What is the classification and working performance of high-voltage circuit breakers
Oil Circuit Breaker
Sealed insulating oil is a type of switchgear used as an arc extinguishing medium for breaking faults, which comes in two forms: multi oil circuit breakers and low oil circuit breakers; It was applied in the power system earlier, with mature technology and relatively cheap price. It is widely used in power grids of various voltage levels.
Oil circuit breakers are used to cut off and connect power sources, and can quickly and reliably cut off current in the event of a short circuit.
The insulating oil in multi oil circuit breakers is not only used as an arc extinguishing medium, but also as the main insulation between the contacts after the contacts are disconnected, as well as between the live parts and the grounding shell. Multi oil circuit breakers have the characteristics of high oil consumption, large amount of metal consumables, easy fire or explosion, large size, low processing technology requirements, durability, and low price. At present, except for a few models of outdoor multi oil circuit breakers such as 35kV that are still in use in the power system, the production and use of other multi oil circuit breakers have been discontinued.
The insulation oil in low oil circuit breakers is mainly used as an arc extinguishing medium, while the insulation between the live parts and the ground is mainly made of porcelain bottles or other organic insulation materials. This type of circuit breaker is called a low oil circuit breaker due to its low oil consumption.Low oil circuit breakers have the advantages of fewer consumables and lower prices, but they require regular maintenance and pose a risk of fire and explosion. Although low oil circuit breakers are currently in use, they have gradually been replaced by new types of circuit breakers such as Vacuum Circuit Breakers and sulfur hexafluoride circuit breakers.
vacuum circuit breaker
The "vacuum circuit breaker" is named after its high vacuum insulation medium for both the arc extinguishing medium and the contact gap after arc extinguishing; It has the advantages of small size, light weight, and is suitable for frequent operation and arc extinguishing without maintenance, and is widely used in distribution networks. Vacuum circuit breaker is an indoor distribution device in a 3-10kV, 50Hz three-phase AC system, which can be used for the protection and control of electrical equipment in industrial and mining enterprises, power plants, and substations. It is particularly suitable for places that require oil-free, low maintenance, and frequent operation. Circuit breakers can be configured in central cabinets, double-layer cabinets, and fixed cabinets for the control and protection of High-Voltage Electrical Equipment.
Sulfur hexafluoride circuit breaker
Sulfur hexafluoride circuit breakeris a type of circuit breaker that uses sulfur hexafluoride (SF6) gas as an arc extinguishing medium and insulation medium. Abbreviated as Sf6 Circuit Breaker.
The use of sulfur hexafluoride as an arc extinguishing medium in circuit breakers began in the early 1950s. Due to the excellent characteristics of this gas, the voltage and current parameters of this circuit breaker with a single break are significantly higher than those of compressed air circuit breakers and low oil circuit breakers, and do not require high air pressure and a considerable number of series breaks.
In the 1960s and 1970s, SF6 circuit breakers were widely used in ultra-high voltage and large capacity power systems. In the early 1980s, SF6 circuit breakers with 363 kV single break, 550 kV double break, and rated breaking currents of 80 and 100 kA were successfully developed.
Working performance of high-voltage circuit breaker
Rated voltage (nominal voltage): It is a parameter that characterizes the insulation strength of a circuit breaker and is the standard voltage for long-term operation of the circuit breaker. In order to meet the requirements of power system operation, circuit breakers also specify the maximum operating voltage corresponding to the rated voltage of each level. For levels 3-220KV, the maximum operating voltage is about 15% higher than the rated voltage; For 330KV and above, the maximum operating voltage is about 10% higher than the rated voltage. The circuit breaker should be able to operate reliably for a long time at the highest operating voltage.
Rated current: It is a parameter that characterizes the long-term current capacity of a circuit breaker, that is, the maximum current that the circuit breaker allows to pass continuously for a long time.
Rated breaking current: It is a parameter that characterizes the breaking capacity of a circuit breaker. At rated voltage, the maximum current that a circuit breaker can ensure reliable breaking is called the rated breaking current, which is expressed in kiloamperes as the effective value of the periodic component of the short-circuit current at the moment of contact separation of the circuit breaker. When a circuit breaker operates in a power grid below its rated voltage, its breaking current can increase. However, due to the mechanical strength limitation of the arc extinguishing chamber, there is a maximum value for the breaking current, which is called the limit breaking current.
Dynamic stable current: It is a parameter that characterizes the ability of a circuit breaker to pass short-term current, reflecting the ability of the circuit breaker to withstand the electrodynamic effects of short-circuit current. The maximum peak current allowed to pass through a circuit breaker in the closed state or at the moment of closing is called the electrically stable current, also known as the limit passing current. When the circuit breaker is stabilized by dynamic current, it cannot be damaged due to the action of electric force.
Closing current: It is a parameter that characterizes the closing current capability of a circuit breaker. Because when the circuit breaker is connected, there may be a short-circuit fault in the circuit, and the circuit breaker will close a large short-circuit current. In this way, on the one hand, the electric force of the short-circuit current weakens the closing operation force, and on the other hand, due to the breakdown of the contacts before they make contact, an arc may occur, which may cause the contacts to melt and damage the circuit breaker. The maximum peak current that a circuit breaker can reliably close is called the rated closing current. The rated closing current and dynamic stability current are numerically equal, both equal to 2.55 times the rated breaking current.
Thermal stability current and duration of thermal stability current: Steady current is also a parameter that characterizes the ability of a circuit breaker to withstand short-term current, but it reflects the ability of the circuit breaker to withstand the thermal effects of short-circuit current. Thermal stable current refers to the effective value of the maximum periodic component of the current allowed to pass through a circuit breaker in a closed state for a certain duration, at which point the circuit breaker should not be damaged due to short-term heating. According to national standards, the rated thermal stability current of a circuit breaker is equal to the rated breaking current. The duration of the rated thermal stability current is 2 seconds. If it needs to be greater than 2 seconds, it is recommended to use 4 seconds.
Closing time and opening time: These are parameters that characterize the operational performance of circuit breakers. The opening and closing times of various types of circuit breakers are different, but they all require quick action. The closing time refers to the time from the closing coil of the circuit breaker operating mechanism to the contact of the main contact. The opening time of the circuit breaker includes two parts: the inherent opening time and the arc extinguishing time. The inherent opening time refers to the period from the opening coil of the operating mechanism being connected to the separation of the contacts. The extinguishing time refers to the period from the separation of the contact to the extinguishing of the arc in each phase. So, the opening time is also known as the full opening time.
Operation cycle: This is also an indicator of the performance of circuit breaker operation. Short circuit faults in overhead power lines are mostly temporary, and the fault quickly disappears after the short-circuit current is cut off. Therefore, in order to improve the reliability of power supply and the stability of system operation, circuit breakers should be able to withstand one or more closing, opening, or immediately opening actions after closing. This type of operation that involves multiple opening and closing operations at certain time intervals is called an operation loop.