KR20060027946A - Monitoring system of gas insulated switchgear - Google Patents

Abstract

The present invention relates to a system for monitoring a gas insulated switchgear (GIS) used in a substation.

The present invention provides a sensor for detecting a partial discharge; A data acquisition device which collects the partial discharge values sensed by the detection sensors and wirelessly transmits them to a remote monitoring system; A monitoring system for determining whether a partial discharge value wirelessly received from the data acquisition device exceeds a set value; As a result of the determination in the monitoring system, it characterized in that it comprises an alarm device to sound an alarm when the received partial discharge value exceeds the set value.

By using the present invention, the PD sensor data collected from the DAS is wirelessly transmitted to the monitoring room, thereby reducing the wiring work cost from the DAS to the monitoring room and facilitating scalability by changing the equipment, as well as an unmanned substation as well as an unmanned substation. To provide a monitoring system of gas insulated switchgear that can be operated at.

Partial Discharge, Monitoring, Alarm, Text Message

Description

Monitoring System of Gas Insulated Switchgear

1 is an overall configuration diagram of the present invention.

2 is an overall configuration diagram of a modem of the FSK system of the present invention.

3 is a level compensation circuit diagram of the present invention.

4 is another embodiment of a level compensation circuit of the present invention;

5 is an exemplary diagram of a method for transmitting an SMS to a mobile terminal in the present invention.

<Description of Symbols for Main Parts of Drawings>

1: part anti-sense sensor

2: DAS

3: surveillance system

4: Alarm device

5: CDMA equipment

6: mobile terminal

The present invention relates to a system for monitoring a gas insulated switchgear (GIS) used in a substation.

Gas insulated switchgear is a device to protect the system by switching the load in the transmission and transmission system or the electric circuit or cutting off the current in case of an accident such as grounding or short circuit, and an iron container filled with sulfur hexafluoride (SF6) insulation gas. It is a switchgear with built-in switchgear and busbar, such as disconnector, ground breaker and breaker.

However, this device generates partial discharge due to loosening of internal bolts, presence of metal foreign matters, and internal voids in the space, and this partial discharge gradually increases to break the insulation of the gas insulation switchgear. Insulation breakdown is one of the serious accidents of devices (substations).

Therefore, the transmission substation monitors the gas insulation switchgear to monitor and remotely notify such partial discharges, and transmits the result of the monitoring to the monitoring room in the transmission substation. It is taking action.

Conventional gas insulated switchgear monitors install UHF PD (Partial Discharge) sensors that can detect this partial discharge on the outside of a plurality of gas insulated switchgear devices. It is collected by Data Aquisition System and transmitted to the monitoring room tens or hundreds of meters away and when partial discharge occurs above the standard value, the alarm is triggered by the alarm device in the monitoring room.

Therefore, in order to transmit such a remote sensing signal, the sensing value of the PD sensors must be converted into a digital format in the field DAS and transmitted to the monitoring room by wire. In addition, additional wiring work should be performed again when the location change or expansion of DAS is needed due to wired wiring.

On the other hand, since the surveillance personnel in the surveillance room do not know when an accident will occur, it is difficult to leave the surveillance room, so the monitoring personnel must reside in the surveillance room, which increases the cost of the relevant surveillance personnel.

In view of these problems of the prior art, the present invention wirelessly transmits the PD sensor data collected from the DAS to the monitoring room, thereby reducing the cost of wiring work from the DAS to the monitoring room and facilitating scalability by changing equipment. It provides a monitoring system for gas insulated switchgear that can be operated in manned substations as well as unmanned substations.

Now, the configuration and operation of the present invention will be described with reference to FIG.

In the field, detection sensors 1 (PD1, PD2, PD3) (only three are shown in FIG. 1 for convenience of description) for detecting partial discharge are installed in each gas insulated switchgear and the DAS (2) is detected. Send to). The DAS 2 (appropriate number is installed according to the capacity of the DAS 2 and the number of the sensing sensors 1) is used to monitor the partial discharge data collected from the PD 1 in a remote monitoring room (3). To send). A detailed wireless transmission method will be described below with reference to FIG. 2.

