JP3029070B2 - Microcurrent measuring device and method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a minute current measuring device for measuring a minute current flowing through an electric contact. The present invention also relates to a method for measuring a minute current in which a DC signal voltage is superimposed and applied to a high-voltage power cable under a live line and a leakage current is read by a minute current measuring device inserted between the shielded end of the cable to be measured and the ground.

[0002]

2. Description of the Related Art Conventionally, a configuration shown in FIG. 4 has been known as a minute current measuring device for measuring the insulation resistance of a cable to be measured. In FIG. 4, the side of the DC signal voltage device which is superimposed and applied to the AC voltage of the cable to be measured is not shown. measured cable 1 ₁ of the n, 1 ₂ ... input terminal F ₁ 1 _n read from the shielding end of the corresponding, F ₂ ... F _n via the changeover switch 2 ₁ provided corresponding to each cable , 2 ₂ ... 2 _n . This changeover switch may be a manual type or an electromagnetic contactor, and is the same in terms of circuit, and each output is led to one end of the series element 5. In configuration same respective changeover switch, for example, the changeover switch 2 ₁ input terminals F ₁
A normally open contact a1 is connected in series between the power supply and the series element 5, and a normally closed contact b1 is connected in parallel, guided to the terminal E, and grounded. Further, a normally open contact a2 is connected in parallel and led to a safety ground circuit including an arrester 3 and a capacitor 4. While the changeover switch 2 ₁ normally has a contact a1 closes contacts b1 a2 are opened, the cable 1 ₁ to be measured
There shielding edge is selected changeover switch 2 ₁ is opened the contact b ₁ when switched to the measurement position from the constant position is released from the earth connection. And contacts a1 and a2 is close to the verge to galvanically insulated by connecting the shield end to the safety ground circuit with connecting shielded end of the cable 1 ₁ in series element 5. In this case, although the current to be measured does not pass through the contact a2, the contact resistance needs to be low and stable.

[0003] The series element 5 comprises a choke coil or a resistor. A capacitor 6 is connected in parallel between the other end of the series element 5 and the ground.
And the contact RY2a of the relay 9 are connected in series and guided to the amplifier 10. The amplified current is guided to the power meter 11 and displayed. The output meter 11 may be an analog meter or a digital voltmeter capable of directly reading the insulation resistance value, and the output thereof may be read by a computer, calculated, and displayed as the insulation resistance value. The contact RY1a of the relay 7 is connected in series to the discharge resistor 8 and is led to the ground. Further, the contact RY2b of the relay 9 is guided to the anticorrosion layer insulation resistance measurement power supply 12 through the anticorrosion layer insulation resistance measuring circuit standard resistor 14 and the anticorrosion layer insulation resistance direct finger meter 13.

[0004] and the leakage small current DC signal voltage is applied to the cable 1 ₁ charges the capacitor 6 through the contact a1 and the series element 5 which charges the capacitor 4 via the contact a2, a further contact RY1b and RY2a The signal is displayed by the power meter 11 via the amplifier 10. When the corrosion resistance of the anticorrosion layer is measured, the contact RY2b of the relay 9 is closed, and the voltage from the power supply 12 is applied to the shield end via the RY2b, RY1b, the series element 5, and the contact a1, and the ground is formed as a return path. The minute current flowing in the circuit to be performed is read by the corrosion resistance layer insulation resistance direct indicator 13.

[0005] When the measurement of one cable is completed and the measurement is switched to the measurement of another cable, the contact RY1a of the relay 7 is closed to discharge the electric charge remaining in the measurement circuit and stored in the capacitors 4 and 6. The discharged charge is discharged via the discharge resistor 8.

[0006]

As described above, in the microcurrent measuring device, many electric contacts such as a contact of a changeover switch and a contact of a relay exist in a measuring circuit in series and in parallel. The microcurrent measuring device measures a microcurrent flowing through the electric contact, but has a problem that the contact resistance of the contact increases and becomes unstable.
If the current passing through the contact is extremely small and its backup voltage is close to zero, the instability of the contact resistance increases, causing a large noise voltage in the measurement circuit, and achieving the purpose of measuring leakage current. There was a problem that could not be done. The reason why the contact resistance increases and becomes unstable is mainly that an insulating film is formed on the contact surface by harmful components such as hydrogen sulfide existing in the surrounding atmosphere. Nevertheless, when used in a strong current circuit, the backup voltage of the circuit is large (generally, 5 V or more is required per contact) and the coating can be easily broken down, so that there is no practical problem. . However, as shown in FIG. 4, when a very small current of about microamps to nanoamps is measured and there is almost no backup voltage in the measurement circuit, a serious problem occurs.

