Schematic diagram of forward and reverse control of three-phase asynchronous motor

The circuit schematic diagram of the forward and reverse control of the three-phase asynchronous motor. The structural composition of the forward and reverse control circuit of the three-phase asynchronous motor includes auxiliary contacts, shunt terminals, low-voltage tripping, automatic tripping, automatic reset and other components and functions.

Schematic diagram of forward and reverse control of three-phase asynchronous motor

As shown below:

When selecting a circuit breaker, it is important to not only focus on the main indicators such as the circuit breaker's delay curve, but also its many minor functions. These often overlooked performances can not only add icing on the cake of a good design, but also help engineers design sophisticated protection circuits for their applications.

There are many circuit breakers on the market today that are equipped with various optional features that are helpful in circuit protection design.

Here are some of the more common features:

1. Auxiliary contacts (auxiliary switches): They are contacts that are electrically isolated from the main contacts and are suitable for alarm and program switches. Auxiliary contacts can be used to alert operators or control systems, sound an alarm, or connect backup power in important applications.

2. Transmission: The choice of actuator type is not only for aesthetic reasons. A circuit breaker with a transmission rocker switch that switches twice as fast as an on/off switch can save cost and board space. Push-pull actuators are the most stable in the event of an emergency.

3. Shunt terminal: Conventional circuit breakers are considered to be "series tripping" because the contacts, current sensing elements and loads are all connected in series. Schematic diagram of the circuit for forward and reverse control of a three-phase asynchronous motor.

The shunt terminals branch off the main circuit so that the secondary load can be plugged in. If a short circuit or overload occurs in the primary load, the circuit breaker will trip and remove power to both loads.

Unlike the auxiliary contacts, the shunt terminals are connected to the circuit breaker's current carrying path between the switch contacts and the current sensing element, which means that the second load is not protected from overload or short circuit. A separate circuit breaker can be used to protect the secondary circuit, which is otherwise only available for equipment with built-in protection circuitry.

Duplex Control (Remote Trip or Relay Trip): A dual-control circuit breaker combines two electrically isolated sensing elements to perform multiple functions. For example, a dual-control circuit breaker can use a remote actuator or sensor to perform traditional overcurrent protection as well as circuit disconnection. Remote trip is an example of dual control and is often referred to as "relay trip."

4. Low voltage trip: This is an independent voltage sensitive element in the circuit breaker. If the voltage drops below the preset value, it will open the main contact.

Switch circuit breakers with low voltage tripping are widely used for on/off control of wired connected electrical appliances. Safety management departments require that these appliances must be powered off when power outages occur to avoid the danger of sudden restarting of the appliances when power is restored.

5. Automatic Tripping: An automatically tripped circuit breaker will not remain closed during a fault - because the switching device will not fail by forcing the actuator to remain closed.

In a fully automatic trip design, the main contacts will always remain open after a fault occurs when the actuator is held in the "ON" position. Some circuit breakers, known as "cyclic automatic trips," cannot be forced to remain in the ON state during a fault, but will cycle on and off if the actuator is held in the "ON" position. Automatic trip circuit breakers should be used if the circuit breaker is mounted in an easily accessible location (i.e., not enclosed).

6. Automatic reset: For applications where the circuit breaker is not easily accessible, a circuit breaker that automatically resets after a cool-down period is a good choice. If a device that automatically restarts is specified, the possibility of danger is high.