JPH05312889A - Partial discharge judging method - Google Patents

Abstract

PURPOSE:To provide a new partial discharge judging method used in measuring partial discharge of power cable. CONSTITUTION:In the partial discharge measurement of power cable line, as a method of judging whether partial discharge is generated or not the pulse numbers generated in the positive and negative cycle of applied voltage phase are counted respectively for a specified time, and the differences between the counted numbers are obtained simultaneously. In the case where only the condition that the pulse number generated in the positive cycle is at a set value n1 or more, and the absolute value of the difference n1-n2 between both pulse count numbers is at a set level n3 or less is satisfied judgement that partial discharge is generated is made from the relation between the three kinds of pulse count number, and output is made for measurement.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a partial discharge discriminating method used in measuring partial discharge of a power cable line.

[0002]

2. Description of the Related Art Noise removal technology has become extremely important in measuring partial discharge in a conventional insulation diagnostic method for power cable lines. Various methods have been known so far, and the pulse number control method and the noise window method are one of them. For example, Technical Report of the Institute of Electrical Engineers of Japan (Part II) No. 22
The pulse number control method as the noise elimination technique by the instruction circuit described in No. 2 page 19 (April 1986) is
This is a method of directly instructing the value of electric charge corresponding to a predetermined generation frequency. In addition, the noise window method is a method of instructing the magnitude when one or more discharges having a predetermined magnitude or more occur in consecutive five half cycles. It has been reported that these techniques can measure a partial discharge pulse in external noise.

[0003]

By the way, in the above-described pulse number control method, if partial discharge occurs, the discharge charge can be measured with S / N <1 smaller than external noise. It is limited by saturation, and does not give a reference for determining the presence or absence of partial discharge occurrence from the information of a plurality of detected pulses.

The noise window method is effective when at least one pulse is generated in each half cycle during the measurement period of, for example, five half cycles.
Even when the partial discharge is continuously generated, the pulse is not always generated continuously for several cycles, and it cannot be a highly accurate determination standard.

An object of the present invention is to provide a simple partial discriminating method for surely discriminating whether or not partial discharge has occurred.

[0006]

SUMMARY OF THE INVENTION The present invention provides a method for determining whether or not partial discharge has occurred in measuring partial discharge of a power cable line, for a predetermined period of time and for positive and negative cycles of a voltage applied phase. The number of generated pulses is counted, and the difference between the counted numbers is obtained at the same time. Based on the relationship among these three types of pulse counts, (1) the number of pulses generated in the positive cycle is equal to or greater than the set value n ₁ , and
(2) When the number of pulses generated in the negative cycle is greater than or equal to the set value n ₂ , and (3) the absolute value of the difference n ₁ −n ₂ between the two pulse counts is less than or equal to the set value n ₃ This is a partial discharge measuring method in which only partial discharge is judged to be generated and output is measured.

[0007]

The number of pulses generated in the positive and negative cycles of the applied voltage phase is counted for a predetermined time, and the difference between the counted numbers is also obtained at the same time. The number of generated pulses is greater than or equal to the set value n ₁ , and the number of generated negative pulses is the set value n.
_The point is that the partial discharge is judged to be generated only when the condition that the absolute value of the difference (n ₁ −n ₂ ) between the two pulse numbers is ₂ or more and the setting value n ₃ or less is satisfied. This is a cycle in which the frequency of occurrence of partial discharge pulses is positive or negative by counting the pulses generated in the positive period and the negative period of the applied voltage separately and taking the difference between the count numbers. This is because the information that is almost equal is taken in.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a circuit configuration of a method for determining a partial discharge of a power cable line of an embodiment, and FIG. 2 is a time chart of the circuit portion. That is, a voltage is applied to the power cable 2 to be measured by the charging transformer 1, and the partial discharge is detected by the electrode 4 attached to the insulating connection portion 3. When partial discharge occurs, the signal detected by the detection impedance 5 connected to the electrode 4 is amplified by the amplifier 6 and input to the gate circuits 7 and 8. This detection signal is shown in FIG.
However, in the present invention, any signal detection method may be used.

On the other hand, the applied voltage phase information obtained from the tertiary winding 9 of the charging transformer 1 is shown in FIG. This signal is passed through the gate circuit 10 and gate control signals 11 and 12 are output during each half cycle in which positive and negative voltages are applied. The control signals 11 and 12 are shown in FIGS. The gate circuits 7 and 8 allow the signal to pass during each half cycle of the H level depending on whether the gate control signals 11 and 12 are at the H level or the L level shown in FIGS. It is not passed during the L level period. Therefore, the time charts of the gate circuits 7 and 8 are as shown in FIGS. 2 (E) and 2 (G). That is, the gate circuit 7 and the gate circuit 8 are turned on / off in the opposite manner.

The pulse counters 13 and 14 connected to the gate circuits 7 and 8 respectively count the number of predetermined time pulses. Here, the pulse counters 13 and 14
Control (measurement time setting, measurement start timing signal)
Is performed by inputting the counter control signal 16 from the computer 15. After measurement, each pulse counter 13, 14
The pulse counts of N are output to and collected by the computer 15 connected to them, the number of pulses N ₁ generated during the positive cycle of the applied voltage and the set value n ₁ , the number of pulses N ₂ generated during the negative cycle of the applied voltage. And the set value n ₂ and the absolute value of the difference between the pulse count numbers N ₃ = | N ₁ −N ₂ | and the set value n ₃ are respectively compared. And N ₁ ≧ n ₁ and N ₂ ≧ n
Only when ₂ and N ₃ ≦ n _3, the output is made as if partial discharge was detected.

