CN101382568A - Optical fiber voltage measuring method and its measuring device - Google Patents

Abstract

The present invention relates to a fiber-optic voltage measurement method and its device for measuring various transient voltages in a power grid system. A metal induction plate is placed on the surface of a high-voltage conductor to be measured, and the induction plate is used to communicate with the high-voltage conductor and the measured high-voltage conductor respectively. The capacitance formed by the ground forms a capacitive voltage divider. After measuring the voltage division ratio of the capacitive voltage divider and the voltage value on the capacitance between the sensing plate and the measured high-voltage conductor, the voltage value of the measured high-voltage conductor to the ground is obtained by conversion. . The measuring device is composed of a front-end computer with an external metal induction plate, an optical fiber, a photoelectric conversion module and a computer part, wherein the induction plate and the shielded chassis of the front-end machine form a capacitive voltage sensor. Compared with the prior art, the present invention measures the voltage by using a capacitive voltage sensor to directly measure the surface field strength of the electrified body, and has good measurement characteristics, simple structure and convenient use.

Description

Optical fiber voltage measuring method and its measuring device

technical field

The invention belongs to the technical field of power measurement, and relates to a fiber-optic voltage measurement method and a measurement device for measuring various transient voltages in a power grid system.

Background technique

Many system debugging tests in the power system are almost inseparable from the measurement of the grid voltage. With the development of power grid construction at all levels, especially the construction of ultra-high voltage and ultra-high voltage power grids, the workload and difficulty of high voltage measurement are also increasing, especially the measurement of various transient voltages in power systems is more difficult. In the past, there are mainly two conventional voltage measurement methods in the power system, that is, the method using voltage transformer measurement method and the method using the end screen measurement method of high voltage bushing. There are two types of voltage transformers, electromagnetic and capacitive, according to their principles. Generally, the method of measuring voltage with voltage transformers can only be used for steady-state power frequency voltage and transient voltage measurement with slow voltage changes; and when measuring voltage temporarily When the dynamic process has a higher frequency, it can only be measured by the method of the end screen of the high voltage bushing. In addition, in the absence of the above two voltage measurement methods, it is necessary to install an independent voltage divider for voltage measurement. To install an independent voltage divider, it is necessary to select a suitable voltage divider according to the transient characteristics such as the frequency, amplitude, and duration of the measured voltage. When measuring higher voltages, the temporary installation of independent voltage dividers on site will be limited by site space, safety distance and other conditions. In addition, the installation difficulty and workload are relatively large.

In the prior art, for the measurement voltage method using the end screen of the capacitor bushing and installing an independent capacitive (capacitive voltage divider is used more) voltage divider, it is necessary to configure the secondary voltage divider according to the primary capacitance and the measurement voltage range of the measuring equipment. Capacitors, at the same time, shielded cables need to be used to connect the secondary voltage divider capacitors and measuring and recording instruments, among which the characteristics of the secondary voltage divider capacitors, shielded cable characteristics (for higher frequency signals need to be equipped with matching resistors) and shielding connection conditions have a greater impact on the measurement , In addition, the length of the connecting cable should not be too long, otherwise it will increase the attenuation of the signal under test and reduce its anti-interference performance.

With the development of EHV and UHV transmission line construction process, the requirements for measuring various transient voltages are getting higher and higher. The rising edge of the fast transient overvoltage (VFTO) generated during the opening and closing process of the GIS (gas fully enclosed combined electrical equipment) equipment in the power system can reach 3 ns, and the transient frequency can reach 100 MHz. Obviously, the conventional method for measuring this voltage cannot meet the requirements. measurement requirements. For this reason, in recent years, some people in the field have proposed to use optical fiber transmission measurement method, namely photoelectric measurement system, to measure voltage.

The photoelectric measurement system is a measurement system that uses various photoelectric effects or photoelectric communication methods. In this system, the good insulation performance of the optical fiber transmission line is used to isolate the electrical signal of the high-voltage equipment to be measured from the low-voltage measuring instrument to achieve Safe and reliable measurement of high voltage characteristic parameters. At present, there are two types of methods for measuring voltage using optical fiber transmission: one is the measurement system composed of electro-optic effect sensors, the most widely used is the measurement system using Pockels electro-optic effect, and the other is capacitive field Measuring system composed of strong probe (spherical probe). The system characteristics of the measurement system using the Pockel electro-optic effect mainly depend on the characteristics of the electro-optic conversion crystal. The conversion characteristics of this crystal are greatly affected by the temperature. Accurate measurement requires more accurate temperature compensation. The entire measurement system is divided into photoelectric part and Record the measurement part, among which the photoelectric part is more complicated. The measurement principle of the voltage measurement system composed of capacitive field strength probes is to place a pair of metal plates (generally spherical plates) in the electric field to be measured. The plane of the plates is perpendicular to the direction of the electric field. Probe, the electric field strength is obtained from the distance between the plates and the voltage between the measured plates. To measure the voltage with the field strength method, it is necessary to calculate the voltage of the charged body under test based on the relationship between the voltage of the charged body and the electric field strength of the measured point. It is not high and cannot be used for the measurement of higher electric field strength, and the system structure is also relatively complicated.

