Application and Characteristics of Vacuum Relay

Application and Characteristics of Vacuum Relay

Vacuum relay

Vacuum relay is a kind of relay whose contacts are in vacuum. It uses vacuum as medium. Usually it uses glass or ceramics as shell. The contacts are made of non-magnetic high conductivity metal.

Vacuum medium

Vacuum medium has many characteristics, such as very high voltage breakdown performance; very fast medium recovery rate; there is pollution and combustion-supporting gas and vapor in vacuum; arc in vacuum has flower shape, which can eliminate ionization quickly, so that vacuum relay shows excellent performance, especially in high voltage. Voltage, high power and radio frequency circuits are particularly prominent in applications.

Characteristics of Vacuum Relay

Vacuum relay has high resistivity; high rated load-carrying current and conversion current, small contact wear and tear, long service life; small and stable contact resistance, low ohmic noise; relatively speaking, vacuum relay has small size, small distributed capacitance and inductance between poles, small contact opening distance, low excitation power and fast breaking speed; sealed contact is not sealed; Influenced by ambient pressure, moisture, sand or gas. It can work in harsh environment.

purpose

Vacuum relays are widely used in radio communication equipment, radar, power supply, broadcasting and other electronic equipment, such as antenna coupling, tap conversion of radio frequency coil, antenna transceiver conversion, pulse forming network conversion, high-voltage high-power circuit quick switch, automatic grounding (leakage) protection. In addition, it can also be used in corrosive or explosive environments.

protective measures

Because the vacuum medium has very fast recovery rate and arc reduction characteristics, the vacuum relay will cause greater surge current when it is connected to capacitor load, and the instantaneous overvoltage when it is disconnected from inductance load. Considering these characteristics, sometimes the circuit should take appropriate protection measures.

The Position of Relay in Circuit

Electric "hot" conversion usually produces arc, ionized gas or metal vapor from contacts may cause fire jump or breakdown. For relays grounded in internal vacuum medium, to prevent damage caused by deficit or to interrupt greater power, relays should be connected to the end of the load (see figure). In addition, relays such as JPK-1, JPK-12 enclosures and ground insulation can be connected at any position.

Rated Current and Conversion Current

Vacuum relay is different from other types of relay, its rated current refers to the load current (through), under the rated current, the relay temperature does not exceed the specified value, when the relay is "hot" conversion, with the different circuit load, "conversion current" will probably increase or decrease.

DC Conversion

In vacuum relays, the arc voltage is maintained at about 20V, which is independent of the converted voltage, and has the capability of rapid arc reduction, which makes the vacuum relay have stronger conversion ability than the air relay. For example, JPK-10 has made dozens of transformations at 600V and 100A. However, when the voltage is higher than 1KV, the general conversion current should be limited. No more than 15A, if greater current is to be converted, artificial current zeros can be formed by shunting RC circuits at converting contacts.

AC Conversion

AC current has zero point, and conversion is much easier than DC conversion. However, in applications, it is generally smaller than load (through) current. For the same relay, the converted current is larger, and the number of electrical life will be reduced. For example, JPK-10 has withstood hundreds of resistive load conversion at power frequency 380V and 300A, and JPK-6 can withstand power frequency 2. The resistance load of 20V and 50A is converted 10,000 times.

Capacitive discharge

Vacuum relays are often used to make capacitive circuits short to the ground (leakage) to protect personal safety. At this time, the surge current can be larger than the load current. For example, JPK-3 can discharge surge current through capacitance of hundreds of amperes, along with the discharge pulse energy withstanding 100 joules.

Pulse application

Vacuum relays are particularly suitable for use in radar impulse forming networks. For some artificial lines with duty factor and bandwidth, peak rated voltage and peak current of thousands of amperes can be used.