The Purpose And Difference Of 10kv Pole (disconnector, Load Switch, Circuit Breaker And Fuse)
The switch installed on the outdoor pole in the 10kV overhead distribution line is used in the suburban and rural distribution network. It is a mechanical switchgear for breaking, closing, and carrying line load current and fault current. Lv Pole Mounted Circuit Breakers is mainly composed of switch body + FTU. The primary and secondary integrated pole-mounted circuit breaker is generally composed of a switch body with a sensor + FTU (feeder automation terminal).
1. Classification of pole-mounted switches
According to the breaking capacity:
a. Pole-mounted isolating switch: cannot close or break normal load current, has obvious break, and is used for isolating line maintenance
b. Pole-mounted load switch: can close, carry, and break normal load current (≤630A), can carry but cannot break fault current.
c. Upper circuit breaker: can close, carry, and break normal load current (≤630A) and fault current switchgear (≥20kA).
d. Pole fuse: used to break short-circuit current and protect lines
Arc extinguishing method: vacuum arc extinguishing, SF6 arc extinguishing, oil arc extinguishing (eliminated)
Insulation method: air insulation, SF6 gas insulation, composite insulation, oil insulation (eliminated)
According to the controller equipped, it is divided into:
a. Boundary switch: built-in zero-sequence transformer, with zero-sequence protection function, equipped with load switch or circuit breaker
b. Voltage load switch: can automatically open and close according to the voltage changes of the lines on both sides
c. Centralized load switch: cannot actively open the circuit breaker of short-circuit current
SF6 insulating gas is a colorless, odorless, non-toxic, non-flammable gas, and has excellent electrical insulation and arc extinguishing characteristics. The density is 5 times that of air and is not easy to leak.
2. Pole isolating switch
The pole isolating switch, also known as the isolating knife switch, is a control electrical appliance without an arc extinguishing device. Its main function is to isolate the power supply to ensure the safe maintenance of other electrical equipment. Therefore, load operation is not allowed. However, under certain conditions, it is allowed to connect or disconnect low-power circuits. It is the most frequently used electrical device among high-voltage switches.
The pole-mounted isolating switch can be used for power outage maintenance, fault finding, cable testing, and reconstruction of operation mode of line equipment. Pulling open the pole-mounted isolating switch can isolate the equipment that needs to be repaired from other running lines, establish a reliable insulation gap, and provide workers with a visible and obvious disconnection mark to ensure the safety of maintenance or testing work. The advantages of the pole-mounted isolating switch are low cost, simplicity and durability. Generally, it is used as a property boundary switch between the air-added line and the user, and as a boundary switch between the cable line and the overhead line. It can also be installed on one or both sides of the line contact load switch to facilitate fault finding, cable testing, and maintenance and replacement of contact load switches.
The isolating switch cannot be operated with rated load or large load, and cannot separate and connect load current and short-circuit current. Generally, when the power is supplied, the isolating switch is closed first, and then the circuit breaker or load switch is closed; when the power is cut off, the circuit breaker or load switch is disconnected first and then the isolating switch is disconnected.
The isolating switch 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 an excitation current not exceeding 2A and the no-load line with a capacitance current not exceeding 5A. The dynamic stability current of the isolating switch generally does not exceed 40kA, and attention should be paid to calibration when selecting. The operating life of the isolating switch is about 2000 times.
3. Pole-mounted load switch
The pole-mounted load switch is a control device with a simple arc extinguishing device that can open and close the circuit with load. It can switch on and off a certain load current and overload current, but cannot disconnect the short-circuit current. It must be used in series with a high-voltage fuse to cut off the short-circuit current with the help of the fuse.
The load switch is a switching device between the isolating switch and the circuit breaker, mainly used for line segmentation and fault isolation.
The load switch mainly includes gas-generating load switches, vacuum, and SF6 load switches. 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 a gas-blowing arc extinguishing. Because of its simple structure and low cost, it was once widely promoted and used. Vacuum and SF6 load switches are similar in appearance and parameters to vacuum and SF6 circuit breakers. The difference is that the load switch is not equipped with a 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. The mechanical life and rated current breaking times are more than 10,000 times, which is suitable for frequent operation.
The commonly used pole-mounted load switches in work generally use pole-mounted vacuum load switches. The vacuum load switch adopts vacuum arc extinguishing, SF6 insulation, three-phase common box type, VSP5 electromagnetic or spring operating mechanism, current transformer can be built-in, cable or terminal outlet, can be built-in isolation break, hanging or sitting installation. As shown in the figure below:
In addition, the use of pole-mounted SF6 load switch liquid is not small. The SF6 load switch adopts SF6 arc extinguishing, SF6 insulation, three-phase common box type, current transformer can be built-in, cable or terminal outlet, and the outer side can be equipped with an isolation device, hanging or sitting installation. As shown in the figure below:
4. Pole-mounted circuit breaker
A circuit breaker is a switch device that can close, carry and disconnect the current under normal circuit conditions and can close, carry and disconnect the current under abnormal circuit conditions within a specified time. Circuit breakers can be used to distribute electrical energy, start asynchronous motors infrequently, protect power lines and motors, etc., and automatically cut off the circuit when they are seriously overloaded or short-circuited or undervoltage. Its function is equivalent to the combination of fuse-type switches and over-underheating relays.