The monitoring system 3 receiving the partial discharge measurement data from the field DAS 2 records the partial discharge measurement data of each sensor 1 on a storage medium (hard disk, etc.) (not shown) or monitors (not shown). If the value exceeds the standard value, alarm is sent through the alarm device (4) to notify the monitoring personnel of the dangerous condition by sound, and the monitoring personnel can easily acoustically risk the accident by partial discharge. Make it aware. Upon hearing this alert, the surveillance personnel will take the necessary action to prevent the incident.

On the other hand, if the surveillance personnel leave the surveillance room for a while or if they operate an unmanned surveillance room to reduce the cost, even if the partial discharge exceeds the threshold, the alarm will not be heard because the guard is not in the monitoring room at that moment. You may be in a situation where you can't take appropriate action. In order to prevent such a case, when the partial discharge value exceeds the reference value, the SMS is sent to the mobile terminal 6 of the remote monitoring personnel through the CDMA device 5 and the partial discharge value exceeds the reference value. Send a message that there is a risk of an accident. The text message transmission method by the CDMA device 5 will be described below with reference to FIG.

In this way, if the partial discharge accident message is sent to the mobile terminal 6 of the remote monitoring personnel, the monitoring personnel can patrol the site or monitor unattended without having to always stay in the monitoring room.

In particular, in the case of unmanned monitoring, if the partial discharge accident message is transmitted to the central monitoring center (not shown) by wire as well as the wireless mobile terminal 6, the message can be transmitted more reliably.

As described above, since the partial discharge measurement is wirelessly transmitted to the monitoring room, the construction cost by wired wiring is reduced, and when the position change or expansion of the DAS is required, the inconvenience of additional wiring work is required again. Savings. In addition, since the partial discharge is transmitted to the wireless terminal of the monitoring personnel in the form of a text message, the surveillance personnel can carry out the surveillance work while conducting field patrols and other operations, and eventually operating an unmanned surveillance room and an unmanned substation room. The related labor cost burden can be reduced.

Now, a method of wirelessly transmitting partial discharge detection data to the monitoring system 3 in the DAS 2 will be described.

Since the partial discharge detection data of the DAS 2 is digital data, a digital signal modulation method must be used to transmit this digital data to the remote monitoring system 3 wirelessly.

Digital modulation methods include ASK (Amplitude Shift Keying), FSK (Frequency Shift Keying), and PSK (Phase Shift Keying). Substations where gas insulation switchgear is installed are places where various noises such as electromagnetic waves are severe. It is preferable to use this excellent FSK method, and a description will now be made with reference to FIG.

1) Low Noise Amplifier (LNA)

The radio wave received through the antenna ANT is a very weak radio signal from the receiver input side. Therefore, an important point to consider when amplifying this weak radio signal is the signal strength (S / N) of the overall receiving system. Therefore, the RF amplification circuit should use an amplifier with good NF (Noise Figure) to improve the S / N ratio, and the impedance matching should be performed so that the coupling between antenna (ANT) and LNA is excellent in noise. In front of the LNA, a band pass filter (BPF) is used to attenuate radio signals in unnecessary bands, and SAW (surface acoustic wave) filters are used to secure reliability of frequency characteristics with respect to temperature.

2) Mixer

The signal amplified by the LNA first-order signal has a very high frequency. If the amplifier continuously tries to amplify the high frequency signal, the amplification degree of each stage amplifier is generally lower than the low frequency amplification, and it becomes difficult to make an amplification circuit such that the circuit is easy to oscillate.

Therefore, the mixer is used to lower the amplification frequency. The mixer has a process of receiving and mixing local oscillator (LO) signals generated in a phase lock loop (PLL). If the signal frequency is fs and the LO signal frequency is f _L , and the two signals are mixed, the sum of the two signals and the difference signal appear at the output of the mixer. In addition, the signal frequency fs signal and f _L signal are also displayed. In other words,

_{fs · f L = fs + f} L + (fs + f L) + (fs - f L) ( Equation 1)

Becomes Therefore, if you want to select only the desired signal, you need to install a BPF (band pass filter) to get the desired frequency and band after the mixer.