For example, in the time chart shown in FIG. 2, measurement of 5 cycles will be described as an example. Figure 2 now
As shown in (F) and (H), it is assumed that the gate 7 has six output pulses and the gate 8 has eight output pulses.
When the set values are n ₁ = n ₂ = 6 and n ₃ = 2, the number of pulses generated during the cycle in which the applied voltage is positive N ₁ = 6 ≧ n ₁
Is. Further, the number of pulses N ₂ = 8 ≧ n ₂ generated during the cycle in which the applied voltage is negative. Then, the absolute value N ₃ = 2 ≦ n ₃ of the difference between the pulse count numbers is established. In this measuring method, the information that the occurrence frequency of the partial discharge pulse is substantially equal in the positive and negative cycles is incorporated in the determination, and in this case, it is output that the partial discharge has occurred.

Next, an example in which the present invention is realized by a hardware configuration will be described with reference to FIG. That is, the output of the amplifier 6 connected to the detection impedance 5 is the gate circuits 7 and 8
And is input to the up / down counter 20. Pulse counters 13, 1 connected to the gate circuits 7, 8 respectively
Reference numeral 4 counts the number of pulses, and when the number of pulses exceeds a predetermined number, the output changes from the L level to the H level. The up / down pulse counter 20 adds (up counts) the number of pulses generated during a cycle in which the applied voltage is positive, and subtracts (down counts) the number of pulses generated during a negative cycle.
To do. When the absolute value of the total count is larger than the predetermined count number, the output is H level, and when the absolute value is less than the predetermined count number, the L level is output. An AND circuit 21 is connected to the pulse counters 13 and 14 and the up / down counter 20.
The logical product of the outputs of 3 and 14 and the up / down pulse counter 20 is obtained. And the result is display 2
Display on 2.

On the other hand, when a predetermined number of cycles have passed, a reset signal is output from the reset circuit 23 connected to the gate control circuit 10, and this output is output from the pulse counter 13,
14 and the up / down pulse counter 20 so that the pulse number is reset to zero.

In FIG. 4, pulses are counted for a period of 5 cycles, the number of pulses in the positive cycle is 6 or more, the number of pulses in the negative cycle is 6 or more, the number of pulses in the positive cycle and the negative cycle. 3 is a time chart showing the result of determining the occurrence of partial discharge under the condition that the difference in the number of pulses of 2 is 2 or less. From the top, (A) is the detection signal of the detection impedance 5, (B) is the voltage applied to the transformer tertiary winding 9, (C) is the gate control signal 11 from the gate control circuit 10, and (D).
Is a gate control signal 12 from the gate control circuit 10,
(E) is ON / OFF of the gate circuit 7, (F) is output of the pulse counter 13, (G) is ON / OFF of the gate circuit 8, (H) is output of the pulse counter 14, and (I) is up / down. The output of the counter 20, (J) is an AND circuit 21.
, (K) is a reset signal from the reset circuit 23. That is, since the output of the AND circuit 21 immediately before the reset signal is output is at the H level, it is determined that there is partial discharge in this case.

[0014]

As described above, according to the partial discharge discriminating method of the present invention, it is possible to discriminate early and accurately that the partial discharge has started to occur. This is a method of counting the number of pulse generations, by separately counting the pulses generated during the period when the applied voltage is positive and the pulses generated during the negative period, and by taking the difference between these counts, the partial discharge pulse This is because the information that the occurrence frequency of is almost equal in the positive and negative cycles is incorporated into the discrimination.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a method for determining a partial discharge of a power cable line of the present invention,

FIG. 2 is a time chart for explaining an operating state of the circuit of FIG.

FIG. 3 is a circuit diagram showing another embodiment of the method for determining the partial discharge of the power cable line of the present invention,

FIG. 4 is a time chart for explaining an operating state of the circuit of FIG.

[Explanation of Codes] 1 power transformer 2 power cable 3 insulation connection 4 detection electrode 5 detection impedance 6 amplifier 7,8 gate circuit 9 transformer tertiary winding 10 gate control circuit 11,12 gate control signal 13,14 pulse counter 15 computer 16 counter control signal 20 up / down pulse counter 21 AND circuit 22 display 23 reset circuit

Claims (3)

[Claims] 1. A method for determining whether or not partial discharge has occurred in a partial discharge measurement of a power cable line,
The number of pulses generated in the positive and negative cycles of the applied voltage phase is counted for a predetermined time, and at the same time, the difference between the counted numbers is also obtained. From the relationship among these three types of pulse counts, (1) positive cycle The number of pulses generated is a set value n ₁ or more, and (2) the number of pulses generated in a negative cycle is a set value n ₂ or more, and (3) the absolute value of the difference n ₁ -n ₂ between both pulse count numbers. The method for determining partial discharge is characterized in that the partial discharge is determined to occur and output is measured only when the condition that is less than or equal to the set value n ₃ is satisfied. 2. A voltage applied to a circuit that divides a signal from a detected impedance into two and connects them to a pulse counter through a gate circuit respectively, and connects them to a computer that controls these pulse counters to collect the number of pulses. The partial discharge discriminating circuit is characterized in that the number of pulses in the positive or negative period of is counted separately. 3. A reset circuit is connected to the gate control circuit, an up / down pulse counter is provided in parallel with the pulse counter, and the outputs of the pulse counter and the up / down pulse counter are output to an AND circuit to output a reset signal. A partial discharge discriminating circuit characterized in that the presence or absence of partial discharge is judged by the output level of the AND circuit immediately before is output.