WO2012088690A1 - 一种发电机局部放电在线监测高压陶瓷电容传感器 - Google Patents
一种发电机局部放电在线监测高压陶瓷电容传感器 Download PDFInfo
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- WO2012088690A1 WO2012088690A1 PCT/CN2010/080510 CN2010080510W WO2012088690A1 WO 2012088690 A1 WO2012088690 A1 WO 2012088690A1 CN 2010080510 W CN2010080510 W CN 2010080510W WO 2012088690 A1 WO2012088690 A1 WO 2012088690A1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R15/00—Details of measuring arrangements of the types provided for in groups G01R17/00 - G01R29/00, G01R33/00 - G01R33/26 or G01R35/00
- G01R15/04—Voltage dividers
- G01R15/06—Voltage dividers having reactive components, e.g. capacitive transformer
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- the invention belongs to an online monitoring technology for insulation state of large-scale power equipment, and relates to a high-voltage ceramic capacitance sensor for on-line monitoring of local discharge of a generator.
- the insulation condition of the stator winding of large generators is very important for the safe and stable operation of the generator. It is shown that the insulation fault of the stator winding is still one of the main faults of the large generator, and the damage of the insulation of the stator winding is mostly due to local Caused by discharge. Therefore, under the operating conditions of the motor, on-line monitoring of partial discharge is of great significance for early detection of signs of insulation degradation, maintenance of shutdown plans, and prevention of major accidents.
- the on-line monitoring of generator stator partial discharge is based on the phenomena of sound, light and electricity generated by partial discharge, and various measurement methods are developed accordingly. Among them, the sensitivity of electric pulse method to monitor partial discharge is much higher than other monitoring methods, so it has attracted more and more people's attention.
- the monitoring of partial discharge mainly uses electric pulse signal method.
- the representative online monitoring methods for partial discharge electrical measurements in foreign countries include the following six types:
- the SSC St tor S lot Coupler
- the SSC is a microstrip type antenna for detecting a partial discharge signal. Installed under the wedge. This coupler has a [ ⁇ wide frequency response with a typical lower cutoff frequency of 10 MHz and an upper cutoff frequency of 1 GHz. But this type of sensor must be installed when the generator is produced.
- Capacitance coupling method at the high voltage end In the 1970s, M. Kur ts ⁇ used a 375pF, 25kV capacitor on the high-voltage lead terminals of the three-phase winding of the generator to be used as a coupling signal, which was used by early PDAs. The capacitance of the capacitive coupler varies from 375Pf to 1 000pF. Later, when the 80pF coupler was used, the interference below 40MHz was weakened, resulting in higher signal-to-noise.
- Detection method of generator neutral point current sensor combined with high-voltage side direction sensor The method adopted by this type of instrument is to detect partial discharge pulse current signal from generator neutral point ground line by using high-frequency current sensor.
- a direction sensor is installed near the high voltage bus of the generator to detect the interference pulse transmitted from the transformer along the bus.
- the lower limit of the filter is adjustable between 10 kHz, 20 kHz, 50 kHz and 100 kHz, and the upper limit is adjustable between 1 ⁇ , 2 MHz, 5 MHz and 10 MHz.
- Radio frequency component lead radio frequency monitoring method uses the lead of the resistance type temperature measuring element (RTD) embedded in the stator slot as an antenna, and the partial discharge pulse signal on the RTD is coupled by RFCT, and the interference method is still utilized. The frequency domain difference between the partial discharge pulse and the noise pulse distinguishes the two. Disadvantages Similar to the SSC detection method, partial discharges farther away from the sensor are excluded as interference, and the interference of the RTD's own power system can also affect the partial discharge measurement.
- RTD resistance type temperature measuring element
- Detection method for installing an RF antenna on the outer casing of the generator uses a radio frequency antenna installed in the motor casing or outside the gap of the casing to detect severe discharge discharges such as partial discharge, spark discharge and arc discharge.
- the alarm threshold is easy to determine, but the measured signal and discharge amount are not directly related, it is difficult to calibrate, and there is no time domain waveform of the discharge signal, which cannot be further identified and diagnosed.
- This neutral point monitoring method has a low operating voltage (only a few V under normal operating conditions) and is easy to install and debug, so it is used by many in-service monitoring systems.
- the measurement band of the system is limited, and the upper limit of the frequency band is often less than 1 ⁇ .
- Many system bands are tens of kHz to several hundred kHZ, which loses the true discharge information to a large extent.
- the monitoring at the neutral point is because only one sensor is installed, so that the anti-interference means is relatively simple, and only the threshold, filtering or further software processing is used to distinguish the external non-periodic pulse type interference.
- the outlet of the high-voltage end is close to the discharge source, and the signal loss during transmission is small.
- the conventional high-voltage capacitor is bulky, unfavorable for installation, and is rarely used because of the safety and stability considerations for long-term operation under high voltage.
- the neutral point is not suitable for the monitoring of partial discharge:
- partial discharge is more likely to occur in the area close to the phase-out line, so that the discharge pulse must have a long-distance transmission throughout the stator winding to reach Neutral point. Therefore, for a complex capacitive network such as a motor winding, the resulting pulse will be severely distorted due to waveform distortion and amplitude attenuation.
- the neutral point the sensitivity and reliability of the measurement results are greatly reduced due to the aliasing of the three-phase discharge signals and the aliasing of the discharge signals of other high-voltage devices. Direct measurement from the high-voltage end of the generator, the signal transmission loss is small, and the high-frequency component loss is small, so that the more realistic discharge information can be obtained, which is clearly illustrated in the attached table 1.
