KR101735776B1 - Power line monitoring methodology and its device for detection of certain harmonic frequency based on contactless pick-up coil including signal mixing and resonance circuit - Google Patents

Abstract

Provided is a harmonic measurement device for measuring one target harmonic among a plurality of harmonics. The harmonic measurement device includes: a pickup coil part for outputting a voltage signal based on a time-varying current of a power transmission line; a resonance part for matching the resonance frequency with the frequency of the target harmonic to filter the voltage signal; and an amplification part for generating a first mixed signal by mixing between a first reference signal having a sine waveform and a frequency of the target harmonic and the filtered voltage signal and detecting the target harmonic based on the first mixed signal.

Description

TECHNICAL FIELD [0001] The present invention relates to a method and apparatus for selecting a specific harmonic frequency for monitoring the state of a power transmission bus bar using a non-contact pickup coil including a mix of signals and a resonant circuit. COIL INCLUDING SIGNAL MIXING AND RESONANCE CIRCUIT}

The present invention relates to an apparatus and a method for measuring (or detecting) harmonics using a pick-up coil.

Harmonics refers to the amount of physical electricity corresponding to an integer multiple of the fundamental frequency (eg, 2, 3, 4, etc.). For example, when the frequency (fundamental frequency) of the fundamental wave is 60 Hz, the frequency of the second harmonic is 120 Hz, the frequency of the third harmonic is 180 Hz, and the frequency of the fourth harmonic is 240 Hz. That is, the frequency of the n-th harmonic (where n = 2, 3, ...) is n times the fundamental frequency.

If a non-sinusoidal harmonic current flows through the conductor (eg power transmission line) or the transformer, an additional overheating phenomenon occurs above the expected value for the rms value of the waveform. This is the main reason for the skin effect or iron loss, which is expressed as a function of the size and spacing of the conductor and the frequency.

A typical harmonic detector (eg, the Hioki 3194 Power & Harmonics Analyzer) can detect very high numbers of harmonics (eg, third harmonic, fourth harmonic, ..., 28th harmonic, etc.).

However, because these harmonic detectors use digital signal processing, the maximum harmonic is determined by the sampling speed. The sampling rate of the latest harmonic detector is 1 MHz or higher. To this end, existing harmonic detectors use a digital signal processor (DSP), which is complicated and requires advanced software. As a result, conventional harmonic detectors are fairly expensive to keep on-line connecting to a typical power line.

On the other hand, it is statistically confirmed that a power device accident due to harmonics is mostly caused by a specific harmonic wave such as a fifth harmonic wave. Generally, the fifth harmonic, the third harmonic, the seventh harmonic, and the second harmonic In order, the effects of harmonics are high. In particular, harmonics generated by recently used inverters are specified. The harmonics generated by the inverter are determined by the relationship between the carrier frequency and the grid frequency.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a harmonic measurement apparatus and method that are implemented in a very simple form using a pickup coil.

Another object of the present invention is to provide a harmonic measuring apparatus and method for precisely selecting and measuring only a specific harmonic of a selected frequency through a pickup coil.

According to the embodiment of the present invention, a harmonic measuring device for measuring one target harmonic among a plurality of harmonics is provided. The harmonic measuring apparatus includes: a pickup coil part for outputting a voltage signal based on a time-varying current of a power transmission line; A resonance unit matching the resonance frequency with the frequency of the target harmonic to filter the voltage signal; And generating a first mixed signal by mixing between a first reference signal having a sine waveform and a frequency of the target harmonic and the filtered voltage signal and generating a first mixed signal based on the first mixed signal, And an amplifying unit for detecting the amplified signal.

The frequency of the target harmonic may be set to three times, five times, seven times, or two times the frequency of the fundamental wave.

The pickup coil portion may include a Rogowskii coil that is not in contact with the power transmission line and is arranged to surround the power transmission line.

The resonance unit may match the resonance frequency with the frequency of the target harmonic using an adjustable capacitance and an inductance included in the pickup coil part.

Wherein the amplifying unit is configured to mix the second reference signal having a cosine waveform and the target harmonic frequency with the filtered voltage signal when a phase difference exists between the first reference signal and the filtered voltage signal, ) To determine the amplitude of the filtered voltage signal based on the first mixed signal and the second mixed signal.

Wherein the amplification unit is configured such that the integrated value of the first mixed signal is a first constant value based on the amplitude of the filtered voltage signal and the integrated value of the second mixed signal is a second constant value based on the amplitude of the filtered voltage signal The amplitude of the filtered voltage signal may be determined using the first constant value and the second constant value.

According to another embodiment of the present invention, a method is provided in which a harmonic measuring apparatus measures one target harmonic among a plurality of harmonics. A method of measuring the harmonic measurement apparatus includes the steps of outputting a voltage signal based on a time-varying current of the power transmission line through a pickup coil disposed in non-contact with the power transmission line; Matching the resonant frequency to the frequency of the target harmonic and filtering the voltage signal; Generating a first mixed signal through mixing between a sine waveform and a first reference signal having a frequency of the target harmonic and the filtered voltage signal; And detecting the target harmonic based on the first mixed signal.