The problem with the microcurrent measuring device of FIG. 4 is that the contact resistance of the series contact a1, the parallel contact a2 of the changeover switch, the contact RY1b of the relay 7, and the contact RY2a of the relay 9 increases and becomes unstable. It is. The contact resistance of the contact is usually about several tens of mΩ, but easily reaches several Ω to several KΩ when a film is formed on the contact surface.
5 and 6 are diagrams in which the noise generation phenomenon due to the contact surface coating is recorded by a recorder. To the FIG. 5 measured cable 1 ₂ not by applying a DC signal voltage, large pulse-like noise voltage at the output of the shielding and the ground and between the amplifier 10 is continuously observed. This is because the AC grounded by the capacitor 4 of the shielded cable 1 ₂ for contact imperfect parallel contact a2 is unstable. In such a state, it is not an environment where a DC signal voltage can be applied to measure the insulation resistance. In FIG. 6 for the cable ₁₉ , a drift phenomenon was observed in which the level increased with time due to irregular noise voltage mixing in the amplifier output. The reason for this is that not only the parallel contact a2 but also one of the series contacts has imperfect contact. Also in this case, it is not in a state where the insulation resistance can be measured.

In order to overcome the above-mentioned phenomena, all of the switches and relays must be replaced, only the contacts must be replaced, and the contacts must be polished or sprayed with a contact detergent. The effect could not be expected, and there was a defect that the phenomenon was always reproduced.

According to the present invention, there is provided a minute current measuring circuit in which a contact is present in series and in parallel so that a minute current can be measured in an environment in which the surface contact resistance of the contact is stabilized and the noise voltage is reduced. It is to provide a measuring device.

Also, the present invention provides a micro current measuring circuit used for measuring insulation resistance under a live line of a high-voltage power cable. An object of the present invention is to provide a minute current measuring method for measuring a current.

[0011]

A minute current measuring device according to the present invention is provided in a measuring circuit for measuring a minute current to be measured, and is connected to an electric contact through which the minute current passes to recirculate. A flushing power supply for supplying a large flushing current; a flushing start means for supplying a flushing current from the flushing power supply prior to the measurement of the minute current; and a flushing connection between the flushing power supply and the electrical contact. Refluxing means for temporarily configuring a circuit for circulating the current; and the flushing start means having a timer means for interrupting the flushing current after a predetermined time from when the application of the flushing current is started.

Further, according to the insulation resistance measuring method of the present invention, a DC signal voltage is superimposed and applied to a high-voltage power cable under a live line.
An insulation resistance measurement method that measures the insulation resistance of a high-voltage power cable by reading the small current that leaks through the insulation resistance of the high-voltage power cable using a small current measurement device inserted between the shielded end of the cable to be measured and the ground. Prior to the superimposition application of the DC signal voltage, an electrical contact installed in the minute current measuring device and through which the minute current passes is connected, and a flushing current larger than the minute current is refluxed for a short time, and Stabilizing the contact resistance of the contact.

[0013]

The flushing start means (a3, 16, 17, 1)
9), the electrical contacts (a1, RY1b, and RY1b,) existing in the microcurrent measuring circuit from the flushing power supplies (12, 15) via the return connection means (a2, RY3a1, RY3a2).
An environment in which an electric contact surface resistance is destroyed by applying a flushing current (a short-time energization) larger than the minute current to the RY2a) to stabilize contact contact resistance and reduce a noise voltage to enable measurement of a minute current. To appear. Further, the provision of the timer means automatically shuts off the flushing current after a predetermined time has elapsed.

Further, prior to the measurement of the leakage microcurrent in the insulation resistance measurement of the high-voltage power cable, a step of flowing a flushing current through the electric contact for a short time is performed, so that the environment in which the microcurrent can be measured is changed each time the insulation resistance is measured. can get. This prevents the inconvenience of returning to the original unstable state again by opening and closing the changeover switch, the effect of the flushing being temporary obtained by the inventor's experiment.

