Technical performance and reliability analysis of

As we all know, reactive power and voltage are important technical standards in the operation and management of power system. The regulation of reactive power affects not only the loss of electricity, but also the voltage and even the safe operation of electricity. The regulation of electric reactive power depends on the reactive power compensation device. Therefore, whether the reactive power compensation device is reliable, whether the technical conditions can meet the requirements of electricity, and whether the technical parameters can meet the requirements of the operating environment are very worthy of analysis and discussion

1 overview of reactive power compensation devices

from the technical principle, reactive power compensation devices are inductive or capacitive components in electricity. At present, China's medium and low voltage electricity is mainly overhead lines and basically carries inductive loads, so most of the reactive power compensation devices used in the system are capacitive, that is to say, they are composed of capacitors and corresponding ancillary facilities

because most of the loads are concentrated in the distribution network, the capacitor banks used for reactive power compensation for many years are basically installed on the medium voltage side and low voltage side of the electricity, including 35kV, 10kV and 0.4kV voltage levels. In terms of operation needs, the reactive power compensation device is composed of capacitor banks, switching elements, detection and protection elements

as early as the 1970s, users in Xuzhou were required to install 400V low-voltage compensation devices locally, and 10kV capacitor compensation devices were installed in substations. At that time, the automation degree of low-voltage reactive power compensation device was low. Most capacitor banks were switched manually through air switches, and the protection measures were simple and rough. When the whole group of capacitor banks failed, the air switch could be started by the thermocouple element of the air switch to trip and remove the fault. The quality of low-voltage capacitors Chinese enterprises have the talent to produce by themselves. They found that their own plastic extrusion machinery is not reliable enough, the sealing measures are poor, and electrolyte leakage often occurs. At that time, the 10kV capacitor bank installed in the substation was composed of a single capacitor, or connected into a triangle or a star, with a large volume. Generally, a capacitor room should be built for installation; The manufacturing quality of the capacitor is not high. The insulating material is composed of paper and chlorinated biphenyl extractant. The uniformity of the paper layer is not good, which is easy to form local breakdown. Chlorinated biphenyl is toxic and has an impact on human body and the environment; The switching of the device is completed by the oil circuit breaker, and the action times are limited, so frequent switching cannot be achieved; The protection part is composed of an electromagnetic relay and a single fuse. The electromagnetic relay cannot realize zero crossing switching, and the protection characteristics of the fuse are not good

it can be seen that the technical performance of the old-fashioned reactive power compensation device is poor, which is mainly manifested in the low degree of automation and low reliability. It cannot operate safely and reliably in the medium and long term, and the operating life is often only two or three years. The technical performance of compensation device is the key to determine whether it can be widely used

2 technical performance analysis of reactive power compensation device

with the continuous development of electricity, the requirements for power quality and energy conservation and consumption reduction are higher and higher, and the position of reactive power compensation device in electricity is becoming more and more important. Therefore, improving the technical performance of reactive power compensation device has become an urgent problem to be solved. For decades, relevant manufacturers and electricity departments have done a lot of work for this. In recent years, the technical performance of reactive power compensation devices has been greatly improved

2.1 automation level of reactive power compensation device

the early reactive power compensation capacitor has a low degree of automation, so it can not judge the changes of electrical operation parameters, and operators need to switch during operation. When the frequency of network changes is high, the operation is more frequent, and the operators will feel laborious, increasing the workload. With the rapid development of computer technology, the current reactive power compensation device successfully adopts the microcomputer module for the operation management of the device. The degree of automation is relatively high. It can judge the changes of electrical parameters in time and carry out reasonable automatic switching, which will not increase the workload of operators, and the automation level has reached the requirements of electrical operation

2.2 reliability of reactive power compensation device

the technical performance and reliability of the early reactive power compensation device can not meet the operation requirements. Many improvements and improvements have been made to the current products, which can be reflected from the operation of the products. At present, many products put into operation in 2000 in Xuzhou are still in safe operation, and the operation life has exceeded 8 years

the operation reliability of reactive power compensation device is also a problem that manufacturers attach great importance to. At present, many technical measures have been taken to improve the reactive power compensation device. Now, taking 10kV and 400V reactive power compensation devices as examples, the following three factors are analyzed

2.2.1 reliability of components of the device itself

the main components of the new reactive power compensation device include: main components (power capacitors), control and protection detection components (CPU microcomputer controller and electronic circuit components), switching components (switches and other electrical components)

a. power capacitor. In recent years, manufacturers have made significant improvements in product raw materials and production processes. For example, 10kV power capacitors have replaced the past paper media with full film or film paper media, the past chlorinated biphenyl has been replaced with detoxified Dodecylbenzene, and the vacuum sealing technology has been adopted, which has greatly improved the quality and service life of power capacitors. In addition, it also adopts the assembled form, which can be installed outdoors, saving the floor area and investment. 400V capacitors also adopt vacuum sealing technology, and produce self-healing metallized film capacitors and other products to improve their reliability. However, due to the nature and structure of the product itself (for example, the capacitor needs to form layered insulation on the insulation structure), its reliability in insulation cannot be compared with that of switches, insulating pillars and other components. Improper operation during operation will produce inrush current in the capacitor, which will have a negative impact on the capacitor