3) Band Pass Filter

Use BPF to select only the desired signal among the signals mixed in the mixer and displayed on the output side. In the modem of the present invention, 455 kHz is used as an intermediate frequency (IF), and the sum or difference of the signal frequency fs and the LO frequency f _L should always be this IF frequency of 455 kHz. In fact, to get a low IF frequency, most of the time, the difference between two signals is selected. To keep the intermediate frequency constant even if the signal frequency fs changes, it must be configured to generate the desired LO frequency produced by the PLL. In practice, this function is controlled by a small microprocessor.

The IF filter (BPF) must fit the desired center frequency and have a bandwidth large enough for the signal to pass through. In addition, if the characteristic of the center frequency changes due to temperature, etc., it causes a fatal problem, so the IF filter uses a ceramic filter using the piezoelectric properties of the ceramic to secure a stable selection of the intermediate frequency.

4) IF Amp and Limit Amp

The IF frequency signal selected by the BPF is now amplified in earnest. The amplification degree of the IF stage usually has an amplification degree of 60 to 90 dB depending on the system, and the amplification degree is very large, so a strict circuit design is required even if the frequency is selected low. In the frequency modulation scheme, the receiving circuit can sufficiently amplify the signal until it saturates the signal. The amplification degree can be increased because the FSK method has excellent reception sensitivity and is very strong against amplitude noise components. The fully amplified signal is applied to the next QUAD demodulator, and the output signal voltage is generated depending on how much the frequency shift occurs at the center frequency.

5) QUAD demodulator

The signal fully amplified by the Limit IF amplifier is applied to the QUAD demodulator, and the QUAD demodulator extracts the original modulated signal by frequency discrimination. There are many ways of frequency discrimination (FM demodulation). A typical example is the undetected method, which was used mainly in portable FM radios until several years ago. However, this method has a disadvantage in that a demodulation transformer is required in the demodulation circuit. There are many other methods such as PLL and Fostersil method, but most of the methods recently used in ICs for receiving FM or FSK signals are the QUAD demodulation method.

The QUAD demodulator includes most circuits inside the IC, and adds a resonator component called a ceramic delimiter to the outside. The resonator uses a ceramic piezoelectric element, which is a component having excellent frequency stability.

The principle of QUAD demodulation is to extract a frequency difference from the center frequency as an output signal voltage by delaying a portion of the signal by 90 degrees. In general, the signal output voltage of the QUAD demodulator is about 50 ~ 100 mVpp, and when the RF received signal field becomes very small, white noise is started to be included in the output signal. In addition, the output signal is relatively distorted. In particular, most ICs used vary the DC level of the output signal with temperature. Therefore, if the digital data is immediately converted by the comparator using this signal, the error occurrence rate of the data becomes very large. Therefore, the noise component is first removed through the filter. Next, the comparator process is performed using the signal determination reference voltage generated correctly in the mid voltage generator for level determination.

6) LPF after demodulation signal

The demodulated signal in the QUAD demodulator has a sinusoidal shape basically because it is modulated by a sine wave in the transmitter, but as mentioned above, it is a signal containing a lot of distortion and noise. Therefore, LPF is used to remove noise and extract only sinusoidal signals. The cutoff frequency fc of the LPF is half that of the transmitted data.

Therefore, the signal passing through the LPF removes harmonic noise and almost reproduces the modulated signal used in the transmitter. In general, in order to improve the signal-to-noise (S / N) ratio in the communication process when the frequency modulation is performed, it is advantageous to make the modulation index as high as possible, that is, to modulate the frequency shift as much as possible. Because of this limitation, increasing the frequency shift brings about the problem of lowering the data rate. Therefore, first of all, consider the signal-to-noise ratio to increase the frequency modulation as much as possible, and to lower the transmission rate slightly, and select the transmission rate 1200 bps, and perform the frequency shift modulation within the range that the modulation spectrum does not deviate from the law during transmission. Therefore, the pass frequency of LPF should be designed to be 600 Hz.