According to the embodiment of the present invention, a low-cost (economical) harmonic measurement apparatus for measuring the harmonics of the power transmission line using the characteristics of the pickup coil can be provided.

Further, according to the embodiment of the present invention, it is possible to accurately detect only a specific harmonic of a power transmission line using a pickup coil. Specifically, it is possible to detect not only the harmonics of all the frequency regions but also the harmonics of the specific frequency region band of interest. For example, since an LC resonant circuit and a frequency multiplier are used, it is possible to accurately detect only harmonics of a desired frequency.

According to the embodiment of the present invention, a harmonic measuring device (a simple type of harmonic measuring device) can be provided which is simplified as much as possible so as to have only the functions necessary for selectively detecting harmonics of a specific frequency . For example, the pick-up coil may be in the form of a Rogowskii coil and may be installed so that it is not in contact with the power transmission line.

Further, according to the embodiment of the present invention, since the implementation of the harmonic measurement apparatus is simple, the manufacturing cost of the harmonic measurement apparatus can be minimized. For example, a half-phase lock-in amplifier of an analog type including a minimum function is used, so that a harmonic measuring apparatus can be manufactured at a low cost.

1 is a diagram illustrating a harmonic measurement apparatus according to an embodiment of the present invention.
2 is a view showing a structure of a pick-up coil part according to an embodiment of the present invention.
FIG. 3 is a flow chart for detecting a voltage waveform having a frequency component corresponding to a harmonic component to be measured in a voltage measured through a pickup coil of a pick-up coil part according to an embodiment of the present invention.
4 and 5 are diagrams illustrating a lock-in amplifier according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification.

In the present specification, duplicate descriptions are omitted for the same constituent elements.

Also, in this specification, when an element is referred to as being "connected" or "connected" to another element, it may be directly connected or connected to the other element, May be present. On the other hand, in the present specification, when an element is referred to as being "directly connected" or "directly connected" to another element, it should be understood that no other element exists in between.

Furthermore, terms used herein are used only to describe specific embodiments and are not intended to be limiting of the present invention.

Also, in this specification, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.

Also, in this specification, the terms " comprise ", or " have ", and the like are used to specify that there is a feature, a number, a step, an operation, an element, a component, But do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, parts, or combinations thereof.

Also, in this specification, the term 'and / or' includes any combination of the listed items or any of the plurality of listed items. In this specification, 'A or B' may include 'A', 'B', or 'both A and B'.

1 is a diagram showing a harmonic measuring apparatus 100 according to an embodiment of the present invention. 2 is a view showing a structure of a pickup coil part 120 according to an embodiment of the present invention. 3 is a diagram for explaining a method of detecting a voltage waveform having a frequency component corresponding to a harmonic component to be measured in a voltage (or a voltage waveform) measured through a pickup coil of a pick-up coil part 120 according to an embodiment of the present invention. Fig. And FIG. 4 is a diagram illustrating a lock-in amplifier according to an embodiment of the present invention. And FIG. 5 is a diagram illustrating a lock-in amplifier according to another embodiment of the present invention.

The harmonic measuring apparatus 100 includes a pick-up coil part 120, a resonating part 130, and an amplifying part 140.

Pickup coil part 120 includes a pick-up coil having a form (non-contact) surrounding power transmission line 110. The shape of the pick-up coil part 120 is very simple. Harmonic measurement is possible even if the pick-up coil part 120 does not directly contact (or adhere to) the power transmission line 110. The power transmission line 110 may be a high-voltage power transmission line.

The output voltage of the pick-up coil part 120 follows the Maxwell equation and is output in proportion to the differential value of the magnetic flux passing through the pickup coil. That is, the following equation (1) is obtained.

T represents time, di (t) / dt represents a time-varying current, v (t) represents a time-varying current, and M represents a mutual inductance between a coil and a current- t) represents the voltage. That is, the voltage across the pickup coil (e.g., Rogowskii coil) is proportional to the amount of change of the time-varying current.

The output voltage of the pick-up coil part 120 is very linear up to the theoretical infinite value, unlike the current transducer (CT), without saturating the magnetic flux.

For example, when the pick-up coil included in the pick-up coil part 120 is a Rogowskii coil, the pick-up coil part 120 can be arranged as illustrated in FIG. That is, the Rogowski coil included in the pick-up coil part 120 may be disposed so as to surround the power transmission line 110 through which the current to be measured flows. The Rochosky coil is not in physical contact with the power transmission line 110.

On the other hand, an advantage of using a pickup coil (e.g., a Rochosky coil) with a time-varying current is as follows from the viewpoint of analysis in the frequency domain. A comparison between the case of measuring the direct current and the case of measuring the value proportional to the time-varying current will be described.

When a Fourier transform is applied to the output of the pick-up coil part 120, the following equation (2) is obtained.

Where t represents time, di (t) / dt represents a time-varying current, v (t) represents a time-varying current, and M represents a mutual inductance between a coil and a current- t) represents the voltage. In Equation (2), f represents frequency, I represents current, m represents M, and V (f) represents a voltage.

