Introduction to the Characteristics of Various Switches on the Pole Switch

The pole switch on the pole refers to a type of safety switch used on the pole to ensure the safety of electricity consumption. Its main function is to isolate the high voltage of the circuit. There are various forms of pole switches on the market, and their performances are also different.

1. There are 6 ways to classify the pole switch on the pole:

1.1 According to the country of production, it can be divided into two types: domestic and imported;
1.2 According to the arc extinguishing ability of the contacts, it can be divided into circuit breakers and load switches;
1.3 According to the insulation medium, it can be divided into oil insulation, air insulation and SF6 insulation;
1.4 According to the operating mechanism, it can be divided into electromagnetic operating mechanism, spring operating mechanism and permanent magnet operating mechanism;
1.5 According to the function of the controller, it can be divided into circuit breaker, recloser and sectionalizer;
1.6 According to the material of the outlet bushing, it can be divided into porcelain bushing and silicone rubber bushing.

2. Various switch characteristics of pole switches

2.1 Domestic switchgear.
Advantages: designed and manufactured according to the use characteristics of domestic power systems; generally adopt spring operating mechanism, which can perform electric and manual opening and closing operations; the secondary current of the current transformer is designed according to 5 A, and multiple groups and multiple transformer ratios can be set. It is beneficial to meet the different requirements of relay protection, telemetry and metering; generally the circuit breaker itself is equipped with an isolating switch, and there is an operation lock between the circuit breaker and the isolating switch. Disadvantages: The interior of the circuit breaker is mostly air-insulated, and the safety performance is affected by the surrounding environment There is no special operation control box, and the relay protection function is realized by U and W two-phase current releases, so it is impossible to realize the reasonable cooperation between the upper and lower levels of relay protection, and it is easy to cause the circuit breaker to malfunction and refusal to move; the manufacturing process of the operating mechanism is rough and the airtightness is poor, especially in humid air or coastal areas, the mechanism parts may be severely corroded within a short period of time, and normal operation cannot be performed.

2.2 Import circuit breaker.
The common points of all imported circuit breakers are:
2.2.1 The secondary current of the current transformer is designed according to 1 A, and there are two types of specifications, 600/1 and 1000/1;
2.2.2 All circuit breakers are not equipped with isolating switches;
2.2.3 Equipped with special operation control The control and protection functions of the controller and controller are complete, and the selectivity is strong, which is conducive to the cooperation of the upper and lower protection;
2.2.4 SF6 gas insulation under zero gauge pressure is mostly used, and the sealing performance is good, and the internal insulation is not affected by the external environment. The manufacturing process of the operating mechanism is excellent and most of them are sealed in the SF6 gas cavity, free of maintenance on site;
2.2.5 The price is high, almost twice that of domestic circuit breakers;

2.3 Circuit breakers, reclosers, load switches.

The circuit breaker has a strong ability to extinguish the arc, which can cut off the fault current. It is equipped with a controller with microcomputer protection, which can realize the protection of the branch line. The switch body of the recloser is exactly the same as the circuit breaker, and the difference lies in the function of the controller. Open circuit The controller of the recloser has simple functions, only has the functions of control and line current protection, and other functions are realized by FTU. The controller of the recloser has not only all the functions of the circuit breaker controller, but also has more than 3 times of reclosing, a variety of Characteristic curve, phase judgment, program recovery, operation program storage, independent judgment, connection with automation system and other functions, but the price is relatively high. The load switch can close the fault current, break the rated load current, and use vacuum and SF6 to extinguish the arc. Others It is mainly used as a sectional switch of the line, equipped with an intelligent controller, it becomes a sectionalizer, and the cost is relatively low.

3. Characteristics of the operating mechanism of the pole switch

3.1 Electromagnetic operating mechanism
The closing current is large, there are many parts, and the structure is complex. In addition to electric opening and closing, manual opening operation is also possible. Manual closing and power transmission cannot be performed, and the circuit breaker can only be closed with the closing handle when there is no power supply. Not ideal for distribution network automation.

3.2 Permanent magnet operating mechanism
The permanent magnet operating mechanism is a new concept operating mechanism, which can be divided into monostable and bistable. It is characterized by simple structure, the switching state is maintained by the magnetic force of the permanent magnet, there are very few mechanical transmission parts, and the mechanism is tightly sealed. Higher, less affected by external influences. But it is still an electromagnetic operating mechanism in essence. It is difficult to control the large instantaneous power and mechanical characteristics. The controller is more complicated. The starting capacitor and the life, temperature characteristics and reliability of the electronic control circuit It is the "bottleneck" of the overall reliability of the operating mechanism and should be highly valued. The most fatal shortcoming of the permanent magnet operating mechanism is that there is no manual closing handle. It's going to be very tricky.