b. microcomputer control components and electronic circuit components. With the rapid development of electronic technology, these components have high reliability and long life. According to the different use environment, the technical levels of these components are obviously different, which can be roughly divided into four levels: military, industrial, civil and ordinary. The reactive power compensation device shall adopt industrial electronic circuit components. Among electronic circuit components, integrated circuits and other semiconductor devices and capacitors are key devices that affect reliability. In the next four years, there will still be 55 million to 105 million tons of capacity reduction tasks, and their levels should be paid more attention to when selecting. The withstand voltage parameters and working temperature parameters are also important for reliability. In the specific selection, attention should be paid to leaving room. The withstand voltage parameters should be selected at a higher level, and the influence of ambient temperature should be fully considered in the working temperature parameters

c. electrical components such as switches. With the substantial improvement of the manufacturing process level and the implementation of the national compulsory quality certification system, the reliability of the electrical components of the 400V reactive power compensation device has been guaranteed, and the products that have passed the national 3C certification should be selected

in the 10kV reactive power compensation device, the previous products used oil circuit breakers to switch capacitors, which could not meet the needs of frequent switching. With the development of oil-free technology of high-voltage switch, 10kV oil circuit breaker has been replaced by vacuum circuit breaker and SF6 circuit breaker. These two kinds of circuit breakers have long electrical and mechanical life, and can meet the requirements of frequent switching. However, the vacuum circuit breaker will cut off the over-current voltage in the arc extinguishing principle, which will affect the insulation life of the capacitor, so it is appropriate to choose SF6 circuit breaker

whether 10kV reactive power compensation device or 400V reactive power compensation device, inrush may occur when switching capacitors, which is unfavorable for capacitors. The current technology has been able to solve this problem, that is, the microcomputer control device is used to analyze the voltage and current waveforms to realize zero crossing switching, that is, when the voltage crosses zero, the capacitor bank is input, and when the current crosses zero, the capacitor bank is cut off. When selecting reactive power compensation device, we should pay attention to the selection of this technical performance

2.2.2 influence of working environment

it mainly refers to the influence of external factors such as temperature, humidity, rain, dust, small animals and so on. There are generally three installation forms of reactive power compensation devices, namely, the compensation cabinet in the distribution room, the compensation equipment of box type transformer, and the column compensation box of line public distribution transformer. The first two can be regarded as indoor installation, while the column compensation box of public distribution transformer belongs to outdoor installation, and its working environment is the worst

the box body of the device installed outdoors is in direct contact with the external air environment, with poor heat insulation effect. The temperature in the box changes violently, prone to condensation, and vulnerable to the interference of external temperature, humidity, rain, dust, and small animals. These factors affect the reliability and life of the device

a. temperature. In the product technical parameters provided by the manufacturer in recent years, the expression of ambient temperature is different, including 40 ℃, 55 ℃, 60 ℃, 65 ℃, etc. The author has done temperature test experiments in the hottest summer: when the temperature is 37 ℃ on a sunny day, the temperature of the compensation box on the column can reach 59 ℃, the temperature of the metal shell in the box can reach 45 ℃, and the temperature of the fixed parts in the box can reach 48 ℃. Obviously, the device with an ambient temperature of 40 ℃ cannot meet the requirements, and the device with an ambient temperature of 55 ℃ has insufficient margin. Since the most sensitive component affected by temperature in the device is electronic circuit components, and the working temperature of electronic components for industrial use is generally 25 ~ 75 ℃, under the principle of fully considering the ambient temperature and leaving a certain margin, the device temperature parameter of 60 ℃ and above is more appropriate

b. humidity. In the product technical parameters provided by the manufacturer in recent years, the expression of relative humidity is also different. Some expressions are that the relative humidity does not exceed 50% at 20 ℃, 90% at 40 ℃, 90% at 40 ℃, 90% at 40 ℃ and 80% at 40 ℃. According to the situation that the column compensation device is used as an outdoor equipment, the requirements for the above relative humidity are low, especially in southern Jiangsu, where the humidity is very high in the plum rain season in summer, so the parameter of relative humidity should be 95%

c. rain proof, dust-proof and condensation proof. The performance of rain proof, dust-proof and anti condensation is related to the structure and sealing of the box. In principle, there is a contradiction between the measures to prevent rain and dust and the measures to prevent condensation. In relative circumstances, the better the sealing measures are, the better the effect of rain and dust prevention is, while the effect of condensation prevention inside the box is worse. This is because: in the case of not absolute sealing, due to the poor breathing of the box, when the temperature and humidity change greatly, the moist air inside the box cannot convection, and it is easy to condense inside the box. Therefore, there should also be higher technical requirements in the production of the device box. It is necessary to properly grasp the relationship between rain, dust and condensation prevention, and reasonably improve the protection level standard of the box, so that these two problems can be properly solved

2.2.3 influence of abnormal power quality

for abnormal power quality, such as overvoltage, harmonic, voltage flicker, waveform distortion and other interference factors, current products also take protective measures. For example, basically, monitoring devices are installed to monitor these factors; Overvoltage protection measures and measures to suppress harmonics, flicker and waveform distortion are taken. Only because the electronic circuit components have poor resistance to overvoltage and voltage mutation, so