By EECTECH | 21 June 2020 | 0 Comments
Vacuum relay application and characteristics
Vacuum relay application and characteristics
Vacuum relay
Vacuum relays are relays with contacts in a vacuum and using vacuum as a medium, usually with glass or ceramics as the casing, and contacts with non-magnetic high-conductivity metals.
Vacuum medium
Vacuum medium, it has many characteristics, such as extremely high voltage breakdown performance; extremely fast medium recovery rate; there are pollution and combustion-supporting gases and steam in vacuum; arc has a flower shape in vacuum, and deionization occurs rapidly Function, so that the vacuum relay shows excellent performance, especially in the application of high voltage, high power and RF circuits.
Vacuum relay characteristics
The vacuum relay has high electrical strength; the rated load current and the switching current are large, the contact electrical wear is small, and the life is long; the contact resistance is small and stable, and the ohmic noise is low; relatively speaking, the vacuum relay is small in size, with distributed capacitance and inductance between the poles Small, the contact opening distance is small, the excitation power is low, and the breaking speed is fast; the sealed contact is not affected by the surrounding air pressure, moisture, sand or gas. Can work in harsh environments.
use
Vacuum relays are widely used in radio communication equipment, radar, power supply, broadcasting and other electronic equipment, such as antenna coupling, tap change of radio frequency coil, antenna transceiver conversion, pulse forming network conversion, high-speed high-power circuit snap switch, automatic Grounding (leakage) protection. In addition, it can also be used in corrosive or explosive environments.
Safeguard
Due to the extremely fast recovery rate and arc reduction characteristics of the vacuum medium, when the vacuum relay is connected to the capacitive load, it will cause a larger inrush current, and when the inductive load is disconnected, it will cause a transient overvoltage. Considering these characteristics, sometimes the circuit needs to Take appropriate protective measures.
The position of the relay in the circuit
Charging "thermal" conversion usually generates an arc. Ionized gas or metal vapor from the contact may cause flashover or breakdown. For the internal vacuum medium grounded relay, in order to prevent damage caused by shortfall or break more power , The relay should be connected to the ground of the load (see picture). In addition, relays such as JPK-1, JPK-12 and other housings insulated from the ground can be connected at any position.
Rated current and switching current
Vacuum relays are different from other types of relays. Its rated current refers to the carrying current (pass). Under the effect of rated current, the temperature of the relay does not exceed the specified value. When the relay performs "thermal" conversion, as the circuit load varies, The "switching current" may increase or decrease.
DC conversion
In the vacuum relay, the arc voltage is kept at about 20V, which has nothing to do with the converted voltage, and has the performance of rapid arc reduction, which makes the vacuum relay have a stronger conversion ability than the air relay. For example, JPK-10 has been used in 600V, 100A Ten conversions, however, when the voltage is higher than 1KV, the general conversion current should be limited to no more than 15A. If you want to convert a larger current, you can parallel the RC circuit at the conversion contact to form an artificial current zero point.
AC conversion
The AC current has a zero point, and the conversion is much easier than the DC conversion. However, the application is generally smaller than the carrying (passing) current. For the same relay, the converted current is large, and the number of electrical life will be reduced. The application example is, JPK- 10Once the power frequency 380V, 300A withstand hundreds of resistive load conversion, JPK-6 can withstand power frequency 220V, 50A resistive load conversion 10,000 times.
Capacitive discharge
Vacuum relays are often used to short-circuit (leak) capacitive circuits to ground to protect personal safety. In this case, a peak surge current larger than the carrying current can be passed. For example, JPK-3 can discharge through a capacitor of hundreds of amperes. The inrush current is subject to the discharge pulse energy of 100 joules.
Pulse application
Vacuum relays are particularly suitable for use in radar's impulse forming networks. For some artificial lines with a duty cycle and bandwidth, a peak rated voltage and a peak current of thousands of amperes can be used.
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