JP2750713B2 - Simple insulation resistance measurement method for low voltage wiring etc. - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for measuring insulation resistance of electric wiring, and more particularly to a method of measuring and detecting the insulation resistance of a general electric work in a general household or the like locally. The present invention relates to a method for measuring insulation resistance of low-voltage wiring and the like that can be performed.

(Prior art) In power transmission equipment, insulation monitoring is performed before transmission, and more stable power supply is achieved.

However, the monitoring system for insulation in ordinary households has been delayed, and only equipment for performing very rough measurements has been installed.

That is, as a conventional method of measuring the insulation resistance of indoor and outdoor wiring including load equipment for general households, power supply is stopped at a distribution board in each household, a high-voltage DC voltage is applied to a portion to be measured, and the leakage current is measured. In general, a method using a so-called mecca for detecting the presence of a messenger is used.

As a means for measuring without stopping power supply, a method of measuring a zero-phase current component of a commercial frequency component by clamping a zero-phase current transformer on a distribution line has been used.

On the other hand, in recent years, many household electrical facilities use sophisticated electronic circuits equipped with a CPU and the like. Interrupting power supply or applying high voltage to measure insulation resistance may cause an accident, etc. It is a situation that should be avoided as much as possible because it may occur.

Furthermore, with the increase of various filters for noise removal attached to various electronic devices, the capacitance to ground between the electric circuit or the load device and the ground increases, and accurate insulation can be obtained simply by measuring the zero-phase current of the commercial frequency. It has become difficult to determine whether the situation is good or bad. In addition, it has been desired that a method for measuring the insulation resistance of indoor wiring such as a general home outdoors be put to practical use, since a measurer does not enter indoors for measuring insulation resistance.

However, low-voltage paths, such as 100 V or 200 V, that supply power to general electric works such as homes are pole transformers or transformers buried underground, which are generally stepped down from 6.6 KV and then wired to multiple homes and electrical equipment. However, one end of the low-voltage measurement output circuit of the power receiving transformer is generally grounded near the installation location of the power receiving transformer. However, since this ground resistance is not always sufficiently low, it has been extremely difficult to separate and measure the insulation resistance of the wiring in a specific home and the electric equipment connected thereto.

Therefore, when measuring the electrical insulation resistance of a particular household, the method must be one that is not affected by the insulation resistance of other households or other electrical equipment, the capacitance to ground, or the grounding resistance of the transformer on the low-voltage side. .

(Object of the Invention) The present invention has been made in consideration of various circumstances at the same time as solving the above-mentioned conventional problems, and it is not necessary to enter indoors when measuring the electrical insulation resistance of a general electric work such as a general household. It is an object of the present invention to provide a method for accurately and easily measuring insulation resistance without interruption.

(Summary of the Invention) In order to achieve this object, a simple insulation resistance measuring method according to the present invention comprises connecting an injection transformer and a current transformer to a required portion of a wire whose one end is grounded, and via the injection transformer. circuit for detecting a voltage present, and connects the detection voltage and a variable capacitor variable resistor or a variable resistor in parallel between the predetermined portions and ground to apply a measuring signal comprising a frequency f ₁ to the wiring The current transformer is applied so that a magnetic flux in a direction opposite to a magnetic flux induced in the current transformer by the measurement signal applied to the wiring is generated in the current transformer. was allowed to penetrate further, by adjusting the resistance value and the capacitance value of the variable resistor a resistance value or the variable resistance and a variable capacitor so that the frequency f ₁ component contained in the current transformer output is minimized, The resistance value or Insulation resistance of the wiring connecting the injection transformer and the current transformer at the end from the required part, that is, the wiring far from the required part as viewed from the power receiving transformer and the load device connected to the wiring by the resistance value and the capacitance value. Take steps to measure.

(Examples) Hereinafter, the present invention will be described in detail based on examples shown in the drawings.

FIG. 1 is a block diagram showing an embodiment of an apparatus used to carry out the method of the present invention.

Ie, T In FIG. 1, L _1, L ₂ and L _E is connected between one and the earth of the low-pressure path and the power line and the power receiving transformer embedded in the pole or underground (E ₂₎ Ground wire.

