JPH0143654Y2 - - Google Patents

Description

[Detailed description of the invention] The invention consists of an overcurrent cutoff device that cuts off the application of a test voltage when the current flowing through the object to be measured exceeds a set amount, and an overcurrent cut-off device that cuts off the application of the test voltage to the object to be measured. The present invention relates to a dielectric strength tester that measures dielectric strength or insulation resistance and is equipped with a so-called touch sensor that detects whether the test is being performed normally.

Attaching a touch sensor to a DC or AC withstand voltage tester is prohibited in accordance with Utility Model Publication No. 57-11262 and Utility Model Publication No. 57-11262.
11263, and according to this, by detecting a minute alternating current corresponding to the alternating current voltage applied to the object to be measured, the state of contact of the high-voltage test line to the object to be measured or the presence or absence of a disconnection can be detected using a lamp. This can be confirmed using an OK display circuit, etc.

Therefore, it is an object of the present invention to provide a dielectric strength tester of the type mentioned at the beginning which is further improved and equipped with a touch sensor having a simple circuit configuration.

Next, the present invention will be explained based on the illustrated embodiments.

Figures 1 and 2 show an embodiment in which the present invention is applied to an AC withstanding voltage tester. a high voltage transformer serving as a source, 3
is an AC voltmeter that measures the output voltage, 4 is an overcurrent cut-off device inserted into the ground line of the test voltage source, and 4' is an attached device that measures the input voltage of the test voltage source, for example, 100V commercial A relay contact for cutting off the power supply; 5 is a minute alternating current detection part that constitutes a touch sensor together with a part of the circuit of the overcurrent cutoff device 4;
6 is a high voltage side lead wire (line) that can be configured as a high voltage probe, 7 is a ground side lead wire,
Reference numeral 8 denotes an object to be measured (in this embodiment, lead wires 6 and 7 are connected to the primary and secondary terminals of a transformer, respectively).

As shown in more detail in FIG. 2, the overcurrent cutoff device 4 is connected between a changeover switch 11 for switching the set amount of cutoff current, a test voltage source, that is, a high voltage transformer 2, and an object to be measured. a group of resistors 12 inserted in series to the ground side line and each having a value selected to exhibit the same level of voltage drop with respect to the measured current corresponding to the set amount; and a varistor 13 for protection against overvoltage input; Resistor group 12
Among them, an amplifier 14 receives as input the voltage drop generated in the resistor selected by the changeover switch 11, a rectifier/smoothing circuit 15 for its amplified output, and a comparator 16 for comparing its DC output with a reference level.
and a drive circuit 17 using, for example, a thyristor, which holds the relay contact 4' in an open state based on the comparison output. Further, the minute AC detection unit 5 compares the amplified output of the amplifier 21 for the DC output of the rectification/smoothing circuit 15 with a reference level, and uses the comparison output to detect the light emitting diode 2.
3, and a comparator 22 that drives 3.
The resistance value of each resistor group 12 and the gain of the amplifier 14 are such that the measurement current is, for example, 0.5 mA to 0.5 mA.
If a predetermined amount selected in the range of 100mA is exceeded,
The output level of the rectifier/smoothing circuit 15 is set to exceed the reference level of the comparator 16. On the other hand, the gain of the amplifier 21 is such that when a minute AC of, for example, 5 μA flowing through the distributed capacitance Co of the object to be measured 8 flows through the minimum resistance of the resistor group 12, the DC output of the rectifier/smoothing circuit 15 The signal is set to such an extent that it can be further amplified and exceed the reference level of the comparison circuit 22. As a result, the voltage gain of the touch sensor is the product of the gains of both amplifiers 14 and 21.

