Analysis of actual temperature rise of high voltag

Analysis of actual temperature rise of high-voltage switchgear in operation

[Abstract] after analyzing the actual temperature rise data of domestic jyn, KYN handcart cabinets and 8bk20 switchgear produced by the joint venture, it is found that the temperature rise level of switchgear in operation exceeds the data measured in type test. Then, the causes of temperature rise exceeding the standard are further analyzed from the aspects of test conditions, metal expansion effect, fastening bolt pressure, conductor material conductivity and so on. Finally, it is suggested that the switchgear should be selected and maintained according to the actual situation

[keyword] switchgear; Temperature rise; Type test

with the development of electricity and the improvement of equipment technology, 10 and 35 kV system switchgear has been widely used in electricity. The internal overheating of the switchgear has become a common problem in the use of the switchgear. Due to the tightness of the switchgear, there is a problem that the temperature rise of the switchgear exceeds the standard in some heavily loaded areas

the temperature rise of the switchgear exceeds the standard, which directly affects the safe and stable operation of the equipment. The pan based carbon fiber composite (molded products) depends on the types of resins added (thermosetting resin and thermoplastic resin) and the overheating problem is a continuous development process. If it is not controlled, the overheating degree will continue to intensify, and have a great impact on the performance of insulating parts and the service life of the equipment

at present, for the switchgear used in the power system to ensure that all testing operations are carried out in a stable and orderly rhythm, strictly abide by the equipment procurement procedures and technical policies, and ensure that all incoming switchgear pass the type test, especially the requirements for temperature rise are relatively strict. Transportation 1 Maximum experimental force (KN): in 50 rows, the load usually will not reach the design full capacity of the switchgear, and the temperature rise of the switchgear should not be very prominent, but the actual situation is not always the case

1 analysis of actual temperature rise data of switchgear

1.1 domestic jyn handcart cabinet

Table 1 shows the statistics of the relationship between the measured temperature rise and load of two 10 kV main transformer switchgear of the same model and parameters in a substation. The switch cabinet is produced by a switch factory in Fujian and is of jyn type. The test temperature is the surface temperature of the switchgear box

the data shows that with the increase of load, the temperature rise of the switch cabinet accelerates rapidly. When the load is close to 1900 a (about 76% of the rated current of 2500 a of the switchgear), the temperature rise is particularly obvious, up to 47 ℃, which does not meet the standard requirements (the standard is 30 ℃ under full load), while when the load is low (below 1200 a), the temperature rise is not obvious

1.2 domestic KYN handcart cabinet

Table 2 shows the statistics of the relationship between the measured temperature rise and load of the 10 kV main transformer switchgear of a substation. The switchgear is produced by a Switchgear Factory in Yangzhou, KYN type, equipped with VD4 circuit breaker. Before temperature measurement, open part of the top cover and test the surface temperature of the switchgear box and the temperature of the main busbar at the same time

the data shows that the maximum temperature of busbar has reached 100 ℃, and the temperature rise is 88 ℃, which obviously exceeds the standard (the temperature rise standard of busbar is 65 ℃). Due to the prominent problem of temperature rise in the substation, the manufacturer adopted new steel for the No. 1 and No. 2 bus bridges of the 10kV switchgear in the substation, and the specification of the copper bar of the main bus was changed to 2 × TMY120 × 10 (original specification is 2 × TMY100 × 10) And further improve the ventilation system. After the transformation of No. 2 main transformer switchgear, the actual measured temperature is shown in Table 3

the temperature rise has improved slightly after the transformation, but the deviation from the temperature rise data provided by the type test of the switchgear is still large

1.3 handcart cabinet of the joint venture factory

the switchgear of a joint venture factory is produced by a Shanghai switchgear Co., Ltd., the model is 8bk20, and the test position is the appearance of the switchgear box and the internal busbar

here, the temperature rise of the switchgear does not exceed the standard temporarily, but it should be noted that at this time, the load does not reach 70% of the rated capacity, but the temperature rise is close to the upper limit. It can be seen that although the temperature rise of the products of the joint venture is better than that of domestic equipment, there is also a situation that the temperature rise exceeds the standard

the data shows that the actual temperature rise level of the switchgear in operation usually exceeds the temperature rise data measured in the laboratory. Moreover, in most cases, when the temperature rise exceeds the standard, the switchgear is far from reaching the design full capacity

2 cause analysis of the actual temperature rise of the switchgear exceeding the standard

the actual temperature rise inside the switchgear, especially the busbar connection and other parts, is usually higher than the data measured in the type test. There are mainly the following reasons:

(1) the data measured in the type test is usually completed in the laboratory, and the duration is not long, usually no more than 8 h. It does not have the cumulative effect of temperature rise, and cannot be equal to the equipment that operates for a long time and keeps heating

(2) different metals have different expansion effects. The metal expansion coefficient of steel bolts is much smaller than that of copper and aluminum busbars, especially the bolted equipment joints. With the change of load current and temperature in operation, the expansion and contraction degree of aluminum or copper and iron will be different and creep will occur, that is, the metal will slowly plastic deformation under the action of stress, and the creep process is also closely related to the temperature at the joint. Practice has proved that when the operating temperature at the joint exceeds 80 ℃, the joint metal will expand due to overheating, staggering the position of the contact surface, forming tiny voids and oxidizing. When the load current decreases and the temperature drops back to the original contact position, due to the coverage of the oxide film on the contact surface, it is impossible to be the direct contact between metals during the original installation. The increased contact resistance of each temperature change cycle will increase the heat of the next cycle, and the increased temperature will further deteriorate the working condition of the joint, thus forming a vicious cycle

(3) the pressure of fastening bolts at the connecting part is improper. Some installation or maintenance personnel think that the tighter the connecting bolts are, the better the conductor connection. In fact, it is not the case. Especially for aluminum busbar, the elastic coefficient is small. When the pressure of the nut reaches a certain critical pressure value, if the strength of the material is poor, and then continue to increase the improper pressure, it will cause some deformation and uplift of the contact surface, but reduce the contact area and increase the contact resistance, thus affecting the contact effect of the conductor

(4) the conductivity of the selected conductor material does not meet the requirements, most of which are due to the insufficient purity of the conductor raw material

(5) other factors on site, such as improper installation and maintenance process, such as inadequate treatment, unevenness and smoothness of the bus contact surface during processing, connection and installation, and no special power grease, lead to the reduction of effective contact area, increase of contact resistance and heating

3 conclusion

the temperature rise data in the switchgear type test cannot correctly reflect the actual temperature rise level of the switchgear in operation, especially the switchgear with heavy load in long-term operation. Due to the cumulative effect of temperature rise for a long time, the actual temperature rise level of the switchgear in operation usually exceeds the temperature rise data measured in the laboratory. Some manufacturers have not studied the temperature rise level in the actual operation of the switchgear in depth. For example, most manufacturers start the fan according to the standard of 2500 a for the switchgear with a rated value of 3150 A. It is unreasonable to adopt this standard after the switchgear has experienced a long period of high load operation. Usually, the fan has not been started, and the temperature rise has already exceeded the standard

therefore, when selecting switchgear equipment, you cannot blindly trust the laboratory data of the manufacturer, and you cannot blindly apply the laboratory data standards in daily operation, maintenance and management. Practical experience is often very important. Only by paying attention to practice and constantly analyzing and solving problems according to the actual situation, can we truly implement the safe operation management work that is expressed by the industry at the end of the design