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Motor phase failure protection principle, method and object

Article Source:Thermal protectorAuthor:Kangding MetalPopularity:Published time:2019-08-11 17:49

Principle of Phase Break Protection
Phase-breaking protection is a kind of protection method that relies on the disappearance of current in one-phase conductor of multiphase circuit to disconnect the protected equipment, or relies on one-phase or several-phase Voltage-loss of multiphase system to prevent the power supply from being applied to the protected equipment.

The circuit of the motor phase failure protection device has six external terminals. Where N is the neutral line connected to the power supply, A, B, C are connected to the A phase B phase and C phase corresponding to the main circuit, and the two terminals of IN and OUT are connected in series with the control loop power supply. The inside of each external terminal is an inherent part and must be one-to-one. At the same time, the distance between the column and the column should be as large as possible to prevent short circuits between the parallel terminals. Therefore, these intrinsic components must be carefully connected, and it is possible to burn out the protection device when the connection is wrong.

Motor main circuit three items plus zero line wiring diagram


Phase failure protection method and purpose
The methods for motor phase failure protection are: It adopts voltage relay, adopts broken wire voltage protection, adopts thermal relay with phase-break protection, phase-break protection relay designed for phase-breaking operation, and undercurrent relay.

purpose: In the operation of a three-phase motor, as long as one of the following conditions occurs. For example, one-phase contact caused by contact burning, installation and maintenance and other reasons will lead to one-phase break or one-phase fuse of three-phase power supply, which will cause three-phase motor to run out of phase. If it is found to be untimely, it will also cause the burning of the motor and the damage of the equipment, thus affecting continuous production and causing certain losses. In order to ensure the safe operation of the motor, the general important motors are equipped with various phase failure protection devices to prevent the motor from burning in the event of phase loss and to minimize unnecessary losses.

Graphic Connection Diagram of Phase Break Protector
The phase sequence protector wiring does not require other accessories, and the upper three connection points are connected to the live line of the three-phase power supply. The lower end has only contact control, no internal power supply, and requires an external power supply. The contacts of the phase sequence protector are usually used to control the pull-in of the intermediate relay, and the contact of the intermediate relay controls the main power contactor. The phase sequence is incorrect or phase-out, the phase sequence protector contacts act, the intermediate relay coil acts, and the control loop of the main power contactor is disconnected. Disconnect the power of the entire device.
Phase failure protector wiring design

Three-phase phase-failure and phase-sequence protection relays are typically used with motor control circuits, with reference to the drawings:
   Control Circuit Design of Three-Phase Break and Phase Sequence Protection Relay

1. Phase-Break and Phase-Sequence Protection Relay Uses: Phase-break protector is to protect the motor, and phase-sequence protector is to change the phase sequence by changing the position between the phase lines.

2. Phase-breaking protector is also called motor phase-breaking protector or power source phase protector. Generally used in three-phase motor circuit, if there is no one-way power, the torque of the motor will become smaller, the rotor speed will decrease, which will cause the other two currents to increase and burn the motor winding. The principle is to monitor the three-phase electricity through different means. If there is an open circuit condition, the power will be automatically cut off to avoid burning the winding. Due to the rapid development of science and technology, the type of phase-failure protector is controlled by monitoring the voltage of each channel, and monitoring the current of each channel for control.

3. The phase sequence protection relay is an intelligent power protection device. Using a microcontroller and digital processing technology, it integrates voltage display, over-voltage and under-voltage protection, phase loss protection and phase sequence protection. The liquid crystal display has the characteristics of simple operation, small size and high reliability. It can be widely used in various phase sequence protection relay systems to replace traditional phase sequence relays and overvoltage and undervoltage protectors.