SF6 circuit breaker as a new type of high-voltage electrical switchgear developed in recent times, with its superior performance, safety and reliability, easy maintenance and long service life, has been widely used in the power system, but there are many colleagues on SF6 circuit breaker key components SF6 gas pressure gauge, density gauge, SF6 density relay knowledge is still lacking, to installation, maintenance and other work to bring some Difficulties, and even affect the quality of work, misunderstanding of the operation of some of the equipment is a normal state of the phenomenon.
The current of SF6 density relay contacts is very small, and there is almost no arc between the contacts. The spark at the contact is attributed to the inductance in the contact circuit. When the contacts are broken, an overvoltage will exist on the inductor. The overvoltage and supply voltage lie across the contact gap and discharge through the gap just separated. The spark discharge is the only phenomenon due to the energy limitation. The energy displacement and conversion in the capacitance and inductance present between the contacts causes the spark discharge to flicker and become a high frequency signal. In addition, spark discharge can damage the contacts and shorten their service life, so sparks must be eliminated. These are two effective methods of spark elimination.
1. It works by making the energy in the inductor pass through the RC (resistor-capacitor) instead of through the contacts.
2. The second works by causing the load through the diode to consume energy when the contact is broken.
You can choose one method in practice. Be careful to choose an RC with appropriate parameters, which are determined mainly by experiment. As a rule, the RC can be selected based on a load current of 1a / 1 microfarad. when using a diode, the anode and cathode should be connected correctly. If the load on the contacts does not meet the application requirements, this can be handled by connecting several pairs of contacts in parallel. Please adjust the contacts before use so that the synchronization meets the requirements. The best way is to choose a central relay or contactor to expand the load of the contacts.
The so-called density refers to the mass per unit volume of a particular substance under specific conditions. SF6 gas in SF6 circuit breaker is sealed in a fixed and unchanging container, and it has a certain density value under the rated pressure at 20℃. Within the various permissible conditions of circuit breaker operation, although the pressure of SF6 gas varies with the temperature, the density value of SF6 gas always remains the same. Because the insulation and interrupting performance of SF6 circuit breaker depends largely on the purity and density of SF6 gas, it is especially important to detect the purity and monitor the density of SF6 gas. If an ordinary pressure gauge is used to monitor the leakage of SF6 gas, it will not be possible to distinguish whether the pressure of SF6 gas changes due to the real existence of leakage or due to the change of ambient temperature.
In order to achieve the purpose of monitoring density frequently, the national standard stipulates that SF6 circuit breaker should be equipped with pressure gauge or SF6 gas density meter and density relay. The pressure gauge or SF6 gas density gauge is to play a monitoring role, and the density relay is to play a control and protection role. The SF6 gas density meter installed on SF6 circuit breaker with pointer and scale is called density meter; without pointer and scale is called density switch; some SF6 gas density meters also have electrical contacts, that is, they are also used as density relays. They are all special meters used to measure SF6 gas.