Equation (2) has an unusual property that V (f) is amplified by a frequency as frequency increases. On the contrary, in the case of direct current, the gain is zero and is not measured. For example, assume that the current value at the first harmonic of 60 Hz is 1A, the current value at the third harmonic of 180 Hz is 0.1 A, and the current value at the fifth harmonic of 300 Hz is 0.01 A. If a Fourier transform is applied to the measured current after the current is measured as it is, the measured current is output as it is. However, the current value measured by the pickup coil is 60 A (Hz) at the first harmonic, 18 A (Hz) at the third harmonic, and 3 A (Hz) at the fifth harmonic. That is, the ratio between the current at the first harmonic and the current at the fifth harmonic is reduced from 1/100 to 1/20, and the current is output about 5 times more. Therefore, the pickup coil is advantageous for detecting a specific harmonic (e.g., a fifth harmonic, etc.).

More specifically, this can be expressed as shown in Table 1 below. In Table 1, it is assumed that mutual inductance M is 1.

frequency( Hz ) Direct current measurement I Current measurement through pickup coil f * I (f) 60 1A 60x1A = 60 180 0.1 A 180x0.1A = 18 300 0.01 A 300x0.01A = 3

That is, when the harmonic is measured using the current flowing through the power transmission line 110 itself, the gain thereof is sharply reduced, so that it is difficult to grasp frequencies other than the fundamental frequency. However, when a pickup coil is used, the voltage based on the time-varying current is measured, and the voltage is relatively advantageous for grasping frequencies other than the fundamental frequency.

Therefore, the harmonic measuring apparatus 100 mainly measures the harmonics using characteristics of the pickup coil having a gain that is much higher than the fundamental frequency at a specific harmonic generating an accident. The harmonic measuring apparatus 100 can be manufactured at a low cost since it is simplified as much as possible so as to have only functions necessary for selectively detecting a specific harmonic wave.

The resonance unit 130 includes an LC (inductance, capacitance) resonance circuit.

The resonance unit 130 can use the LC resonance circuit to match the resonance frequency with the frequency of the selected harmonic (specific harmonic). In this case, a precise frequency signal measurement can be performed through a small pickup coil.

A circuit for making the imaginary part of the inductance L of the pick-up coil part 120 (for example, Rogowski coil) and the capacitance C of the resonance part 130 (for example, LC resonance circuit) ) (E.g., LC resonant circuit). Assuming that L and C are connected in series, the complex impedance of L and C can be expressed as Equation 3 below.

In Equation (3), Z denotes a complex impedance, R denotes a resistance (load), and? Denotes a frequency constant.

이다. 이는, 대역 통과 필터의 역할을 수행한다.The frequency satisfying Z ^* (complex conjugate)

to be. This acts as a bandpass filter.

3 shows a pickup coil equivalent circuit 120a corresponding to the pickup coil part 120 and an LC resonance circuit 130a corresponding to the resonance part 130. [

In the pickup coil equivalent circuit 120a, i _p (t) represents a current flowing in a wire or a conductor (e.g., the power transmission line 110), M represents mutual inductance between the wire and the pickup coil, e (t) the voltage across the pick-up coil (such as, v (t) of equation (2)) represents a, R denotes a lead resistance of the pickup coil, L denotes the inductance of the pickup coil, i _s (t) is a pick-up coil The current flowing through the resistor is shown. In e (t), the influence of the leakage inductance of i _p (t) appears as mutual inductance (M).

The LC resonance circuit 130a is coupled to e (t). Specifically, the LC resonance circuit 130a includes a capacitance for matching a frequency corresponding to a desired harmonic (target harmonic). The value of the capacitance can be adjusted. The inductance L included in the LC resonant circuit 130a and serving as a reference becomes the inductance (inductance L of the pickup coil) included in the pickup coil equivalent circuit 120a. That is, the LC resonant circuit 130a can match the resonant frequency with the frequency of the target harmonic by using the adjustable capacitance and the inductance included in the pickup coil equivalent circuit 120a.

(단, C는 커패시터(C₁)의 커패시턴스)로 표현될 수 있다. 도 3에는, 공진 주파수(f_r)가 180Hz 인 경우에, 저항(R_load)에서 측정되는 전압(V_R_load)의 파형(필터링이 완료된 실제 전압 파형)이 예시되어 있다. 저항(R_load)에서 측정되는 전압은 후술하는 증폭부(140)에 기본 신호(예, V(t))로써 입력될 수 있다.The LC resonance circuit 130a performs a filtering operation to detect a voltage waveform having a frequency component corresponding to a harmonic component to be measured among the voltages measured through the pickup coil. The LC resonant circuit 130a illustrated in FIG. 3 includes a capacitor C ₁ and a resistor R _load . In Figure 3, the resonant frequency (f _r )

(Where C is the capacitance of the capacitor C ₁ ). In Fig. 3, a waveform of the voltage V_R _load measured at the resistor R _load (the actual voltage waveform that has been filtered) is illustrated when the resonance frequency f _r is 180 Hz. The voltage measured at the resistor R _load may be input as a basic signal (e.g., V (t)) to the amplification unit 140, which will be described later.