- the technical problem to be solved by the present invention is to provide a high-voltage ceramic capacitance sensor for on-line monitoring of partial discharge of a generator, which has good safety and stability under long-term operation under high voltage.
- the present invention provides a high-voltage ceramic capacitance sensor for on-line monitoring of partial discharge of a generator, which comprises an epoxy casing made of an insulating material and shaped like a pillar insulator, and an epoxy resin umbrella group is arranged on the circumference of the casing.
- the epoxy casing is provided with a circular metal electrode and an external lead at one end, and a metal base is disposed at the other end; a ceramic capacitor core is disposed in the casing, and the ceramic capacitor core has two upper and lower copper electrodes.
- the upper electrode embedded in the copper electrode and the outer casing is connected by a conductive metal rod, and the other end of the upper electrode embedded in the outer casing is fixedly connected to the circular metal electrode, and the lower copper electrode of the ceramic capacitor core is connected.
- the ceramic capacitor core is composed of two pieces of porcelain welded in advance through a withstand voltage test and a partial discharge test;
- the circular metal electrode has a screw at one end thereof, and the circular metal electrode is fixed on the upper electrode embedded in the outer casing by a screw;
- the metal base is internally provided with a sampling impedance, one end of the sampling impedance is connected to the lead bolt through a metal strip, and the other end is coaxially mounted on the base by a metal strip.
- a sampling impedance one end of the sampling impedance is connected to the lead bolt through a metal strip, and the other end is coaxially mounted on the base by a metal strip.
- the ceramic capacitor core is a barium titanate lead bismuth high performance porcelain material; as a preferred embodiment of the present invention, the composition and mass percentage of the ceramic capacitor core ceramic material are : Sr: 40-60%, Ti: 20-60%, Pb: 10-20%, Bi: 10-20%;
- the conductive metal rod has a diameter of ⁇ 4;
- both sides of the circular metal electrode are concave concave-shaped structures, and the outer edge is also circular.
- the partial discharge on-line monitoring high-voltage ceramic capacitance sensor of the present invention has at least the following advantages:
- the sensor of the invention is installed at the high voltage end of the generator for partial discharge monitoring, wherein the capacitance ranges from 20 pF to 2000 pF, and the electric resistance is 90 kV or Higher, capable of long-term operation in the high-voltage environment to monitor the insulation condition of the motor stator winding;
- the installation position of the ceramic capacitance sensor for online monitoring of the present invention is close to the high-voltage end, the partial discharge signal with the least distortion can be collected And has a higher sensitivity.
- the invention utilizes a pair of such sensors on the busbar of one phase of the generator to realize an anti-interference method for discriminating the pulse delay, thereby distinguishing whether the signal obtained by the sensor is from the internal discharge of the generator or from the external power system. Interference. DRAWINGS
- FIG. 1 is a side cross-sectional view of a high-voltage ceramic capacitance sensor for on-line monitoring of a partial discharge of a generator according to the present invention
- FIG. 2 is a view showing a mounting position and a system frame of a high-voltage ceramic capacitance sensor for on-line monitoring of a partial discharge of a generator according to the present invention
- Figure 3 is a device diagram of a sensor unit measurement loop
- Figure 4 is a correction pulse time domain diagram and a frequency domain diagram, where a) a time domain diagram, b) a frequency domain diagram;
- Figure 5 is the response waveform of the l OOpF capacitive sensor, where a) the time domain waveform, b) the frequency domain waveform.
- the correspondence between the label and the component in the figure is as follows:
- the partial discharge on-line monitoring of the high-voltage ceramic capacitor sensor of the present invention includes a pillar-like insulator made of an insulating material.
- the epoxy casing has a resin umbrella group 7 disposed on the circumference of the casing, and the epoxy casing is provided with a circular metal electrode 2 and an external lead 1 at one end, and a metal base 11 at the other end.
- a ceramic capacitor core 5 is disposed in the outer casing, and the ceramic capacitor core 5 is composed of two pieces of porcelain welded in advance by a withstand voltage test and a partial discharge test, and the ceramic capacitor core 5 has two upper and lower copper electrodes.
- the upper and lower copper electrodes have an M4 screw hole for easy connection.
- the upper copper electrode is connected to the upper electrode 3 embedded in the outer casing through a conductive metal rod 4, and the other end of the upper electrode 3 embedded in the outer casing is fixedly connected to the circular metal electrode 2, and the circular metal electrode 2 - the end of the center has a screw, such that the circular metal electrode 2 is fixed to the upper electrode 3 embedded in the outer casing by a screw, and the other end is connected to the generator outlet bus through the external lead 1; the lower portion of the ceramic capacitor core 5
- the copper electrode is connected with a metal strip 6, and the other end of the metal strip 6 is attached to a lead bolt 8 provided in the middle of the lower portion of the epoxy casing.
- the metal base 11 and the epoxy casing are fixed together by a wire buckle, and the metal base 11 is internally provided with a sampling impedance 9 , one end of the sampling impedance 9 is connected to the lead bolt 8 through the metal band 6 , and the other end is installed through the metal band 6
- the coupled signal is taken out, and in addition, a hole is formed in the lower edge of the metal base 11 for mounting the fixing screw.