Contents of the invention

The purpose of the present invention is to solve the problems existing in the prior art, to provide a fiber-optic voltage measurement method with reasonable design, good measurement accuracy and stability, and easy implementation and application. type voltage measuring device.

The fiber-optic voltage measurement method of the present invention comprises the following implementation steps: placing a metal induction pole plate on the surface of the measured high-voltage conductor, utilizing the capacitance C2 formed by the induction pole plate and the measured high-voltage conductor (high-voltage wire) and the ground respectively Form a capacitive voltage divider with C1 (see accompanying drawing 1), since the voltage on the capacitor C2 is proportional to the voltage of the high-voltage conductor to the ground, after measuring the voltage division ratio of the capacitor voltage divider and the voltage value on the capacitor C2, According to the capacitance voltage division ratio and the voltage value of C2, the voltage value of the measured high-voltage conductor to ground is obtained. In actual work, the voltage division ratio K of the capacitive voltage divider can be measured by standard voltage divider calibration, and the voltage signal on the capacitor C2 can be collected by a data collector connected to the metal sensing plate and placed at a high potential, and then regenerated The voltage signal on the capacitor C2 is sent to the computer system through the electro-optical converter (optical transmitter), optical fiber and photoelectric converter (optical receiver) connected to the data collector in turn to process, record and display the voltage data, and finally divide the voltage according to the capacitance The voltage value of the measured high-voltage conductor to ground is obtained by converting the voltage divider ratio of the device and the voltage value of C2.

The optical fiber voltage measurement device used to realize the above voltage measurement method is a device that can be used for the measurement of various transient voltages (including external VFTO with extremely high frequency) in the power system. It is composed of machine, optical fiber, photoelectric conversion module and computer part. The metal induction plate and the shielded chassis of the front-end machine form a capacitive voltage sensor. In the shielded chassis of the front-end machine, there are data collectors and electro-optical conversion modules. The capacitive voltage sensor The signal output end is connected to the input end of the electro-optical conversion module through the data collector, the output end of the electro-optical conversion module is connected with the input end of the photoelectric conversion module through an optical fiber, and the output end of the photoelectric conversion module is connected to the signal input end of the computer.

Compared with prior art, the present invention has the advantage that:

a) Using a capacitive field strength sensor to directly measure the surface field strength of the charged body can improve the accuracy and stability of the measured voltage;

b) Integrate voltage sensing, measurement and photoelectric conversion into one, which can effectively improve anti-interference performance;

c) The data acquisition unit block is placed at a high potential and controlled by a computer, which has the characteristics of wide measurement range, good frequency response, large signal recording capacity, and flexible measurement;

d) Using digital optical fiber communication, it can realize 10km long-distance measurement;

e) Small size flat induction plate is adopted, with wide frequency response;

f) Simple structure, convenient installation and use, low cost and high cost performance.

Description of drawings

Fig. 1 is a schematic diagram of the voltage measurement of the present invention.

Fig. 2 is a schematic structural block diagram of a specific embodiment of the measuring device of the present invention.

Fig. 3 is a schematic structural diagram of a capacitive voltage sensor in the measuring device of the present invention.

Fig. 4 is a schematic structural diagram of another capacitive voltage sensor in the measuring device.

Detailed ways

Referring to accompanying drawing, the measurement principle of fiber-optic voltage measuring method and measuring device thereof of the present invention is: place a metal induction pole plate on the surface of high-voltage conductor (high-voltage conductor), metal induction pole plate and high-voltage conductor form capacitance C2, and Ground forms capacitor C1.

