JPH0517508B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a partial discharge measuring method for measuring partial discharge in a power cable.

There are three partial discharge measurement methods: wideband, medium band, and narrowband, depending on the amplification band used. Among these, the wideband method uses the wideband, the low frequency method uses the medium band, and the low frequency method uses the medium band. and the method using a narrow band is called the tuning method.

In each of these methods, the difference in characteristics due to the degree of amplification is noticeable for specimens in which the pulse generated by partial discharge does not propagate as a traveling wave through the specimen, a so-called lumped constant specimen. To some extent,
Each specimen of a so-called distributed constant system in which a traveling wave propagates responds differently.

For example, in the broadband method, the bandwidth is widened in order to reduce distortion changes in the pulse waveform, so high frequency components are likely to be attenuated, and as shown in the characteristics in Figure 1, the discharge generation position is There is a problem that the further away, the greater the attenuation. In addition, the low frequency method has the smallest change in response depending on the position of discharge occurrence, that is, it uses an integral effect, but it has the disadvantage of being easily affected by noise, as does the wide band method. Although this low frequency method has excellent response characteristics as shown in FIG. 1, the amplification bandwidth is close to the frequency component of pulsed noise such as that of a thyristor, so it is particularly susceptible to its influence. In addition, the tuning method uses a resonant circuit because it is easy to obtain amplification and is not easily affected by noise, but as shown in Figure 1, the disadvantage is that the response varies oscillally depending on the location of the discharge. There is. Therefore, in the broadband method and the tuning method, the response obtained differs depending on the position of discharge generation, making it extremely difficult to accurately measure the amount of discharge in the specimen.

SUMMARY OF THE INVENTION An object of the present invention is to provide a partial discharge measuring method that can measure the amount of discharge in a test cable without being significantly influenced by the position of discharge, while using a tuning method that is less susceptible to noise. Located in
The gist is to apply a test voltage to the cable under test to generate a partial discharge, detect the pulse caused by the discharge by a coupling capacitor connected to the cable under test, and tune the pulse using the resonant frequency of the resonant circuit. In the partial discharge measuring method of measuring the discharge charge by causing the resonant circuit to
A plurality of discharges measured from the plurality of resonant frequencies using at least two different frequencies, each having a different partial discharge occurrence position in the test cable that causes a maximum value and a minimum value in the detection sensitivity of the discharge charge. This partial discharge measuring method is characterized in that the partial discharge of the test cable is determined by composing the measured values of the electric charges.

Next, the method according to the present invention will be explained in detail based on the embodiments shown in FIG. 2 and below.

In the tuning method, the response becomes oscillatory, as shown in FIG. 1 above, and the period of this oscillation depends on the tuning frequency of the amplifier. for example,
Resonant frequency in a 600m long cable
If it is 400KHz, the vibration period t will be 2.5μs,
When the reflected pulses are delayed by 2.5/2=1.25 μs, the signals cancel each other and the response becomes small, and when the reflected pulses are further delayed by 2.5 μs, they are added together and the response becomes large. As a result, for example, in a cable with a propagation velocity v of about 180 m/μs, = v・
Since t/2=180・1.25/2=113, a local maximum value and a local minimum value are generated every 113 m. This characteristic is as shown by the dotted line in Figure 2, and if the resonant frequency is set to 200KHz, local minimum and maximum values will similarly occur every 113 2 = 226 m, as shown by the dotted line. Become.

Therefore, from these two characteristics, for example, a characteristic with relatively little vibration between these two characteristics can be obtained, and measurement can be performed that is not significantly influenced by the position where the discharge occurs. Note that the characteristic when matched in FIG. 2 is the sensitivity change due to the ideal amount of discharge when there is no reflected pulse.