The electric lines L ₁ and L ₂ are generally branched into a plurality of parts and distributed to a large number of homes. General electric work is located at the end of each electric line, that is, farther than the branch point of each branch electric line when viewed from the power receiving transformer T. Objects H ₁ , H ₂ , H _0, etc. are connected, and insulation resistances R ₁ , R ₃ , R ₀ exist between these general electric works (including wiring for load installation) and the ground. , Insulation resistance between low-voltage path and ground
R ₂ and R ₄ exist. At the same time, the load equipment (including the wiring of the load equipment) and the low-voltage path have a ground capacitance C ₁ ,
There are C ₃ , C ₀ and C ₂ , C _4, etc.

It illustrates the case of measuring by the method of the present invention the insulation resistance on Load device H ₀ of this state of the distribution line.

For this, connect the oscillator OSC to the infusion transformer OT with couples injection transformer OT inside or outside of the wire of the home where the load device H ₀ as shown in the figure is installed (path) in this example Then, a measurement signal having a frequency of ₁ is injected into the electric circuits L ₁ and L ₂ .

It goes without saying that the measurement signal frequency ₁ is different from the commercial frequency and the frequency of its harmonic component.

Further, a zero-phase current transformer ZCT is passed through the wiring circuit by a clamp or the like, and its output is input to a filter FIL for extracting _one frequency component, and the output of the filter FIL is connected to a rectifier DT.
After the rectification, the value is displayed on the meter M. In addition, injection transformer
The voltage between the nearby tracks and the earth point of attachment OT detected by the high input impedance amplifier A _1, and applies the output of the amplifier A ₁ at line L _p which was allowed through the transducer ZCT, conductor lines L _p Is terminated by a variable resistor RV.

The conducting wire is passed through the current transformer so that a magnetic flux in the opposite direction to the magnetic flux induced in the current transformer by the measurement signal is generated.

In the circuit thus configured, the value of the variable resistor RV connected to the conducting wire is changed so that the value of the meter M is minimized, and the insulation resistance _R0 is determined from the resistance value of the minimized variable resistor RV. Measure.

Hereinafter, the principle of the present invention will be described in detail with reference to the drawings and mathematical expressions.

FIG. 2 shows an equivalent circuit for a system in which a current flows due to the applied low-frequency voltage for measurement in order to make the operation of the embodiment of FIG. 1 easier to understand.

That is γ in FIG. 2 is a ground resistance of a ground line L _E. R and C represent the total insulation resistance and total ground capacitance for the low-voltage paths 1 and 2, respectively. C = C ₁ + C ₂ + C ₃ + C ₄ , and C ₀ and R ₀ are the capacitance and insulation resistance of the load equipment in the home to be measured, and R ₀ , If necessary, C ₀ can also be measured.

₁ as the measurement signal in this figure, that is, shows the case where the oscillator OSC ₁ is selected will be described using the following equation taking this state as an example. When the voltage V ₁ of the frequency ₁ is applied to the electric path through the injection transformer, a frequency at this time
₁ of the leakage current I ₁ is Becomes Generally, the ground resistance γ is γ as compared with the insulation resistance R.
<< Because R is a formula (1) Where Substituting B ₁ = ω ₁ (C + C ₀ ) _γ gives the above equation (2) It can be expressed as.

The voltage E _{1 at} frequency ₁ between the electric circuit and the ground is And substituting the above (2) and rearranging Becomes Here, if B ₂ = ω ₁ C _γ is substituted, the above equation (5) becomes It can be expressed as.

By the way, the injected measurement signal voltage V ₁ is converted into a sine wave ν ₀ sin
If the current I ₁ when ω ₁ t is expressed as i ₁ , from equation (3) And the voltage E ₁ at this time is expressed as e ₁ Becomes

Thus amplifier A ₁ input terminal, for example, the ground-side electrical path L ₂ and ground
Connect between E _3, a voltage e ₁ obtained in the amplifier A ₁ output wire
Through L _p terminated by the variable resistor RV, the variable resistor of the current resistance value flowing through the conducting wire L _p When Rm is e ₁ / Rm, and the current transformer by measuring signal conductor lines L _p ZCT If the current is passed through the current transformer ZCT so that a magnetic flux in the opposite direction to the magnetic flux induced in the filter is generated, the filter FIL output can be calculated from the equations (7) and (8). Becomes

When the output of the filter FIL is rectified by the rectifier DT as shown in the figure, the output X becomes Becomes

As can be seen from the above equation (10), the minimum output input is And A ₃ , B ₂ , and B ₃ in equation (11) are re-substituted. It is. That is, Rm = _R0 , and the insulation resistance _R0 is measured from the value of the variable resistor that minimizes the output X.

