High breaking high pressure AC vacuum load switch

This paper introduces the structure and working principle of VFX high-breaking AC vacuum load switch-fuse combination, expatiates the development content of the product and solves the key technical process. Finally, the new high-breaking high-voltage AC vacuum load switch- Combination of electrical advantages. Vacuum load switch - fuse combination of electrical appliances in China is the most promising a load switch. load switch according to the insulation medium is divided into gas-type load switch, pressure load switch, vacuum load switch and SF6 load switch.  

China in the initial stage of development to gas and pressure-type load switch-based, and gas-based load switch due to poor arc suppression capability, is now rarely used. Compressed load break switch by compressed air for arc, breaking with visible arc, the maximum breaking transfer current is small, about 1200A. The SF6 gas in the Kyoto Protocol is included in one of the six restricted greenhouse gases and is a highly potent greenhouse gas. Although SF6 density is greater than air, but with turbulence, it can still move to the upper part of the atmosphere. And once it arrives there, its greenhouse effect will be 24,900 times larger than CO2. The existence of SF6 is estimated to be between 8000 and 10,000 years, the most optimistic estimate is not less than 3200 years. So the vacuum load switch in China is the most promising a kind of load switch.

The principle and the role of load switch

The load switch is a split switch with a dedicated arc extinguishing contact, an arc extinguishing device and a spring disconnecting device. Structurally, the load switch is similar to the disconnector (has a visible break point in the open state), but it can be used to open and close the circuit, which is similar to the circuit breaker. However, the circuit breaker can control any circuit, and the load switch can only open and close the load current, or cut off the load current, so only for cutting and switching under normal circumstances, and can not be used to disconnect the short-circuit fault current. However, it is required that its structure be able to pass fault current at short circuit time without damage.

The advantages of the load break switch is the lower price, and more for 10 kV or less of the distribution line, the arc method of air, compressed air, SF6 and vacuum arc and so on several. With the continuous development of science and technology, the type and quality of load switches have increased and improved.The load switch has a simple arc extinguishing device, its arc suppression capacity is limited, in the circuit normal work, used to turn on or off the load current, but when the circuit is broken, can not be used to cut off the huge short-circuit current, load switch off , There are visible break points, is its characteristics.

The difference between the disconnector and the load switch

Isolation switch does not have a special arc extinguishing device, the arc ability is weak, it is generally used to isolate the voltage, will have been cut off by the short circuit, no load current flowing through the circuit connected or cut off, and can not be used to turn on or cut off the load Current. The main purpose of the disconnector is when the electrical equipment to be power outage maintenance, use it to isolate the power supply voltage, and cause a clear disconnect point to ensure the safety of maintenance personnel.

The load switch is a split switch with a dedicated arcing contact, an arc extinguishing device and a spring disconnecting device. Structurally, the load switch is similar to the disconnector (which has a visible break point in the open state), but it can be used to open and close the circuit, which is similar to the circuit breaker. However, the circuit breaker can control any circuit, and the load switch can only open and close the load current, or cut off the load current, so only for cutting and switching under normal circumstances, and can not be used to disconnect the short circuit fault current. However, it is required that its structure be able to pass through the short-circuit fault current without damage. Since the extinguishing device and the contact of the load switch are designed to be cut and connected to the load current, the load switch should, in most cases, be used in conjunction with a high voltage fuse, which serves as a task for cutting off the short circuit fault current. load break switch opening and closing frequency and operating life is often higher than the circuit breaker.

Different Short - circuit of Load Switch

With the successful development of the electric switch mechanism dedicated to the load switch, the load switch to achieve a long-range control of the sub-operation, which for the external type of energy meter load control switch to bring new opportunities for development. Most of the external cost control load switch, the use of small circuit breaker structure type, due to increased pre-paid function, making the product function is not only a simple over-current protection, need to have controllable homogeneous operation performance. 

 Therefore, the power system on the cost control load switch the reliability of the higher requirements, not only to successfully complete the line overload, short circuit protection, and requires its short circuit protection and troubleshooting points, the product performance can continue to To ensure the normal power supply circuit. Installed in the line of the load break switch, due to the power system in the transformer capacity, transmission line impedance, the user side and the transformer distance, the load side of the line is very different, resulting in short circuit flows through the load switch fault current size varies. Based on the load switch is generally installed in the terminal of the line, the actual short circuit current of the majority of 630 ~ 6 000A, therefore, by a group of the same specifications of the type of load switch (small circuit breaker) in different short-circuit test current test analysis, Help to study the actual situation of products in different circuits, help to study the product failure reasons and key functional components.

How to choose the right load switch

load break switch is mainly used to break and close the load current, can also be used in conjunction with high-voltage switch with the high-voltage fuse, instead of circuit breakers. As the load switch is easy to use, the price is reasonable, so the load switch in the 10kV distribution system has been widely used. In the design of a reasonable choice of load switch, to protect the safe and reliable operation of the power grid is of great significance. 
Load switch and the correct combination of the fuse The difference between the load switch and the fuse is that the fuse has a short circuit current capacity, and the load switch only as a load current switching. It is generally believed that the load switch divides the operating current and the fuse is breaking the short-circuit current.
But when the failure occurs, because the three-phase current is not necessarily the same, and the fuse promised error, inevitably there is a three-phase fuse between the fuse time difference, the Prime Minister cut off the fault, if the load switch can not break the load current, Resulting in a transfer current and two-phase operation, causing damage to the power receiving equipment.

Fuse with impactor, with a trip device with a load switch, you can solve the problem of missing phase operation. When the fuse of the fuse melts, load switch tripping device is disconnected immediately after the striker operation. Production plant more use of four-bar linkage, when the load switch closing operation, the sub-gate spring at the same time energy storage, when the four-link mechanism dead point, closing the spring energy release, switch for closing operation, this time The energy of the gate spring is still maintained by the axle mechanism, once the impactor attack, axle out of the column, the sub-gate spring energy release, switch for sub-gate operation. Therefore, in use must be selected with a striker fuse and a mechanical trip device with the load switch.