The purpose and classification of control relay

Update:11-07-2020
Summary:

The purpose and classification of the control relay is […]

The purpose and classification of the control relay is an automatic electrical appliance. It is suitable for long-distance connection and disconnection of AC and DC small-capacity control circuits and is used for control, protection, and signal conversion in electric drive systems. The input quantity of the three-phase relays is usually the electric quantity such as electric current, voltage, etc. It can also be the non-electric quantity output quantity such as temperature, pressure, speed, etc. It is the electric signal or parameter change of the output circuit issued when the contact is actuated.
The characteristic of relay is that the step change of output will occur when the change of its input reaches a certain program. Control relays have a wide range of uses and are customarily divided into the following categories according to their input volume:

1.Voltage relay It is a relay that acts according to the change of circuit voltage, such as AC and DC voltage relays for motor voltage loss and undervoltage protection. AC voltage relays for wire-wound motor braking and reverse control are used for DC motor reverse. And the DC voltage relay for reverse connection braking. The intermediate relay used to increase the number or capacity of contacts in the control circuit is also essentially a voltage relay whose operation value does not need to be adjusted.

2. Current relay It is a relay that operates according to the change of circuit current. It is used for overload and short circuit protection of motors and other loads, and magnetic field control or demagnetization protection of DC motors.

3.Time relay This is a relay with a certain time interval from receiving the signal to the action of the actuator, such as a relay used to delay the switching of the starting resistance when starting the motor, the motor energy consumption braking and the program control of the production process, etc.

4.Thermal relay is a relay for AC motor overload and phase failure protection.

5.Temperature relays are used for various equipment as overheat protection or temperature control relays.

6.Speed ​​relay Relay for monitoring motor speed and steering changes.

Edit the main technical parameters of this paragraph

(rated parameter) It refers to the rated value of the input, the rated voltage and rated current of the contact, the working capacity of the contact, the mechanical and electrical life of the relay, etc.

A. Action parameter and setting parameter The action value and return value of the input value are collectively referred to as action parameters such as pull-in voltage and current, release voltage and current, action temperature and return temperature. The action parameters that can be adjusted are called setting parameters.

B. Return coefficient This coefficient refers to the ratio of the return value of the relay to the operating value. The return coefficient calculated by the current is the ratio of the return current and the operating current. The return coefficient calculated by the voltage is the ratio of the return voltage and the operating voltage.

C.  Reserve factor The ratio of the rated value of the relay input or the normal operating value to the action value is called the reserve factor, also known as the safety factor. In order to ensure the reliable operation of the relay without misoperation, the reserve factor must be greater than 1 and is generally 1.54.

D. Sensitivity It refers to the power or coil magnetomotive force required to make the relay operate. For comparison, sometimes the operating power or ampere turns required for each pair of normally open contacts is used as the sensitivity index. Electromagnetic relays have lower sensitivity and the operating power reaches 0.01W. Semiconductor relays have higher sensitivity and the operating power only needs 0.000001W.

E. Operation time The relay operation time refers to its pull-in time and release time. The time interval from when the relay receives the control signal to when all contacts reach the working state is called the pull-in time, and the time interval from when the control signal is accepted until all contacts return to the released state is called the release time . According to the length of action time, the relay can be divided into two categories: instantaneous action type and delay action type.