JPH0645270Y2 - Insulation resistance measuring device - Google Patents

Description

[Detailed Description of the Invention] [Industrial field of application] The present invention relates to an insulation resistance measuring device for measuring the insulation resistance of a multi-phase low-voltage distribution line such as a 3-phase low-voltage distribution line.

[Conventional technology]

Conventionally, for monitoring insulation deterioration of a three-phase low-voltage distribution line, which is a multi-phase low-voltage distribution line, in many cases, the insulation resistance of the distribution line is measured by manual measurement using an insulation resistance meter, and First, the insulation resistance is judged to be good or bad. In this case, complicated and dangerous measurement work and measurement result judgment work are required.

Therefore, an insulation monitoring device has been devised which injects a low-frequency voltage signal into the neutral point of the power distribution line to automatically measure the insulation resistance of the power distribution line and automatically monitors the insulation deterioration.

Then, the conventional insulation resistance measuring device used for the monitoring device, by automatic control of the microprocessor, transmits a low-frequency distribution signal of a predetermined frequency f different from the transmission AC (50 Hz or 60 Hz) of the distribution line to the distribution line. While injecting as a zero-phase voltage to the ungrounded neutral point, the zero-phase transformer (ZCT) is used to detect the zero-phase current of the distribution line, and the zero-phase voltage of the distribution line based on the injection of the voltage signal, Measure the current.

In addition, zero-phase voltage and current measurement values (vector values),
Based on the effective value V, I and the phase angle θ of the, and based on the effective value V, I and the phase angle θ,
The resistance component r and the reactance component x of the impedance of the distribution line are r = V / (Icosθ), x = 1 / (2πfC) = V / (Isin
θ): (C is the capacity), and the resistance component r is output as the measured value of the insulation resistance.

Since the voltage signal is injected into the neutral point of the distribution line and the impedance of the distribution line is measured from the zero-phase voltage and current, the coil component of the distribution line can be ignored and the reactance component x can be regarded as the capacitance component. .

Also, based on the measurement of the insulation resistance, the monitoring device automatically determines whether the insulation resistance is good or bad, and displays and informs of the insulation deterioration.

[Problems to be solved by the device]

By the way, when the insulation resistance is measured by injecting the voltage signal as described above, the measurement value is true due to the measurement phase shift (rotation) of the signal based on the circuit impedance of the device such as the impedance of the zero-phase transformer. The impedance coordinates (coordinates of the resistance axis and the reactance axis orthogonal to each other) are obtained by rotating the impedance coordinates (hereinafter referred to as measured impedance coordinates) by an angle corresponding to the phase shift.

Then, based on the effective values V and I and the phase angle θ calculated from the measured values, for example, from the measured impedance coordinates of the resistance axis R ^* and the reactance axis X ^{* in} FIG.
r and the reactance component x are calculated. At this time, the resistance component r, which is calculated from the measured phase shift of the angle from the true impedance coordinate of the resistance axis R and the reactance axis X in FIG.
The reactance component x deviates from the true resistance component ro (= insulation resistance) of the distribution line and the reactance component xo by an amount corresponding to the angle, and an insulation resistance measurement error occurs.

Therefore, in the case of the conventional insulation resistance measuring device, there is a problem that the insulation resistance cannot be accurately measured and the insulation deterioration cannot be accurately monitored.

Even when the insulation resistance meter is used, the insulation resistance cannot be accurately measured due to the measurement phase shift based on the circuit impedance of the resistance meter.

The present invention provides an insulation resistance measuring device for accurately measuring the insulation resistance of a distribution line from the zero-phase voltage and current of the distribution line when a low-frequency voltage signal is injected into the neutral point without error in phase shift. Is intended.

[Means for Solving the Problems]

 Means for achieving the above object will be described below.

