm) apocrypha
(mm) Height
(mm) Material frequency range C27-B11 14.48 26.92 11.1x3 Iron powder and small other mixtures 500 kHz

Table 1 Toroidal Core Dimensions and Material Characteristics Signal processing for restoring the differential signal of the surge current induced in the current detection coil wound on the toroidal core to the original surge current waveform and converting the amplitude of the surge current into the sustain width of the sound pulse. The circuit was designed as shown in Figure 4.

The signal processing circuit for detecting the surge current will be described below.

에 의해 검출코일에 유기되는

은 자속쇄교수(magnetic flux)의 시간 변화량에 비례하며, 다음과 같이 나타낼 수 있다.Surge current flowing in branch wire of PE conductor passing through toroidal core

induced in the detection coil by

is proportional to the change in magnetic flux over time, and can be expressed as:

(1)

(One)

은 토로이달 코어에 감긴 검출코일의 감긴 수이고,

는 코어의 단면적,

는 자속밀도이며, 검출신호는 1차 측의 서지전류의 미분파형으로 나타난다.

과

로 구성되는 수동성 적분기를 사용하여 미분신호를 검출하고자 하는 서지전류로 복원시킨다. 복원된 전압

가

과

가 대단히 큰 경우 즉, ωL+1/ω

<<

조건에서 식 (2)와 같이 나타낼 수 있다. 여기에서 ωL은 토로이달 코일의 자체리액턴스이며, 정확도를 높이기 위해서는 코일의 자체인덕턴스 L이 저항

에 비하여 대단히 작고 시정수

가 충분히 커야 한다. in equation (1)

is the number of turns of the detection coil wound around the toroidal core,

is the cross-sectional area of the core,

is the magnetic flux density, and the detection signal appears as a differential waveform of the surge current on the primary side.

class

The differential signal is restored to the surge current to be detected using a passive integrator composed of . restored voltage

go

class

is very large, that is, ωL+1/ω

<<

In the condition, it can be expressed as in Equation (2). Here, ωL is the self reactance of the toroidal coil, and to improve accuracy, the self inductance L of the coil is

is very small compared to

should be large enough.

(2)

(2)

는

의 전압에 비례하며, 지속폭

로 변환하기 위한 지연시간은

과

그리고

로 결정된다. 자심인 토로이달 코어는 자기포화 문제로 일반적으로 높은 서지전류를 측정하는데 사용하지 않지만, 자기포화를 방지하기 위한 방법으로 SPD의 PE단자와 서지보호기의 잔존수명 표시기능을 갖는 낙뢰계수기의 PE단자는 굵은 선(AWG9)에 직접 연결되고, 가는 선(AWG24)은 토로이달 코어를 관통하여 연결되는 분류회로를 설계하였다. 즉, PE단자에 연결된 굵은 선으로 많은 전류가 흐르고, 토로이달 코어를 관통하는 가는 선은 작은 전류가 흘러 자기포화를 방지할 수 있다.and

Is

is proportional to the voltage of

The delay time to convert to

class

and

is determined by The toroidal core, which is a magnetic core, is not generally used to measure high surge current due to the problem of magnetic saturation, but as a method to prevent magnetic saturation, the PE terminal of the SPD and the PE terminal of the lightning counter with the remaining life display function of the surge protector are A shunting circuit is designed in which the thick wire (AWG9) is directly connected and the thin wire (AWG24) is connected through the toroidal core. That is, a large current flows through the thick line connected to the PE terminal, and a small current flows through the thin line penetrating the toroidal core, thereby preventing magnetic saturation.

s 유도뢰 전류의 파형은 고주파 성분을 포함하고 있으며, 이 8/20

s 임펄스전류의 등가주파수는 약 25kHz이다. 따라서 분류회로를 구성한 도선의 전기저항은 표피효과(skin effect)를 고려하여 산출하여야 한다.8/20

s The waveform of the induced lightning current contains high-frequency components, and this 8/20

The equivalent frequency of the s impulse current is about 25 kHz. Therefore, the electrical resistance of the wire constituting the shunting circuit must be calculated in consideration of the skin effect.