7) Level Reward

The demodulated signal in the QUAD demodulator is a very small signal whose output signal level is about 50 to 100 mVpp. In order to convert the output signal to a TTL level that can be read by the microprocessor of the monitoring system 3, the noise contained in the signal must be removed first, but the necessary level is required to convert the signal into a TTL level square wave signal. The center voltage value for the determination is obtained. This center voltage value is exactly the average DC level of the signal output from the demodulator. How accurately this signal voltage is reproduced will affect the rate of bit error for the transmitted data. There are several ways to obtain the center voltage value, but the typical circuit applied to the comparator circuit is to use the circuit shown in Fig. 3, which can be useful when the data is Manchester coded, but the general data transmission In the event of a data error may occur.

In order to solve the disadvantage of the circuit of FIG. 3, a more advanced circuit using an analog switch can be used as shown in FIG. This circuit uses the precharge signal sent from the transmitter to get the correct center voltage. When receiving data, the switch is turned off to use the voltage charged in C1. Since the amount of charge charged in C1 discharges slowly, the center voltage should be compensated by the preamble signal periodically. The drift of the demodulation output according to temperature is compensated for each preamble signal, and when the actual data is received, the switch is not reflected to reflect the input state. Therefore, the correct voltage determination level can be obtained every time data is received. .

Since the circuits of FIGS. 3 and 4 all reflect the input state continuously or periodically, the demodulator is not affected even if drift occurs due to temperature. However, because the above methods require proper program control according to Manchester decoding program or preamble signal for control, it is difficult to develop a small low-cost RF MODEM at the expense of transmission rate or the hardware combination is not easy. It can also be.

8) Phase Lock Loop (PLL)

In the overall configuration of FIG. 2, the VCO, a 1 / N divider, a phase comparator, a reference frequency generator (fref), and the entire loop filter of the PLL constitute a PLL. The PLL serves to generate a desired high frequency while maintaining high stability by using a stable reference frequency generator [fref: VCTCXO (detailed below)] in the RF modem of the present invention. The PLL is always used for transmission and reception, and is controlled programmatically by the microprocessor to generate the transmit frequency directly during transmission and to generate the LO signal required for the mixer during reception.

9) Reference frequency signal (fref) generator (VCTCXO)

The reference frequency signal source of the PLL is required to have a very high frequency stability. In particular, VCTCXO (Voltage Control-able Temperature Compensated Crystal Oscillator) should be used to satisfy the frequency stability of radio waves regulated by domestic radio regulations. The frequency stability requires (+/-) 6 PPM, and the VCTCXO used in the modem of the present invention is (+/-) 2.5 PPM (@ -30 to + 85 ° C) is used.

10) Square wave-sine wave conversion circuit

In FIG. 2, an LPF circuit is added to a portion where transmission data is input. Because digital data are square pies, direct FSK modulation using this square wave signal causes the occupied frequency bandwidth to far exceed the limits specified by the national radio laws. Therefore, a circuit for converting the square wave to the sinusoidal wave before modulation is needed. As described in the LPF at the rear of the demodulator, the transmission rate was determined to be 1200 bps in consideration of the signal-to-noise ratio. Therefore, the frequency used as the input signal for the transmitter is a square wave signal of 600 Hz, which is half of the transmission rate. A sine wave appears in.

11) SPDT (Single-Pole / Double-throw) Switch

In FIG. 2, an SPDT switch is used at the input / output portion of the antenna and the output portion of the VCO. This is for converting the RF signal in a desired direction. An important characteristic of the SPDT switch is the ability to isolate the signal when the switch is off, that is, the isolation value is important.

12) LPF at end of transmitter

In FIG. 2, an LPF is further provided at the end of the transmitting unit after the PA (Power Amp). This LPF is a circuit for removing various spurious signals included in the transmission signal.

13) Receive Signal Strength Indicate (RSSI)

RSSI is one of the output signals below the limit amp in FIG. This signal outputs a voltage signal proportional to the strength of the received RF signal and is used to find an empty channel that none of the allocated RF frequency channels use. Since domestic radio law prohibits transmission when there is radio signal more than 2 uV, it is regarded as other user. Therefore, by using this RSSI signal level, the microprocessor determines whether there is another sender or whether the currently selected channel is noisy channel. Find a channel. The conversion to the TTL level required by the microprocessor is accomplished by comparing the RSSI signal against a constant voltage source and obtaining a TTL level signal as its output.