The present invention relates to an insulation resistance measuring device for measuring the insulation resistance of a multi-phase low-voltage distribution line, wherein voltage injection is performed by sequentially injecting low-frequency voltage signals of two frequencies different from the transmission AC into an ungrounded neutral point of the distribution line. Means, a current detecting means for detecting a zero-phase current of the distribution line, and an effective value and a phase angle of the zero-phase voltage and current of the distribution line at the time of injecting each of the both voltage signals based on the detection result of the detecting means. And impedance calculation means for calculating the resistance value of the impedance of the distribution line based on the voltage signals and the measured value of the reactance component from the RMS value and the phase angle, and the resistance component of the voltage signals, A correction operation that corrects the measured phase shift of the impedance from the geometric calculation based on the measured value of the reactance component and calculates the insulation resistance of the distribution line. We have taken technical measures to equip them with arithmetic means.

[Action]

Therefore, based on the injection of the voltage signal of 2 frequencies, the frequency of the zero phase voltage and the current of the distribution line are changed to 2
The impedance component is used to calculate the resistance component and the reactance component of the impedance of the power distribution line based on the measurement results.

At this time, the calculation of the resistance component and the reactance component based on both the voltage signals based on the measurement phase shift is performed by the same measurement impedance coordinate obtained by rotating the true impedance coordinate by a predetermined angle.

If the resistance component and the reactance component are calculated as r ₁ , x ₁ and r ₂ , x ₂ based on the above two measurements, the resistance components r ₁ and r ₂ are different due to the measurement phase shift, and Except in the special case where the reactance components x ₁ and x ₁ become equal as the phase shift becomes 90 ° or 270 °, the point (r ₁ , x
_The line segment connecting ( ₁ ) and (r ₁ , x ₂ ) is parallel to the reactance axis of the true impedance coordinate, and the intersection of the line segment and the resistance axis of the true impedance coordinate is the point of the true resistance component. .

Therefore, based on the inclination of the line segment connecting the points (r ₁ , x ₁ ), (r ₁ , x ₂ ), the correction calculation means corrects the measured phase shift from the geometric calculation to obtain the true impedance coordinates. Based on this, the insulation resistance of the distribution line is calculated.

In the special case, the reactance components x ₁ and x ₂ are calculated as the insulation resistance of the distribution line based on the true impedance coordinates.

〔Example〕

Next, the present invention will be described in detail with reference to FIGS. 1 to 4 showing one embodiment thereof.

In Fig. 1, (1) is a neutral point (1) 'where 3 is not grounded.
It is a low voltage phase distribution line, and 50Hz or 60Hz transmission AC flows. (2) is an insulation monitoring device formed by using an insulation resistance measuring device, (3) is a microprocessor that controls and calculates the device (2), and forms an impedance calculating means and a correction calculating means described later. To do.

(4) is a voltage generator whose oscillating frequency is variable by the processor (3), which forms a low-frequency voltage signal V (f) which sequentially changes to two frequencies f ₁ and f ₂ at the time of measurement and outputs the voltage signal V (f). To do.
(5) is an injection switch that is turned on and off by the processor (3), and (6) is an injection transformer that is supplied with the voltage signal V (f) through the switch (5) on the primary side. Two
The secondary side is provided between the neutral point (1) 'and the ground, and forms a voltage injection means together with the generator (4) and the switch (5) to transfer the voltage signal V (f) to the neutral point (1)'. Inject.

Reference numeral (7) is a zero-phase transformer (ZCT) for detecting a zero-phase current of the distribution line (1), which forms a current detecting means and outputs a detection signal I (f) having a voltage proportional to the zero-phase current. . (8),
(9) is two input amplifiers for amplifying each of the voltage signal V (f) and the detection signal I (f), and (10) is a bias resistor provided on the input side of the amplifier (9).

Reference numeral (11) is a multiplexer for selectively outputting the output signals of the amplifiers (8) and (9), and its operation is controlled by the processor (3). (12) is an A / D converter for converting the output signal of the multiplexer (11) into a digital signal, and the voltage signal V
(F), digital data of the detection signal I (f) is output to the processor (3).

