JPS63289464A - Insulation resistance measurement compensated for phase - Google Patents

Abstract

PURPOSE:To enable correction of a phase deviation of a measuring signal at all times without requiring a costly part, by permitting automatic adjustment of a phase against variations in phase characteristic of an insulation resistance measuring circuit. CONSTITUTION:An AC signal voltage with a frequency f1 is inputted into an electric circuit through an earth wire of a transformer or through a current transformer connected to the electric circuit. Currents for measuring phases with frequencies f1-fS and f1+fS (f1>>fS) respectively are inputted anew through a connection wire piercing the current transformer. Phase of the AC signal voltage with the frequency f1 necessary for detection of a leakage current compo nent gained from the current transformer synchronizing the AC signal voltage is adjusted automatically so that a component of the frequency fS becomes zero as contained in an output obtained from the synchronous detection. Then, phase deviations caused among equipment of an insulation resistance measuring apparatus are made up for thereby enabling compensation for insulation resis tance of the electric circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of compensating for temperature changes, secular changes in circuit constants, etc. of a device that measures the insulation resistance of electrical circuits or the like in a live line state.

(Prior Art) Conventionally, it has been common practice to monitor the condition of an electrical circuit using a method of measuring the insulation resistance of the electrical circuit as shown in FIG. 2, for example, in order to detect troubles in the electrical circuit such as leakage at an early stage.

This is done by passing the grounding wire LE of the power receiving transformer T having the load Z through the transformer OT connected to the low frequency signal oscillator O8C having a frequency J1 different from the commercial power supply frequency, or by passing the grounding wire LE in series with the grounding wire LE. A low frequency voltage is applied to the electrical circuits 1 and 2 by inserting and connecting an oscillator, etc., and the insulation resistance Ro and ground stray capacitance that exist between the electrical circuit and the ground are reduced by the zero-phase current transformer ZCT that penetrates the grounding wire LE. C.O.
After detecting the leakage current caused by the low frequency voltage that returns to the ground line via the amplifier AMP and amplifying it with the amplifier AMP, only the component of frequency j1 is selected by the filter FIL, and this is transmitted to the oscillator O8C, for example. The output signal is used for synchronous detection with a multiplier MULT to detect the effective component of the leakage current (that is, the component in phase with the applied low-frequency voltage), thereby measuring the insulation resistance of the Mi circuit. Ta.

To help understand the present invention, the measurement theory thereof will be further explained.

If the low frequency signal voltage applied to the ground line LE is a sine wave, for example, V sinωlt (ω1=2π, fl), then the frequency f that returns to the ground line Lx via the ground point E is
The leakage current I of l is expressed as and is a component in phase with the applied AC voltage.

In other words, if a value proportional to the first term on the right side of equation (1) is detected by means such as synchronous detection, the value will be inversely proportional to the insulation resistance RO. can be found.

However, in the conventional method, the leakage current that returns to the grounding wire is detected by the current transformer ZCT, and the leakage current component of the frequency f1 included in the zero-phase current transformer output is selected and outputted by the filter FIL. Normally, the phase of the leakage current at frequency fl shifts in the current transformer->amplifier->filter system, so it is necessary to compensate for this phase shift in order to obtain a value inversely proportional to Ro from these synchronous detection outputs.

For this purpose, as shown in the figure, the first
A fixed phase shifter PS is inserted into the input end or the second input end of the phase shifter PS, thereby correcting the phase shift and achieving mutual synchronization. That is, by providing the phase shifter PS with the phase shifter PS, the first . The phase difference between the voltages applied to the second input terminal was set in advance to be zero.

However, in the conventional method as described above, the current transformer ZCT
The phase characteristics of the filter FIL, phase shifter PS, etc. change due to changes in temperature or changes in the characteristics of the parts used over time. As a result, a phase error with the initial setting value occurs, making it impossible to provide accurate results. There was a drawback that would go away. To deal with these problems, the effects of phase errors have traditionally been minimized by using extremely high-quality current transformers or filters with little characteristic variation, but it is still difficult to completely eliminate the effects. Met.

(Object of the Invention) The present invention has been made in order to eliminate the drawbacks of the conventional insulation resistance measurement method as explained above, and is capable of constantly correcting the phase shift of the measurement signal at low cost without requiring expensive parts. The purpose of the present invention is to provide an insulation resistance measurement method that can always provide accurate measurement results.