3.3 Spring operating mechanism
The domestic spring operating mechanism has complex structure, outdated design concept, poor airtightness, and short mechanical life. The imported spring operating mechanism is represented by the triangular plate type operating mechanism, which has a very simple structure and few parts. The whole mechanism is sealed in the SF6 gas chamber. The failure probability is extremely low. Its function can not only satisfy the electric operation, but also can perform manual opening and closing operations. Even if the controller fails, it can manually resume power transmission as soon as possible. It is the most ideal operating mechanism.

4. Selection of switches for pole switches

Distribution network automation is aimed at automatic fault diagnosis, automatic isolation of faulty areas, and automatic restoration of power transmission in non-faulty areas. The selection of switches should also be based on this, and different options are used for different control methods.

4.1 Local control mode, that is, primary automation.
In this way, the line is short and the segments are small, so a recloser should be used. Make full use of the recloser and action time limit cooperation of the recloser to realize automatic isolation of faulty areas and automatic recovery of power supply in non-faulty areas.

4.2 For distributed intelligent control methods.
FTU is required to transmit various detected signals through point-to-point communication, and transmit the status of the circuit breaker in the fault area and other information to the adjacent FTU, identify the fault area, and realize automatic isolation and restoration of power transmission, that is, FTU+recloser or intelligent FTU+circuit breaker device.

4.3 Centralized control mode
The information detected by the FTU monitoring terminal is sent to the main power distribution server through the communication system, and the main power distribution server performs comprehensive calculation and management. After the main line fails, the feeder circuit breaker in the station first disconnects the faulty line and performs a reclose. If the reclosing is successful, the control center will not make a judgment; if the reclosing is unsuccessful, the control center will, after automatic judgment, remotely control the circuit breaker of the automation system to isolate the faulty area and restore the power supply to the non-faulty area. In this control mode, the faulty section is isolated It is carried out when there is no current and voltage in the line, so the load switch can be used in the sectionalizer to reduce the cost. The branch line is equipped with a circuit breaker and a microcomputer protection, which can accurately and timely cut off the faulty branch, reduce the number of automatic actions, and shorten the scope of power failure and time. This mode is more economical and practical to use load switches for sections and circuit breakers for branches.

5. Precautions for pole switches

Common types of pole switches include pole-mounted circuit breakers, pole-mounted load switches, and pole-mounted isolating switches. The performances of the three are completely different, and the ways of use are different.

5.1 Circuit breaker on pole
It is mainly used for segmental switching, control and protection of distribution lines, and can break and close short-circuit current.

5.2 Oil-immersed circuit breaker.
The oil-immersed circuit breaker is an early product, which tends to be eliminated due to poor breaking capacity, flammable oil, leakage, and easy to cause secondary accidents.

5.3 Vacuum circuit breaker.
There are two types of vacuum circuit breakers: box type and column type. The rated current is usually 400A and 630A. As far as the rated current is concerned, there is not much difference in price between the two. The rated breaking short-circuit current is 12.5kA, 16kA, and 20kA. The rated current breaking times are more than 10,000 times, and the rated breaking short-circuit current breaking times are 30-50 times, which can be operated frequently. According to the relative insulation quality, it can be divided into oil-immersed insulation, air insulation and SF6 insulation.

5.4 SF6 circuit breaker.
The rated current of the SF6 circuit breaker is 400A, 630A, and the rated breaking short-circuit current is generally 12~5kA. Some manufacturers have 16kA products. 50 times, suitable for frequent operations.

5.5 Tips for use:
5.5.1 Although the oil-immersed circuit breaker is an obsolete product, there are still some in the power grid more or less, and its short-circuit trip function can be canceled during operation and used as a load switch.

5.5.2 Pay attention to the verification of the short-circuit current at the installation site. The short-circuit current used for calibration should consider the development and changes of 5-10 years. Vacuum switches and SF6 switches are maintenance-free products. If there is no major problem after installation, it is generally considered to be replaced after 5 years. If the short-circuit breaking current is less than the local The expected short-circuit current is very likely to cause damage to the switch when it is broken.

5.5.3 Select the primary rated current of the current transformer for protection to be 2-3 times greater than the maximum current that may occur at the installation point, and an inrush delay device should be configured. If the primary current of the protection CT ratio is the same or similar to the maximum current at the installation point , even if the switch operates below the maximum current of the installation point, it is in an unstable state due to the small margin of the protection stability range. Only when the switch is closed for the second time can the switch be closed successfully. When a large load is put into the impact of the starting current and the impact of load fluctuations, it will cause a fault-free trip. The time setting of the electronic surge delayer can be very precise, the time setting can be adjusted from 0-5S, and the general time setting should be above 0.05S.

