JPS5873880A - Method for measuring insulation resistance - Google Patents

Abstract

PURPOSE:To calculate and measure an insulation resistance by integrating a leakage current for a section of each half period of a low-frequency voltage being a measuring signal, in synchronization with the voltage and in an integration time which is an integer multiple of the basic frequency of a commercial frequency component. CONSTITUTION:A partial voltage transformer T02 is connected to a commercial supply circuit 4 to lower the voltage of the latter, and thereby a rectangular wave is obtained at an output of a wave-shaping circuit WS. The frequency of this wave is divided into 1/4 by a frequency divider DIV, and a wave thus obtained is given to a voltage injecting circuit OS and impressed via a transformer T00. A leakage current fed back to an earthing line EL is detected, for instance, by a current detecting probe CD and passed through an amplifier AMP, and thereby a wave with a current waveform and the leakage current component of a commercial frequency component added thereto is obtained as an output of the amplifier. Even when the harmonic component of the commercial frequency component is contained, an average value is not affected thereby, by setting the integration time of an integrator INTEG at an integer multiple of the basic period of the commercial frequency component. Accordingly, a voltage reversely proportional to a value of an insulation resistance can be obtained at an output OUT, and thereby the insulation resistance can be measured.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for detecting insulation resistance of an electric circuit or the like in a live line state or in an oil-free state.

The second type grounding tube of the conventional transformer is passed through the core of the transformer to which the low chest wave voltage, which is the copper 11 regular signal, is applied, or the second type grounding edge is cut and the low frequency voltage is connected to it. Apply a full low frequency voltage to the electrical circuit through this grounding wire by applying a ratio, detect all of the th8 city #L returning to the grounding wire, and calculate this leakage current (from both the commercial frequency component and the applied four-frequency component). (The current generated by the ground stray capacitance of the circuit or load is the reactive component, and the current in-phase with the applied voltage, which is generated by the insulation resistance of the circuit or load, is the effective component.) ) is detected through the same M detection or multiplication operation, and insulation is removed (
Various methods have been proposed, such as a method of obtaining a voltage 1 that is inversely proportional to 1i+ and using this to measure the insulation resistance, and a method of applying it to the electric circuit instead of the low voltage t-ground wire using the method described below. . □ However, these conventional methods have the drawback that they require a filter that separates the commercial frequency component and the t-wave component from the leakage current, and a highly accurate effective component detection circuit. Is the method of the present invention a new method to extremely easily measure insulation resistance? This is a proposal.

The first diagram is a diagram for simply explaining the assembly of electric circuits, and the same diagram shows the case of a single phase 24)+1, but the present invention is not limited to this. The secondary side of the high voltage transformer TOI, which is the primary side of the high voltage circuit 2, 2''i, is grounded by a second grounding line EL.The cold paths 1 and 3 have a ground stray capacitance C and an insulation resistance R. The ground edge EL passes through the core of the oscillation transformer Too of the oscillator O8C that oscillates a low-frequency rectangular wave voltage, or the transformer to which a low-frequency rectangular wave voltage is applied (simply penetrates it or winds it with several turns A). ing.

, and the ground l1IllEL passes through the leakage 1 through the current probe CD for detecting flow (either directly or by winding several turns). Also, these relationships are based on the electric line 1.1”
i) It is clear that the same result can be obtained even if the current probe CD is passed through the lance Too.

Figure wJ2 is an equivalent circuit of Figure 1, but the behavior of the commercial frequency component is ignored. This will be discussed later.

r is the output impedance of the low wave application circuit. By converting the negative phase characteristic of the square wave oscillator O8C into Laplace 1, we obtain H(81
Then, the initial response of the current is found as follows.

However, the amplitude of the rectangular wave pulse is iE.

If 'FL>r, then FIG. 3 shows the initial response i 1 (t) to the input waveform V (t+).