(Summary of the Invention) In order to achieve this object, the present invention inputs an alternating current signal voltage of frequency f1 to an electric line via a grounding line and via a current transformer coupled to the electric line, and also newly inputs an alternating current signal voltage to the current transformer. Frequency f1-fs as well as frequency fl+,
f's (where ft>fs) is input, and the output obtained by synchronously detecting the leakage current component obtained from the current transformer and the AC signal voltage. The phase of the AC signal voltage of frequency f1 necessary for synchronous detection is automatically adjusted so that the component of frequency fs contained in This compensates for the insulation resistance of the electrical circuit.

(Example of the invention) The present invention will be described in detail below based on the illustrated embodiments.

First, before explaining the measuring method according to the present invention, the conventional method and its drawbacks will be explained in some detail to aid understanding.

The leakage current component of frequency f1 shown by equation (1) is current transformer ZCT and amplifier AMP in FIG.

The phase shift that occurs when passing through the filter FIL system is θ
Then, the filter FIL output ■1 is...
(2) This is applied to the first input of the synchronous detector MULT.

Further, the voltage applied to the second input terminal of the multiplier MULT is set to, for example, a constant amplitude a. 5in (ω1t+01), the output of the multiplier M[JLT2 is (□ means to remove the component with an angular frequency of 01 or more -) (4) Therefore, θ= Since the output Do when θl is constant, the insulation resistance R is +■+ao.

A value that is inversely proportional to can be measured. Therefore, the above is true when the phase shift θ-01 is not zero.

The error E of D is = l −cos (θ−θ1)−ωIC0ROsin
(θ-01)...(6).

Now, in order to examine the influence of phase shift, for example, if the phase error is θ-θ1-1 (degrees), fl=25 in equation (6).
Hz, when Ro=20 and ΩyCo=5〃F, ωx
coRo? 15.7, but the error ε is 27.4 inches, indicating that the measurement error becomes significantly large.

The present invention proposes a method for suppressing the occurrence of errors due to the above-mentioned phase shift as much as possible.

FIG. 1 is a circuit diagram showing an embodiment of the insulation resistance measuring method according to the present invention, and the same symbols as in FIG. 2 have the same meanings. That is, in the same figure, T is a transformer, 1 and 2
is the secondary side low current circuit of this transformer, and the second
A grounding wire LE that has undergone preliminary grounding work is connected. A transformer OT and a current transformer ZCT are coupled to the ground line LE,
The output end of the current transformer ZCT is connected to one input end of a synchronous detector MULT1 via an amplifier AMP1 and a filter FIL, and the other input end of MLILT1 is connected to one end of a phase control circuit PC. Furthermore, the current transformer ZCT includes a phase control circuit PC, a multiplier MULT2, an amplifier AMP2, and a resistor r.

The connection is made via the connection line 3 which is connected to the . Said MLILT2
The other input terminal of the 90° phase shifter P is connected to the phase control circuit PC.
The phase control circuit PC is connected to the primary side of the transformer OT via a power amplifier PAMP. On the other hand, M
The output end of IJLTI is connected to phase control circuit PC via filter BP and rectifier DET. Note that the phase control circuit PC has a signal oscillation source with frequencies f1 and fs and a phase control device.

The operation of each device and the function of each block in the circuit configured as described above will be explained in detail below using mathematical formulas.

A signal acO5ωs (a+5==2jrf5
), and a signal e having a frequency f1 is input to the other input terminal of the MULT2 through the phase control circuit PC and the 90° phase shifter PS. When cosω1t is input, the multiplier ML
The output e of ILT2 is e=aeocosω1t11ωSωst= ]1(co
s (ω1yus)t+ω5(ω1→5)tJ...
...(7).

Therefore, the current 1' flowing from the output of the amplifier AMP2 to the connection line 3 is: ■'=□ O e = < (cos (ω1-1-6+5)i+ωS(ω
1"-"5) tJ -・-・-(81) On the other hand, by applying a voltage of Vsinω1t to the ground line LE via the phase control circuit PC, the bias power amplifier PAMP, and the transformer OT, the current transformer ZCT As the output, a leakage current component I corresponding to the equation (2) and a current I' corresponding to the equation (8) inputted via the connection line 3 are obtained.

When the output current I+I' of the current transformer ZCT is input to the filter via the amplifier AMP, the output of the filter FIL becomes the current I+1' with a phase shift caused by the amplifier AMP and the filter F I L.

If the above I+I' is IO, then Io is t10-1)]... (9) Here, θ1 and θ-1 are current transformer ZCT → amplifier AMP → filter FIL at frequencies f1+fs and fl-fs. is the amount of phase shift in the system.