[m]이고 반경이

[mm]인 전선의 전기저항은 다음의 식 (3)과 같이 산출한다.Length considering skin effect

[m] and the radius is

The electrical resistance of [mm] wire is calculated by the following formula (3).

(3)

(3)

]는 전선의 저항률, d[

]는 침투깊이(skin depth)는 식 (4)와 같이 산출한다.where ρ[

] is the resistivity of the wire, d[

], the skin depth is calculated as in Equation (4).

(4)

(4)

[Hz]는 주파수,

[H/m]는 투자율로 4

이고,

[

/m]는 도전율로 연동선의 경우 이며, 표준 연동선의 침투깊이

이다.here

[Hz] is the frequency,

[H/m] is the magnetic permeability of 4

ego,

[

/m] is the conductivity in the case of annealed copper wire, and is the penetration depth of standard annealed copper wire

to be.

s 임펄스전류를 입사시켜 측정한 전류 분배율은 표 2와 같다.The characteristics of AWG9 and AWG24 are classified as shown in Table 2, and the resistance of AWG24 is about 31 times greater than that of AWG9. Calculating this, a current of about 1/32 of the incident current is distributed in the AWG24 wire according to Kirchhoff's current law. Therefore, when a large current surge occurs, most of the current flows in a thick line, and magnetic saturation of the toroidal core can be prevented. 8/20 on the classification circuit used

Table 2 shows the current distribution ratio measured by applying the s impulse current.

AWG cross-sectional area
() resistance
(Ω/m) Length (mm) Calculated Current Dividing Factor
(%) Measured current division ratio
(%) 9 6.63 0.0053 30 96.85 96.77 24 0.205 0.0842 60 3.15 3.23

Table 2 Current distribution ratio according to the resistance of AWG9 and AWG24 The calculated current distribution ratio and the measured current distribution ratio are almost the same with a difference of less than 1%, resulting in an incident of about 32 times the maximum current that can be measured by the toroidal core. Current can be distributed and processed.

25kA이고, ClassⅡ에서는

20kA로 규정되어 있다. PE도체에 흐르는 총 서지전류로부터 나누어지는 I 와 i 전류는 표 3과 같으며, 단상과 삼상에 따른 전류분배 예시는 표 3, 도 5와 같다.In international standard IEC61643-11, the maximum surge current that can flow through each phase conductor and neutral wire is

25 kA, and in Class II

It is specified at 20 kA. The I and i currents divided from the total surge current flowing through the PE conductor are shown in Table 3, and examples of current distribution according to single-phase and three-phase are shown in Table 3 and FIG. 5.

type number of power lines surge current
(guided lightning)
8/20s
20 kA surge current
(direct strike)
10/350s
25 kA phase 2 (line, neutral): i3 Total 40 Total 50 I 38.75 48.44 i 1.25 1.56 three phase 4 (R, S, T, neutral): i5 Total 80 Total 100 I 77.5 96.88 i 2.5 3.12

s와 10/350

s 임펄스전류에 대한 분류전류의 측정결과8/20

s 임펄스전류에 의한 토로이달 코어의 자기포화의 임계값은 약 3.3kA이다. 따라서 서지보호기의 잔존수명 표시기능을 갖는 낙뢰계수기는 최대 100kA의 서지전류까지 측정할 수 있다. 토로이달 코일의 출력전압은 입사되는 임펄스전류의 미분에 상응하므로 이 출력전압신호를 임펄스전류에 비례하는 파형으로의 변환을 위해

