Function and classification of power switches
The switching device is a combination or opening circuit in action. When it is not moving, it is connected or isolated. The essential function is the function of "impedance converter", which is about the impedance of a point in the circuit by O → ∞ or ∞ → O. "Arc" is difficult to avoid but indispensable break elements during this rapid transformation. For the contact mechanical switch in the high voltage large current circuit, only the arc can complete the above transformation 2, which is how to limit its adverse effect.
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Power switches refer to various high-power switching electrical appliances operating in power generation, transmission, power distribution, and electrical units (see Figure 1-1), which works control and protection of the operation of the power system.
Switch devices typically include two parts: components and kneading components. Components include circuit breakers, isolation switch, load start, fuse, low-voltage automatic switch, etc. The complete set of electrical appliances includes various switchgear, a gas cabinet, a ring cabinet, a box, a substation, and a variety of closed combination electrical appliances. With the continuous development of modern power electronics, sensing technology, microelectronic devices, materials science and superconducting technology, the concept of high and low voltage power switch equipment is constantly evolving and expanding, there will be more new sets of indennel or limited flow. Facilities to adapt to the operational needs of the modern grid. This book only discusses the current limits and turning devices of various types of switched electrical appliances or impedance transformations, and is now described below.
i circuit breaker (Circuit-Breaker)
The circuit breaker is the most important and most comprehensive switching electrical appliance in the power system. The circuit breaker plays a dual role of control and protection, which can complete the specified consideration task or operation cycle in carrying, unloaded (no load transformer and no-load power line) and various short-circuit conditions. It distinguishes that the most significant feature of other switching devices is that highly arc extinguishing devices must be available. Since the opening circuit is not easy under the condition of high voltage strong current, the arc generated by the opening process does not extinguish, the circuit cannot be turned off, regardless of high pressure circuit breaker or low-voltage automatic air circuit breaker (habit, automatic switch ) Must have strong arc extinguishing capacity.
I Isolation switch (Disconnector)
Isolation switch is a switching electrical appliance used to isolate power or other charged devices. Since the contacts of the high-voltage circuit breaker are packaged in an arc extinguishing chamber, it cannot be directly seen whether it is separate or closed, so in order to allow the detected device to reliably isolate the charged portion, it is not allowed to pass the circuit breaker The leakage current of the fracture insulated (surface along the extinguishing chamber solid medium) causes a hempic sensation or damage to the human body, and a voltage isolation apparatus must be connected in series on both sides of the high-voltage circuit breaker. This is the isolation switch. After the isolation switch is opened, a significantly visible insulation gap is formed in the gas space. It distinguishes the obvious feature of other switches is "breaking down, no leakage". Its function determines its inert arc extinguishing capacity, so it must be closing the circuit breaker, and then the circuit breaker is separated. Only when the line current is small, or each phase two terminals have no obvious voltage changes in the separate state, it has the ability to deliver the circuit. Isolation switch must be capable of carrying short-circuit currents in the current and abnormal conditions of normal operation. A low pressure cutting switch is similar to the high pressure separation system in the low voltage distribution system.