The general KrO value can be sufficiently low (for example, several Ω), and C
Even if the value of is large, the islands are 10μ) & 1 degree, so the constant Cr is less than several m,'s,ec. Also, the input waveform V(t)O
t = 11 Te (D' falling t) tllRa type i 2
(t) Becomes genus Ia l.

i 1(tl+ i 2(If you calculate the DC component of 11 -
It is obvious then.

Therefore, if the time t1 is sufficiently large compared to the time constant Cγ, the repeated rectangular wave signal of the input V (tl, where tl is the hemithoracic period (i.e., it'') m and the hemithorax period T, as shown in (■) in Fig. If you select this and apply all of it,
It is possible to obtain a response current waveform as shown in (■) in FIG. The DC component of one period T of the current waveform O) in FIG. 4 becomes zero.

Therefore, the half-cycle current waveform i from 1=0 to t=-
5 (becomes 11Fi. As 'ro<-, i=o to t
If we calculate the integral value A of i5(t) up to =TO (assuming the constant of integration as KO), if cr < t, then generally n>r, so similarly from Kt=・ to i'== 7. i 3 up to (y, ≦T)
(When calculating the integral value B of 11, by the way, in an actual live carp state, the leakage current includes the current waveform 1B (tl) as well as the leakage f!1. current due to the commercial frequency component. If the line voltage of a single-phase ZLK circuit is vo volts and the number of waveforms is fo, then the current due to the commercial frequency component is 14 (tl is 0 = 2πfo, and the detection period is 1 = 0 to -). The current is i5(
t) + i 4(t).

By the way, the integration time TQ or Tl in the above ■ and ■
If it is set to an integral multiple of the fundamental period 1/fo of the t-curving frequency component, it becomes zero, i 5 (tl + i 4 (tl of t = 〒O or j = T %). It is clear that the influence of commercial frequency components disappears.

In other words, it is no longer necessary to remove the commercial frequency component from the detected current i5(tl+i4(tl) using a filter, etc.Also, even if the leakage current contains harmonic components of the commercial frequency component in addition to the commercial frequency component, If 〒O゛ or Ttt'' is set as an integer multiple of the fundamental period of the commercial frequency component, there will be no change in the average value mentioned above, such as in the example of Fi.In the above explanation, single-phase 2Iw
The case of equation 0 was shown as equation 0, but even in circuits such as single-phase 3-wire, 3-phase 3-wire, etc., the [phase] equation is different from the above.
” However, under the above conditions, the above-mentioned influence on the average value ◆ disappears.

Now, CR(T0 mafc is CR(□τ1, then ■
, or the insulation resistance can be immediately calculated and measured using the average values A and B expressed by the equation 0.

A → □ ・ □ sKg R ■ T1 B → □ ・ - Le ◎ Wing However, for example, when c=10 itk' and R=100 and Ω, cm=1 [second], which satisfies the 0 formula, so O! @ or T1 is required to be several tens of seconds, and it is difficult to apply such a low frequency rectangular wave voltage to the electric circuit by transformer coupling or the like. During this time, wA¥ is solved as follows.

It is from formulas ■ and ■. ,To,'? If ``'7fl'' is a fixed value, by calculating A and B, it is possible to calculate R, which is inversely proportional to 9 insulation resistance, by equation 0, regardless of 9CIt.

For example, if 〒1=2T o is selected, the [phase] formula becomes.

Also, a value proportional to is obtained. At this time, 〒1-TO may be an integral multiple of the commercial frequency component period, and T0゜T1 may not be an integral multiple of the commercial frequency component period.O Figure 5 shows one embodiment of the present invention. . Descriptions of parts that are the same as the symbols in FIG. 1 will be omitted. Commercial voltage circuit 4
A voltage dividing transformer tow is connected to step down the voltage, and then the waveform is shaped by a waveform shaping circuit WS to obtain a rectangular wave train t-. commercial frequency f
Period of output of Vv8 when o = 50 Hz 1/f
o becomes 20 crystals 3, and this can be compared with the frequency divider DIV t!
Divide the frequency by l/4 and 1. In addition to the pressure injection circuit 08, a rectangular wave signal indicated by ■ in FIG. 4 is applied via a transformer Toof passing through the ground line EL or the electric lines 1 and 3t. For example, if the leakage current that returns to the ground line ELK is detected by a current detection probe CD and amplified by an amplifier Ah/1P, the output of AMP is w, and the current waveform shown by ■ in Figure 4 and the leakage current component of the commercial frequency component. The output of O AMP is led to an integrator I N '1'' E G.