과

가 연결된 수동성 적분기를 접속하고 커패시터

의 단자 양단에 전압이 출력되도록 설계하였다. 출력되는 전류에 비례하는 전압이 높을 수 있으므로 100Ω의 저항을 토로이달 코일의 출력에 직렬로 연결하여 전압을 낮추어 회로가 파손되지 않도록 설계하였다.Table 3 8/20

s and 10/350

Measurement result of shunt current for s impulse current 8/20

The critical value of magnetic saturation of the toroidal core by the s impulse current is about 3.3 kA. Therefore, the lightning counter with the function of displaying the remaining life of the surge protector can measure up to 100kA of surge current. Since the output voltage of the toroidal coil corresponds to the derivative of the incident impulse current, in order to convert this output voltage signal into a waveform proportional to the impulse current

class

Connect the passive integrator connected to the capacitor

It is designed so that voltage is output across the terminals of . Since the voltage proportional to the output current can be high, a 100Ω resistor is connected in series to the output of the toroidal coil to lower the voltage so that the circuit is not damaged.

)는 RECTRON semiconductor사의 R3000을 사용해 정극성과 부극성의 서지전류을 모두 검출할 수 있도록 하고, 입사되는 큰 서지전류를 고려하여 최대 반복피크역전압(maximum repetitive peak reverse voltage)이 충분히 높은 부품으로 선정하였다. 입사전류파형에 상응하는

과

적분기의

단자에 나타나는 출력전압

는 브릿지다이오드를 경유하여 커패시터에 충전된다. 커패시터

의 충전전압은 커패시터

의 피크값까지 상승한다. 즉 커패시터

의 단자전압의 피크값

은 입사전류의 피크값에 상응하는 신호이다. 서지의 피크전압은

을 통하여 충전되고

와

를 통하여 방전된다. 이외에 다른 방전경로는 없다.bridge diode (

) uses RECTRON Semiconductor's R3000 to detect both positive and negative surge currents, and was selected as a component with a sufficiently high maximum repetitive peak reverse voltage considering the large incident surge current. Corresponding to the incident current waveform

class

integrator

Output voltage appearing at the terminals

is charged in the capacitor via the bridge diode. capacitor

The charging voltage of the capacitor

rises to the peak value of i.e. capacitor

Peak value of terminal voltage of

is a signal corresponding to the peak value of the incident current. The peak voltage of the surge is

is charged through

Wow

discharged through There is no other discharge path other than that.

은 커패시터

의 과전압으로부터 트랜지스터

(2N2222: NPN transistor)을 보호하는 역할을 한다.

의 콜렉터(collector)는 정상상태에서 3V로 logic High이며,

의 전압이

의 개시(threshold) 전압(일반적으로 0.7V)보다 높은 상태에서는 logic Low로 된다.

는 pull up 저항이며,

는 노이즈 및 채터링 (chattering)을 감소시키기 위해 사용된다.

는

의 피크값이다.

의 콜렉터에 대한 출력은 다음과 같은 식 (5)로 표현할 수 있다.The output of the signal processing circuit is converted into a negative pulse whose duration is proportional to the amplitude of the surge current.

silver capacitor

from the overvoltage of the transistor

(2N2222: NPN transistor) to protect.

The collector of is logic high at 3V in normal state,

the voltage of

In a state higher than the threshold voltage (typically 0.7V), it becomes logic Low.

is the pull up resistance,

is used to reduce noise and chattering.

Is

is the peak value of

The output to the collector of can be expressed by the following equation (5).

