KR100978459B1 - Partial discharge counter for ultra high voltage power cable - Google Patents

Abstract

PURPOSE: A partial discharge counter for an ultra high voltage power cable is provided to a wrong operation due to a noise of a counter. CONSTITUTION: If the output of a partial discharge detecting sensor is higher than the output signal of a noise detecting senor, peak values are generated for more than one cycle, and the peak value is over a set value, a digital signal processor(12) determines that a partial discharge is generated one time to output a counted signal. A setup display unit(13) shows the set counted number and a set value. A counter(14) display the number of the partial discharge according to the counted signal of the digital signal processor.

Description

Partial Discharge Counter For Ultra High Voltage Power Cable

 The partial discharge counter for the ultra-high voltage cable detects the occurrence of the partial discharge, determines only the presence of the partial discharge, and operates the counter. This method has the advantages of constant monitoring of on-line partial discharge system and low cost.

 In addition, it is possible to monitor the partial discharge at all times, thereby overcoming the protection blind spots of the portable partial discharge diagnosis system. As a result, it can be an inexpensive diagnostic system while performing on-line functions. In addition, the installation cost is simple because of the ease of installation. The partial discharge counter for power cables uses a detection sensor for underground cables that is commonly used. The partial discharge signal captured by the sensor is processed to process the partial discharge signal captured by the sensor, and the number of partial discharges generated is counted.

The partial discharge counter for ultra high voltage cables uses an antenna sensor that responds in the UHF (Ultra High Frequency) band, which is the frequency band of the partial discharge, and detects the number of partial discharges occurring in any section of the high voltage cable, and then detects the detected signal. It is a system that can analyze and count in real time and minimize the risk of power accident.

 Detecting a partial discharge does not lead to a major accident in a short time, but if the degree of partial discharge is increased, there is a high possibility of a serious power accident in which the ultra-high voltage cable is exploded. For this reason, it is essential to measure the number of partial discharges in any section of a tens of kilometers of ultra-high voltage power cable. As an alternative, the partial discharge counter for the ultra high voltage power cable enables failure detection of the ultra high voltage cable through a count of the number of partial discharges for any section. In the future, the ultra-high voltage power transmission system needs more safety and more power transmission due to increased power demand, so it is necessary to further predict failure using the partial discharge counter for real-time high voltage power cable for underground cables.

 At least one partial discharge detection sensor (1) is installed at any one or more of the outer surface of the power cable to detect the signal of the UHF band by the partial discharge, It is provided apart from the power cable, to detect the signal of the UHF band A surge inflow prevention circuit (7) connected to the noise detection sensor (2) and the output terminal of the partial discharge detection sensor and the noise detection sensor to block the inflow of overvoltage and overcurrent, and connected to the output terminal of the surge inflow prevention circuit, other than 500-1500 MHz A band pass filter 8-1 for filtering a signal of a signal; a peak value detection circuit 8-2 for detecting only a peak value of an output signal of the band pass filter; and at least one capacitor; To a peak value reset circuit 8-4 which resets the peak value when a peak value having a value larger than the peak value held by the peak value detection circuit is detected by the peak value detection circuit. The low frequency conversion means 8, the A / D converter circuit 10 for converting the analog output signal of the low frequency conversion means 8 into a digital signal, and the output voltage of the A / D converter circuit 10 By using the phase angle information, the phase angle detection circuit 11 for detecting the phase angle of the peak values by the peak detection circuit, the output signal of the partial discharge sensor 1 is the output of the noise detection sensor 2 The digital signal processor 12, which is larger than the signal and the peak value is generated more than the set number of times in the phase angle and the peak value is more than the set value, and outputs a count signal by determining the partial discharge once, the set number of times And a setting indicator (13) for setting and displaying a set value, and a counting portion (14) for displaying the number of partial discharges according to the counting signal output from the digital signal processing portion (12). It relates to a power cable for partial discharge counter

 The present invention is to solve the problem that the on-line partial discharge diagnosis system is expensive and the portable partial discharge monitoring device is not monitored, and is an economical diagnostic device using the partial discharge characteristics of the ultra-high voltage power cable. The characteristics of partial discharges in ultra-high voltage cables can be summarized into four categories in terms of diagnosis. First, partial discharges occurring in ultra-high voltage cables do not cause an accident due to rapid discharge within minutes or hours even if detected. This is because progress such as breakdown occurs slowly. Second, however, progress in ultra-high voltage power cable partial discharge can lead to accidents. Therefore, detecting the increase in the number and the number of partial discharges is the key to diagnosing ultra-high voltage power cables using partial discharges. Third, constant monitoring is necessary because it is difficult to predict partial discharges. Finally, partial discharges in ultra-high voltage cables occur in synchronization with the phase voltage frequency. That is, partial discharge due to an abnormal defect in the ultra-high voltage power cable is generated in a constant pattern for each phase in the phase of the phase voltage frequency.