[0015]

FIG. 1 shows an embodiment of a micro-current measuring device for measuring insulation resistance under a live line of a high-voltage power cable. This embodiment is embodied based on the following knowledge and concept of the inventor. That is, the effect of the flushing is temporary with respect to the contact on which the insulating film is already formed, and once the changeover switch is opened and closed, the state returns to the original unstable state again. It is considered that this is because the contact position of the contact is slightly shifted each time the contact is opened and closed. For this reason, flushing must be performed immediately before each measurement. In addition, the current required for flushing is determined based on the time required for visually confirming the lighting of the flashing success confirmation lamp (for example, 2 seconds).
Several tens to several hundreds mA are desirable. However, as shown in FIG. 4, a choke coil or a resistor exists as a series element 5 of the low-pass filter in the measurement circuit.
2a etc. may exist separately. When power is supplied via the serial element, the output voltage of the flashing power supply is unnecessarily dropped by the serial element. In this case, two power supplies for flushing activated by the reflux connection means (a3, RY3a1, RY3a2, etc.) may be provided separately, or a series element may be short-circuited during flushing to make all target contacts collective. It is necessary to construct a circulation circuit. Furthermore, it is safe if there is a display indicating that the energization was successful by breaking the insulating coating of the contact.

In FIG. 1, reference numerals 1 to 14 are the same as corresponding elements shown in FIG. Usually it is connected to an auxiliary contact a3 in the open state so as to change-over switch 2 _1, 2 ₂ ... 2 _n is exemplified by the changeover switch 2 _1. The auxiliary contact a3 is originally utilizing contacts idle state changeover switch 2 ₁ owns. The auxiliary contact a3 is connected to an alternating current (AC) low voltage power supply by a power supply 1 for flashing.
Opening / closing of a primary circuit connected to 5 is performed. The flushing power supply 15 is activated when the auxiliary contact a3 is closed and an AC low-voltage power supply is applied, passes through the current limiting resistor 18 via the contacts a2 and a1, which are closed at the same time as the auxiliary contact a3.
, Ie, a circuit for recirculating the flushing current. A timer 16 is connected to the primary circuit of the power supply 15 and is driven simultaneously with the closing of the auxiliary contact a3. The contact 17 is opened after a lapse of a predetermined time (for example, 2 seconds) so that the flushing power supply 15 is not operated unnecessarily. Fifteen
Is inactive. The flushing current flowing through the contact is larger than the minute current to be measured, and its absolute value is on the order of mA. The timer 16 is reset when the changeover switch is returned to the normal position, and waits for the next cable measurement. A relay 19 is connected to both ends of the current limiting resistor 18 and operates when the output voltage of the flushing power supply 15 becomes substantially equal to the output voltage.

One contact RY3a2 of the relay 19
Is connected between the connection point between the relay 7 and the series element 5 and the ground. The other end RY3a1 of the relay 19 has one end connected between the relay 9 and the amplifier 10 and the other end led to the anticorrosion layer insulation resistance measuring power supply 12 through the current limiting resistor 20. The relay 19 operates when a voltage substantially equal to the output voltage of the flushing power supply 15 is applied to both ends thereof, and closes the contacts RY3a1 and RY3a2. Then, the power supply 12 for measuring the anticorrosion layer insulation resistance is used as a power supply for temporary flushing, and the current limiting resistor 20 and the contact R
Y3a1, contact RY2a, contact RY1b, contact RY3a
A return circuit for the flushing current flowing back to the power supply 12 via the power supply 2 is formed. When the flushing is successful, the output voltage of the power supply 12 almost appears at both ends of the current limiting resistor 20,
The light emitting diode 21 is turned on by the divided voltage.

[0018] Using the minute current measuring apparatus of FIG. 1 under live wire from the constant position selector switch 2 ₁ to be measured cable 1 ₁ immediately before the insulation resistance measurement when measuring the insulation resistance of the cable Switch to measurement position. Then, the contact points a1,
a2 and a3 are closed, the contact b1 is opened, the power supply 15 for flushing is operated, and the flushing current flows through the circulating circuit composed of the current limiting resistor 18, the contacts a1, a2 and the power supply 15, and flows to the surface of each contact. Destroy the resulting insulating coating.
When the flushing is successful, the relay 19 is operated by applying a voltage substantially equal to the output voltage of the power supply 15, and the contacts RY3a1 and RY3a2 are closed. Then, the contact points RY3a1, RY2a, RY1b, and RY
A flushing current flows from the power supply 12 via the circulating connection 3a2. By switching in this way the change-over switch 2 ₁ to the measurement position, the flushing each runs automatically stampede expression for contact group present in the right and left as a boundary series elements 5. Finally, when the two flushings succeed, the light emitting diode 21 lights up to notify the success. The timer 16 opens the contact 17 after a set time, and as a result, the relay 19 is deenergized and the contact RY3a
1 and RY3a2 are opened, and the light emitting diode 21 is turned off.