- the ceramic capacitor core 5 is lead lanthanum titanate ( ⁇ mBi 2 0 3 ⁇ nTi0 2 ) high performance porcelain, where Sr: 40-60%, Ti: 20-60%, Pb: 10-20%, Bi: 1 0-20%, thus, the ceramic capacitor of the present invention
- the core 5 has a dense microcrystalline microstructure with high dielectric strength and low dielectric loss.
- 0. 1-1% of the rare earth compound Ce0 2 was added to the batch to control the volatilization of Bi 2 0 3 in the batch, the grain boundary characteristics were improved, and the electric strength was greatly improved.
- Adding 0. 1-2% content of MgTi0 3 to the porcelain material produces peak shifting and unfolding effect, which greatly improves the capacitance characteristics of the ceramic capacitor.
- the capacitance value of the ceramic capacitor core 5 depends on the frequency band of the measurement system.
- the general selection range is 20pF-2000pF, and the appropriate capacitance value is selected to make the entire measurement system have the best response.
- the ceramic capacitor core 5 of the present invention has a dielectric constant of several thousand, so that the volume of the capacitor can be made small, and the overall compact structure is advantageous for the transmission of high-frequency signals.
- the porcelain In order to obtain a dense and uniform porcelain, the porcelain is required to have sufficient fineness.
- the present invention treats raw materials with ultrafine pulverizing equipment, optimizes the pulverization process of porcelain, strictly controls the grain size and distribution of the ceramics, and refines the grain size of the ceramics from an average of 3 micrometers to less than 1 micrometer to obtain a ceramic fine crystal structure. Improve the electrical strength of ceramic capacitor cores.
- the invention controls the uniformity of the binder polyvinyl alcohol (PVA) in the ceramic ceramic core blank, controls the particle size of the blank by screening and performs the grain size matching, and controls the content of the binder and moisture in the blank and the molding pressure. And improved pressurization to eliminate delamination defects.
- PVA binder polyvinyl alcohol
- the capacitor ceramic core of the invention consists of two pieces of porcelain welding which have been tested by the withstand voltage test and the partial discharge test in advance, so that it is possible to overcome the difficulty in forming the ceramic body due to the excessive thickness of the single piece.
- the chamfering amount of the ceramic body and improving the electrode structure By controlling the chamfering amount of the ceramic body and improving the electrode structure, the amount of the margin of about 0.3 ⁇ is changed to the full electrode printing silver electrode, and the initial discharge voltage of the electrode edge is increased. After the above measures are taken, the partial discharge performance and the pass rate of the sensor core of the invention are greatly improved.
- the invention adopts an adjustment formula, that is, to increase the content of the chopping material from 100 parts to 150-220 parts (ie, the epoxy resin: t: the weight ratio of the real material is 100: (150-220)) toughen the epoxy resin encapsulant
- the epoxy resin By adding accelerators and improving the curing process system, the expansion coefficients of the epoxy resin and the ceramic capacitor core 5 and the upper and lower copper electrodes are matched, which overcomes the disadvantages of cracking and partial discharge performance degradation of the sensor during the hot and cold cycle.
- Its epoxy encapsulant can withstand 10 cycles of thermal cycling from -40 ° C to +85 ° C without cracking.
- the sensor capacitor core fabricated by the above improvement measures basically meets the requirements of VHF partial discharge detection.
- the molded capacitor ceramic core has two upper and lower copper electrodes, and the upper and lower copper electrodes have a screw hole of M4, and the conductive metal rod 4 can be simultaneously screwed into the copper electrode on the capacitor core 5 and the screw hole of the electrode 3 embedded in the housing.
- M4 the conductive metal rod 4 is changed from the original ⁇ 10 metal rod to ⁇ 4 , and the thinned metal rod can filter the vibration of the generator bus bar during operation to prevent damage to the capacitor body.
- the lower copper electrode is connected to the lead bolt 8 provided in the lower portion of the epoxy casing through the conductive metal strip 6.
- the capacitor is epoxy encapsulated.
- the present invention selects an acid anhydride-cured epoxy resin system excellent in electromechanical properties and moisture resistance.
- the shape of the sensor shown in Figure 1 is obtained by connecting the fired ceramic capacitor and the corresponding screw hole to the epoxy resin which is prepared in advance. It can be seen from the figure that this shape is similar to the post insulator, with a group of epoxy umbrellas to increase the insulation distance and reduce the volume of the entire sensor.
- the upper electrode 3 embedded in the housing is provided with a M12 copper screw hole in addition to the screw hole of the M4 used for connecting the capacitor core body, and is matched with a corresponding circular metal electrode 2 with a screw.
- the metal electrode 2 is fixed on the casing.
- the circular metal electrode 2 is a circular pie-shaped structure with both sides concave, and the outer edge is also a circular structure.
- the outer lead 1 of the other end of the circular metal electrode 2 can be firmly connected to the generator outlet bus, so that the sensor and the generator bus are connected together.
- the external lead 1 has a rubber insulation layer that can withstand the bus voltage of the generator and ensure the cleaning of the high voltage end.
- the metal base 11 and the epoxy casing are fixed together by a threaded wire.
- the metal base 11 is internally provided with a sampling impedance 9 .
- One end of the sampling impedance 9 is connected to the lead bolt 8 and the other end is mounted on the coaxial wire base 10 on the base 11 .
- a hole is formed in the lower edge of the metal base 1 1 for fixing the screw of the entire sensor. Make sure that the external lead 1 and the generator busbar are well fixed.
