Application of Thermal Relay in Railway Signal Motor

Photocoupler

The railway signal motor reversible operation circuit is shown in the figure below. In the figure, FR is a thermal relay, which mainly functions as overload protection.

The working principle of the system is as follows: In order to make the motor rotate forward and reverse, two contactors KM1 and KM2 are used to change the phase sequence of the three-phase power supply of the motor (but the two contactors can not be sucked at the same time, otherwise the short circuit of the power supply will be caused. A reliable interlock should be adopted in the circuit. Figure 4 shows the control circuit that operates in both the forward and reverse directions of the motor with double interlocking of the button and the contactor. The interlocking circuit analysis is as follows: (1) Contactor interlock: KM1 coil circuit is connected to the normally closed auxiliary contact of KM2, and KM2 coil circuit is connected to the normally closed contact of KMI. When the forward contactor KM1 coil is energized. KMI's auxiliary normally closed contact disconnects the KM2 coil circuit: if the KMI is electrically connected, the KM2 must be powered off first, and the auxiliary normally closed contact is reset, which prevents the KM1 and KM2 from simultaneously attracting each other. Short circuit, this line is called the interlocking link. (2) Button interlock: In the circuit, the positive and negative control circuit is operated by the control button. The buttons SB2 and SB3 both have a pair of normally open contacts and a pair of normally closed contacts. These two contacts are respectively associated with KMI. , KM2 coil circuit connection. For example, the normally open contact of button SB2 is in series with the contactor KM2 coil, while the normally closed contact is in series with the contactor KM1 coil loop. The normally open contact of button SB3 is in series with the contactor KM1 coil, while the normally closed contact pressure KM2 coil circuit is connected in series. Thus, when SB2 is pressed, only the coil of contactor KM2 can be energized and KM1 can be powered off. When SB3 is pressed, only the coil of contactor KMI can be energized and KM2 can be powered off. If SB2 and SB3 are simultaneously pressed, then two None of the contactor coils can be energized.

This plays the role of interlocking. After the motor is running in the forward (or reverse) direction, it is not necessary to press the stop button to stop the motor when the motor is running in the reverse direction. Instead, the reverse (or forward) start button can be directly pressed to make the motor run in the opposite direction.