When the voltage of the high-voltage conductor to the ground is V (AC voltage, the same below),

Voltage on C2: $V_2=\frac{C_1}{C_1+C_2}V---\left(1\right)$

make $K=\frac{C_1+C_2}{C_1}---\left(2\right)$

Then V=KV ₂ (3)

When the high-voltage conductor-to-ground voltage V and the voltage V2 on the capacitor C2 are known, the voltage division ratio K can be obtained according to the formula (3), or when the voltage division ratio K and the voltage V2 on the capacitor C2 are known, according to the formula (3) The voltage of the high-voltage conductor to the ground can be obtained. In practical applications, the voltage division ratio K of the capacitive voltage divider can be measured by standard voltage divider calibration, and V2 can be measured by the fiber optic voltage measuring device, and then the voltage V of the high-voltage conductor to ground can be calculated by formula (3).

The structure of an embodiment of the fiber-optic voltage measuring device of the present invention is shown in Figure 2, and the whole device is divided into a high-voltage live part (front-end computer), an optical fiber, and a photoelectric conversion unit as a terminal machine and a ground computer part. The front-end processor is mainly composed of a capacitive voltage sensor used to convert the electric field signal into a voltage signal, an analog-to-digital data collector used to convert the analog voltage signal of the sensor into a digital signal and store it, and an electro-optical sensor used to complete the electrical-optical conversion. Transformation module (optical fiber communication module), battery pack (front-end computer working power supply) and fully shielded chassis, a range and measurement control module is directly installed between the capacitive voltage sensor and the data collector, between the data collector and the electro-optical conversion There is a data communication module between the modules, and the input/output end of the data communication unit is connected with the output/input end of the range and measurement control module at the same time. Photoelectric switch for machine power supply. The performance of the shielded chassis is extremely important to the stability and reliability of the entire measurement system. When the shielded chassis cannot become a complete metal shield (without gaps), the shielding effect is not only related to the thickness of the shielding layer, but the most important thing is to deal with The gap at the metal connection; In addition to completing the shielding function, the shielding case also forms a capacitive voltage sensor with the sensing plate, so this part is also the key to the entire shielding effect. The terminal is composed of three parts: photoelectric conversion module (fiber optic communication module), fiber optic remote control power switch launch control module, computer and measurement system software, among which the measurement control software of the computer adopts the purchased digital acquisition module with its own software, this software The function is simple, and the operation is quite different from the conventional data collector software, which is basically satisfactory for use. The optical fiber used in the measurement device is a four-core optical cable with a length of 200m, which can meet the needs of communication and remote control switches.

In the present invention, the capacitive voltage sensor is the basis of the entire measurement device, and the performance of the voltage sensor determines the measurement performance of the entire system. The main parameters of the capacitive voltage sensor are: voltage output range; impedance characteristics; frequency characteristics; structural performance, etc. The capacitive sensor that the designer initially prototyped is shown in Figure 3. The induction plate in the figure is a circular thin metal plate, which is placed 30mm away from the surface of the shielding case. The induction plate is connected to an external voltage dividing capacitor (secondary capacitor), and the voltage is output from the voltage dividing capacitor. There is a distance of 30mm between the plate and the shielding case to enable the sensor to output a higher voltage signal, and a voltage dividing capacitor is connected to reduce the output impedance of the sensor. However, after many tests, it was found that this sensor still has the following problems: ①. Due to the existence of a secondary voltage dividing capacitor, the frequency response of the sensor is not high, which cannot meet the design requirements; ②. The sensing plate is 30mm higher than the shielding case, and the system The uniformity of the electric field is not good; ③. The structure is not easy to form a whole. To this end, designers have made new improvements to the above sensors. The structure of the improved capacitive voltage sensor is shown in Figure 4. It consists of a shielded case, a metal sensing plate embedded on the shielded case, and a polyester insulating film filled between the metal sensing plate and the shielded case. The upper surface of the induction pole plate is flush with the upper surface of the shielding case, and the thickness of the polyester insulating film between the metal induction pole plate and the shielding case is less than 0.1mm. Compared with the sensor shown in Figure 3, the improved new sensor reduces the relative height of the sensing plate and the shielding case, and fills the polyester film with better high-frequency characteristics between the plate and the shielding case, and its thickness is less than 0.1mm , to increase the capacitance value of the sensing plate and the shielding case, and reduce the output impedance; the sensing plate and the shielding case are on the same plane, which is conducive to improving the overall electric field uniformity and the overall rigidity of the structure; removing the secondary voltage dividing capacitor, the output directly to the backstage equipment. After testing the performance of this improved capacitive voltage sensor, its performance has reached the design requirements.