The filter output current (1)0 is input to one input terminal of the synchronous detector M[JLTl, and the other input terminal is connected to the phase control circuit PC and an alternating current voltage a having a frequency f1. If sin (ωft+θ') is input, the output D' of the synchronous detector MLILTI is a component below the frequency fs.

θ' is the amount of phase shift for phase compensation) -2 C(sin(-ωst+L1-0')+sln
(mst 10θ□−θ′ month...... (9) By the way, since ωS(ω1), it can be approximated, and by substituting the (conversion) equation into the C111 equation, (!
-Nyosha ae, a, sin (θ-θ') cos
(ωs t 10-sheiko)・・・・・・・・・ (
2) It becomes. When θ = θ', the frequency fs component of the second term is zero, as is clear from equation (to)).Furthermore, the DC component of the synchronous detector output D' expressed by the first term is the original multi-current circuit. You can find out how to measure the insulation resistance of That is, the synchronous detector M
The frequency fS component in the output θ' of ULTI is filtered by filter B.
P, the output is rectified by a rectifier DET, and a phase control circuit P is set so that the DC component of the output of the rectifier DET becomes zero.
Voltage a input from C to synchronous detector MIJLTI. sI
If the phase shift amount θ' for phase compensation of I+ (ω1 is 10θ′) is automatically adjusted, it is possible to measure the insulation resistance of the electric circuit without being affected by the phase shift amount 0.

Also, as shown in Fig. 3, the output D of the synchronous line detector MLILTI
′ and the voltage Bcosωst input from the phase control circuit PC to one input terminal of the multiplier MULT2 are further applied to the multiplier MLIL.
By inputting the respective input terminals of T3, the corresponding ML]LT3
For the output D I+, D” = D' x acoSωsi0□−θ−
1 rtrs, J, this DC component do is ωS (when ωl, cos-L-1≧1, so θ
〉θ′, do<O, when θ×θ′, d
If o>0, it is possible to determine the control direction of the phase θ' by measuring the DC component do.

In the above explanation, when performing phase adjustment), the phase of the signal applied to the second input of the synchronous detector is adjusted, but the phase of the filter FIL applied to the first input of the synchronous detector is It is clear that the same result can be obtained by adjusting the phase of the output signal.

Furthermore, the frequencies fx+fs and fx-fs sent to the connection line 3
In order to obtain a current of It is clear that by providing a current having a frequency fl+fs and fl-fs, it is possible to generate a current having a component that applies the frequencies fl+fs and fl-fs.

In addition, although the above example shows the case of a single-phase two-wire electric circuit,
It may be a single-phase three-wire electric circuit or a three-phase three-wire electric circuit.

(Effects of the Invention) As explained above, the present invention enables automatic phase adjustment of fluctuations in phase characteristics of an insulation resistance measuring circuit, and is therefore very effective in realizing an extremely stable measuring method. .

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a block diagram showing a conventional method for measuring insulation resistance, and Fig. 3 is a block diagram showing an embodiment of the present invention.
The figure is a block diagram showing a modified embodiment of the present invention. T......Trans, 1,2...
...Electric circuit. LE・・・・・・Ground wire, E・・・・・・
...Grounding point. ZCT・・・・・・・・・Current transformer, AMP・-
・・・・・・Amplification i, FIL・・・・・・
···filter. MULT, MULTl, MTJLT2, MTJLT
3-...0. .・・・Multiplier circuit, OT・・・・・・・Input transformer PS・・・・・・・Phase shifter, PC
...... Phase control circuit, BP...
······filter. DET・・・・・・・・・ Rectifier circuit. Patent applicant: Toyo Tsushinki Co., Ltd. Figure 3

Claims (1)

[Claims] Input an alternating current signal voltage of frequency f_1 to the electric line through the grounding line of the transformer or to the electric line via a current transformer coupled to the electric line, and detect the leakage current component of frequency f_1 that returns to the grounding line. In the method of measuring the insulation resistance between the electrical circuit and the ground from the output obtained by synchronously detecting the current transformer using the AC signal voltage, the frequencies f_1-f_s and Frequency f_1+
In the output obtained by applying a phase measuring current of f_s and synchronously detecting the leakage current component that returns to the ground wire and the AC signal voltage, the frequency component of the frequency f_s included in the output approaches zero. A method for measuring insulation resistance with phase compensation, characterized in that the phase of the alternating current signal voltage is adjusted.