The current situation and prospect of optical fiber temperature hot spot monitoring system in high voltage equipment
Direct monitoring of the hot spot temperature of high-voltage equipment such as transformer/transformer windings has very practical significance for improving the safe operation of the equipment, extending the insulation life of the equipment, and judging the actual load capacity of the equipment in real time to improve the economic efficiency of the equipment. At present, the actual application of power transmission and transformation and power generation industry in my country is almost zero, which highlights the gap between my country and developed countries in the field of power transmission and transformation equipment.
This paper discusses the current development status of the mature use of fluorescent optical fiber sensors in the world to monitor the hot spot temperature of high-voltage equipment, analyzes the problems and current status quo of the domestic popularization and application of this new technology, and analyzes the feasibility, methods and prospects of its application.
High-voltage electrical equipment such as transformers are the key equipment of the power transmission and transformation system. Their safety, reliability and service life are vital to the safe and reliable operation and life of the entire power transmission and transformation system. Most of these high-voltage equipment adopt a closed structure and work in a high-voltage, high-current, and strong magnetic field environment for a long time, causing heat to accumulate. The heat and temperature rise increases the loss of the power transmission system. If the heat dissipation is not good, it will endanger the normal operation of the equipment, and even cause failures. The adverse social effects and economic losses are immeasurable.
Due to the maturity and cost of technical products, there are currently no reliable technologies and mature products on the market that can fully meet the online temperature monitoring of high-voltage electrical equipment. Now these key equipment generally do not have hot spot monitoring systems installed, which makes the transmission and transformation system vicious accidents. There is a lack of effective technical means for forecasting, preventing and monitoring. The marketed market of the mature and commercialized fluorescent optical fiber temperature sensing system fills the gap in this market. Because the optical fiber temperature sensor product is fully insulated and small in size, it can directly measure the highest temperature of the heating point inside the high-voltage electrical equipment. In this way, real-time monitoring and monitoring of temperature, prediction and prevention of accidents can be achieved. At the same time, operating data can be collected in real time, the insulation life of the equipment can be predicted, the actual load capacity of the equipment can be judged, and a scientific basis can be provided for whether the equipment can be overloaded and safely operated, and economic benefits can be improved. .
1-The significance of real-time online temperature monitoring for high-voltage electrical equipment such as high-voltage transformers
1. It is the future development trend to embed fiber-optic temperature sensors near the hotspots inside high-voltage equipment such as transformers, and to detect the hotspot temperature inside the equipments such as windings from multiple sensors. From a safety point of view, the hot spot temperature of the windings of transformers operating with different capacities at different peripheral temperatures cannot exceed the maximum hot spot temperature allowed by the insulation material's heat resistance class. For example, the maximum hot spot temperature limit of an oil-immersed transformer is 140°C. If the hot spot temperature of the winding exceeds this temperature, part of the oil will generate gas due to cracking, and the performance of the insulating material will decrease, resulting in gas or insulation shock. Accident occurred while wearing.
2. From the perspective of the life of high-voltage equipment such as transformers, the selected insulation materials of various heat-resistant grades have temperature indicators for thermal aging life. The life of high-voltage equipment depends on the aging of the insulation, and the aging of the insulation mainly depends on the operating temperature. As far as oil-immersed transformers are concerned, when the hot-spot temperature of the winding is 98℃, it has a rated lifespan; when the hot-spot temperature of the F-class dry-type transformer windings is 140℃, it has a rated lifespan. Therefore, during the operation of the product, attention must be paid to the hottest spot temperature of the equipment, and it cannot exceed the allowable value of the hot spot temperature of the heat resistance class. According to the latest research, every time the hot spot temperature of the winding increases or decreases by 6Kv, the expected insulation life will be halved or doubled (in the past, dry-type transformers were thought to be IOKv for every increase or decrease). When the transformer is in operation, the temperature distribution of the winding is not uniform. The key factor that determines the insulation life is the absolute temperature of the hottest spot of the winding, not the average temperature of the winding. The newly revised power transformer load guideline (EC-354) believes: "The temperature reached in the hottest area of the winding is the most important limiting factor for the load value of the transformer, so every effort should be made to accurately determine this temperature value." . Therefore, for large-capacity transformers, it is necessary to ensure that the hot spot temperature of the winding is within the qualified range in structure, and the maximum allowable value of the hot spot temperature of the winding can be controlled during operation, and the hot spot temperature can reduce the expected life of the insulation, and Try to reduce the hot spot temperature to compensate for the life sacrificed due to temperature rise.
