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What is a switchgear?

Publish Time: 2022-05-04 16:35:32     Author: DELIXI

Switchgear: refers to the line in a certain solution will be the primary equipment and secondary equipment of complete sets of power distribution equipment, that have been assembled on line, the equipment is used for control, protection, stationary and handcart type, the outlet and inlet line of the voltage grade and can points, high voltage switchgear (stationary and handcart type) and low voltage switchgear (stationary and draw-out type).  Switch cabinet structure is roughly similar, mainly divided into bus room, circuit breaker room, secondary control room (instrument room), feeder room, between the rooms generally have steel plate isolation.  

Internal components include: bus (busbar), circuit breaker, conventional relay, integrated relay protection device, measuring instrument, isolating knife, indicator light, grounding knife, etc.  

From an application perspective

Incoming Cabinet

Also called receiving cabinet, is used to receive electric energy from the grid equipment (from the incoming line to the bus), generally installed with circuit breakers, CT, PT, isolating knife and other components.  

Outgoing Cabinet

Also called feeder cabinet or power distribution cabinet, it is used to distribute electric energy (from the bus to each outlet). It is also installed with circuit breakers, CT, PT, isolating knives and other components.

Bus connection cabinet  

It is also called bus breaking cabinet, which is used to connect two sections of bus (from bus to bus). In single bus section and double bus system, bus connection is often used to meet the requirements of users to choose different operation modes or to ensure selective cutting load in case of failure.  

PT Cabinet

The voltage transformer cabinet is generally installed directly on the bus to detect the bus voltage and realize the protection function.  The voltage transformer PT, isolating knife, fuse and lightning arrester are mainly installed inside.

Isolation Cabinet

The isolation cabinet is used to isolate the busbar at both ends or to isolate the electrical equipment and power supply equipment. It can provide operators with a visible endpoint to facilitate maintenance and overhaul operations.  Because the isolation cabinet does not have the ability to break off and connect the load current, it cannot push and pull the handcart of the isolation cabinet when the circuit breaker with it is closed.  In the general application, it is necessary to set the interlock between the circuit breaker auxiliary contact and the isolation handcar to prevent the operator from misoperation.  

Capacitor cabinet

Also called compensation cabinet, is used to improve the power factor of the power grid, or reactive power compensation, the main components are connected together into a group of capacitor banks, switching control loops and fuses and other protective appliances.  Generally installed side by side with the incoming cabinet, one or more capacitor cabinets can run side by side.  After the capacitor cabinet is disconnected from the power grid, the components in the cabinet cannot be directly touched, especially the capacitor bank, because the capacitor bank needs a period of time to complete the discharge process.  Within a certain period of time (depending on the capacity of the capacitor bank, such as: 1 minute) after the power failure, it is not allowed to re-close, in order to avoid overvoltage damage to the capacitor.  For automatic control function, we should also pay attention to the reasonable distribution of capacitor banks switching times, so as to avoid the damage of one group of capacitors, while the other groups are seldom switching. 

Measuring Cabinet

Mainly used for measuring electricity (KWH), and high voltage, low voltage points, generally installed with isolation switch, fuse, CT, PT, active watt-hour meter (traditional meter or digital meter), reactive watt-hour meter, relay, and some other auxiliary secondary equipment (such as load monitoring instrument).  

GIS Cabinet

Also called enclosed combination electric cabinet, it is the circuit breaker, isolating switch, grounding switch, CT and PT, lightning arrester, such as bus close combination in metal casing, and then to insulation and arc extinguishing performance good gas (usually with sulfur hexafluoride SF6) and ground insulation measures as alternate with, is suitable for high voltage level and high capacity level in the grid,  Used for power distribution and control. 

Circuit Breaker

Under the normal operation of the circuit breaker, the circuit breaker is in the closed state (except for special application), and the circuit is connected.  The circuit breaker can be switched on or off under the control of the integrated protection device when the automatic control or protection control operation is carried out.  Circuit breaker can not only on the normal load current, and can withstand a certain time of short-circuit current (several times or even dozens of times of normal working current), and can break the short-circuit current, cut fault lines and equipment.  Therefore, the main function of the circuit breaker is to break and connect the circuit (including breaking and connecting normal current, breaking short circuit current).  Because in the process of breaking and connecting the circuit, the moving contact and the static contact of the circuit breaker inevitably produce an electric arc.  In order to protect the contact, reduce the loss of the contact material and reliably break the circuit, measures must be taken to extinguish the arc as soon as possible, one of which is to use different extinguishing media to fill the dynamic and static contacts of the circuit breaker.  According to the different circuit breakers of arc extinguishing media, they can be divided into oil circuit breakers (more oil, less oil), sulfur hexafluoride (SF6) circuit breakers, vacuum circuit breakers, air circuit breakers, etc.  The circuit breaker is the main primary equipment in the high and low voltage switchgear that we often come into contact with in engineering.  

The isolation knife switches 

Isolation switch (or isolation switch) is mainly used to isolate high voltage power supply, to ensure the safety of the line and equipment overhaul, can break the current is very small (generally only a few amperes).  Since there is no special arc extinguishing device, it cannot be used to separate the fault current from the normal working current, and it is not allowed to carry out the breaking operation with load.  


Fuse is a simple circuit protection appliance. Its principle is that when the current flowing through the fuse reaches or exceeds a fixed value for a certain time, the melt itself melts and cuts off the circuit.  Its action principle is simple, easy to install, generally not used alone, mainly used with other electrical appliances.  

Load switch

Load switch has a simple arc extinguishing device, arc extinguishing medium generally uses air, can be connected and broken off a certain current and over current, but can not break the short circuit current, can not be used to cut off the short circuit fault.  Therefore, it is absolutely not allowed to replace the circuit breaker with a simple load switch;  If a load switch is to be used, it must be used in conjunction with the aforementioned high voltage fuse (in fact, fuses and load switches are often used in series as a simple overload protection to reduce the cost of the project).  


In simple terms, transformer is the use of alternating electromagnetic field to achieve different voltage level conversion equipment (in fact, the conversion of electrical energy), the voltage before and after the transformation does not change in frequency.  According to its use can be divided into many kinds, such as power transformer, rectifier transformer, voltage regulator, isolation transformer, as well as CT, PT and so on.  What we often encounter in the engineering site is the power transformer.

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