Analysis of the Fault Characteristics and Causes of Phase Loss in Three-Phase Motor Windings

Phase loss is a unique electrical fault of three-phase motors, which may occur during the testing stage of the motor or during its operation stage. It may be caused by problems in the manufacturing quality of the motor or issues during its use.

The damaged characteristics of the motor windings burned out due to phase loss operation are very obvious. When observed from the end of the motor windings, regularly distributed burn marks can be seen. For motors with a delta connection, the windings show a distribution where one phase is damaged and two phases are in good condition. For motors with a star connection, it shows a distribution where two phases are faulty and one phase is in good condition. The pole-phase group of the fault is burned black or turns dark brown, while the remaining one or two phases of the windings are intact or slightly charred.

1.Which manufacturing quality problems can lead to the phase loss operation of the motor?

The phase loss operation can be attributed to connection faults. In the manufacturing process of the three-phase motor, the connection problems involved include the connection of a single-phase winding, the connection between the winding and the lead wire, the connection for judging the lead wire and the terminal, and the connection with the terminal block. If any of these links is disconnected, it may lead to the phase loss operation of the motor.

When checking the phase loss fault, if it is a connection problem inside the motor, it can basically be attributed to a manufacturing quality problem; otherwise, it is a problem during the use of the motor.

Regarding the connection of the three-phase motor, we have carried out specific analysis and discussion from the perspective of resistance balance. Recently, a friend asked about the number of joints in the motor windings. There is no specific regulation on this issue in the technical standards of the motor. However, from the analysis of actual manufacturing reliability, the number of joints inside the windings should be minimized as much as possible, because the unreliability of any connection may become the cause of faults such as inter-turn short circuits, inter-phase short circuits, ground faults, and phase loss. Therefore, from the perspectives of design and process, the number of joints should be reduced to the greatest extent possible, and reliable connection schemes should be adopted for the necessary joint positions.

Regarding the connection process of the windings, different manufacturers have different measures, but the ultimate requirement for reliability is the same. In response to this problem, many equipment manufacturers have developed relatively professional equipment, which can better solve the connections between electromagnetic wires, between electromagnetic wires and lead wires, and between lead wires and terminals, greatly reducing the connection faults of the motor windings.

2.Phase loss faults during the use process

It is obviously unfair and unscientific to simply attribute the phase loss fault to a problem during use. However, most phase loss faults are caused by inappropriate use. When any motor is connected to the power supply, it will involve switches. The performance compliance of the switches, the connection between the power cord and the motor, and the compliance of the power inlet directly affect the normal operation of the motor. Therefore, regular and irregular inspections and maintenance are the key to avoiding such problems.

In order to avoid such problems, especially for large motors and high-voltage motors, control devices such as phase loss protection, overcurrent and overvoltage protection, and current and voltage unbalance protection have emerged. Although it seems to increase some costs, the safety of the operation of the motor and equipment reduces accident losses from another aspect.