Next, a method of transmitting a text message to the mobile terminal 6 by SMS in the monitoring system 3 will be described with reference to FIG.

When the partial discharge data received from the DAS 3 is received by the monitoring system 3, the monitoring system 3 sounds an alarm when the partial discharge data exceeds the set value, and texts the mobile terminal 6 of the monitoring personnel. Send a message (SMS) to notify remote monitoring personnel of an accident due to partial discharge.

This SMS notification is sent to the mobile terminal 6 via the mobile communication server server 8 using the SMS sending equipment 7 (dedicated equipment or commercial equipment) installed in the monitoring room in the monitoring system 3, as shown in FIG. ) Or use the SMS sending device 10 connected to the SMS sending service server 9 of the SMS sending service company with the SMS sending device if there is no SMS sending device in the monitoring room. A method of sending an SMS to the mobile terminal 6 may be used via the server 8.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, but various improvements, modifications, substitutions or additions can be made without departing from the gist of the present invention. Those skilled in the art will readily understand.

By using the present invention as described above, by transmitting the PD sensor data collected from the DAS to the monitoring room by wireless to reduce the wiring construction cost from the DAS to the monitoring room, and easy to expand by changing the equipment, as well as manned substations In addition, it will provide a monitoring system for gas insulated switchgear that can be operated in unmanned substations.

Claims (13)

Sensing sensors for sensing partial discharge; A data acquisition device which collects the partial discharge values sensed by the detection sensors and wirelessly transmits them to a remote monitoring system; A monitoring system for determining whether a partial discharge value wirelessly received from the data acquisition device exceeds a set value; And a warning device for causing an alarm to sound when the received partial discharge value exceeds a set value as a result of the determination in the monitoring system. 2. The monitoring system of a gas insulated switchgear according to claim 1, wherein the transmitting of said partial discharge value from said data acquisition device to a remote monitoring system is performed by a wireless modem. 3. The monitoring system for a gas insulated switchgear according to claim 2, wherein said modem uses an FSK modulation method. The method of claim 3, wherein the modem A low noise amplifier for amplifying the received radio wave; A mixer for mixing the output of the low noise amplifier with a local oscillating signal produced at a PLL; A bandpass filter for filtering a frequency corresponding to a difference between a signal frequency and the local oscillation frequency at an output from the mixer; An amplifier for amplifying the output of the band pass filter; And a demodulator for demodulating a signal at an output of the inter-amp. The monitoring system for a gas insulated switchgear according to claim 4, wherein said demodulator is a QUAD demodulator. 5. The monitoring system for a gas insulated switchgear according to claim 4, further comprising a level compensation device for extracting a center voltage value corresponding to a reference voltage for converting an output of said demodulator into a square wave of a TTL level. 7. The monitoring system of a gas insulated switchgear according to claim 6, wherein said level compensation device uses Manchester coded data. 7. The monitoring system of a gas insulated switchgear according to claim 6, wherein the level compensation device uses a preamble included in the data. 5. The monitoring system of a gas insulated switchgear according to claim 4, wherein said PLL uses a reference frequency generator to maintain a high stability desired high frequency. 5. The monitoring system for a gas insulated switchgear according to claim 4, wherein said intermediate amplifier further comprises a reception signal strength measuring device for forming an output voltage proportional to the strength of a received RF signal. The method of claim 3, wherein the modem And a low pass filter for converting transmission data from square waves to sine waves. The gas insulated switchgear according to claim 1, further comprising an SMS sending device for sending a related text message to the mobile terminal of the monitoring personnel when the partial discharge value received as a result of the determination in the monitoring system exceeds a set value. Surveillance system of the device. A sensing step of sensing partial discharge; A data acquisition step of collecting the partial discharge values detected in the sensing step and transmitting them wirelessly to a remote monitoring system; A determination step of comparing the partial discharge value received in the data acquiring step with a setting value to determine whether the setting value is exceeded; And a warning step of causing an alarm to sound when the received partial discharge value exceeds a set value as a result of the determination in the determining step.

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