Figure 3 is a configuration diagram for realizing the present invention. In this case, a test voltage, for example, AC HV, is applied to the test cable Ca through a blocking impedance Zb, and a partial discharge is generated. I'm starting to let them do it. In addition, the test cable
A coupling capacitor Ck is connected to Ca to detect pulses caused by discharge, and this coupling capacitor
A series body of two interference prevention impedances 2a, 2b and tuned amplifiers 3a, 3b each having a unique resonance frequency are connected in parallel to Ck via a lead wire 1 made of a coaxial cable. , 3b are connected to the mixing circuit 4,
The output of the mixing circuit 4 is connected to an indicator 5.

Here, the AC voltage HV is gradually increased to cause a discharge in the test cable Ca, and the discharge pulse amount is measured to determine the discharge amount. If amplification is performed, the outputs are combined in the mixing circuit 4, and the indicator 5 is instructed, the discharge amount of the test cable Ca will be indicated as is.

The interference prevention impedances 2a and 2b prevent the plurality of tuned amplifiers 3a and 3b from interfering with each other, and simultaneously prevent the plurality of tuned amplifiers 3 from interfering with each other.
a, 3b can be activated, but the discharge is repeated several times, and the tuned amplifiers 3a, 3b are activated for each discharge.
In the case of operating the impedances by switching them one by one, these interference prevention impedances 2a and 2b are unnecessary.

Various methods can be considered for combining the outputs of the tuned amplifiers 3a and 3b in the mixing circuit 4.
By using the always large outputs of the two tuned amplifiers 3a and 3b, it is possible to eliminate abnormally small responses to partial discharges occurring anywhere along the cable under test Ca. This larger response can be obtained by using an OR circuit in the mixing circuit 4. In addition to extracting the larger one in this way, it is also possible to use an AND circuit, and in this case, the average value of the outputs of the two tuned amplifiers 3a and 3b can be indicated. Furthermore, by devising a combination of logic circuits, it is possible to obtain a response closer to the ideal shown in FIG.

Furthermore, in the embodiment, the number of tuned amplifiers has been explained as two, but the number can be further increased as shown by the dotted line in FIG. 3, and by combining the outputs of these many tuned amplifiers. , it is possible to obtain even better response characteristics. Furthermore,
Of course, there is no problem even if a DC voltage is applied as the test voltage.

As explained above, the partial discharge measurement method according to the present invention partially uses the tuning method, but by using multiple resonance frequencies and synthesizing their outputs, it is almost independent of the location where the discharge occurs. It becomes possible to obtain response characteristics close to those of the low frequency method. It also has the advantage of being able to remove response characteristics with abnormally low sensitivity, making it possible to perform tests on the safe side.

[Brief explanation of the drawing]

Figure 1 is a sensitivity characteristic diagram for each conventional discharge measurement method.
FIG. 2 and subsequent figures show an embodiment of the partial discharge measuring method according to the present invention, FIG. 2 is a characteristic diagram thereof, and FIG. 3 is a circuit configuration diagram for realizing the method. Code Ca is the test cable, Ck is the coupling capacitor, Zb is the blocking impedance, 1 is the lead wire, 2a and 2b are the interference prevention impedances,
3a and 3b are tuned amplifiers, 4 is a mixing circuit, and 5 is an indicator.

Claims (1)

[Claims] 1. Applying a test voltage to a test cable to generate a partial discharge, and detecting a pulse due to the discharge by a coupling capacitor connected to the test cable,
In the partial discharge measuring method of measuring the discharge charge by tuning the pulse using the resonant frequency of the resonant circuit, the resonant frequency of the resonant circuit is the supply voltage that causes a maximum value and a minimum value in the detection sensitivity of the discharge charge. using at least two different frequencies with different partial discharge locations on the test cable;
A partial discharge measuring method characterized in that a partial discharge of the test cable is determined by composing a plurality of measured values of discharge charges measured from the plurality of resonance frequencies. 2. The partial discharge is determined by the larger measurement value at different resonance frequencies.
Partial discharge measurement method described in section. 3. The partial discharge measuring method according to claim 1, wherein the partial discharge is determined by an average value of measured values at different resonance frequencies.