On the other hand, when only the LC resonance circuit 130a is used, the width of the band of the filtered signal is very large. The Q (quality factor) at the resonance represents the quality of the frequency selection characteristic. When the Q value is low, only the LC resonance circuit 130a may be insufficient to detect and detect a desired harmonic. Therefore, when the amplifier 140 (e.g., a lock-in-amplifier) is used (e.g., the signal filtered by the LC resonance circuit 130a passes through the amplifier 140) Or detection) is possible.

The amplification unit 140 includes a lock-in amplifier.

When the lock-in amplifier is used for harmonic detection, the harmonic measuring apparatus 100 can very accurately select and measure only the harmonics of the selected frequency. That is, narrow band detection is possible.

Specifically, if a frequency multiplier is applied to the fundamental frequency, a more inexpensive lock-in amplifier can be manufactured. The frequency multiplier may be included in the amplification unit 140 and used for selection of a desired frequency.

FIG. 4 illustrates a lock-in amplifier 140a according to an embodiment of the present invention.

The lock-in amplifier 140a of FIG. 4 includes a mixer 141a and an integrator 142a.

When the lock-in amplifier 140a is applied to the voltage signal passed through the resonance section 130 (or the LC resonance circuit 130a), the desired high frequency band can be obtained more reliably.

Assuming that the signal to be detected (detected) is V (t), the mixer 141a mixes the signal V (t) with a sinusoidal waveform signal having a frequency of? (E.g., Vr1 and outputs the result as shown in the following equation (4). In Equation (4), it is assumed that there is no phase difference between the basic signal (e.g., V (t)) and the reference signal (e.g., Vr1 (t)).

In Equation 4, w represents the frequency of a voltage signal (e.g., V (t)) that passes through the resonant portion 130 (or the LC resonant circuit 130a) and V0 represents a fundamental signal having w t)), and Ω represents the voltage frequency (desired frequency) of the reference signal (eg, Vr1 (t)). Where V (t) is VO · sin (wt) and Vr1 (t) is sin (Ωt).

w ≠ Ω and w = Ω will be described.

First, when w ≠ Ω, the mixed signal (eg, V (t) · Vr1 (t)) becomes 0 on average (or close to 0) with respect to time.

In the case of w = OMEGA, the mixed signal (e.g., the signal of Equation 4) can have a sinusoidal waveform and become a DC (direct current) offset only signal. The mixed signal (e.g., V (t) · Vr1 (t)) is a waveform that is shifted upward or downward with the amplitude magnitude maintained (e.g., in the waveform graph in which the horizontal axis represents time and the vertical axis represents voltage, (I.e., a waveform shifted in parallel with the offset in the vertical axis direction). V (t) - Vr1 (t) = - V0 {cos [(2?) T] - 1}.

That is, only when the base signal (e.g., V (t)) has a frequency exactly matched to the reference signal (e.g., Vr1 (t)), the integrator 142a generates a mixed signal (t)) is integrated with respect to the time (t) is represented by a constant. The integrator 142a may perform integration in a predetermined period. The integration result value by the integrator 142a may be an integral value or an integral average value. The lock-in amplifier 140a amplifies the basic signal (e.g., V (t)) when the integral value generated by integrating the mixed signal (e.g., V (t) · Vr1 (t) It can be determined that the target harmonic is included in the target harmonic.

On the other hand, the amplitude (e.g., VO) of the basic signal (e.g., V (t)) can be derived based on the integrated mean value 143a of the obtained mixed signal. (Considered) that an abnormality has occurred in the transmission of the power transmission line 110 when the magnitude of the derived amplitude (e.g., VO) becomes equal to or greater than the threshold value. As a result, the temperature of the power transmission line 110 can be detected to be high. Specifically, the condition for determining the abnormality of the power transmission line 110 (hereinafter, referred to as a 'first condition') is a condition for determining the abnormality of the power transmission line 110 by comparing the obtained amplitude value (for example, VO that can be derived through the integrated mean value 143a of the mixed signal) The size may be maintained above the threshold for more than the threshold time. For example, the harmonic measuring apparatus 100 can output a harmonic alarm signal when the first condition is satisfied.

The selection of the desired frequency? Will be described.

It is possible for the lock-in amplifier 140a to select a frequency that is multiplied by the signal frequency using the frequency multiplier. For example, suppose the signal frequency waveform with frequency w is sin (wt), the frequency waveform of the reference signal (eg, Vr1 (t)) with the desired frequency Ω is sin (2wt), sin ... can be.

At this time, the frequency for multiplication is input to the lock-in amplifier 140a (or frequency multiplier) in accordance with the frequency and phase of the signal (e.g., Vr1 (t)). For example, when the desired frequency? Is input to the lock-in amplifier 140a, the lock-in amplifier 140a generates a reference signal having a sin (? T) waveform (e.g., Vr1 (t)). The basic signal (for example, V (t)) input from the resonator 130 and the reference signal (for example, Vr1 (t)) are mixed by the mixer 141a.

A process of generating a reference frequency (Ω) having no phase difference with respect to a basic signal (eg, V (t)) (eg, , A process of generating a doubled signal), the complexity in manufacturing the lock-in amplifier 140a can be reduced. That is, even if the lock-in amplifier 140a performs only the mixing process with the sinusoidal waveform (for example, the mixing process of the mixer 141a), the desired harmonic detection is possible.