- Partial discharge is essentially a short distance of electrons and ion currents in a limited time, which occurs as a certain amount of electricity flow when a partial discharge occurs.
- the magnitude of this total current is determined by how much of the pico-charge is transferred during discharge.
- the current appears as a voltage pulse on the impedance of the insulating medium of the motor, so the ceramic capacitor sensor of the present invention can be used to couple such voltage pulses to characterize the partial discharge inside the motor. Less.
- the coupling capacitor exhibits a higher impedance (0. 9095 X 1 0 7 ⁇ ⁇ 0.
- the signal obtained on the sensor enters the signal conditioning unit through the multiplexer to amplify or reduce, and then the high-speed data is collected and displayed on the computer for signal analysis and processing. Because the detected partial discharge frequency component is relatively high, an anti-interference method based on pulse delay can be used in the field.
- an anti-interference method based on pulse delay can be used in the field.
- C1 and C2 are installed at one location, and the signals from the inside of the generator and the signals from the external power system have different arrival times on C1 and C2.
- the length of the RF coaxial cable can be adjusted so that the signal from the external power system reaches the same time on the two sensors through the two sensors, and the discharge signal from the inside of the motor is very long after the arrival time of the two sensors.
- This method can effectively suppress external interference.
- Capacitance 10. 5kV, 50Hz, (20 2000) pF (2 ⁇ 200) pF
- Capacitance sensor withstand voltage: AC 1 minute 90kV withstand voltage
- Insulation resistance 20 C , lkV ( DC ) under >10" ⁇ ⁇ Dielectric loss: 20 C , 10. 5kV (AC ) ⁇ 0.11 %
- Capacitance temperature characteristics - 25 C ⁇ 80 C temperature range, capacitance change ⁇ 30 %
- Capacitor AC voltage characteristics Motor voltage level 10. At 5kV, the voltage changes by 20% and the capacitance changes to ⁇ 1%.
- TeKt ronix's arbitrary waveform generator is used to input a 1. 5V, rise time 2. 3ns correction pulse to the capacitive sensor.
- Figure 4 shows the time domain waveform and spectrum of the correction pulse.
- the response frequency of the 100pF capacitive sensor is mainly at 40MHz, 1 30MHz and 220MHz, which belongs to the very high frequency range, thus verifying that the sensor system can perform VHF partial discharge measurement.