Pole-mounted circuit breakers refer to circuit breakers installed and operated on poles, commonly known as "watchdogs". They are a type of switch device that can cut off or connect lines under normal circumstances, and when a short-circuit fault occurs in the line, the faulty line can be manually or automatically switched through operation or the action of relay protection devices. The main difference between circuit breakers and load switches is that circuit breakers can be used to disconnect short-circuit currents. Pole-mounted circuit breakers are mainly used for segmented switching, control, and protection of distribution line sections, and can open and close short-circuit currents.
According to the arc extinguishing medium used, pole-mounted circuit breakers can be divided into oil circuit breakers (basically eliminated), sulfur hexafluoride (SF6) circuit breakers, and vacuum circuit breakers.
In the past, both sulfur hexafluoride (SF6) circuit breakers and vacuum circuit breakers were widely used in distribution network projects. Now, the circuit breakers in distribution lines mainly use outdoor AC high-voltage intelligent vacuum circuit breakers. Intelligent vacuum circuit breakers have fault detection, protection control and communication functions. Generally installed at the responsibility demarcation point of 10kV overhead lines, they can realize automatic removal, single-phase grounding and automatic isolation of short-circuit faults. They are ideal products for distribution line transformation and distribution network automation construction.
Intelligent vacuum circuit breakers can be operated manually, electrically, by remote control and by remote host. The circuit breaker consists of three parts: the main body, the operating mechanism, and the controller (with a built-in isolating switch). The circuit breaker can be configured with CT (protection current transformer), ZCT (zero-sequence current transformer), and u (voltage transformer) as the detector of the controller as needed.
Vacuum circuit breakers are divided into SF6 insulated vacuum circuit breakers and air insulated vacuum circuit breakers according to the insulation material. SF6 insulated vacuum circuit breakers use vacuum arc extinguishing, SF6 insulation, three-phase common box type, spring operating mechanism, current transformer can be built-in, cable or terminal outlet, optional isolation device on the outside, hanging or sitting installation. Air insulated vacuum circuit breakers use vacuum arc extinguishing, air insulation, three-phase solid-sealed pole type, spring or permanent magnet operating mechanism, external current transformer, terminal outlet, optional isolation device on the outside, sitting installation. As shown in the figure below:
5. Drop-out fuse
Drop-out fuse, commonly known as Link, is the most commonly used short-circuit protection switch for 10kV distribution line branch lines and distribution transformers. It has the characteristics of economy, easy operation, strong adaptability to outdoor environment, etc., and is widely used in 10kV distribution lines and distribution transformers for protection and equipment switching and cutting operations.
The drop-out fuse is installed on the branch line of the 10kV distribution line, which can reduce the scope of power outage. Because it has an obvious disconnection point of the high-voltage drop-out fuse, it has the function of an isolating switch, creating a safe working environment for the maintenance section line and equipment, and increasing the sense of security of the maintenance personnel. Installed on the distribution transformer, it can be used as the main protection of the distribution transformer, so it has been popularized in 10kV distribution lines and distribution transformers.
The fuse can be installed on the power supply side of the load switch or on the power receiving side of the load switch. When it is not necessary to frequently replace the fuse, the former arrangement should be adopted so that the load switch can be used as an isolating switch to isolate the voltage applied to the current-limiting fuse.
The components of the drop-out fuse mainly include insulator, lower support seat, lower moving contact, lower static contact, mounting plate, upper static contact, duckbill, upper moving contact, fuse tube, etc.
6. Differences between pole switches
The main differences are as follows:
The isolating switch has no arc extinguishing device, so it is only suitable for cutting off no-load current, and cannot cut off load current and short-circuit current. Therefore, the isolating switch can only be safely operated when the circuit is safely disconnected, and it is strictly forbidden to operate with load to avoid safety accidents.
Because the load switch has an arc extinguishing device, it has a certain arc extinguishing ability, but it is not as strong as the arc extinguishing ability of the circuit breaker. It can separate and connect normal working current. In the case of short circuit, it can only silently bear the short-circuit current. If it is manually or electrically disconnected at this time, it may explode. Therefore, the load switch is generally used with a current-limiting fuse (the load switch + fuse is not a standard configuration, and it can also be used without a fuse). The fuse disconnects the circuit in the event of overload or short circuit. In order to save costs, the load switch + fuse can replace the circuit breaker.
The circuit breaker has a strong arc extinguishing ability and can separate and connect normal working currents, as well as fault currents. The protection function of the circuit breaker is realized by the relay protection device. The high-voltage circuit breaker does not have the thermal trip, magnetic trip, undervoltage trip and other devices of the low-voltage circuit breaker. Whether the line is faulty is determined by the relay protection device, and the circuit breaker only performs the trip according to the instructions of the relay protection. Because the load switch and the isolating knife cannot break the fault current, there is no need to send them instructions when the line fails. The circuit breaker is a switch with strong arc extinguishing ability and must be used together with the relay protection device.
Through , we can draw the following conclusions:
Isolating switch-can only break and connect the system no-load current, and as the obvious disconnection point of the main wiring system, it is the obvious disconnection point of the system during the maintenance process. Common models: GW9, HGW9, GW4, GW5, etc.
Load switch-can break and connect the normal load current of the system, but cannot break the fault current of the system. Common models: FZW32
Circuit breaker-in addition to breaking and connecting the normal load current of the system, it can also break and connect the fault and short-circuit current of the system. Commonly used models: ZW32, ZW20, ZW7, ZW8, LW3, etc.