FIG. 5 illustrates a lock-in amplifier 140b according to another embodiment of the present invention.

)가 발생하는 경우에 사용될 수 있고, 희망 주파수를 가지는 고조파의 진폭(또는 기본 신호(예, V(t))의 진폭(예, VO))을 도출하는데 사용될 수 있다.The lock-in amplifier 140b illustrated in FIG. 5 differs from the lock-in amplifier 140a illustrated in FIG. 4 in that the phase difference can be distinguished (or amplitude can be checked). The phase difference demarcation function (or amplitude verification function) may be used to determine the phase difference between the base signal (e.g., V (t)) and the reference signal (e.g., Vr1

), And can be used to derive the amplitude of the harmonic (or the amplitude of the fundamental signal (e.g., V (t)) (e.g., VO) with the desired frequency.

The lock-in amplifier 140b includes mixers 141b1 and 141b2 and integrators 142b1 and 142b2. The integrators 142b1 and 142b2 may perform integration in a predetermined cycle.

When the lock-in amplifier 140b is applied to the voltage signal passed through the resonance section 130 (or the LC resonance circuit 130a), the desired high frequency band can be obtained more reliably.

)가 존재한다고 가정한다.Assuming that the signal to be detected (detected) is V (t), the mixer 141b1 mixes the signal V (t) with a sinusoidal waveform signal having a frequency of? (E.g., Vr1 (t) , And outputs the result as shown in Equation (5) below. In Equation (5), the phase difference between the basic signal (e.g., V (t)) and the reference signal (e.g., Vr1

) Are present.

는 기본 신호(예, V(t))와 기준 신호(예, Vr1(t)) 간의 위상 차이(또는 기본 신호의 주파수(w)와 기준 신호의 주파수(Ω) 간의 위상 차이)를 의미한다. 여기서, V(t) = VO·sin(wt+

) 이고, Vr1(t) = sin(Ωt) 이다. Ω는 락인(lock-in)을 위한 타겟 주파수를 나타낸다. Ω는 기본 신호(예, V(t))의 파형에 비해 특정 위상만큼 밀려 있을 수 있다.In Equation 5, w represents the frequency of a voltage signal (e.g., V (t)) that passes through the resonant portion 130 (or the LC resonant circuit 130a) and V0 represents a fundamental signal having w t)), Ω represents the voltage frequency (desired frequency) of the reference signal (eg, Vr1 (t)),

Means the phase difference between the fundamental signal (e.g., V (t)) and the reference signal (e.g., Vr1 (t)) or the phase difference between the frequency w of the fundamental signal and the frequency? Where V (t) = VO · sin (wt +

) And Vr1 (t) = sin (? T). And? Represents the target frequency for lock-in. Ω may be pushed by a specific phase relative to the waveform of the fundamental signal (eg, V (t)).

w ≠ Ω and w = Ω will be described.

First, when w ≠ Ω, the mixed signal (eg, V (t) · Vr1 (t)) becomes 0 on average (or close to 0) with respect to time.

] - cos[

]} 이다.Next, in the case of w =?, The mixed signal (e.g., the signal of Equation 5) can have a sinusoidal waveform and become a DC only offset signal. V (t) Vr1 (t) = - V0 {cos [(2?) T +

] - cos [

]} to be.

That is, only when the base signal (e.g., V (t)) has a frequency exactly matched to the reference signal (e.g., Vr1 (t)), the integrator 142b1 mixes the mixed signal (or an average value) generated by integrating the time t (t) with respect to the time t becomes DC (or a constant).

For example, when the desired frequency? Is input to the lock-in amplifier 140b, the lock-in amplifier 140b generates a reference signal having a sin (? T) waveform (e.g., Vr1 (t)). The basic signal (for example, V (t)) input from the resonator 130 and the reference signal (for example, Vr1 (t)) are mixed by the mixer 141b1. The lock-in amplifier 140b amplifies the basic signal (e.g., V (t)) when the integral value generated by integrating the mixed signal (e.g., V (t) · Vr1 (t) It can be determined that the target harmonic is included in the target harmonic.

(또는 기본 신호(예, V(t))의 진폭(예, V0))의 명확한 값을 얻기 위하여, 기본 신호(예, V(t))와 cos(Ωt) 파형을 가지는 기준 신호(예, Vr2(t)) 간의 혼합이 추가로 필요하다. 예를 들어, 락인 증폭기(140b)가 사인 파형(예, sin(Ωt))만을 이용하여 기본 신호(예, V(t))와 기준 신호(예, Vr1(t)) 간의 혼합을 수행하면,

가 60도인지 300도 인지 불분명한 경우가 발생하여, 기본 신호(예, V(t))의 진폭(예, V0)이 명확하게 도출될 수 없다. On the other hand, a phase shift between a basic signal (e.g., V (t)) and a reference signal (e.g., Vr1

(E. G., V (t)) and cos (? T) waveforms to obtain a clear value of the amplitude (or amplitude of the fundamental signal (e.g., V Vr2 (t)) is additionally required. For example, if the lock-in amplifier 140b performs mixing between a base signal (e.g., V (t)) and a reference signal (e.g., Vr1 (t)) using only a sinusoidal waveform

The amplitude of the basic signal (e.g., V (t)) (e.g., V0) can not be clearly derived.