For example, as explained in equation 0, the integration time of the integrator lNT12G is set to 〒1-〒0, and this integration time is selected to be an integer multiple of the commercial frequency component period, and in Niko, it is set as 〒1-〒o-1/
Let it be f o. These relationships are shown in Figure 4. ■ in FIG. 4 means a curved chest wave component waveform. j-':TQ
The output of the frequency divider DIV is controlled by the control signal generator CUNT so that the integration starts from and ends at the above-mentioned integration time T1.
In addition, the integrator is controlled by a signal INT that controls the start and end of integration. In this case, the output waveform #E4-■ is obtained as the output of the integrator INTEG. 1 in Figure 4 = T4
The integral value corresponds to B-A in equation 9. Turn on the switch SWI t only at the time when the integrator output 1i = 74, store it in the holder consisting of the capacitor C1 and the buffer amplifier BF, and then reset the integrator with the signal RES at t = 3.
Reset with ET (?4<T3<〒).

By repeating this operation, the waveform shown in Figure 4 is obtained at the buffer amplifier HF output, and this is passed through a low-pass filter consisting of a 2W capacitor C2 to the output OUT. It is possible to obtain a voltage that is inversely proportional to the insulation resistance value, and thereby the insulation resistance 11411 can be constant.

In addition, when applying the low frequency rectangular wave voltage to the electric circuit, it is also possible to use transformer coupling, or, for example, to disconnect the ground line ELi and apply it in series thereto. Further, in detecting the leakage current, a zero-phase current transformer may be used, or, depending on the situation, a resistor may be inserted in series with the ground and the voltage across the resistor may be detected.

This method has the advantage of making it possible to measure insulation in a live line state, but in order to operate it in a power outage state, each circuit shown in Figure 5 must be operated with a gold battery and the waveform shaping circuit WS
It is preferable to connect an oscillator 1 with a frequency corresponding to the commercial frequency to the input of the oscilloscope.

Although the method of the present invention is extremely simple, its measurement accuracy is high and it is of great industrial value.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of the construction of −j constant. The $2 diagram is a diagram showing the conversion system'f) home price circuit. FIG. 3 is a diagram showing the initial response of the equivalent circuit of FIG. 2. FIG. 4 is a diagram showing corrugated tubes of various parts. FIG. 5 is a diagram showing an embodiment of the present invention. 〒oo: Transformer 1"ol: Transformer tow: Voltage transformer R: Insulation resistance C: Stray capacitance to ground Z: Load O8 = Voltage injection circuit CD: Current detection probe 1, 3, 4: Low voltage line 2: High voltage line W8: Waveform shaping circuit DIV: Frequency divider AMP: Amplifier INTEG: Integrator 8W1: Switch OSC: Square wave oscillator C0NT: Control signal generator Patent applicant Toyo Tsushinki Co., Ltd.

Claims (1)

[Claims] A low-frequency rectangular wave voltage, which is a measurement signal, is applied to the electrical circuit through the grounding wire of the transformer by electromagnetic casting or series coupling, and the leakage current that returns to the grounding wire is detected to measure the insulation resistance of the electrical circuit. In the method, for each hemithorax period in synchronization with the low frequency rectangular wave voltage, the nuclear leakage current is integrated over the equinox time consisting of an integral multiple of the fundamental thoracic period of the commercial frequency component. 11. A method for determining insulation resistance, characterized by calculating and determining.