Selection and use of switching appliances on the m

Selection and use of column switch apparatus

Abstract: column switches commonly include column circuit breakers, column load switches, and column disconnectors. The performance of the three is completely different, and the place and mode of use are different. This paper introduces the matters that should be paid attention to when selecting the three

key words: Tips for the selection and use of column switches

1 column circuit breaker

is mainly used for sectionalized switching, control and protection of distribution line sections, and can disconnect and close short-circuit current

(1) oil immersed circuit breaker. Oil immersed circuit breaker is an early product, which tends to be eliminated due to its poor breaking capacity, flammable oil, leakage and easy to cause secondary accidents

(2) vacuum circuit breaker. There are two types of vacuum circuit breakers: box type and column type. The rated current is usually 400A and 630A. In terms of the rated current, the price difference between them is small. The rated breaking short-circuit current is 12.5ka, 16kA and 20KA. The mechanical life and rated current are breaking more than 10000 times, and the rated breaking short-circuit current is breaking several times, which can be operated frequently. According to the relative ground insulation quality, it can be divided into oil immersed insulation, air insulation and SF6 insulation

(3) SF6 circuit breaker. The rated current of SF6 circuit breaker is 400A and 630A, and the rated breaking short-circuit current is generally 12.5ka. At present, some manufacturers have 16kA products, with mechanical life, rated current breaking more than 10000 times, and rated breaking short-circuit current breaking times, which is suitable for frequent operation

(4) tips for use:

① although oil immersed circuit breakers are obsolete products, there are still some in the electricity more or less. During operation, their short-circuit tripping function can be cancelled and used as load switches

② pay attention to the calibration of short-circuit current at the installation site, evaluate the mechanical properties of materials and structural parts, and provide leading suppliers with test equipment solutions. The short-circuit current used for calibration should consider the development and changes of the year. Vacuum switches and SF6 switches are maintenance free products. If there is no major problem after installation, it is generally considered to replace and overhaul after 5 years. If the short-circuit breaking current is less than the local expected short-circuit current, it is very easy to cause the switch damage during breaking

③ the primary rated current of the current transformer for protection should be times larger than the maximum current that may appear at the installation point, and the inrush current delayer should be configured. If the primary current of the protection CT transformer is the same or similar to the maximum current at the installation point, even if the switch operates below the maximum current at the installation point, it is in an unstable state due to the small margin of the protection stability range. When the line is closed for power transmission, because there are many distribution transformers in the distribution line, The impact of inrush current may increase the sales of switches from 16.3 billion yuan in 2002 to 59 billion yuan in 2010, and the secondary closing can be successful. When a large load is put into operation, the impact of starting current and the impact of load fluctuation will cause fault free tripping. The time setting of electronic inrush current delayer can be very accurate, and the time setting s is adjustable. Generally, the time setting should be more than 0.05s

④ it is not suitable to set too many circuit breakers on one line, which is determined by the non selectivity of circuit breaker protection. When the line fails, it may cause multiple switches to act and trip at the same time, which will affect the reliability of power supply

⑤ pay attention to the gas leakage inspection after the installation of SF6 switch, especially in the first one or two months after the new installation

⑥ SF6 switch is not suitable for installation in cold areas. When installing in areas below -20 ℃, the working curve of SF6 gas should be negotiated with the manufacturer. After gas leakage or liquefaction, when the short-circuit current is disconnected, the switch will explode due to arc reignition

⑦ the selected circuit breaker should have reclosing function. Due to the wide range of distribution lines, there are many instantaneous faults and rates, such as lightning strike and instantaneous line contact between lines, and the circuit breaker protection is very sensitive to short-circuit current, which acts instantaneously to trip, resulting in power failure of users, while manual trial transmission is often able to send out, which increases the labor intensity of operators, on the other hand, it may increase the number of households during power failure, contrary to the installation of circuit breakers to isolate fault points The original intention of improving the reliability of power supply. From the actual operation experience of our bureau, real permanent fault tripping is rare, and it should be very necessary to realize the reclosing function. To realize the reclosing function, the products of general manufacturers need external power supply (active): if there is a low-voltage power supply, low-voltage direct introduction can be considered. If there is no low-voltage power supply, the external power transformer is equipped with a battery, and some manufacturers use the form of solar energy and battery. The realization of passive reclosing is based on the sampling of the induced current of the protection CT and the supply of the controller as the power supply. For example, the VT vacuum circuit breaker produced by Ningbo Tian'an group is relatively active. Due to the reduction of components, it also points out the direction for the development of China's plastic granulator technology and the reliability of the circuit breaker

⑧ it is advisable to choose the combination of circuit breaker and disconnector. Since the manufacturer considers the operation sequence and mutual locking when leaving the factory, the possibility of misoperation is reduced

2 the load switch on the column

has the capacity of carrying and opening and closing the rated current, but cannot break the short-circuit current. It is mainly used for line segmentation and fault isolation

(1) gas generating load switch. Gas producing load switch is a kind of gas blowing arc extinguishing switch, which uses a slit composed of solid gas producing materials to produce a large amount of gas under the action of arc. Because of its simple structure and low cost, it was once widely used

(2) vacuum, SF6 load switch. It is similar to the shape and parameters of vacuum and SF6 circuit breakers. The difference is that the load switch is not equipped with protection CT and cannot disconnect the short-circuit current, but it can withstand the short-circuit current and close the short-circuit current. It has the characteristics of long service life and maintenance free. The mechanical life and the number of interruptions of rated current are more than 10000 times, which is suitable for frequent operation

(3) tips for use:

① from the use of our bureau, the fault rate of gas generating load switch is high, the arc extinguishing cover has fallen off, and the one pole switch has been burned for many times. The main reason for the burning is that the dynamic and static contacts cannot be fully contacted when closing, and the local contact resistance increases, causing the carbonization and breakdown of epoxy insulator due to overheating

② the gas generating load switch will sometimes produce arc leakage during live closing, affecting personal safety. According to the manufacturer, the arc extinguishing process of the switch design mainly considers live load separation. When the main and auxiliary contacts are not synchronized during closing, arc leakage is easy to occur

③ the arc extinguishing cover of gas generating load switch needs irregular maintenance, and it needs to be inspected and repaired after disconnecting the full load for about 20 times. It is not as good as vacuum type and SF6 switch, which can be disconnected for more than 10000 times, and the workload of long-term operation and maintenance is large

④ the operating mechanism of gas generating load switch can be divided into hook type and down operating lever type. The down operating lever type should be locked when installing the operating handle, and the specific body of the lock needs to be replaced and maintained from time to time, which is inconvenient for operation. The operating rod should be installed more than 2.5m above the ground, otherwise it is easy to be damaged by external forces

⑤ the current price of vacuum load combination switch is equivalent to that of gas producing switch, and its reliability and safety are unmatched by gas producing load switch, so it should be preferred when selecting

3 column disconnectors

(1) column disconnectors are mainly used to isolate circuits. There are obvious fractures in the opening state, which are convenient for line maintenance, reconstruction of operation mode, three pole linkage and single pole operation. We know that any search engine is a form of collecting all the pages on the web

(2) tips for use:

① the disconnector can reliably carry the working current and short-circuit current, but cannot disconnect the load current. It can open and close the no-load transformer with excitation current not exceeding 2a and the no-load line with capacitance current not exceeding 5A

② generally, the dynamic stable current of the disconnector does not exceed 40ka, and attention should be paid to calibration when selecting

③ the operating life of the disconnector is about 2000 times. (end)