또는 기본 신호(예, V(t))의 진폭(예, V0)을 명확히 파악하는 것이 가능하다.The lock-in amplifier 140b may be configured to detect the reference signal (e.g., V (t)) of the base signal (e.g., V (t) And further performs mixing between the basic signal (e.g., V (t)) and the reference signal (e.g., Vr2 (t)). Here, Vr2 (t) = cos (? T). In this way,

Or the amplitude of the basic signal (e.g., V (t)) (e.g., V0).

) = 3 이라고 가정하면, 이 때의 V0는

의 값에 따라 달라진다. 락인 증폭기(140b)를 통한 기본 신호(예, V(t))의 진폭(예, V0)을 명확히 결정하기 위하여, 도 5에 예시된 바와 같이, 기본 신호(예, V(t))와 코사인 파형을 가지는 기준 신호(예, Vr2(t))를 추가적으로 혼합한다.For example, a signal (e.g., V (t) · Vr1 (t)) obtained by mixing a basic signal (e.g., V (t)) with a reference signal having a sinusoidal waveform ), The constant value 143b1 is 0.5 VO · cos (

) = 3, then V0 at this time is

≪ / RTI > (E. G., V (t)) and cosine (e. G., V (t)), as illustrated in Figure 5, to explicitly determine the amplitude (E.g., Vr2 (t)) having a waveform is further mixed.

)와 cos(

)의 삼각 함수 관계(예, sin²(x) + cos²(x) = 1)에 의해, 해당 V0가 10으로 결정될 수 있다. (For example, V (t) · Vr2 (t)) obtained by mixing a basic signal (for example, V (t)) and a reference signal having a cosine waveform The constant value 143b2 is 0.5 V0 sin ( ) = 4, then sin (

) And cos (

The corresponding V0 can be determined to be 10 by the trigonometric relationship (e.g., sin ² (x) + cos ² (x) = 1).

That is, the lock-in amplifier 140b amplifies the unknown base signal amplitude (e.g., V0) through mixing between the base signal (e.g., V (t)) and the reference signal (e.g., Vr1 Can be confirmed.

Specifically, the mixer 141b2 mixes the base signal (e.g., V (t)) with the reference signal (e.g., Vr2 (t)) and outputs the result as shown in Equation 6 below.

는 기본 신호(예, V(t))와 기준 신호(예, Vr1(t), Vr2(t)) 간의 위상 차이를 의미한다. In Equation 6, w represents the frequency of a voltage signal (e.g., V (t)) that passes through the resonant portion 130 (or the LC resonant circuit 130a), and V0 represents a voltage signal having w t)), Ω represents the voltage frequency (desired frequency) of the reference signal (eg, Vr2 (t)),

Is the phase difference between the base signal (eg, V (t)) and the reference signal (eg, Vr1 (t), Vr2 (t)).

] - sin[

]} 이다.(t) Vr2 (t) =? V0 {sin [(2?) t +

] - sin [

]} to be.

For example, when the desired frequency? Is input to the lock-in amplifier 140b, the lock-in amplifier 140b generates the reference signal Vr2 (t) having the cos (? T) waveform. The basic signal V (t) input from the resonator 130 and the reference signal Vr2 (t) are mixed by the mixer 141b2.

Next, the operation sequence of the amplifying unit 140 will be described.

The desired frequency Ω of the reference signal (eg, Vr1 (t), Vr2 (t)) means the frequency of the harmonic to be measured.

For example, when the frequency of the harmonic to be measured is 180 Hz, the reference frequency (?) Can be set to 180. If there is a frequency that matches the desired frequency Ω among the frequencies w of the basic signal V (t) input from the resonance unit 130, the mixed signal (eg, V (t) · Vr1 (or an average value) generated by integrating the time t (t), V (t), Vr2 (t) with respect to the time t is derived as DC (or constant). That is, a harmonic having a desired frequency (?) Can be detected. The amplification unit 140 performs the following danger detection determination sequence based on the derived integral value (or integral average value). If no frequency matching the desired frequency OMEGA exists among the frequencies w of the fundamental signal V (t) input from the resonance unit 130, the amplification unit 140 outputs any value (or signal) . This is because the integral value (or integral average value) of the mixed signal (for example, V (t) · Vr1 (t), V (t) · Vr2 (t)) is not a constant and is 0 Because.

Next, the danger detection determination sequence of the amplifying unit 140 will be described.

If there is no phase difference between the basic signal (eg V (t)) and the frequency (Ω) to lock-in (ie the frequency w of V (t) The amplification section 140 amplifies the signal having a specific amplitude (for example, Vr1 (t), Vr2 (t)) through mixing between a reference signal having a sinusoidal waveform or a cosine waveform (Hereinafter referred to as a 'first amplitude value'). Here, the first amplitude value is derived based on an integral value (or integral average value) generated by integrating the mixed signal (e.g., V (t) · Vr1 (t), V (t) · Vr2 It can mean amplitude.