3. From the perspective of the operating efficiency of power transmission and transformation equipment, after the transformer is equipped with a stable and reliable temperature control system, we can give full play to the load capacity of the equipment within a reasonable range according to the parameters provided by the system, thereby improving the equipment The economic efficiency of operation. Take an IOOMVA transformer in North America as an example:
(1) Rated power: IOOMVA
(2) Assuming that additional capacity can be increased due to the installation of a temperature control system: 10%
(3) Assuming that the annual overload working time of the system is: 450zJ, hour/year
(4) Economic benefits brought by power transmission and transformation: $80/MWh
(5) Annual economic benefit obtained from 10% overload load = lx2x3x4=$360,000
(6) Installation cost of temperature measurement system: $10,000
(7) Assuming a transformer life of 20 years: 180,000hr
(8) Life loss factor at 110% load (125℃): 34 The average cost increased due to the installation of the temperature control system = "(5/6)*7*3)=$85 due to the installation of the temperature control system Average annual economic benefit: $360,000 a $85 = $359,915
2-the technical difficulties of hot spot temperature monitoring and monitoring of high-voltage equipment
There are many technical difficulties to directly measure the hot spot temperature of high-voltage equipment. The main problems are: high-voltage insulation, strong electromagnetic interference, long-term reliability and stability of the system, etc. At present, domestic high-voltage electrical equipment temperature control technology mainly uses thermal resistance (Pt1OO), thermocouple (high resistance wire) and other electrical sensors for temperature measurement, pressure thermometer, infrared temperature measurement, light transmission type "optical fiber" temperature sensor module and GpRS Wireless transmission, etc. For the above technical methods, the first difficulty encountered is the problem of high-voltage insulation: electrical sensors, pneumatic temperature measurement systems (such as WD ZK/BWY/Japan WR series, etc.), and infrared temperature measurement methods are all faced with incomplete solutions. Metal wires, metal parts or shielding measures, installation of pressure bulbs or infrared probes in high-voltage areas may cause insulation hazards to the safety of high-voltage equipment.
The second is the problem of electromagnetic interference. The weak current temperature signal is interfered in a strong magnetic field environment, which makes the stability and reliability of the system questionable. The third problem is that metal wires and metal parts produce eddy currents in the electromagnetic environment, causing losses and self-heating. The fourth system life issue, especially the light-transmitting point-type "optical fiber type" temperature sensor, the wireless transmission type temperature sensing system and the air pressure temperature measurement system, the system life issue is particularly prominent: "optical fiber type" Temperature sensors (such as OPt-e-3000, DTS-2, etc.) and GPRS wireless transmission temperature sensing system (such as A--11 wireless temperature measurement system) are stored in the module, the power supply battery and other parts have a long working life in a high-temperature environment Shortage and maintenance difficulties, etc., cause the overall reliability of the system to decrease, and its practicability is affected. The pneumatic temperature measurement system will cause the entire temperature measurement system to be scrapped as the internal pressure of the bulb leaks.
In summary, thermal resistance, thermocouple and other electrical sensors need to use metal wires to transmit signals. Due to electromagnetic interference, metal parts/wires are in a strong electromagnetic environment, there are serious electromagnetic interference and eddy current heating, and Can not guarantee long-term stable and reliable high-voltage insulation performance, so that it has inherent shortcomings in high-voltage electrical temperature monitoring applications.
Pressure-type temperature sensors have the problem of high-pressure gas or liquid leakage in the temperature measurement chamber, and their reliable working life, sensitivity and accuracy cannot be guaranteed. The installation of metal temperature bulbs in high-voltage and strong electromagnetic environments is also a big problem. GpRS wireless transmission and light transmission type point-type "fiber-type" temperature sensor module has poor reliability and stability, high false alarm rate, difficult maintenance, and problems such as replacing the transmitter/temperature measurement module battery at a certain interval, and there is also damage The original insulation problem of the equipment makes it difficult to promote this product.
Infrared temperature measurement is a non-contact visual temperature measurement, which can only measure the surface temperature of the equipment under visual conditions, and is susceptible to environmental temperature and electromagnetic field interference. It is not easy to realize online automatic monitoring and monitoring, and manual operation is required. Moreover, the internal space of electrical equipment is small, and the heating point is usually hidden, and the safe distance for installing the infrared probe cannot be guaranteed. In addition, this method also needs to know the emissivity of the measured object, to ensure that the radiation of the measured object fully reaches the infrared detector, and to eliminate the background noise as much as possible. In addition, the thermal probe of traditional technology products is too large (for example, optje-3000 is 6X3.2X2.8em), and there are problems with metal parts (such as shielding nets, shielding shells, pressure bulbs, infrared probes, etc.). The installation of the temperature system inside transformer windings or other high-voltage electrical equipment brings inconvenience and adversely affects the time response speed of the system to temperature.
The above methods are more severely affected by harsh environmental conditions and electromagnetic interference. The limitations of technical means make it impossible for them to fundamentally remove these effects, so they cannot fundamentally solve the core problems of improving the reliability and stability of the system and reducing the negative impact of the temperature measurement system on the original equipment. These have become these technical methods. The bottleneck of further development of the application.
