Discussion on using load switch or circuit breaker in ring main unit

  If the cabinet type is classified according to the switchgear, there are load switch cabinet, circuit breaker cabinet, GIS, etc
, and there is no ring main unit
Ring network cabinet is a conventional name, which originally refers to the load switch cabinet used for ring network power supply
Now it is often regarded as a synonym of load switch cabinet, regardless of whether it is used for ring network power supply
The load switch cabinet can be used for ring network power supply, medium voltage dividing room dispatching, and medium voltage terminal substation power supply
The specification requirements of the transformer that is allowed to use the load switch and fuse protection by the power supply departments in various regions are different
For example, the transformer capacity is generally required not to be greater than 1000KVA in Beijing, and 1600KVA in Shenzhen The load switch cabinet has simple structure, low cost (ha ha, a few imported products are not cheap), small volume, and most of them can be installed against the wall
Generally, there is only fuse protection but no relay protection
The current carrying capacity of the main bus of the load switch cabinet is generally less than or equal to 630A, the rated breaking current of the load switch is generally less than or equal to 630A (1700A in a few cases), the rated current (fuse) of the transformer cabinet (outgoing cabinet) is generally not more than 125A, and the transfer current of the high-grade load switch can reach 2800a
Some load switch cabinets can be installed with special vacuum circuit breakers, SF6 circuit breakers, or adopt air pressure and other arc extinguishing methods
The short-circuit breaking capacity is close to or reaches the level of the switch cabinet
After adding relay protection, such cabinets should be regarded as circuit breaker cabinets All of us are familiar with the medium voltage circuit breaker cabinet
From the old fixed cabinet gg1a to the current common handcart armored cabinet (floor type and middle type), the circuit breaker has changed from more oil and less oil to vacuum and SF6, the operating mechanism has changed from manual operation, electromagnetic operation and motor spring energy storage, and the operating power supply is AC or DC
No matter whether the relay protection adopts GL to shunt, DL time limit to the current combined relay protection, The common characteristics of the medium voltage circuit breaker cabinet are complex structure, high cost, large volume, large maintenance workload, equipped with relatively perfect relay protection devices, and different types of bus main connection lines can be designed according to needs
The short-circuit current breaking capacity can reach more than 50kA, and the current carrying capacity of the main bus can reach more than 3150A
The mechanical life of the general circuit breaker exceeds that of the load switch 1
Traditionally, load switch and circuit breaker are very different
The load switch is mainly used for breaking and closing the load current
The load switch can be used in conjunction with the high-voltage fuse to replace the high priced circuit breaker and cut off the fault current, that is, the short-circuit current
In this way, the arc extinguishing function of the load switch is relatively weak and the manufacturing cost is reduced; It is precisely because the traditional load switch is not used to cut off the fault current, so it is not necessary to connect with the protection device and automatic device
Therefore, most load switches are operated manually and cannot be operated electrically
In the design of the circuit breaker, it is considered that not only the load current can be switched off and on, but also the short-circuit current after the fault can be cut off
It must be connected with the protection device and the automatic device, so it has the manual and electric switching functions
However, in modern times, especially with the introduction of foreign technology, load switches are more and more like circuit breakers
Individual load switches have increased the arc extinguishing capacity and increased the electric operation function 2
Fln36-12/630-20 indoor AC high-voltage sulfur hexafluoride load switch is generally used as “ Ring main cabinet ”, It is mainly used for connection between distribution networks
Most of them do not install protection or cut off fault current
Kyn44a-12 armored movable AC metal enclosed switchgear is a complete set of power distribution equipment for indoor 3
6 ~ 12kV three-phase AC 50Hz single bus and single bus section system; It is mainly used for power distribution of industrial and mining enterprises and institutions, substation power transmission and distribution switchgear of power system and large-scale high-voltage motor starting
It is used for control, protection and monitoring
Because its protection function is very complete, it is suitable for the protection of power distribution equipment, so as to prevent the possibility of overstepping protection after equipment problems occur
I checked that kyn44a-12 switch cabinet can use domestic VS1, USM or imported VD4 Vacuum Circuit breakers, but it can not be matched with vb series vacuum circuit breakers In the main network, the “ Binary ” Generally, circuit breakers are not used, mainly because they are unnecessary 1
The main function of the circuit breaker is to cut off the fault current, that is, to cooperate with the relay protection
In the main network (not for users), it is the category of distribution network automation, and the protection mode of the whole system is the current type (which is also the final form of the development of distribution network automation at this stage)
Unfortunately, there is no city in China that can well realize this mode, The main reason is that it is not considered to be a systematic project, and there are too many places that need to be transformed (replaced), which basically exceed the original investment estimate
2
If the transformation is not carried out according to the requirements, the direct consequence is that the relay action selectivity cannot meet the requirements, so automation is impossible
You can refer to the recent implementation instructions for distribution network automation in Beijing Olympic village
3
Therefore, most distribution automation in China now adopts the voltage type protection mode, which has been relatively mature
When the line fails, the voltage type protection directly trips the substation, and then finds and isolates the fault point through the sectionalized switching (load switch)
The sectionalized switch does not participate in the removal of fault current
Therefore, it is not necessary to use a circuit breaker
4
Moreover, under normal conditions, the breaking times of load switch are far greater than that of circuit breaker, which is also a major reason for selecting load switch
5
As for a line exceeding 630A in the main network, this situation is generally regarded as an obstacle, and a new line needs to be shunted, because the main network cable needs to have a 50% margin of 1260a?? Haohao, what a terrible cable & ldquo; Three out ” Whether to use the circuit breaker depends on the situation
As for the outgoing line of the user:   1
The trend is to install a circuit breaker, and the protection action is required in the case of single-phase grounding at the user side
The reason is that 80% of the faults at the user side are single-phase grounding
It will be very troublesome to jump directly to the substation
2
In terms of responsibility, it is also necessary to install circuit breakers at the user's side and provide corresponding protection
It is also clear who is responsible for the power failure
Manufacturer of distribution cabinet: http://www
jtcele
com/