The data collector of the present invention can adopt a device whose module model is PicoScope 5204, which includes a range and measurement control module, a data communication module and corresponding firmware. Since the input impedance of the data collector is generally only 1MΩ, the output impedance of the capacitive voltage sensor is about 1MΩ when the power frequency is 50Hz, and the direct connection of the data collector to the capacitive voltage sensor will cause a large frequency amplitude error. A high-resistance attenuator should be connected between the tor and the capacitive voltage sensor. After the high-resistance attenuator is connected, when the input signal frequency changes from 50Hz to 250Mhz, the amplitude error of the collected signal is ≤1%. If the deep storage data is selected to be above 100M, the signal length can be recorded at a sampling rate of 1G/s greater than 100ms. In this way, high-speed transient waveforms can be recorded more completely when measuring the overvoltage of VFTO and open-type isolating switch opening and closing empty busbars.

The data communication module of the device is a module connecting the front-end machine and the terminal machine with optical signals, and the selection of the communication module is based on the interface form of the collector. For the domestic 50MHz collector, the interface form is RJ45, and the communication modules selected at this time are: RJ45 to optical fiber and optical fiber to RJ45; imported collectors have a USB interface, and the selected modules are USB to optical fiber and optical fiber to USB. The RJ45 optical fiber interface is more popular in China, and the USB optical fiber interface is rarely produced in China. After testing the domestically produced USB optical fiber interface, its data transmission rate is low and its performance is unstable. Finally, an imported USB optical fiber converter was selected. After testing And performance test, the USB fiber optic converter can meet the requirements of use.

The photoelectric switch in the device in Figure 2 is selected as the optical fiber remote control power switch, and its static power consumption is: voltage 12V, current 15mA; power supply current 45mA. Both the electro-optical conversion module and the photoelectric conversion module adopt the USB optical communication module of the model USB2.0 Ranger444.

Claims (6)

1. A fiber-optic voltage measurement method, characterized in that a metal induction plate is placed on the surface of the measured high-voltage conductor, and the induction plate is used to form a capacitance divider with the capacitors C2 and C1 formed by the measured high-voltage conductor and the ground. After measuring the voltage division ratio of the capacitor voltage divider and the voltage value on the capacitor C2, the voltage value of the measured high-voltage conductor to ground is converted according to the voltage division ratio of the capacitor voltage divider and the voltage value of C2. 2. The fiber-optic voltage measurement method according to claim 1, characterized in that the voltage division ratio of the capacitor voltage divider is measured by calibration of the standard voltage divider, and the capacitance is collected by a data collector connected to the metal induction plate. The voltage signal on C2, and then through the electro-optical converter, optical fiber and photoelectric converter, the voltage signal on the capacitor C2 is sent to the computer system for processing, recording and displaying the voltage data, and finally according to the voltage division ratio of the capacitor voltage divider and the value of C2 The voltage value is converted to obtain the voltage value of the measured high-voltage conductor to the ground. 3. A fiber-optic voltage measurement device for realizing the measuring method described in claim 1 or 2, characterized in that it consists of a front-end computer (1), an optical fiber, a photoelectric conversion module and a computer with an external metal induction plate Partial composition, the metal induction plate and the shielded chassis of the front-end machine (I) form a capacitive voltage sensor, and a data collector and an electro-optical conversion module are arranged in the shielded chassis of the front-end machine (I), and the signal output terminal of the capacitive voltage sensor The data collector is connected to the input end of the electro-optical conversion module, the output end of the electro-optical conversion module is connected to the input end of the photoelectric conversion module through an optical fiber, and the output end of the photoelectric conversion module is connected to the signal input end of the computer. 4. The fiber-optic voltage measuring device according to claim 3, characterized in that a measuring range and measurement control module is directly provided between the capacitive voltage sensor and the data collector, and a measuring range and measurement control module is directly provided between the data collector and the electro-optical conversion module. In the data communication module, the input/output end of the data communication unit is connected with the output/input end of the range and measurement control module at the same time, and a photoelectric switch is arranged between the electro-optical conversion module and the data collector. 5. The fiber-optic voltage measuring device according to claim 3 or 4, characterized in that said capacitive voltage sensor consists of a front-end machine (1) shielded chassis, a metal induction plate embedded in the shielded chassis, and a filling The polyester insulating film is formed between the metal induction plate and the shielding case, and the upper surface of the induction plate is flush with the upper surface of the shielding case. 6. The optical fiber voltage measuring device according to claim 5, characterized in that the thickness of the polyester insulating film filled between the metal sensing plate and the shielding case is less than 0.1mm.

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