(13) is a resistance value indicator into which the display signal of the measurement result of the processor (3) is input, and displays the measured insulation resistance value. (14) and (15) are an insulation normality indicator and an insulation defect indicator to which a notification signal of the determination result of the processor (3) is input. Displays Yes and No. A deterioration contact signal generator (16) is driven by a notification signal of the determination result of the processor (3) and generates a contact signal for notification and control external output when insulation deterioration is identified.

A processor (3), a generator (4), a switch (5), a transformer (6), (7), an amplifier (8), (9).
The multiplexer (11) and the converter (12) form an insulation resistance measuring device.

Then, by the timer operation of the processor (3) or manual activation, the device (2) operates at a relatively long interval, for example, about once a day, and the insulation resistance is measured.

At this time, based on the control of the processor (3), the generator (4) sequentially outputs the voltage signals V (f) of the predetermined two frequencies f ₁ and f _{2 in} a relatively short time, and the switch (5).
Is turned on during a stable period of each of the voltage signals V (f) of the two frequencies f ₁ and f _{2, and} the voltage signal V (f) of the two frequencies f ₁ and f ₂ is passed through the transformer (6) to the neutral point. (1) 'is sequentially injected as a zero-phase voltage.

Note that the two frequencies f ₁ and f ₂ are set to two different low frequencies, which are different from the frequency of the power transmission AC.
It is set to 60Hz and 62Hz respectively at 50Hz, and is set to 50Hz and 52Hz respectively when the transmission AC is 60Hz.

Then, based on the injection of the voltage signal V (f), the zero-phase current of the distribution line (1) changes according to the frequency of the voltage signal V (f), and the zero-phase current of the distribution line (1) changes. It is detected by (7).

Further, the voltage signal V (f) and the detection signal I (f) of the transformer (7) are input to the multiplexer (11) via the amplifiers (8) and (9) of constant gain, and at this time, the processor (3) ), The voltage signal V for one or several cycles at the time of injecting the voltage signal V (f) of each of the frequencies f ₁ and f ₂
(F), the detection signal I (f) is output from the multiplexer (11) to the converter (12) in time series.

Then, the converter (12) inputs the input voltage signal V
(F) and the detection signal I (f) are digitally converted in a minute cycle, and N instantaneous values (t), (t) (zero-phase voltage and current per cycle of the frequencies f ₁ and f ₂ respectively) t = 1,
, N) sampling data is output to the processor (3).

At this time, the impedance calculation means of the processor (3) controls the frequency, the zero phase voltage of each of f ₁ and f ₂ and the current of 1
From the Fourier transform processing based on the instantaneous values (t) and (t) for a period, the voltage signals V at the frequencies f ₁ and f ₂ are obtained.
(F) Zero phase voltage when injected, current measurement,
The effective values V, I of and the phase angle θ of are calculated.

By the way, the measured value based on the voltage signal V (f) of the frequency f ₁ is set to ₁ , _1, and the voltage signal V (f) of the frequency f ₂ is set.
When the measured value based on the above is ₂ , ₂ , the impedance of the distribution line (1) can be obtained from the vector operations of (1) and (2) below. _{1/1 = 1 = r 1} + jx 1 ...... (1) Formula _{2/2 = 2 = r 2} + jx 2 ...... (2) Equation Incidentally, _{1, 2} was determined from the arithmetic distribution line (1) Where r ₁ and r ₂ are impedances ₁ and
₂ shows the resistance component, and x ₁ and x ₂ show the reactance components of impedances ₁ and ₂ .

And there is no measurement phase shift due to the circuit impedance of the device (2) based on the transformer (7), amplifier (8), (9), etc., and the measured values ₁ , ₁ and ₂ , ₂ can be obtained from the true impedance coordinates. Then, at this time, since the resistance component of the distribution line (1) does not change with frequency,
Resistance components r ₁ and r ₂ are both true resistance components of the distribution line (1)
r ₀ , that is, the true insulation resistance becomes equal.