(2.7)

(2.7)

는 마이크로콘트롤러에 입력되는 음펄스 로직 Low 상태의 지속폭(서지 감지시간)이며,

는 1MΩ,

은 200kΩ,

은 22nF,

는

에 충전된 서지전압의 피크값,

는

의 베이스(base)와 이미터(emitter)간의 컷오프(cut-off) 전압으로 약 0.3V이다. 서지전류의 진폭에 따른 신호처리회로의

과

, 그리고 지속시간

는 실험을 통하여 표 4와 같이 측정되었으며, 이의 도식적 결과를 그림 5에 나타내었다.in equation (5)

is the duration (surge detection time) of the negative pulse logic Low state input to the microcontroller,

is 1 MΩ,

silver 200 kΩ,

silver 22nF,

Is

The peak value of the surge voltage charged in

Is

The cut-off voltage between the base and emitter of is about 0.3V. of the signal processing circuit according to the amplitude of the surge current.

class

, and duration

was measured as shown in Table 4 through experiments, and its schematic results are shown in Figure 5.

Surge current (kA) T (ms)

(V)

(V)

(V) 0.5 3.6 4 One One 9.0 7 4 2 12.0 12 8 3 12.9 13 10 4 14.3 18 15 5 16.5 30 27 6 17.2 36 33 7 17.9 42 39 10 19.2 60 57 20 21.9 120 117 30 23.4 180 177 40 24.5 240 237 50 25.3 300 297 60 26.0 360 357 70 26.5 420 417 80 27.0 480 477 90 27.5 540 537 100 27.9 600 597

,

및 T의 측정결과V _{3,peak}Table 4 for the size of surge current

,

and the measurement result of TV _{3,peak}

The design and manufacture of the mounting mechanism are described as follows.

The size of the surge current detection sensor for MOV life prediction is relatively small, 50.0 x 106.0 x 68.4mm. The exterior material uses flame retardant plastic, and has a PE terminal connected to ground and a PE terminal connected to SPD. The lightning counter that has the function of displaying the remaining life of the surge protector has a terminal block cover installed to meet the IP20 waterproof/dustproof rating to prevent electric shock accidents to the human body. IP20 means that the conductor cannot be touched by human fingers. There is an LCD and a function key on the upper surface of the lightning counter that has the function of displaying the remaining life of the surge protector. The structure for fixing the lightning counter having the function of displaying the remaining life of the surge protector has a structure that can be mounted on an international standard EN 60715 DIN rail such as that used in electrical appliances such as widely used circuit breakers. In Figure 7, (a) is a picture of the external appearance of the lightning counter with the function of displaying the remaining life of the surge protector, and the picture installed with the SPD is shown in (b).

The inside of the lightning counter having the function of displaying the remaining life of the surge protector is composed of a PCB including a toroidal current sensor and a signal processing circuit, and the shape of the internal PCB is shown in FIG. 7 .

Therefore, the present invention is a low-cost, low-current current transformer, which can simply and easily measure up to a high surge current range, so it is convenient to use and has a remarkable economical effect.

200: main current flow part
201: detection current flow unit
202: low current current transformer
203: signal condition circuit part
204: microcontroller unit
205: display unit
206: Ministry of Communication

Claims (2)

As a method for measuring high current using a low current current transformer, the surge current is divided into a main current flow unit 200 and a detection current flow unit 201 according to resistance values, and a low current current transformer 202 is used to measure the surge current. In the high surge current measurement method using a low current current transformer for detecting current,
The current is distributed using a wire thinner than the main current flowing part or an ultra-low resistance so that the current can be distributed to the wire for measuring the surge current without directly passing through the current transformer, and then the current transformer 202 has a magnetic flux proportional to the current. A linkage appears, and a voltage proportional to the amount of time change of the flux linkage is induced on the secondary side, and then, in the signal conditioning circuit 203, it is transmitted to the microcontroller 204 through an integrator or attenuator so that the microcontroller can process The microcontroller 204 measures and calculates the corresponding current, and displays the calculated value through the display unit 205, but the display unit is an LCD, voice or monitor, and the calculated current value is displayed through the communication unit 206. High surge current measurement method using a low current transformer, characterized in that the low surge current is 1 kA or less and the high surge current is 100 kA or more. The high surge current measuring method using a low current current transformer according to claim 1, wherein the low current current transformer is a toroidal coil type current detector made of iron powder material.

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