During operation, the AC voltage set by the sliding transformer 1 is applied from the secondary side of the high-voltage transformer 2 to the object to be measured 8, and if the contact state between the lead wires 6, 7 and the object to be measured 8 is normal. For example, a minute alternating current causes a voltage drop in the resistor group 12 through the distributed capacitance Co. Normally, this current is 5 μA or more for an applied voltage of 1 KV, assuming that the capacitance of the device under test 8 is at least 20 pF, and the corresponding voltage drop is
4 and appears as a DC voltage at the output of the rectifier/smoothing circuit 15. Since this DC voltage is sufficiently lower than the level corresponding to the 0.5 mA to 100 mA which is the cut-off current, it does not reach the reference level of the comparator 16, and is further amplified by the amplifier 21, so that the voltage is applied to the comparator 22. exceeds the standard level. Therefore, the light emitting diode 23 emits light,
It is reported that high voltage is normally applied to the object to be measured. In this state, the high voltage is increased while being monitored by the voltmeter 3, and when the measured current exceeds the predetermined amount selected by the changeover switch 11 during the measurement process, the DC output level of the rectifier/smoothing circuit 15 changes to the comparator 16.
exceeds the reference level, and the drive circuit 17 maintains the relay contact 4' in an open state based on the comparison output.
On the other hand, if the light emitting diode 23 does not emit light because the minute alternating current does not flow, it can be seen that the lead wires 6 and 7 are disconnected or have poor contact.

In addition, when the minute alternating current detection part 5 is configured to operate with an alternating current input, the amplifier 21 is made to directly follow the amplifier 14. Further, it is convenient if the gain of the amplifier 21 is adjustable in accordance with the object to be measured, that is, its distributed capacitance and the test voltage. Furthermore, if the touch sensor is incorporated into an OK display circuit that applies a test voltage for a predetermined period of time and displays a lamp display if there is no abnormality, instead of using a lamp, the output of the comparator 22 drives a relay and To enable an OK display circuit to operate only when alternating current is detected.

Figure 3 shows an embodiment in which the present invention is applied to a DC withstand voltage tester, in which a diode 31, a smoothing capacitor 32 and a discharge resistor 33 are connected to the secondary circuit of the high voltage transformer 2 in Figure 1. For example, a high voltage rectifier circuit consisting of a high voltage rectifier circuit and a transformer 35 supplied with power from a 2KHz oscillator 34 are added, and the voltmeter 3 is replaced with a direct current one. In this case, the rectifier/smoothing circuit 15 of the overcurrent shielding device 4 becomes unnecessary, so the amplifier 21 of the minute alternating current detection section 5 directly follows the amplifier 14. When the lead wires 6 and 7 are in normal contact with the object to be measured 8, the high frequency current supplied from the transformer 35 flows through the distributed capacitance Co, and therefore the amplifier 14 has a level corresponding to this minute alternating current. An amplified output is generated, which has no effect on the comparator 16 in terms of level, but is further amplified in the minute alternating current detection section 5 to cause the light emitting diode 23 to emit light at a high frequency. In order to ensure reliable operation, a high frequency blocking circuit may be provided at the input terminal of the comparator 16, and in some cases, a high frequency rectification/smoothing circuit may be provided in the minute alternating current detection section 5.

In FIGS. 1 and 3, the overcurrent cutoff device 4 is inserted into the ground line, but depending on the level of high voltage, it may be inserted into the high voltage line, that is, the high voltage lead wire 6. The circuit according to FIG. 2 can also be constructed floating above ground. The present invention also provides an insulation resistance meter with an overcurrent shield device that applies a DC test voltage to the object to be measured and measures the insulation resistance based on the measured current, as shown in Fig. 3, particularly a super insulation resistance meter. It is also applicable to

As described above, according to the present invention, by inserting an overcurrent cut-off device into the test voltage or ground side and following the amplifier of the touch sensor, the circuit can be partially shared, and both circuits can be connected to the ground. Therefore, it becomes possible to realize an overcurrent, break-type withstand voltage tester, insulation resistance tester, etc. with a touch sensor that has a simple and inexpensive circuit.

[Brief explanation of the drawing]

1 and 2 show a circuit configuration according to a first embodiment of the present invention, and FIG. 3 shows a circuit configuration according to a second embodiment of the present invention. 1...Sliding transformer, 2...High voltage transformer, 4...
...Overcurrent cutoff device, 5...Micro alternating current detection section, 8
...Object to be measured.

Claims (1)

[Scope of utility model registration request] Dielectric strength or insulation resistance in which an overcurrent cutoff device is inserted into the line that applies voltage from the test voltage source to the object under test, which amplifies and detects the measured current and cuts off the voltage application when it exceeds a predetermined amount. In the dielectric strength tester for measuring the voltage, the amplifier of the overcurrent cutoff device is followed by the amplifier of the touch sensor that amplifies and detects minute alternating current corresponding to the alternating voltage applied to the object to be measured. Dielectric strength tester with touch sensor.