- the effect of the amount of the binder on the partial discharge starting voltage and the breakdown field strength is shown in Table 1 below: Effect of the amount of binder on the partial discharge initial voltage and the breakdown field strength sing
Description
一种发电机局部放电在线监测高压陶瓷电容传感器
技术领域
本发明属于大型电力设备绝缘状态在线监测技术， 涉及一种发电机局部放 电在线监测高压陶瓷电容传感器。
背景技术
大型发电机的定子绕组绝缘状况对发电机的安全稳定运行至关重要， 有资 料表明目前定子绕组绝缘故障仍是大型发电机的主要故障之一， 而定子绕组绝 缘的损坏则大多数是由于局部放电造成的。 因此在电机运行条件下， 进行局部 放电在线监测， 对于及早发现绝缘劣化征兆、 制定停机计划检修、 防止重大事 故发生等具有重要意义。
发电机定子局部放电在线监测根据局部放电所产生的声、 光、 电等现象， 相应地开发出多种的测量方式。 其中电脉冲法监测局部放电的灵敏度大大高于 其它的监测方法， 因此越来越受到人们的关注， 局部放电的监测也主要釆用电 脉冲信号法。 国外具有代表性的局部放电电测类在线监测方法包括以下六种：
1. 发电机中性点耦合法和射频监测法： 1980年美国 Wes t inghouse公司将 射频电流传感器 ( Radio Frequency Current Transformer , RFCT )装设在发电 机中性点接地线上， 用于监测大型汽轮发电机定子绕组断股所产生的电弧， 开 发了商用的发电机射频监测， RFCT的频率范围大致为 0. lkHz-10MHz。
2.发电机定子槽微带天线槽耦合器法：加拿大开发了定子槽耦合器（Sta tor S lot Coupler , SSC )。 SSC是一种用来检测部放电信号的微带型天线。 安装在槽 楔下面。 这种耦合器具有^ [艮宽的频率响应， 典型下限截止频率为 10MHz , 上限截 止频率为 lGHz。 但这种传感器必须在发电机生产时就安装上去。
3. 高压端的电容耦合法： 最早在 70年代 M. Kur t s釆用在发电机三相绕组 的高压引线端各搭接一个 375pF、 25kV的电容器， 作为耦合信号之用， 早期 PDA 所釆用的电容耦合器的电容值在 375Pf-1 000pF之间变化， 后来发现利用 80pF 耦合器时， 能够消弱 40MHz以下的干扰， 从而信噪比较高。
4. 发电机中性点电流传感器与高压侧方向传感器相结合的检测方法： 这类 仪器所釆用的方法是一方面利用高频电流传感器从发电机中性点接地线检测局 部放电脉冲电流信号， 另一方面在发电机高压母线附近装设方向传感器以检测 从变压器方向沿母线传来的干扰脉冲。 滤波器的下限 1 0kHz、 20kHz , 50kHz 和 1 00kHz之间可调， 上限在 1ΜΗζ、 2MHz、 5MHz和 1 0MHz之间可调。
5. 测温元件引线射频监测方法： 该方法将埋置在定子槽里的电阻式测温元 件（RTD ) 的引线作为天线， 通过 RFCT耦合 RTD上的局部放电脉冲信号， 其干 扰方法仍然是利用局部放电脉冲和噪声脉冲的频域区别将两者区分开来。 缺点 类似 SSC检测方法， 离传感器较远的局部放电会被当作干扰排除掉， 而且 RTD 本身的电源系统的干扰也会影响局部放电测量。
6.在发电机的外壳上安装射频天线的检测法： 这种方法用安装在电机外壳 或外部紧挨外壳空隙处的射频天线来检测严重的局部放电、 火花放电和电弧放 电等破坏性放电脉冲频率高于 4MHz的电磁波信号。 这种方法对发电机进行监测 时报警阈值容易确定， 但是测到的信号和放电量没有直接联系， 难以标定， 并 且没有放电信号的时域波形， 无法做进一步的识别和诊断。
国内在大型发电机定子局部放电在线监测方面的工作开始于 80年代， 也研 制出了相应装置， 一些装置己在几个电厂试验运行。 国内现有的发电机局部放 电在线监测系统中， 大都釆用在中性点引出线安装传感器（分为电压耦合和电流
耦合两种方式）。 在中性点不接地或经阻抗接地系统中， 釆用在中性点并联耦合 电容釆集放电信号； 而在直接接地系统中， 则釆用两个高频电流互感器钳在接 地线上釆集放电信号。 这种中性点监测法工作电压低 (正常运行状态下仅为数 V) , 且安装调试方便， 因此被许多已投运的监测系统釆用。 但是由于放电脉冲在到 达中性点时高频分量已有严重的衰减， 就使得系统的测量频带受到限制， 频带 的上限往往低于 1ΜΗζ。 许多系统频带为几十 kHz到几百 kHZ , 这在 ^艮大程度上损 失了真实的放电信息。 在中性点的监测由于只安装一路传感器， 使得抗干扰手 段相对单一， 仅仅利用阈值、 滤波或进一步的软件处理艮难分辨外来非周期脉 冲型干扰。 高压端出口处离放电源近， 传输中信号损失少， 但以往由于传统高 压电容器体积大， 不利于安装， 以及基于在高电压下长期运行的安全性与稳定 性考虑， 很少被釆用。
