What Is a Control Relay?

The control relay is an automatic electrical appliance, which is suitable for connecting and breaking AC and DC small-capacity control circuits over long distances, and is used for control, protection and signal conversion in electric drive systems. The input quantity of the control relay is usually electricity such as current and voltage, and it can also be non-electric quantity such as temperature, pressure, and speed. The output quantity is the electrical signal or parameter change of the output circuit when the contact operates. The characteristic of the relay is that when the input quantity changes to a certain program, the output quantity will change stepwise.

The control relay is an automatic electrical appliance, which is suitable for connecting and disconnecting AC and DC small-capacity control circuits over long distances, and is used for control, protection and signal conversion in electric drive systems.

Control relays have a wide range of uses and types, and are customarily divided into the following categories according to their input amounts:

Depending on how it works,

Relay protection is an application technology. Its development is based on related basic technologies such as machinery, electronics, communications, and computers. It is closely related to and interacts with related professional technologies such as telecontrol, monitoring, and change point station automation. In recent years, the development of relay protection technology has been increasingly affected by substation automation technology. The development history of substation automation technology can be roughly divided into early telecontrol technology, mid-term monitoring technology and recent substation automation technology.

Injuries and equipment damage.

Relay contacts are severely burned or welded

1. The load current is too large, the cause should be found out, and appropriate measures should be taken to reduce the load current.

2. If sparks or arcs are too large, fire-fighting circuits should be used.

3. Dust accumulates on the contacts. The contact surfaces should be cleaned.

4. The contact burns too much, and the contact surface has poor contact. You should trim the contact surface or replace the contact.

5. The contact overtravel is too small, the contact should be replaced.

6, the contact pressure is too small, you should adjust the contact spring or replace the spring.

7. During the relay closing process, the vibration is overexcited or vibration occurs many times. The cause should be found out, and corresponding measures should be taken to reduce vibration or eliminate vibration.

Relay contact virtual connection

1. The actual voltage of the relay coil is too low (below 85% of the rated voltage). You should check the power supply voltage and control the power supply voltage of the circuit. Try to avoid low voltages below 24V. If it is necessary to use 24V voltage, you can use Parallel contacts to improve work reliability.

2. The contact resistance of some contacts or crimping connections in the control line is too large, which causes the line voltage drop to be too large. The contact condition of the line connection should be checked in time.

Contact wears too fast or sparks too much when relay controls inductive load

1. Cause of failure: Due to the frequent action of the relay contacts, and the pressure of the contacts is relatively small, when the breaking task is heavy, the problem of excessive contact wear often occurs ^[1] .

2. Exclusion method:

A resistance-capacitance absorption device is connected in parallel at both ends of the contact, and a capacitor is used to absorb the stored energy of the inductor when the contact is opened, so that the arc energy is reduced and extinguished quickly.

Connect a resistance-capacitance absorption device or a freewheeling resistor, a freewheeling diode, etc. in parallel at both ends of the inductive load. When the contact is opened, the electromagnetic energy is consumed in the parallel circuit because the discharge current is in the opposite direction. Therefore, pay attention to the diode polarity.