In order to provide a low-cost diagnostic method while utilizing the partial discharge characteristics of the ultra-high voltage power cable, the present invention has developed a partial discharge counter for an ultra-high voltage power cable. The purpose of the present invention is as follows.

 First, the partial discharge counter of the present invention detects and counts only signals that occur in synchronization with the phase voltage frequency. By counting only signals synchronized with the phase voltage frequency, it can be distinguished from noise randomly invading from the outside. It also prevents malfunction by comparing with the noise signal through the noise sensor.

 Second, in the installation of the partial discharge counter of the ultra-high voltage power cable, it is difficult to supply power from the outside. Therefore, in supplying power, it is easy to supply power because the clamp type current transformer is installed on the underground cable without using an external power source to supply power to the device by inducing a voltage from the current flowing through the underground cable.

 Third, it has two counters. One is a cumulative type counter that counts and accumulates the number of partial discharges. The other is a reset type counter that is responsible for counting for a predetermined time. In this way, it becomes possible to judge whether the partial discharge of the ultrahigh voltage cable is advancing or increasing.

 Fourth, in counting the signal occurring in synchronization with the phase voltage frequency, each time the count is performed, 50 to 60 times per second (depending on the phase voltage frequency) will occur and 3000 to 3600 times per minute. Since the purpose of this device is to inform the operator to manage the problem where it occurs, the number of times of endless increase is meaningless once it is recognized, so the reference density level setting function should be used for counting. . In other words, if the reference density is set to 100, the count is increased by one when the number of partial discharges occurs 100 times.

 First, it is complicated by counting the number of partial discharges that are synchronized with the commercial frequency in the partial discharge detection method using the partial discharge detection sensor when diagnosing the failure of underground transmission lines buried or laid in the ground as a means of transmitting electric energy. It has the effect of replacing the continuous monitoring function of expensive on-line partial discharge diagnosis system.

 Second, since the ultra-high voltage power cable partial discharge counter operates by comparing the output of the partial discharge detection sensor and the noise detection sensor, it prevents malfunction due to noise.

 Third, the ultra-high voltage power cable partial discharge counter does not use a separate external power source to supply power, so it installs a clamp-type current transformer on the underground cable to induce voltage from the current flowing through the underground cable to supply power to the device. Easy, simple structure and low-cost implementation makes it easy to expand the site.

 Fourth, in counting the ultra-high voltage power cable partial discharge, there is an effect that the presence of ultra-high voltage cable partial discharge and how much partial discharge occurs using the reference level setting means.

 Fifth, in counting the partial discharge of the ultra-high voltage power cable, the reference density setting means is used to set the partial discharge to be counted once per operation, thereby preventing the loss of information due to too many factors.

 Sixth, it has two counters, and in counting the number of partial discharges, it is possible to display the cumulative number of times and the number of times of occurrence during a certain period of time. In this way, when the number of partial discharges increases, it is effective to inform the administrator that the degree of partial discharge has progressed.

 At least one partial discharge detection sensor (1) is installed at any one or more of the outer surface of the power cable to detect the signal of the UHF band by the partial discharge, The noise is installed spaced apart from the power cable, to detect the signal of the UHF band A surge inflow prevention circuit (7) connected to an output terminal of the detection sensor (2) and the partial discharge detection sensor and the noise detection sensor to block the inflow of overvoltage and overcurrent, and connected to the output terminal of the surge inflow prevention circuit other than 500-1500 MHz A band pass filter 8-1 for filtering a signal, a peak value detection circuit 8-2 for detecting only a peak value of an output signal of the band pass filter, and at least one capacitor; The peak value reset circuit 8-4 resets the peak value when a peak value having a value larger than the peak value held by the peak value detection circuit is detected by the peak value detection circuit. Phase of the output and phase voltage of the low frequency converting means 8, the A / D converter circuit 10 for converting the analog output signal of the low frequency converting means 8 into a digital signal, and the A / D converter circuit 10 By using the angle information, the phase angle detection circuit 11 for detecting the phase angle of the peak values by the peak detection circuit, the output signal of the partial discharge sensor 1 is the output signal of the noise detection sensor 2 If the magnitude is larger and the peak values are generated more than the set number of times within the phase angle of 15 and the magnitude of the peak value is more than the set value, the digital signal processor 12 determines the partial discharge and outputs the counting signal. A setting indicator 13 for setting and displaying the number of times and the set value, and a counting portion 14 for displaying the number of partial discharges according to the counting signal output from the digital signal processing portion 12; It relates to a power cable for partial discharge counter

It will be described the configuration and operation according to the present invention for achieving the above object.