FIG. 3 shows the relationship between the output X of the rectifier DT when the resistance value Rm of the variable resistor RV is changed. That is, the insulation resistance can be measured by the resistance value of the variable resistor when the indication of the meter M is minimum.

FIG. 4 is a block diagram showing a modified embodiment of the present invention. As shown in FIG. 4, a variable capacitor is connected in parallel with the variable resistor to a conductor passing through a current transformer.

By configuring the circuit in this way, the current i ₂ flowing through the conductor L _p is And the filter FIL output is i ₁ −i as in the previous embodiment.
_Because it becomes _2. It can be expressed as.

Further, when the output of the filter FIL is rectified by the rectifier DET of the next stage, the rectifier DET output X ₁ becomes And the output X is minimized according to equation (14). When ω ₁ Cm is eliminated from Eqs. (15) and (16), When A ₃ , B ₂ , and B ₃ in equation (17) are replaced, It turns out that it becomes.

That is, by adjusting the variable capacitor and the variable resistor so that the output X is minimized, the insulation resistance value R ₀ can be measured from the value Rm of the variable resistor.

The outputs of the amplifiers A ₁ and AMP also include commercial frequency components, but since they are removed by the filter FIL and do not affect the method of the present invention, these components have been omitted from the mathematical expressions.

Furthermore, the injection transformer OT and the current transformer ZCT are of a split type, and the probe for detecting the voltage between the electric circuit and the ground is a non-contact type, for example, a portable measuring instrument using the recently proposed "optical voltage sensor". can do.

Further, the single-phase three-wire system if one ground path has been described for the case of single-phase two-wire path in this embodiment may be a three-phase three-wire path or the like, the earth capacitance C ₀ It is clear that if it is necessary to replace the variable resistor RV with a variable capacitor CV and use a similar technique.

(Effects of the Invention) Since the present invention determines the insulation resistance by the method as described in detail above, the insulation resistance of a part of the multi-branched electric circuit or the load equipment connected to the part is reduced by another method. It can be accurately measured in a simple manner without being affected by parts, and is a particularly effective means for individually monitoring insulation in each household.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a measuring circuit according to the present invention, FIG. 2 is an equivalent circuit diagram of the electric circuit and the measuring circuit shown in FIG. 1, and FIG. 3 is a relation between a resistance value and an output. FIG. 4 is a view showing a modified embodiment of the present invention. T ...... trans, OSC ...... oscillator A _1, AMP ...... amplifier, FIL ...... filter, OT ...... injection transformer, ZCT ...... ZCT, DT ...... rectifier, M ...... meters, CV
…… variable capacitor, RV …… variable resistor.

Claims (2)

(57) [Claims] 1. A one end is coupled an injection transformer and current transformer to a required portion of the ground line, and the required portion and ground to apply a measuring signal comprising a frequency f ₁ via a infusion transformer wiring A voltage existing between the current transformer and the detected voltage is applied to a conductor terminated with a variable resistor, and the conductor is connected to a magnetic flux induced in the current transformer by a measurement signal applied to the wire. flux in the opposite direction is caused to penetrate the modified current transformer to produce the current transformer, further, the resistance value of the variable resistor such that the frequency f ₁ component is minimum contained in the current transformer output Adjusting the resistance value of the variable resistor, and measuring the insulation resistance of the wiring connected to the injection transformer and the current transformer from the required part of the wiring to the end of the wiring and the load equipment connected to the wiring. Simple insulation resistance measurement method for low voltage wiring etc. . 2. A method in which a variable resistor and a variable capacitor are connected in parallel instead of the variable resistor, and the injection transformer and the current transformer are coupled by adjusting the variable resistor and the variable capacitor. A simple insulation resistance measuring method for low-voltage wiring and the like, characterized by measuring the insulation resistance of a wiring at an end from a required portion of the stiffened wiring and a load device connected to the wiring.