However, in reality, due to the measurement phase shift based on the circuit impedance of the device (2), the measured values ₁ , ₁ and
₂ and ₂ are obtained from the measured impedance coordinates rotated by a predetermined angle corresponding to the phase shift from the true impedance coordinates, and at this time, the resistance components r ₁ and r ₂ are displaced from the resistance component r ₀ on the true impedance coordinates. Will have different values.

That is, as shown in FIG. 2, the measured impedance coordinates of the resistance axis R ^* and the reactance axis X ^* are rotated by an angle from the true impedance coordinates of the resistance axis R and the reactance axis X based on the measurement phase shift, and the measurement is performed. Assuming that impedances ₁ = (r ₁ , x ₁ ) and ₂ = (r ₂ , x ₂ ) are obtained from the measured values ₁ , ₁ and ₂ , _{2 based on the} impedance coordinates, respectively, it is clear from the figure. To the resistance component
r ₁ and r ₂ have different values deviated from the true resistance component r ₀ .

By the way, looking at the points (r ₁ , x ₁ ), (r ₁ , x ₂ ) from the true impedance coordinates as described above, the resistance components r ₁ , r ₂ are always equal, and therefore the points (r ₁ , The line segment connecting (x ₁ ), (r ₁ , x ₂ ) has a special case where the angle becomes 90 ° or 270 ° due to the measurement phase shift, that is, the resistance axis R ^* coincides with the reactance axis X and the reactance As is clear from FIG. 2, except for the special case where the axis X ^* coincides with the resistance axis R, it becomes parallel to the reactance axis X of the true impedance coordinate, and the line segment and the true impedance coordinate The intersection with the resistance axis R is
It is the point of the true success component r ₀ , that is, the true insulation resistance.

Then, the resistance axis R ^* and the reactance axis X ^* are two axes α and β orthogonal to each other, and the line segment connecting the points (r ₁ , X ₁ ), (r ₂ , x ₂ ) is defined as the following equation (3). In this case, the resistance axis R viewed from the coordinates of the two axes α and β can be expressed by the equation (4). Note that K and M in the formula are constants.

β = Kα−M (3) Equation β = − (1 / K) α (4) Further, the line segment of Equation (3) is a point (r ₁ , x ₁ ), (r ₁ , x ₂ ), the constants K and M are obtained from the following equations (5) and (6), respectively.

K = (x ₁ -x ₂ ) / (r ₁ -r ₂ ) ... (5) Formula M = (x ₁ r ₂ -r ₁ x ₂ ) / (r ₁ -r ₂ ) ... (6) Formula , (3) and the intersection of (4) with (α ₁ , β ₁ ), α ₁ , β _{1 can be} obtained from the following equations (7), (8), respectively.

α ₁ = MK / (K ² +1) (7) Formula β ₁ = −M / (K ² +1) (8) Formula α ₁ and β ₁ are r ₀ ′, x in FIG. _Since it becomes ₀ ′, the resistance component r ₀ can be expressed by the following equations (9), K and M in equations (5) and (6).
Can be obtained by substituting.

In the special case, the line segment connecting the points (r ₁ , x ₁ ) and (r ₁ , x ₂ ) is parallel to the reactance axis X and is perpendicular to the resistance axis R. At this time, Since the components x ₁ and x ₂ always have the same value equal to the resistance component r ₀ , the reactance component is
The resistance component r ₀ is obtained from x ₁ and x ₁ .

Therefore, the impedance calculation means of the processor (3) calculates the effective values based on the voltage signals V (f) of the frequencies f ₁ and f ₂ and the vector calculation of the phase angle θ to calculate the resistances of the impedances ₁ and ₂ described above. The components and reactance components r ₁ , x ₁ and r ₂ , x ₂ are calculated as the measured values.

Furthermore, by the correction computing means processor (3), based on both components r _2, x ₂ of the two-component r _1, x ₁ and impedance _second impedance _1, wherein (5), (6), (9)
The true resistance component r ₀ is calculated by correcting the measured phase shift from the geometrical calculation of the equation, and the data value of the calculated resistance component r ₀ is output as the measured value of the insulation resistance.

