1. Fault inspection

When the fault occurs, the main circuit breaker of unit 1 of the EMU trips. Disconnect the air switches 1 and 2 of the air conditioner power supply of car 3, and press the reset button to reset the main circuit breaker to close normally. Inspection found that the insulation resistance of the output end of the outdoor fan contactor of the air conditioner unit of car 3 to the ground is. . Further inspection found that the socket U of the condenser fan connector is grounded.

Disassemble and inspect the connector, and find that there are short circuit traces between the eight and D positions of the insulator in the connector. The sealant at the tail of the connector is in good condition and there is no abnormality in appearance. Remove the sealant at the tail of the connector, perform the insulation test again, and find that the eight and D positions of the insulator in the connector are still connected. Remove the pin from the connector, and remove the .D from the eight-position insulator inside the connector. Water marks are found on the wire that exits from the position. Remove the connector shell, and find that there is a breakdown phenomenon between the eight and D positions of the insulator in the connector (Figure 1). Further disassemble the connector, and find that the sealing rubber ring has an indentation. Analysis shows that the rubber ring is pressed off due to inadequate assembly.

The failure mode of the connector insulator burnout is shown in Figure 2. The connector disassembly inspection and ground fault replication test showed that due to the improper assembly of the sealing rubber ring, the connector insulator burnout failure caused the rubber ring to be pressed and sealed.

The failure mode of the connector insulator burnout is shown in Figure 2. The connector disassembly inspection and ground fault replication test showed that due to the improper assembly of the sealing rubber ring, the connector insulator burnout failure caused the rubber ring to be pressed and sealed.

2. Cause analysis

2.1 Principle analysis

The air conditioner grounding detection principle is shown in Figure 3. The air conditioner uses an inverter to supply power to the outdoor condensing fan (C'.F) through the air supply fan inside the air conditioner. At the same time, the vehicle sets a single-phase three-side grounding detection circuit AC400V load detection. When the intermediate connector is grounded, it reports a "main transformer three-side grounding" fault.

The high-voltage power supply three-side grounding detection principle is shown in Figure 4. When the load on the tertiary side of the EMU and the positive and negative ends of the trunk are grounded, when the voltage of the transformer in the tertiary side grounding detection circuit (URT) reaches 100V, the UR3 relay coil is excited, and its normally open contact is closed, which makes the relay coil excited, and the URR3-1.URR3-2 relay coil is excited, the vehicle main circuit breaker is controlled to disconnect, and the "main transformer tertiary side grounding" fault is reported through the information control device.

2.2 Connector structure analysis

The air conditioner outdoor fan connector consists of a plug and a socket. The plug consists of a shell assembly. .Insulator assembly. Sealing body. Claw. Pin. Connecting nut and other components, and the socket consists of a square disk shell. Shell sealing ring. Insulator assembly. Sealing body. Socket assembly and other components. According to the connector disassembly analysis, the compression pad is not well sealed after pressing, there is water on the connector, and the water on the connector plug. The socket docking surface enters, resulting in a short circuit between pins and grounding.

Comprehensive analysis shows that the cause of the connector short circuit failure is that the size control of individual connectors is not strict, the cumulative error exceeds the use requirements, resulting in gasket deviation, and water intrusion during use causes the condenser fan power line U to be grounded.

3. Preventive measures

(1) Check the insulation performance of the online connector and add putty protection at the connection to effectively prevent water from entering the interior.

(2) Optimize the key dimensions and tolerances of each key dimension related to waterproof performance to improve the design sealing performance.

(3) Identify key dimensions and strengthen control in subsequent production processes.

(4) Conduct a comprehensive inspection of connectors that have not been optimized in size, and determine the subsequent sampling ratio and waterproof test method.

(5) Add waterproof performance test spot checks to the warehousing stage of connector raw materials.