The above operation has forcibly eliminated the instability of the contact resistance that may have been present at each contact and provided an environment with low noise voltage required for insulation resistance measurement. Thereafter, normal insulation resistance measured for the cable 1 ₁ is performed. In each case of measuring the insulation resistance of another cable, the flushing current is applied immediately before the measurement to remove the instability of the contact resistance.

[0020] Figures 2 and 3 are views recorded noise stable environment configuration status in the case of measuring the insulation resistance of the cable 1 ₂ and 1 ₉ after flushing the apparatus of Figure 1, conventional in FIG. 5 and FIG. 6 respectively. 2 and 3 clearly show that the noise voltage has been removed. Insulation resistance measurement results, it was confirmed both cable 1 _1, 1 ₉ are both 5000MΩ more excellent.

In the above embodiment, the power supply 12 for measuring the corrosion resistance of the anticorrosion layer is used as the power supply for flushing at the subsequent stage of the series element 5. However, a separate dedicated power supply may be provided. Further, the flushing power supply 15 may have a dual-purpose duty, but in this case, it is necessary to pay attention to the operating potentials and polarities of both circuits.

[0022]

According to the present invention, there is provided a micro-current measuring device comprising: a flushing start means; and a flashing start means, provided that the contact resistance of electric contacts existing in series and in parallel in a circuit increases and becomes unstable or may become unstable. Through the operation of the reflux connection means, a flushing current larger than a very small current is passed from the flushing power supply through the reflux circuit connecting the electrical contacts, thereby reducing or stabilizing the contact resistance therapeutically or prophylactically, and reducing the noise voltage. Reduction can be achieved. Therefore, it is possible to eliminate the trouble and cost of replacing or polishing the contacts as in the related art, and to eliminate the instability caused by the contact resistance by removing the fundamental defect of always reproducing. Further, since the present invention includes the timer means, the power of the flushing power supply is not wasted.

Also, the method of the present invention includes the step of flowing a flushing current through the electrical contact before measuring the insulation resistance when measuring the insulation resistance of the high-voltage power cable under a live line. The insulation resistance can be measured under a stable environment in which the noise voltage generated from the contact resistance is reduced.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

[Figure 2] Voltage recording view after observed flushing the measurement target cable 1 ₂ using the apparatus of FIG.

FIG. 3 is a voltage recording diagram after flushing observed for a cable to be measured ₁₉ using the apparatus of FIG. 1;

FIG. 4 is a circuit configuration diagram showing a conventional minute current measuring device.

[5] voltage recording showing the presence of the observed noise voltage to be measured cable 1 ₂ using the apparatus of FIG.

FIG. 6 is a voltage recording diagram showing the presence of a noise voltage observed on the measurement target cable 19 using the apparatus of FIG. 4;

[Explanation of symbols]

1 ₁ to 1 _n Measurement target cable 2 ₁ to 2 _n switch 5 Series element 7 Relay 9 Relay 12 Corrosion protection layer insulation resistance measurement power supply 15 Flushing power supply 16 Timer 19 Relay a1, a2, a3, b1, RY1a, RY1b, RY1b, RY2
a, RY2b, RY3a1, RY3a

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) G01R 19/00-19/32 G01R 27/16 G01R 31/02 G01R 31/12

Claims (2)

(57) [Claims] 1. A flashing power supply which is provided in a measuring circuit for measuring a minute current to be measured and which supplies a flushing current larger than the minute current, which is connected to an electric contact through which the minute current passes, and Prior to the measurement of the current, a flushing start means for supplying a flushing current from the flushing power supply, and a reflux connection for temporarily forming a circuit for connecting the flushing power supply and the electric contact to reflux the flushing current. A minute current measuring device, characterized in that the flushing start means comprises timer means which works to cut off the flushing current a predetermined time after the flushing current is started to flow. 2. A DC signal voltage is superimposed and applied to a high-voltage power cable under a live line, and leaks through an insulation resistance of the high-voltage power cable by a minute current measuring device inserted between a shielded end of a cable to be measured and the ground. In an insulation resistance measuring method for measuring the insulation resistance of a high-voltage power cable by reading an incoming minute current, prior to superimposing application of the DC signal voltage, the minute current is installed in the minute current measuring device and the minute current passes. and lined with electrical contacts, the greater flushing current than minute current refluxed briefly, and performing a stabilization of the contact resistance of the electrical contact, the insulation resistance measurement method.