The special case is detected because the reactance components x ₁ and x ₂ are equal, and in this case, the reactance component x ₁ or x ₂ is calculated as the true resistance component r ₀ .

Then, the value of the insulation resistance obtained on the display (13) is displayed numerically based on the measurement value of the insulation resistance output from the correction calculation means, and is preset by the deterioration determination means of the processor (3). The presence or absence of insulation deterioration of the distribution line (1) can be determined from the comparison between the determination reference value rs and the measured value r ₀ .

Further, based on the determination result of the deterioration determining means, when the insulation is normal and there is no deterioration, it is displayed that the display (14) is not deteriorated, and when the insulation is deteriorated, the display (15) is displayed. Insulation deterioration is displayed by lighting, and a contact signal is output from the generator (16) to the outside.

The flow chart of the operation of the device (2) is as shown in FIG.

The measurement in the example, when determining the magnitude of the phase shift as an error of the measurement system, for example, as shown in FIG. 4, the resistance component r ₁ of the impedance _1, the reactance component x ₁ and the true resistive component r _0, the reactance Based on the component x ₀ , the angle may be calculated from the following equations (10) and (11) indicating the angle δ formed by the vector of the impedance ₁ and the resistance axis R ^* and the resistance component r ₀ .

δ ＝ tan ^-1 (x ₁ / r ₁ ) …… (10) Formula Further, in the above-described embodiment, the case where the present invention is applied to the insulation monitoring has been described, but it is needless to say that the present invention can be applied to the case where only the insulation resistance is measured.

Further, it is needless to say that the multi-phase low voltage power distribution line having four or more phases can be measured in the same manner as in the embodiment.

[Effect of device]

As described above, according to the insulation resistance measuring device of the present invention, 2
A low-frequency voltage signal with a low frequency is injected as a zero-phase voltage into the neutral point of the distribution line, and the zero-phase current of the distribution line at the time of injection of both voltage signals is detected, and two frequency zeros based on both voltage signals are detected. The resistance component and the reactance component of the impedance of the distribution line are calculated from the phase voltage and the current, respectively, and the measured phase shift of the impedance is corrected by geometric calculation based on the calculated two types of resistance component and reactance component. By calculating the insulation resistance of the line, it is possible to accurately measure the insulation resistance of the multi-phase low-voltage distribution line without a measurement phase shift.

[Brief description of drawings]

FIG. 1 is a block diagram of one embodiment of the insulation resistance measuring device of the present invention, FIG. 2 and FIG. 4 are impedance coordinates for the measurement description of FIG. 1, and FIG. 3 is a description of the operation of FIG. The flow chart, FIG. 5, is impedance coordinates for explaining the measurement of the conventional insulation resistance measuring device. (1) …… 3-phase low voltage distribution line, (1) ′ …… Neutral point,
(3) -Microprocessor, (4) -Voltage generator, (5) -Injection switch, (6) -Injection transformer, (7) -Zero-phase transformer, (8) , (9) …… Input amplifier, (11) …… Multiplexer, (12) …… A / D converter.

Claims (1)

[Scope of utility model registration request] 1. An insulation resistance measuring device for measuring insulation resistance of a multi-phase low-voltage distribution line, wherein a voltage for sequentially injecting low-frequency voltage signals of two frequencies different from the transmission AC to a non-grounded neutral point of the distribution line. Injection means, current detection means for detecting a zero-phase current of the distribution line, and zero-phase voltage and current effective value and phase of the distribution line at the time of injection of each of the voltage signals based on the detection result of the detection means. Impedance calculating means for calculating an angle and calculating a measured value of a resistance component and a reactance component of the impedance of the distribution line based on the voltage signals from the RMS value and the phase angle, and the resistance component of the voltage signals. A correction for correcting the measured phase shift of the impedance from the geometric calculation based on the measured value of the reactance component to calculate the insulation resistance of the distribution line Insulation resistance measuring device equipped with a calculating means.