JPS6013471B2 - Balanced partial discharge test circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high voltage partial discharge test circuit for insulation testing of electrical equipment, and relates to partial discharge pulses generated in an unspecified product and partial discharge pulses and switch noise generated in other than the test product. Figure 1 shows a conventionally known example of a high-voltage partial discharge test circuit that can easily separate external noise such as noise and accurately measure the street lighting pulses generated in a mystery product. Explain with reference to.

This partial discharge test circuit consists of a high voltage power supply 1, a protective resistor 2,
Capacitors 3 and 6, detection impedances 4 and 7
, a high impedance element 5, and a sample 8. To measure partial discharge using this circuit, the terminal voltages of detection impedances 4 and 7 are input to amplifiers 11 and 12 via high frequency cables 9 and 10, and the pulses from there are sent to a size discriminator 113. After putting it in,
It is measured with a corona measuring device 14. In this case, since the high impedance 5 is connected, the corona generated in the sample 8 generates a pulse voltage having a higher peak value between the terminals of the detection impedance 7 than between the terminals of the detection impedance 4. Therefore, the pulse size discriminator 13 operates to output a corona pulse, and causes the corona measuring device 14 to measure the corona pulse.
On the other hand, due to the presence of high impedance 5, corona and external switch noise generated in places other than the high voltage power supply 1 and the like will wave between the terminals of detection impedance 4 compared to between the terminals of detection impedance 7. Generates a high pulse voltage with a high value. In this case, the pulse size discriminator 13 does not output a corona pulse, and the pulse is not measured. The conventional high-voltage partial discharge test circuit described above requires the use of two high-frequency cables, two amplifiers with equivalent performance, and a pulse size discriminator.

SUMMARY OF THE INVENTION An object of the present invention is to provide a high-voltage partial discharge test circuit with a simple configuration that can distinguish and measure partial discharge pulses generated in a sample under test from external noise generated elsewhere.

The present invention eliminates pulses generated in parts other than the sample, that is, external noise, by a balancing action within the partial discharge test circuit, making it possible to measure only the partial discharge pulse of the sample with a single corona measuring device. This is what I did.

As the erasing means, a balance section is provided which is composed of a variable impedance element whose impedance can be adjusted to be equal to that of the high impedance element and two pulse transformers. Next, one embodiment of the present invention will be described with reference to FIG.

This example is an example of a DC high voltage partial discharge test circuit,
DC high voltage generator 1, protective resistor 2, smoothing capacitor 5
, high impedance element 16, voltage measurement resistor voltage divider 1
7, ammeter 18, capacitors 9 and 22, high impedance element 21, sample 25, balance section 28 including variable impedance element 20 and pulse transformers 23 and 24, high frequency cable 26 connected to this, and corona It is composed of a detector 27. In order to explain the operation of the example shown in FIG. 2, an example of its equivalent circuit is shown in FIG. This circuit consists of capacitors 9 and 22,
Power supply side impedance 41, sample free capacitance 29,
High resistance 30, stray capacitance 31 between points A and B in the same figure
, a variable resistor 32, a variable capacitance 33, pulse transformer primary windings 34 and 37, pulse transformer ferrite cores 35 and 38, pulse transformer secondary windings 36 and 39, impedance 40, and the like. Reference numeral 41 denotes a power supply side impedance, which collectively includes the internal impedance of the DC high voltage generator 1, the protective resistor 2, the smoothing capacitor 15, the high impedance element 16, the resistance of the resistive voltage divider 17, and the like.

As the high-impedance element 16, for example, a high-resistance material is used so that its value is at least two orders of magnitude higher than the impedance insulation value of the capacitor 19. As a result, the value of the power supply side impedance 41 is much larger than the impedance of the capacitor 19. Stray capacitance 31 is determined by the geometry between points A and B, and the absolute value of the impedance is considerably larger than the high resistance 30, but this value cannot be ignored in order to improve the accuracy of balance. The high resistance 30' is a resistor having a value that is at least two orders of magnitude higher than the absolute value of the impedance of the capacitors 19 and 22. It may be replaced with this high resistance three-way inductance. The value of capacitor 22 is assumed to be considerably larger than the value of stray capacitance 29 of the sample. 4 impedances are the equivalent impedances expressed collectively for the measuring device 27 side when viewed from the pulse transformer secondary windings 36 and 39 side. In addition, pulse transformers 35 and 38
The impedances viewed from the primary side of each capacitor 19 and 22 are set to have the same value, and the capacitances of the capacitors 19 and 22 are also set to have the same value. By adjusting the circuit constants in FIG. 3 to the above conditions, the influence of the power source impedance 41 and stray capacitance 29 on the current distribution flowing through the equivalent circuit in the same figure can be ignored. First, in the circuit shown in Figure 2, if external noise occurs such as a corona pulse generated by something other than the test product or a high-frequency pulse that enters the DC high-voltage generator path from a low-voltage power supply, those voltages will not be applied. The location can be considered to be closer to the DC high voltage generator than point A.