事实上中性点并不适合于局部放电的监测： 对于高压电机来说， 局部放电比 较容易发生在靠近相出线端的区域， 这样放电脉冲必须在整个定子绕组内有一 个长距离的传输才可以到达中性点。 因而对于电机绕组这样一个复杂的容性网 络来说， 最后得到的脉冲由于波形畸变、 幅值衰减将严重失真。 并且在中性点 处由于三相放电信号混叠、 其他高压设备放电信号混叠等原因使得测量结果的 灵敏度和可靠性大大降低。 从发电机高压端出口处直接测量， 信号传输损耗小， 高频分量损失少， 因 此可以获得比较真实的放电信息， 附表 1很清楚的说明了这一点。
表 1. 定子绕组局部放电到各个监测点的通道传输特性
电压 频率范围 10 ~ 200 5 ~ 75 1 ~ 80 6 ~ 100 传输 (MHz)
特性 传输损耗 (dB) -20 ~ -60 -30 ~ -71 -38 ~ -81 -47 ~ -85 但以往由于高压端出口处传统高压电容器体积大， 不利于安装， 在高电压下 长期运行的安全性与稳定性需要进一步提高。 发明内容
本发明所要解决的技术问题是提供一种发电机局部放电在线监测高压陶瓷 电容传感器， 在高电压下长期运行时具有较好的的安全性与稳定性。
为实现上述目的， 本发明提供了一种发电机局部放电在线监测高压陶瓷电 容传感器， 包括由绝缘材料制作的外形类似支柱绝缘子状的环氧外壳， 该外壳 的圓周上设置有环氧树脂伞群， 所述环氧外壳一端设置有圓形的金属电极和外 接引线， 另一端设置有金属底座； 所述外壳内设置有陶瓷电容芯体， 该陶瓷电 容芯体带有上下两个铜电极， 所述上铜电极与外壳内嵌的上电极通过导电金属 杆连接， 所述外壳内嵌的上电极的另一端与所述圓形的金属电极固定连接， 所 述陶瓷电容芯体的下铜电极连接有金属带， 该金属带的另一端连接在环氧外壳 下部中间设置的引线螺栓上。
作为本发明的优选实施例， 所述陶瓷电容芯体由预先通过耐电压测试及局 部放电测试的两片瓷体焊接组成；
作为本发明的优选实施例， 所述圓形的金属电极一端中心有螺杆， 所述圓 形的金属电极通过螺杆固定在外壳内嵌的上电极上；
作为本发明的优选实施例， 所述金属底座内部安装有取样阻抗， 该取样阻 抗的一端通过金属带与引线螺栓连接， 另一端通过金属带安装在底座上的同轴
线座上；
作为本发明的优选实施例， 所述陶瓷电容芯体为钛酸锶铅铋高性能瓷料； 作为本发明的优选实施例， 所述陶瓷电容芯体瓷料的组分及质量百分含量 为： Sr: 40-60%, Ti : 20-60%, Pb: 10-20%, Bi : 10-20%;
作为本发明的优选实施例， 所述瓷料内掺杂有 0. 1-1%的 Ce02;
作为本发明的优选实施例， 所述瓷料内掺杂有 0. 1-2%的 MgTi03;
作为本发明的优选实施例， 所述导电金属杆的直径为 Φ 4；
作为本发明的优选实施例， 所述圓形的金属电极的两面均为内凹的圓饼形 结构， 外缘也为圓形结构。
本发明发电机局部放电在线监测高压陶瓷电容传感器至少具有以下优点： 本发明传感器安装在发电机高压端用于局部放电监测， 其中， 电容的取值范围 是 20pF ~ 2000pF, 耐电强度为 90kV或更高， 能够长期运行在高压环境下对电机 定子绕组绝缘状况进行在线监测； 另外， 由于本发明在线监测用陶瓷电容传感 器的安装位置靠近高压端， 因此， 可以釆集到失真最小的局部放电信号并且具 有较高的灵敏度。 本发明利用在发电机一相的母线上安装一对这种传感器可以 实现鉴别脉冲时延的抗干扰方法， 从而可以区分出传感器获得的信号是来自于 发电机内部的放电还是来自于外界电力系统的干扰。 附图说明
图 1是本发明发电机局部放电在线监测高压陶瓷电容传感器的侧面剖视图； 图 2是本发明发电机局部放电在线监测高压陶瓷电容传感器的安装位置及系 统框架图；
图 3是传感器单元测量回路的装置图；
图 4是校正脉冲时域图和频域图， 其中 a)时域图， b)频域图；
图 5是 l OOpF电容传感器响应波形图， 其中 a)时域波形， b)频域波形 图中标号与元件对应关系如下：
具体实施方式
下面结合附图对本发明发电机局部放电在线监测高压陶瓷电容传感器进行 详细描述： 请参阅图 1所示， 本发明发电机局部放电在线监测高压陶瓷电容传感器包 括由绝缘材料制作的外形类似支柱绝缘子状的环氧外壳， 该外壳的圓周上设置 有环氧树脂伞群 7 , 所述环氧外壳一端设置有圓形的金属电极 2和外接引线 1 , 另一端设置有金属底座 11。 所述外壳内设置有陶瓷电容芯体 5 , 该陶瓷电容芯体 5 由预先通过耐电压 测试及局部放电测试的两片瓷体焊接组成， 陶瓷电容芯体 5 带有上下两个铜电 极， 该上下铜电极都有一个 M4的螺孔便于连接。 所述上铜电极与外壳内嵌的上 电极 3通过导电金属杆 4连接， 所述外壳内嵌的上电极 3的另一端与圓形的金 属电极 2 固定连接， 所述圓形的金属电极 2—端中心有螺杆， 如此， 圓形的金 属电极 2通过螺杆固定在外壳内嵌的上电极 3上， 而另一端通过外接引线 1与 发电机出口母线相连； 所述陶瓷电容芯体 5的下铜电极连接有金属带 6 , 该金属 带 6的另一端连接在环氧外壳下部中间设置的引线螺栓 8上。
所述金属底座 11与环氧外壳通过丝扣固定在一起， 且金属底座 11 内部安 装有取样阻抗 9 , 该取样阻抗 9的一端通过金属带 6与引线螺栓 8连接， 另一端 通过金属带 6安装在底座 11上的同轴线座 10上， 以便取出所耦合的信号， 此 外， 金属底座 11下沿开设有孔， 用于安装固定螺丝。
所述陶瓷电容芯体 5为钛酸锶铅铋 (