3-The development status and application feasibility of optical fiber temperature measurement technology
The fluorescent optical fiber sensor temperature measurement system is specially designed for the temperature monitoring and monitoring application of high-voltage electrical equipment. Safe type, easy to install inside small high-voltage equipment, can well adapt to high-voltage and high-current detection environment, and fundamentally solve the defects of electrical, pressure and infrared temperature measurement systems. The material that constitutes the optical fiber sensor temperature measuring probe has excellent chemical and mechanical properties, and is especially suitable for high-voltage environments without negative impact on large systems. The optical fiber sensor can provide a more accurate and reliable coil hot spot temperature value for the monitoring system, so that the designer can accurately grasp the impact of temperature on the equipment, so as to accurately control the risk within a safe range. Since 2002, Shenbian has tried to use optical fiber sensors in transformers for temperature measurement. Later, it has successfully carried out commercial applications in many large transformers exported to the United States. It has worked well so far and has become the first practical application of equipment in China. manufacturer. At present, the technical maturity and commercialization of optical fiber temperature measurement systems have been greatly improved over a few years, and the current price has dropped exponentially. The time for this technology to be applied to high-voltage electrical temperature monitoring in a large area is ripe. Regarding the application of new optical fiber temperature measurement technology in high-voltage electrical temperature monitoring and monitoring, many experts from the State Grid Corporation and the Electric Power Design Institute have been paying attention and calling on national regulatory agencies, equipment manufacturers, power generation and transmission and transformation enterprises and enterprises since 2002. Scientific research institutions actively promote the promotion and application of this technology. The main points of view are as follows:
1. Optical fiber sensor is a new technology suitable for temperature measurement of high-voltage equipment and improving system safety. At present, there are few practical applications in our country, but it is very worthy of popularization and application in the field of high-voltage power transmission and transformation.
2. It is recommended that domestic high-voltage equipment manufacturers accept this technology as an industrial standard and install it on high-voltage equipment.
3. It is recommended that owners of the power transmission and transformation and power generation industries include this technology in the bidding documents in the bidding documents.
4. It is recommended that domestic electric power research departments actively carry out research on the application of this technology in high-voltage power transmission and transformation system equipment.
5. The principle of this method is simple, the technology is advanced, and the cost is rapidly decreasing with the rapid expansion of the market. When it reaches a certain amount of application, its cost will not be much higher than the cost of conventional temperature measurement equipment. Especially when it is installed with large equipment such as transformers and thyristor valves, its cost can be ignored. This has become a concern for users. Favorable reasons.
4-the main problems hindering the application of optical fiber sensing technology in high-voltage electrical equipment
1. Lack of national authoritative standards: National competent authorities have not issued corresponding industry standards, and owners of power transmission and transformation industries and design institutes are unwilling to take the initiative to take the policy and technical risks brought about by the application of new technologies.
2. The application of this technology puts forward higher requirements for equipment manufacturers in terms of manufacturing process and quality control: Since the system can directly measure and read the winding hot spot temperature, manufacturers are required to better solve the problem during design and manufacturing. Heat dissipation and cooling, winding arrangement, current density, hot spot distribution, magnetic leakage and circulating current eddy current loss, etc., while also solving the process problems of the installation process of the optical fiber probe in the coil and the core.
3. The market's awareness of new technology is not high, and the promotion of new technology products needs to be strengthened.
4. Users are waiting for mature products with stable quality and appropriate price to be put on the market.
5-Market status and application prospects
The fluorescent optical fiber sensor product developed and produced by Xi'an Heqi Optoelectronics Technology Co., Ltd. is specifically designed for temperature monitoring of high-voltage electrical equipment. It has reached the world's leading level in terms of product performance, quality, and cost, and has the highest The cost-performance ratio.
The application of optical fiber sensing technology can greatly improve the safety and reliability of power transmission and transformation equipment, improve equipment operation efficiency, and reduce labor intensity. With the improvement of market awareness, the launch of mature products, the improvement of design and manufacturing processes, and the gradual establishment of industry standards, the prospect of optical fiber sensor technology in the field of high-voltage electrical equipment temperature monitoring is unquestionable.
6-Conclusions and recommendations
The characteristics of optical fiber sensing technology products are very prominent, and they are especially suitable for temperature monitoring of high-voltage electrical equipment. Compared with the traditional technology, the advantages are very obvious. It can bring direct benefits to the power transmission and transformation and power generation industries. It is a special New technology worthy of full promotion. It is recommended that the relevant national administrative departments actively study the promotion and application of this technology in the power industry, actively cultivate the market, put forward clear needs to domestic research institutions, and promote the marketization and productization of applied technology. It is recommended that manufacturers actively study the application of this technology in equipment manufacturing, and improve the core competitiveness of enterprises through technological progress. For example, before embedding optical fiber sensors in high-voltage equipment such as transformers, simulation calculations can be used to analyze the distribution of the hot spot temperature of the high-voltage equipment to determine the approximate location of the hottest spot. In terms of process design, the following measures can be taken: design a smooth oil circuit, use appropriate winding current density, use transposed wires to reduce circulating current consumption and eddy current consumption, and use high-power and high-efficiency coolers.
It is suggested that the owner and design department actively promote the application of this technology in the industry on the basis of sufficient market research, and include the technology in the scope of the standard requirements of the project bidding document. It is recommended that system integrators actively focus on this new technology product, carry out targeted application development, and improve the added value of this technology.