Among these voltage application points, the one that produces the maximum response of the detection terminals 23 and 24' is between point A and ground. In FIG. 3, if the values of variable resistor 32 and variable capacitor 33 are equal to the values of high resistance 30 and stray capacitance 31, respectively, then capacitor 19, variable resistor 32, variable capacitor 3
The combined impedance of 3 is 22 capacitors and 3 high resistors.
0, equal to the combined impedance of the free capacitance 31.
Therefore, the potential differences generated between the respective terminals of the pulse transformer primary windings 34 and 35 are equal due to the pulse generated between point A and ground in FIG. The secondary windings 36 and 39 are
Although the primary windings 34 and 37 are connected to produce a potential difference proportional to the difference in voltage between their respective terminals, since the voltages between both terminals are equal, no signal appears at both ends of the impedance 40. Next, the current distribution when a partial discharge occurs in the sample 25 in FIG. 2 is the same as when a pulse is applied between point B and ground in FIG. 3.

At this time, the capacitor 22 and the pulse transformer primary winding 3
The impedance composed of 7 is much smaller than the impedance composed of high resistance 30, stray capacitance 31, capacitor 19, variable resistor 32, variable load 33, and primary winding 34 of the pulse transformer. becomes. Therefore,
The terminal voltage of the primary winding 37 is much higher than the terminal voltage of the primary winding 34, and a voltage proportional to the difference between the two voltages is generated between the terminals of the impedance 40, which is measured as a true corona pulse. Ru. In this way, when dealing with external noise, the voltage is reduced and the output voltage of the pulse transformer is not measured due to the balancing effect, while when dealing with partial discharge pulses that occur in the test product, high impedance elements are not included. Most of the current flows through the branches, allowing true corona pulses to be measured with good sensitivity.

FIG. 4 shows another embodiment of the present invention, which is an example of application of the present invention to a mystery product having a capacitor bushing 41 and a tank 42.

In the same example, a balance section 45 containing two pulse transformers is arranged near a terminal 43 connected to a ground potential metal foil of a capacitor bushing 41. capacitor 1
The other end of the balancing variable impedance element 20, which has one end connected to the terminal 9, is connected to the primary winding 34 of the pulse transformer via a high frequency cable 44. Terminal 43 is connected to the primary winding 37 of the pulse transformer. The difference between the example in FIG. 4 and the example in FIG. 2 is that the capacitance between the center conductor of the capacitor bushing 41 and the ground potential metal foil is utilized as an element having the function of the capacitor 22 in FIG. It is a point.

This embodiment has the effect of reducing the number of capacitors to be prepared in addition to the sample. FIG. 5 shows another embodiment of the variable impedance element used in the present invention, which differs from the variable impedance element shown in FIG. 3 in that a variable inductance element 46 is added.

This embodiment can be applied to the case where an isoductance is used as the high impedance element shown in FIG. Although the embodiment shown in FIG. 2 concerns a DC high voltage partial discharge test circuit, it goes without saying that the present invention can also be applied to an AC partial discharge test circuit. As described above, according to the present invention, external noise generated in parts other than the sample is eliminated by the balancing action within the partial discharge test circuit, so that a single corona measuring device can detect the partial discharge pulse of the sample. can only be measured.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing a conventional partial discharge test circuit, Fig. 2 is a circuit diagram showing an embodiment of the present invention, Fig. 3 is a circuit diagram showing an equivalent circuit of the circuit in Fig. 2, and Fig. 4 is a circuit diagram showing an example of the present invention. FIG. 5 is a circuit diagram showing another example of the variable impedance element. 1... DC high voltage generator, 2... Protection resistor, 15.
... Smoothing capacitor, 16, 21 ... High impedance element, 19, 22 ... Capacitor, 2, 0 ... Variable impedance element, 23, 24 ... Pulse transformer, 26 ... Sample, 27. ...Corona measuring device, 28...
- Balance part, 31... Stray capacitance, 32... Variable resistance, 33... Variable capacitance, 34, 37... Primary winding, 35
, 38. ．． - Ferrite core, 36, 39... Secondary winding, 40... Impedance, 41... Capacitor bushing, 42... Tank, 45... Balance section, 46... Variable inductance element. Power 'Z diagram Thread J diagram Kimu Zuen J diagram

Claims (1)

[Claims] 1. In a partial discharge test circuit that applies and measures a high voltage from a high impedance power supply to the specimen through a high resistance,
A parallel circuit consisting of a variable resistor that can be set to a resistance value of the high resistance and a variable capacitor that can be set to a stray capacitance value of the high resistance is connected to a first capacitor to connect the primary winding of a first pulse transformer. A series circuit of a second capacitor having the same capacity as the first capacitor and a primary winding of a second pulse transformer is connected in parallel to the sample under test, and and a balanced partial discharge test circuit, characterized in that one end of a secondary winding of a second pulse transformer is connected, and a pulse is taken out from the other end and input to a corona measuring device for measurement.