The figure for the present invention is composed of Figures 1 to 5 and Figure 1 shows the overall schematic diagram to explain the operation thereof. The partial discharge detection sensor that monitors the partial discharge in the field monitors the ultra-high voltage cable and sends the partial discharge detection value due to the abnormal fault to the partial discharge counter. The partial discharge counter synchronizes the partial discharge detection value with the supplied phase voltage, compares this value with the value set by the setting button, and counts and displays the counter when the condition is satisfied. The display of such a counter has a structure initialized by a reset button.

FIG. 2 specifically illustrates FIG. 1.

Hereinafter will be described a specific operation with respect to FIG.

1) Partial discharge sensor (1)

When partial discharge occurs due to an abnormal defect in the ultra-high voltage power cable, the partial discharge is emitted in the form of an electromagnetic signal, and the discharge frequency at this time has all frequency components. Among them, the partial discharge sensor is designed to detect in the UHF band.

2) noise sensor (2)

In order to prevent malfunction of the counter device due to electromagnetic signals other than abnormal defects inside the high voltage cable, a noise sensor is installed to compare the electromagnetic signal and the noise signal during partial discharge. The noise sensor is designed to detect only partial discharge signal except noise signal.

3) Surge inflow prevention circuit (7)

Surge signals generated by lightning or ground faults are short-pulse signals with 8-20usec waves and waves. Since these surge signals are not partial discharge signals inside the high voltage cable, they should be separated from the partial discharge signal and should not be introduced into the partial discharge counter. In order to fulfill this role, a surge inflow prevention circuit is provided at the first stage of the partial discharge counter.

4) Frequency converting means (8)

Since the UHF band signal, which is the signal output from the partial discharge sensor, and the random signal, which is the signal output from the noise sensor, are high frequency, it is difficult to process in the commonly used ADC circuit. Therefore, the low frequency conversion device converts the low frequency signal of several tens of kHz band so that the general purpose ADC can process it. That is, the signal output from the partial discharge detection sensor passes a band pass filter circuit to filter low frequency signals such as a surge signal, and then draws a curve that changes only the peak value of the original signal by the peak detection circuit. This trend curve becomes a low frequency signal in tens of kHz units. The low frequency signal maintains a peak value in the peak holding circuit. This peak holding signal is converted into a digital signal in the ADC circuit. When the conversion is completed in the ADC circuit, the digital signal processor sends a reset signal to the peak reset circuit to reset the signal held in the peak reset circuit. This signal processing (band pass filter-peak detection-peak maintenance-ADC-peak reset) is repeated 128 times per one period of the synchronization signal.

5) Phase angle detection circuit (11)

Synchronizes partial discharge data with sync pulse. The synchronous pulse is provided with a clamp-type current transformer in the underground cable without using a separate external power supply, induces a voltage from the current flowing through the underground cable, and supplies the same to the partial discharge counter. If the supplied voltage is directly input into the circuit, the device may be damaged, and the voltage drop is performed through the voltage drop circuit, and the signal is converted into a TTL level signal that can be processed by the circuit. The TTL level signal is a synchronous pulse output as a square wave signal of 0 to 5 Vpeak, and the data is transmitted to the digital signal processor in synchronization with the partial discharge data by the synchronization means.

6) Digital Signal Processing Unit 12

After reading the converted data from the ADC circuit 128 times per cycle of the phase voltage frequency, the reset pulse is applied to the peak reset circuit 128 times to initialize the peak-maintained signal to 0V. The partial discharge data synchronized with the phase voltage frequency is counted and displayed on the counter when it exceeds the value set by the setting. The set value is set by an external button, and the set value and the counted value are stored internally.

7) Setting means (5)

There are two kinds of setting means in counting the partial discharge data. One is reference level setting means for setting the reference level of the partial discharge so as to count only signals above the level, and the other is reference density setting means for setting how many times the partial discharge data above the reference level is counted once per operation.

8) Counting part (14)

The counter has a cumulative counter and a reset counter, and the former has a structure that does not erase the record by accumulating the counter since the initial installation. The latter has a structure in which the accumulated coefficients for a certain period can be externally initialized by the reset button.

9) Setting indicator (13)

Apparatus showing the reference level and reference density settings of the partial discharge signal. It is configured in the form of LCD and set manually by the administrator. It also shows frequency information and real-time data values other than the set values.