The harmonic measuring apparatus 100 may determine that the transmission of the power transmission line 110 is abnormal when the magnitude of the first amplitude value is equal to or greater than the threshold value. As a result, the temperature of the power transmission line 110 can be detected to be high. The condition for this (for example, the first condition) may include that the magnitude of the first amplitude value is maintained above the threshold value for more than the threshold time. On the other hand, if the transformer exceeds 60 Hz, which is the regular grid frequency, the loss to core loss is huge. The eddy current loss is proportional to the square of the frequency, and the loss of hysteresis is proportional to the frequency.

A method of measuring (or detecting) one target harmonic among a plurality of harmonics will be described. Here, the frequency (desired frequency) of the target harmonic may be a phase frequency, and the target harmonic may be a fifth harmonic, a third harmonic, a seventh harmonic, or a second harmonic. That is, the desired frequency of the target harmonic may be three times, five times, seven times, or two times the frequency of the fundamental wave.

이다.The pick-up coil part 120 of the harmonic measuring apparatus 100 outputs a voltage signal based on the time-varying current of the power transmission line 110. Specifically, the voltage signal output from the pickup coil part 120 can be generated based on the mutual inductance between the power transmission line 110 and the pickup coil part 120, and the time-varying current of the power transmission line 110. In other words,

to be.

The resonance unit 130 of the harmonic measurement apparatus 100 matches the resonance frequency with the desired frequency of the target harmonic and filters the voltage signal output from the pickup coil unit 120. [

The amplification unit 140 of the harmonic measurement apparatus 100 generates a first reference signal (for example, Vr1 (t)) having a sine wave form (or generating) , V (t), V (t)) through mixing between the input signals V (t) and V (t). The amplification unit 140 detects the target harmonic based on the first mixed signal (e.g., V (t) · Vr1 (t)). More specifically, when the integration value generated by integrating the first mixed signal (e.g., V (t) · Vr1 (t)) with respect to time t is a constant, the amplification unit 140 amplifies the filtered voltage signal (E.g., V (t)) includes a target harmonic.

) = 3)에서의 상수값(예, 3)일 수 있고, 제2 상수값은 VO와 제2 상수값 간의 관계식(적분을 통해 도출되는 식, 예, 0.5V0·sin(

) = 4)에서의 상수값(예, 4)일 수 있다.The amplification unit 140 also has a cosine waveform and generates (or generates) a signal having a desired frequency between a second reference signal (e.g., Vr2 (t)) and the filtered voltage signal (e.g., V And generates a second mixed signal (e.g., V (t) · Vr2 (t)) through mixing. The amplification unit 140 amplifies the basic signal (for example, V (t) · Vr1 (t)) based on the first mixed signal , V (t)) (for example, VO). More specifically, the amplification unit 140 amplifies the first signal (e.g., V (t), V (t)) including the amplitude of the basic signal The first constant value and the second constant value including the amplitude (e.g., VO) of the fundamental signal (e.g., V (t)) is obtained as the integral value of the second mixed signal (e.g., V (E.g., V (t)) by applying a trigonometric relationship (e.g., sin ² (x) + cos ² (x) = 1) to the first constant value and the second constant value (E.g., V0). Here, the first constant value or the second constant value including the amplitude (e.g., VO) of the basic signal (e.g., V (t)) is the amplitude of the basic signal (e.g., V (t) Lt; / RTI > For example, the first constant value may be expressed by a relational expression between VO and the first constant value (expression derived through integration, e.g., 0.5 VO · cos (

) = 3), and the second constant value may be a formula derived from a relational expression between VO and a second constant value (eg, 0.5V0 · sin (

) = 4) (e.g., 4).

On the other hand, the embodiments of the present invention are not only implemented by the apparatuses and / or methods described so far, but may also be realized through a program realizing a function corresponding to the configuration of the embodiment of the present invention or a recording medium on which the program is recorded And such an embodiment can be easily implemented by those skilled in the art from the description of the embodiments described above.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, It belongs to the scope of right.

Claims (13)

A harmonic measuring apparatus for measuring one target harmonic among a plurality of harmonics,
A pickup coil part for outputting a voltage signal based on the time-varying current of the power transmission line;
A resonance unit matching the resonance frequency with the frequency of the target harmonic to filter the voltage signal; And
Generating a first mixed signal by mixing between a first reference signal having a sinusoidal waveform and a frequency of the target harmonic and the filtered voltage signal to generate a first mixed signal, And an amplifying section for detecting the amplified signal,
The frequency of the target harmonic is set to three times, five times, seven times, or two times the frequency of a fundamental wave,
Wherein the pick-up coil included in the pick-up coil part has a first end located at a first point on the power transmission line and a second end located at a second point on the power transmission line, the distance being a predetermined distance downward from the first point. Having an end,
Wherein the pick-up coil is twisted to wrap the power transmission line from the first point to the second point,
The voltage signal output from the pickup coil part is generated based on the following equation (1)
Wherein,
Generating the first reference signal using a frequency multiplier,
Wherein,
And a phase difference between the first reference signal and the filtered voltage signal