· mBi203 · nTi02 ) 高性能瓷 料， 其中 Sr : 40-60% , Ti : 20-60% , Pb: 10-20%, Bi : 1 0-20% , 如此， 本发明陶 瓷电容芯体 5具有致密的微晶显微结构，具有高的绝缘强度，低的电介质损耗。 此外， 在配料中添加 0. 1-1%的稀土化合物 Ce02进行改性， 控制了配料中 Bi203 的挥发， 改善了晶界特性， 使耐电强度大大提高。 在瓷料中加入 0. 1-2%含量的 MgTi03, 产生移峰和展开效应， 使陶瓷电容器电容温度特性得到很大改善。 在本发明中， 所述陶瓷电容芯体 5 的电容值大小取决于测量系统的频带， 一般选择范围为 20pF-2000pF ,选取合适的电容值使得整个测量系统具有最佳的 响应。 本发明陶瓷电容芯体 5 的介电常数高达数千， 使得电容器的体积可以做 得很小， 而整体的结构紧凑有利于高频信号的传输。
为了获得致密且均匀的瓷质， 要求瓷料具有足够的细度。 为此， 本发明釆 用超细粉碎设备处理原材料， 优化瓷料粉碎工艺， 严格控制瓷料粒度及分布， 使瓷料粒度由平均 3微米细化至 1微米以下， 以获得陶瓷细晶结构， 提高陶瓷 电容瓷芯的耐电强度。 本发明通过改善陶瓷瓷芯成型坯料中粘合剂聚乙烯醇（PVA )的均勾性， 通 过筛分控制坯料粒径和实行粒级配合， 控制坯料中粘合剂和水分的含量及成型 压力和改进加压方式， 消除了层裂缺陷。
在瓷芯烧成工艺方面， 通过降低烧制初期排胶阶段的升温速率等工艺手段， 消除了层裂和变形缺陷， 减小了气孔尺寸及数量。 为提高陶瓷传感器耐电强度， 本发明电容瓷芯由预先通过耐电压测试及局 部放电测试的两片瓷体焊接组成， 这样， 可以克服单一瓷片过厚造成陶瓷坯体 成型困难。 通过控制瓷体倒角量和改进电极结构， 即由 0. 3匪 左右的留边量改 为全电极印刷银电极， 提高了电极边缘起始放电电压。 釆取上述措施后， 本发 明传感器瓷芯局部放电性能和合格率大幅度提高。
本发明釆取调整配方，即提高凑料含量 100份到 150-220份（即环氧树脂： ： t真料的重量比为 100: ( 150-220 ) )对环氧树脂包封料增韧， 加入促进剂和改进 固化工艺制度等措施， 使环氧树脂、 陶瓷电容芯体 5 和其上下铜电极的膨胀系 数匹配， 克服了传感器冷热循环中开裂和局部放电性能下降的弊病。 其环氧包 封料能耐受 -40°C -+85 °C 10次冷热循环而不开裂。 经过上述改进措施制作的传感器电容芯体基本满足甚高频局部放电检测的 要求。
成型的电容陶瓷芯体有上下两个铜电极， 上下铜电极都有一个 M4 的螺孔， 导电金属杆 4可以同时旋进电容芯体 5上铜电极和壳体内嵌上电极 3的螺孔 M4 中， 导电金属杆 4 由原先的 Φ 10的金属杆换为 Φ 4的， 变细的金属杆可以过滤 工作时发电机母线的振动， 防止电容器本体损坏。 下铜电极与环氧外壳下部中 间设置的引线螺栓 8通过导电金属带 6连接。 这样整个环氧树脂壳体的高压端 和低压端就和电容芯子 5 的上下两极牢固的连接起来， 结构紧凑、 连线简短有 利于减少线路的杂散参数。
为了增加放电距离， 以便在空气中使用， 提高陶瓷电容器的防潮防污能力
以及提高电容器耐电强度， 需对电容器进行环氧树脂包封。 对环氧树脂的配方 和工艺进行了研究后， 本发明选用机电性能和耐潮性优良的酸酐固化环氧树脂 体系。 把烧制好的陶瓷电容和相应的螺孔连接好放在事先做好的模具浇灌环氧 树脂就得到了类似图 1 所示的传感器外形。 从图中可以看出这种外形类似支柱 绝缘子， 具有环氧树脂伞群， 以增加绝缘距离减少整个传感器的体积。 所述壳体内嵌的上电极 3上除了与电容芯体连接所用的 M4的螺孔外， 还设 置一个 M12的铜螺孔， 配合相应的带螺杆的圓形的金属电极 2 , 能够把圓形的金 属电极 2 固定在壳体上， 考虑到传感器高压端在运行电压下不能有局部放电， 圓形的金属电极 2 为两面都内凹的圓饼形结构， 外缘也为圓形结构。 圓形的金 属电极 2另一端的外接引线 1可与发电机出口母线牢固连接， 从而使得传感器 和发电机母线连在一起。 外接引线 1 具有橡胶绝缘层， 能够耐受发电机的母线 电压， 并保证高压端的清洁。
金属底座 11与环氧外壳通过丝扣固定在一起， 金属底座 11 内部安装有取 样阻抗 9 , 该取样阻抗 9的一端与引线螺栓 8连接， 另一端安装在底座 11上的 同轴线座 10上，金属底座 1 1下沿开设有孔，用于固定整个传感器的螺丝安装。 确保外接引线 1与发电机母线固定良好， 用射频同轴线从金属底座 11上的 同轴线座 10取信号， 待后续测量电路的正常工作后， 就可以利用这种传感器进 行电机内部局部放电的监测。 请参阅图 2 所示， 传感方法的原理是这样的： 局 部放电本质上是在有限的时间内一个短距离上的电子和离子流， 每当局部放电 发生时就表现为一定电量的流动， 这个总的电流的大小决定于放电时有多少皮 库电荷的传输。 电流在电机绝缘介质的阻抗上表现为一个电压脉冲， 所以可以 用本发明的陶瓷电容传感器耦合这样的电压脉冲以表征电机内部局部放电的多
少。 在工频电压下， 耦合电容表现为较高的阻抗（ 0. 9095 X 1 07Ω ~ 0. 2894 X 10s Ω )远远大于取样阻抗（ 200 Ω ~ 2k O ) 的值， 几乎承受了全部的工频高压， 起 到了保护取样阻抗和后续电路的作用； 而在甚高频范围内 （5MHz ~ 1 00MHz )耦 合电容则表现为一个艮低的阻抗（< 144. 7 Ω ),和取样阻抗相当或小于取样阻抗， 从而可以从取样阻抗上甚高频的局部放电信号。 取样阻抗后面一般并联一个保 护器， 它的作用是在出现较大的浪涌电流以及传感器发生严重性故障时保证后 面测量回路（放大器、 示波器等） 的安全。 传感器上取得的信号经过多路转换 装置进入信号调理单元进行放大或缩小， 再应用高速数据釆集卡釆集信号显示 在计算机上进行信号分析处理。 由于检测的局部放电频率分量比较高， 使得一种基于脉冲时延的抗干扰方 法可以在现场使用， 请参照图 2 所示， 在靠近电机一相高压端的位置和有一定 距离的母线上的另一位置分别安装两个同样规格的这种传感器 C1和 C2 ,对于来 自发电机内部的信号和来自外部电力系统的信号就在 C1和 C2上有不同的到达 时间。 为了便于观察可以调整射频同轴电缆的长度， 使得从外部电力系统来的 信号经两个传感器上到达釆集单元的时间相同， 而来自电机内部的放电信号经 两个传感器的到达时间就有很大的差别， 借助这种方法就可以有效的抑制外来 干扰。 本发明的效果：
