JPH0690246B2 - Signal generation method for measurement of insulation resistance measuring device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a measuring signal generating method for an apparatus for measuring the insulation resistance of an electric circuit or the like in a live state.

[Conventional technology]

 FIG. 2 shows a conventional insulation resistance measuring method.

The commercial frequency signal is detected from the electric line by the signal detection unit and divided by the frequency dividing circuit. The frequency division number is always constant, and generally, the measurement signal after frequency division is set so as to be between 10 Hz and 20 Hz. This is 20
This is because when the frequency is higher than Hz, high performance is required for the attenuation characteristic of the filter that removes the commercial frequency component described below, and when it is 10 Hz or lower, the conversion efficiency of the injection transformer described later deteriorates. The measurement signal is applied to the ground wire by the injection transformer via the power amplifier.

The amplitude of the applied voltage of the measurement signals A, current I _gr1 and the current I _gc1 flowing through the earth capacitance C _g through an angular frequency of the measurement signal in the insulation resistance R _g as ω is given by equation (1).

However, X _cg is the reactance of the electrostatic capacitance C _{g to} the ground. Similarly, the amplitude B of the ground voltage of the commercial frequency circuit is
Current flowing in the insulation resistance R _g as the current I _gc2 and the electrostatic capacitance C _g
The current I _gc2 flowing in is given by equation (2).

After the vector sum of the currents given by equations (1) and (2) is fed back to the ground line and detected by the current transformer, the output voltage that passes through the filter is the phase of the current transformer of the measurement signal frequency and the filter. The delay is ψ ₁ , and the in-phase delay of the commercial frequency is ψ _2. Becomes However, the proportional constants K ₁ , K ₂ , K ₃ , and K ₄ of the amplitude are related to the current conversion rate of the current transformer, the passband gain of the filter part, the stopband gain, etc. and are complicated when expressed by an identity, so it is easy. It is expressed as shown in equation (4).

Synchronous rectification of the voltage of the vector sum of the voltages shown in equation (3) at the measurement signal frequency and smoothing by the smoothing section is equivalent to integration of the equation at one cycle of the measurement signal frequency, so the smoothed output is (4 ) It becomes like a formula.

(Smooth output of I _gr1 component) (Smooth output of I _gc1 component) (Smooth output of I _gr2 component) (Smooth output of I _gc2 component) That is, the signal of the commercial frequency component becomes “0” when synchronously rectified with a signal obtained by dividing the commercial frequency.

Further, by correcting the phase delay amount ψ ₁ by the current transformer and the filter unit of the measurement signal frequency on the synchronization signal side by the phase correction unit, ψ ₁ in the equation (4) can be set to “0” (4 )ceremony The output is proportional to the insulation resistance.

[Problems to be solved by the invention]

However, when the commercial frequency is different, the frequency division number is constant, so that the measurement signal frequency also changes and the phase delay ψ ₁ of the current transformer and the filter unit also changes.

Therefore, the smoothed output of the I _gc1 component does not become “0” and an error occurs. Therefore, there is a drawback that the phase must be corrected every time the commercial frequency is different. Further, a change in the measurement signal frequency proportional to the difference in the commercial frequency appears as a difference in the conversion efficiency of the injection transformer and the current transformer.

Since the difference in conversion efficiency is the difference in amplitude, there is a drawback that the circuit constants of the filter section and the amplification section must be changed.

It is an object of the present invention to solve the above problems and to economically manufacture an insulation resistance measuring device.

[Means for solving problems]

From the result of the equation (4), it should be noted that the frequency division number n of the commercial frequency may be a natural number of 2 or more in order to make the signal of the commercial frequency component zero by integrating it in one cycle of the measurement signal frequency. , A circuit that keeps the measurement signal frequency constant for all commercial frequencies that are likely to be used, and the measurement signal frequency is always 1 / n of the commercial frequency (where n is a natural number of 2 or more) ) And decided to try to solve the problem.