Generating a second mixed signal through mixing between a second reference signal having a cosine waveform and a frequency of the target harmonic and the filtered voltage signal,
Wherein,
When the integral value of the first mixed signal is a first constant value based on the amplitude of the filtered voltage signal and the integral value of the second mixed signal is a second constant value based on the amplitude of the filtered voltage signal, The first constant value, the second constant value, and sin ² (

) + cos ² (

) = 1 to determine the amplitude of the filtered voltage signal,
And outputs a harmonic alarm signal when the determined amplitude is maintained over the threshold for a period longer than the threshold value
Harmonic measuring device.
[Equation 1]

M is a mutual inductance between the power transmission line and the pick-up coil part, i _p (t) is a current flowing through the power transmission line, t is a time, The method according to claim 1,
The pick-
Wherein the power transmission line is not in contact with the power transmission line
Harmonic measuring device. The method according to claim 1,
The resonator may include:
Using the adjustable capacitance and the inductance included in the pick-up coil part to match the resonant frequency to the frequency of the target harmonic
Harmonic measuring device. The method according to claim 1,
When the phase of the first reference signal and the phase of the filtered voltage signal coincide with each other, the first mixed signal is defined as Equation (2) below
Harmonic measuring device.
&Quot; (2) "

V is the filtered reference voltage, V is the filtered reference voltage, Vr1 (t) is the first reference signal, VO is the amplitude of the filtered voltage signal, w is the frequency of the filtered voltage signal, Frequency, t: time)
delete delete The method according to claim 1,
The first mixed signal is defined by Equation (2) below and the second mixed signal is defined by Equation (3) below
Harmonic measuring device.
&Quot; (2) "

&Quot; (3) "

V is the filtered reference voltage, Vr1 (t) is the filtered reference voltage, Vr1 (t) is the first reference signal, Vr2 (t) is the second reference signal, VO is the amplitude of the filtered voltage signal, w is the filtered voltage Frequency of the signal,?: Frequency of the first reference signal and the second reference signal, t: time,

: The phase difference) CLAIMS What is claimed is: 1. A method for measuring one target harmonic among a plurality of harmonics,
Outputting a voltage signal based on a time-varying current of the power transmission line through a pickup coil disposed in non-contact with the power transmission line;
Matching the resonant frequency to the frequency of the target harmonic and filtering the voltage signal;
Generating a first reference signal having a sinusoidal waveform and a frequency of the target harmonic using a frequency multiplier;
Generating a first mixed signal through mixing between the first reference signal and the filtered voltage signal;
And a phase difference between the first reference signal and the filtered voltage signal

Generating a second mixed signal through mixing between a second reference signal having a cosine waveform and a frequency of the target harmonic and the filtered voltage signal if the first mixed signal is present;
When the integral value of the first mixed signal is a first constant value based on the amplitude of the filtered voltage signal and the integral value of the second mixed signal is a second constant value based on the amplitude of the filtered voltage signal, The first constant value, the second constant value, and sin ² (

) + cos ² (

) = 1; determining an amplitude of the filtered voltage signal using a trigonometric function relationship; And
And outputting a harmonic alarm signal when the determined amplitude is maintained above a threshold value for a predetermined time or more,
Wherein the outputting step comprises:
And outputting a voltage signal satisfying Equation (1) below,
The pick-up coil having a first end located at a first point on the power transmission line and a second end located at a second point on the power transmission line, the distance being a predetermined distance downward from the first point,
Wherein the pick-up coil has a twisted shape to wrap the power transmission line from the first point to the second point
Measuring method of harmonic measuring device.
[Equation 1]

M is a mutual inductance between the power transmission line and the pickup coil, i _p (t) is a current flowing through the power transmission line, t is a time, 9. The method of claim 8,
Wherein the filtering comprises:
Using the adjustable capacitance and the inductance of the pickup coil to match the resonant frequency to the frequency of the target harmonic
Measuring method of harmonic measuring device. 9. The method of claim 8,
Wherein the generating the first mixed signal comprises:
Generating the first mixed signal based on Equation (2) below when the phase of the first reference signal and the phase of the filtered voltage signal coincide with each other
Measuring method of harmonic measuring device.
&Quot; (2) "

V is the filtered reference voltage, V is the filtered reference voltage, Vr1 (t) is the first reference signal, VO is the amplitude of the filtered voltage signal, w is the frequency of the filtered voltage signal, Frequency, t: time)
delete delete 9. The method of claim 8,
Wherein the generating the first mixed signal comprises:
And generating the first mixed signal based on Equation (2) below,
Wherein generating the second mixed signal comprises:
And generating the second mixed signal based on Equation (3) below:
Measuring method of harmonic measuring device.
&Quot; (2) "

&Quot; (3) "

V is the filtered reference voltage, Vr1 (t) is the filtered reference voltage, Vr1 (t) is the first reference signal, Vr2 (t) is the second reference signal, VO is the amplitude of the filtered voltage signal, w is the filtered voltage Frequency of the signal,?: Frequency of the first reference signal and the second reference signal, t: time,

: The phase difference)

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