电容量： 10. 5kV, 50Hz下， （ 20 2000 ) pF士 （ 2 ~ 200 ) pF
电容传感器耐压： 通过交流 1分钟 90kV耐压
起始放电电压： >55kV
绝缘电阻： 20 C , lkV ( DC ) 下〉 10"ΜΩ
介质损耗： 20 C , 10. 5kV ( AC ) 下 <0. 1 %
电容温度特性： - 25 C ~ 80 C温度范围内， 电容量变化 < 30 %
电容交流电压特性： 电机电压等级 10. 5kV时， 电压变化土 20% , 电容变化 为 <1%。
湿闪试验： 传感器表面充分凝露后， 立即施加工频电压直至传感器表面发 生闪络， 闪络电压平均值为 70. 5kV。 实验中利用 HAEFELY公司的局部放电检测仪， 以 IEC60270的常规实验方法 同时进行测量， 测试回路参见图 3。
1)、 对传感器单元的校正：
不加电压，利用 TeKt ronix的任意波形发生器向电容传感器输入一个 1. 5V、 上升时间 2. 3ns的校正脉冲， 图 4为校正脉冲的时域波形和频谱图。
2)、用电晕放电源取代脉冲发生器，通过试验变压器施加高压，当达到 4. lkV 时， 由局部放电监测仪 TE571 观察到有电晕出现。 实验室利用上述取样单元得 到的电晕放电信号如图 5所示。
由频率响应图可以看出， 100pF电容传感器的响应频率主要在 40MHz , 1 30MHz 以及 220MHz , 属于甚高频范围， 由此验证了此传感器系统可以进行甚高频的局 部放电测量。 所述粘合剂的用量对局部放电起始电压及击穿场强唱的影响如下表 1所示： 粘合剂用量对局部放电起始电压及击穿场强唱的影响
以上所述仅为本发明的一种实施方式， 不是全部或唯一的实施方式， 本领域 普通技术人员通过阅读本发明说明书而对本发明技术方案釆取的任何等效的变 换， 均为本发明的权利要求所涵盖。
Claims
1.一种发电机局部放电在线监测高压陶瓷电容传感器， 其特征在于： 包括 由绝缘材料制作的外形类似支柱绝缘子状的环氧外壳， 该外壳的圓周上设置有 环氧树脂伞群 ( 7 ), 所述环氧外壳一端设置有圓形的金属电极 ( 2 )和外接引线
( 1 ), 另一端设置有金属底座（11 ); 所述外壳内设置有陶瓷电容芯体（5 ), 该 陶瓷电容芯体（ 5 )带有上下两个铜电极，所述上铜电极与外壳内嵌的上电极（ 3 ) 通过导电金属杆（4 )连接， 所述外壳内嵌的上电极（3) 的另一端与所述圓形 的金属电极（2 ) 固定连接， 所述陶瓷电容芯体（5 ) 的下铜电极连接有金属带
( 6 ), 该金属带 （6 ) 的另一端连接在环氧外壳下部中间设置的引线螺栓（8 ) 上。
2.如权利要求 1 所述的发电机局部放电在线监测高压陶瓷电容传感器， 其 特征在于： 所述陶瓷电容芯体（5) 由预先通过耐电压测试及局部放电测试的两 片瓷体焊接组成。
3.如权利要求 1 所述的发电机局部放电在线监测高压陶瓷电容传感器， 其 特征在于：所述圓形的金属电极（2)—端中心有螺杆，所述圓形的金属电极（2 ) 通过螺杆固定在外壳内嵌的上电极（3)上。
4.如权利要求 1或 2所述的发电机局部放电在线监测高压陶瓷电容传感器， 其特征在于： 所述金属底座（11 ) 内部安装有取样阻抗（9 ), 该取样阻抗（9 ) 的一端通过金属带（ 6 )与引线螺栓（ 8 )连接， 另一端通过金属带（ 6 )安装在 底座（11 )上的同轴线座（10)上。
5.如权利要求 1或 2所述的发电机局部放电在线监测高压陶瓷电容传感器， 其特征在于： 所述陶瓷电容芯体（5 )为钛酸锶铅铋高性能瓷料。
6.如权利要求 5 所述的发电机局部放电在线监测高压陶瓷电容传感器， 其 特征在于：所述陶瓷电容芯体瓷料的组分及质量百分含量为： Sr : 40-6030-55% , Ti : 20-48% , Pb: 10-20%, Bi : 10-20%。
7.如权利要求 6 所述的发电机局部放电在线监测高压陶瓷电容传感器， 其 特征在于： 所述瓷料内掺杂有 0. 1-1%的 Ce02。
8.如权利要求 6或 7所述的发电机局部放电在线监测高压陶瓷电容传感器， 其特征在于： 所述瓷料内掺杂有 0. 1-2%的 MgTi03。
9.如权利要求 1 所述的发电机局部放电在线监测高压陶瓷电容传感器， 其 特征在于： 所述导电金属杆（4 ) 的直径为 Φ 4。
10.如权利要求 1所述的发电机局部放电在线监测高压陶瓷电容传感器， 其 特征在于： 所述圓形的金属电极（2 ) 的两面均为内凹的圓饼形结构， 外缘也为 圓形结构。
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| CN102981106A (zh) * | 2012-11-12 | 2013-03-20 | 华北电力大学 | 一种三相交叉互联电缆中间接头局部放电的在线检测方法 |
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