5.5.4 It is not advisable to install too many circuit breakers on a line, which is determined by the non-selectivity of circuit breaker protection. When a line fault occurs, multiple switches may trip at the same time, which will affect the reliability of power supply.

5.5.5 SF6 switch Pay attention to the gas leakage inspection after installation, especially in the first one or two months after new installation.

5.5.6 SF6 switches are not suitable for installation in cold regions. When installing in regions below -20°C, the working curve of SF6 gas should be negotiated with the manufacturer. After the gas leaks or liquefies, when the short-circuit current is broken, the switch will explode due to arc reignition .

5.5.7 The selected circuit breaker should have the reclosing function. Due to the wide range of distribution lines, there are many transient faults and high rates, such as: lightning strikes, instantaneous contact between lines, and circuit breaker protection is very sensitive to short-circuit current, and instantaneously acts on tripping, resulting in power outages for users, and manual testing Sending can often be sent again, which increases the labor intensity of operators. On the other hand, it may increase the number of households during power outages, which violates the original intention of installing circuit breakers to isolate fault points and improve power supply reliability. Judging 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 an external power supply (active): if there is a low-voltage power supply, the low-voltage direct introduction can be considered. If there is no low-voltage power supply, an external power transformer is equipped with a battery. Some manufacturers also use solar energy and a battery. To achieve passive reclosing is to sample the sensed current from the protection CT and supply the controller as the power supply, such as the VT3-12 vacuum circuit breaker produced by Ningbo Tianan Group, which improves the reliability of the circuit breaker due to the reduction of components relative to the active one.

5.5.8 It is advisable to choose a circuit breaker and isolating switch combined electrical appliance, because the manufacturer considers the operation sequence and locks each other when leaving the factory, thus reducing the possibility of misoperation.

5.6 Pole load switch

It has the ability to carry and switch rated current, but cannot break short-circuit current, and is mainly used for line segmentation and fault isolation.

5.6.1 Gas generating load switch. The gas-generating load switch uses a slit composed of solid gas-generating materials to generate a large amount of gas under the action of the arc to form gas-blown arc extinguishing. Because of its simple structure and low cost, it was once widely used.

5.6.2 Vacuum, SF6 load switch. Similar to vacuum and SF6 circuit breakers in appearance and parameters, the difference is that the load switch is not equipped with protective CT and cannot break short-circuit current, but can withstand short-circuit current and close short-circuit current. It has the characteristics of long life and maintenance-free, mechanical life, rated current open The number of interruptions is more than 10,000 times, which is suitable for frequent operations.

5.6.3 Tips for use:
From the point of view of our bureau's use, the failure rate of the gas-generating load switch is relatively high, the arc extinguishing cover has fallen off, and the one-pole switch has been burned many times. The main reason for the burn is that the dynamic and static contacts cannot be fully contacted when they are closed, and the local contact resistance increases and overheats. Cause carbonization breakdown of epoxy resin insulators.

The gas-generating load switch sometimes produces arc light leakage when it is switched on with electricity, which affects personal safety. According to the manufacturer, the arc extinguishing process of the switch is mainly considered when the live load is divided. When the main and auxiliary contacts are not synchronized when the switch is closed, it is easy to occur. Arc leaks.

The arc extinguishing cover of the gas-generating load switch needs to be maintained irregularly. It needs to be inspected and repaired after about 20 times of breaking the full load. It is not as good as the vacuum type and SF6 switch, which can be broken more than 10,000 times, and the long-term operation and maintenance workload is heavy.

The operating mechanism of the gas generating type load switch can be divided into a hook type and a lower operating rod type. The lower operating rod type should be locked when installing the operating handle, and the lock body needs to be replaced and maintained from time to time, which is inconvenient to operate. The operating rod should be installed more than 2.5M above the ground, otherwise it is easily damaged by external force.

The price of the vacuum load combination switch is equivalent to that of the gas-generating switch, but its reliability and safety are unmatched by the gas-generating load switch, so it should be preferred when selecting.

5.7 Pole-mounted disconnector

5.7.1 The pole-mounted isolating switch is mainly used for isolating circuits. It has an obvious fracture in the opening state, which is convenient for line maintenance and reconfiguration of the operation mode. It has two forms of three-pole linkage and single-pole operation.

5.7.2 Tips for use:
The isolating switch can safely carry the working current and short-circuit current, but it cannot break the load current. It can open and close the no-load transformer with the excitation current not exceeding 2A, and the no-load line with the capacitive current not exceeding 5A. Generally, the dynamic and stable current of the isolating switch does not exceed 40kA, and attention should be paid to the calibration when selecting it. The operating life of the isolating switch is about 2000 times.