That is, since the measurement signal frequency is constant with respect to the change of the commercial frequency, the phase correction may be constant, and further, since there is no difference in the conversion efficiency of the injection transformer and the current transformer, the circuit constants of the filter and the amplification unit are constant. Can be a constant value.

Further, since the measurement signal frequency is 1 / n of the commercial frequency (where n is a natural number of 2 or more), the function of removing the commercial frequency component in the synchronous rectification unit and the smoothing unit is the same as the conventional one. When 50Hz, 60Hz, and 400Hz are used as commonly used commercial frequencies, the measurement signal frequency is 1/5 of 50Hz and 1 of 60Hz.
/ 6, 10Hz which is 1/40 frequency of 400Hz is considered.

〔Example〕

A circuit for implementing the above means will be described with reference to the block diagram shown in FIG. By providing multiple circuits for dividing the commercial frequency and switching the output with electrical contacts such as analog switches or mechanical contacts such as relays and switches, a constant measurement signal frequency can be maintained against changes in the commercial frequency. obtain.

As a method of switching contacts, commercial frequency is constantly measured,
A method of automatically switching in response to the change of the commercial frequency is conceivable, but a method of manually switching may be used. Because the commercial frequency is generally constant for each insulation resistance measurement circuit,
This is because it is unlikely that the commercial frequency will change after the insulation resistance measuring device is installed. Also, as another implementation method, the first
There is a method shown in FIG. This is a programmable frequency division IC that is generally commercially available for circuits that divide the commercial frequency.
This is a method of arbitrarily setting the frequency division number by using a programmable frequency dividing circuit using. The frequency division number is set using electrical or mechanical contacts. A constant measurement signal frequency is obtained by defining the frequency division number for each commercial frequency and setting the frequency division number in accordance with the commercial frequency of the insulation resistance measuring device installation circuit. Since the measurement signal frequency becomes constant, the current conversion rate and phase delay of the injection transformer and the current transformer for detection, as well as the passband gain and phase delay of the filter section, become constant with changes in the commercial frequency. Becomes Therefore, it is not necessary to perform the phase correction and the change of the circuit constants of the filter unit and the amplification unit, which are conventionally performed every time the commercial frequency is different, and the economical efficiency and the workability of manufacturing are improved.

〔The invention's effect〕

(1) Since the insulation resistance measuring device, which has been conventionally adjusted only for a specific commercial frequency, can be used at an arbitrary commercial frequency, the product model can be reduced and the product inventory can be reduced.

(2) Since the measurement signal frequency becomes constant, adjustment work and work procedure can be simplified.

(3) At the same time, the circuit constants of the filter section, the amplification section, etc. become constant, and the economical efficiency improves.

[Brief description of drawings]

FIG. 1 (a) is a block diagram showing an embodiment of an insulation resistance measuring device using a method of providing and dividing a plurality of frequency dividing circuits in the present invention. FIG. 1 (b) is a block diagram showing an embodiment of an insulation resistance measuring apparatus using a method of providing a programmable frequency divider in the present invention. FIG. 2 is a block diagram showing a conventional insulation resistance measuring device.

Claims (1)

[Claims] 1. A grounding wire of a transformer through an injection transformer,
A measurement signal voltage obtained by dividing the commercial frequency is applied, and a leakage current component of the measurement signal returned to the ground line is detected by a current transformer coupled to the ground line, and synchronous rectification is performed by the measurement signal. Thus, in the device for detecting the component due to the insulation resistance in the leakage current component, a plurality of circuits for dividing the commercial frequency are provided and switched by an electric type or mechanical contact, or an arbitrary frequency dividing number is changed by an electric type. Or
A method for generating a measurement signal for an insulation resistance measuring apparatus, which is capable of generating a low frequency signal voltage for measurement at a constant frequency at any commercial frequency by providing a circuit set by mechanical contacts.