 Next, the structure and installation method of the ultra-high voltage power cable 18 will be described in FIG. 3 and FIG. 4 for on-site application of the partial discharge counter for the ultra-high voltage power cable. 3 shows a cross-sectional view of an ultra high voltage cable 18 which is generally used. The core conductor 22 serving as the transmission path of the electric power and the sheath 20 for safety and ground circuits, the insulator 21 which is insulated between the core conductor 22 and the sheath 20, and the wiring and safety of the sheath. Anticorrosive layer 19.

4 shows the installation form of the partial discharge counter when the power cable 18 is laid underground. As shown in Fig. 4, the length of the cable manufacturing is determined, considering the ease of laying work, and the cable wires are divided into regular sections in order to make the sheath current three-phase balanced. In FIG. 4, the sheath terminal A1 is connected to the sheath terminal B2 of the A phase power transmission terminal, and the sheath terminal B2 of the B phase power transmission terminal, and the sheath terminal B1 of the B phase power transmission terminal is connected to the sheath terminal C2 of the C phase power transmission terminal. The C1 sheath terminal of the phase transmission stage is connected to the sheath terminal A2 of the phase A receiver. This connection is called a cross connection or a cross bond 21. By cross-connecting the sheath terminals in this way, the current flowing through the sheath is added in a vector manner to reduce the sheath current. The partial discharge detection sensor 1 is installed in the cross bond 21 portion, and the number of times of receiving the partial discharge signal is counted.

In order to overcome the difficulty of supplying power due to the installation work, as shown in FIG. 5, the power is directly supplied from the ultra-high voltage power cable 18 using a clamp type current transformer. 5 shows a power supply unit for receiving power from the ultra-high voltage cable 18 of FIG. The winding is wound around the stratified core 18 using the stratified core 23 on the ultra-high voltage cable 18 to receive a current. The supplied current is converted into a DC current through the full-wave refinery circuit 4-1, the smoothing circuit 4-4, and the constant voltage detection circuit 4-5. After that, a voltage necessary for the partial discharge counter 3 is supplied via a regulator. The constant voltage detection circuit 4-5 controls the switch 4-2 to normally open the switch 4-2 and closes the switch 4-2 when an overcurrent flows to prevent damage to the apparatus. The diode 4-3 prevents reverse current, and the battery 4-6 charges normally and supplies voltage to the partial discharge counter when a power failure or other problem occurs.

Claims (2)

In the partial discharge counter for the ultra-high voltage electric cable,  At least one partial discharge detection sensor (1) installed at any one or more of the outer surfaces of the power cable to detect a signal in the UHF band due to the partial discharge;  A noise detection sensor 2 spaced apart from the power cable and detecting a signal in a UHF band;  A surge inflow prevention circuit (7) connected to the output terminals of the partial discharge detection sensor and the noise detection sensor to block inflow of overvoltage and overcurrent;  A band pass filter 8-1 connected to an output terminal of the surge inflow prevention circuit to filter signals other than 500 to 1500 MHz;  A peak value detection circuit (8-2) for detecting only a peak value among the output signals of the band pass filter;  A peak value reset including at least one capacitor and resetting to the peak value when a peak value having a value larger than the peak value held by the peak value holding circuit is detected by the peak value detecting circuit 8-2. Low frequency converting means 8 composed of a circuit 8-4;  An A / D converter circuit (10) for converting an analog output signal of the low frequency converting means (8) into a digital signal;  A phase angle detection circuit (11) for detecting phase angles of peak values by the peak value detection circuit (8-2) by using the output of the A / D converter circuit (10) and phase angle information of a phase voltage;  The output signal of the partial discharge detection sensor 1 is larger than the output signal of the noise detection sensor 2, and the peak values are 360 degrees at 0 degrees within one cycle of 220V 60Hz commercial power, i.e., 1/60 second. A digital signal processor 12 for outputting a count signal by determining one partial discharge when a predetermined number of times or more occurs within a phase angle of 15 degrees with respect to one phase in the phase and the peak value is greater than or equal to the set value;  A setting indicator (13) for setting and displaying the set number of times and the set value;  A counter 14 for displaying the number of partial discharges according to the counter signal output by the digital signal processor 12;  Partial discharge counter for ultra-high voltage power cable, characterized in that configured to include   The counting unit 14 for displaying the number of partial discharges according to the counting signal output from the digital signal processing unit 12 is composed of at least one counter, and the counter is a cumulative type counter for counting the total number of partial discharges. 1), the partial discharge counter 3 for ultra-high voltage power cable, characterized in that it comprises any one or more of the reset type counter (14-2) that can reset the number of partial discharges to zero.  Partial discharge counter for ultra-high voltage power cable, characterized in that configured to include

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