Analysis of Connector Short Circuit Fault

Analysis of Connector Short Circuit Fault

1. Fault inspection

When the fault occurs, the main circuit breaker of Unit 1 of the EMU trips. Disconnect the air conditioning power supply 1 and 2 of Car 3, press the reset button to reset, and the main circuit breaker can be closed normally. Upon inspection, it was found that the insulation resistance between the output end of the outdoor fan contactor of the air conditioning device in Car 3 and the ground is.. Further inspection revealed that the condenser fan connector socket U was grounded.

Disassembling and inspecting the connector, it was found that there were traces of a short circuit between the eight and D positions of the insulator inside the connector. The sealant at the tail of the connector is in good condition and has no abnormal appearance. Remove the sealant from the tail of the connector and conduct another insulation test. It was found that the eight and D positions of the insulation inside the connector are still connected. Remove the pin from the connector and remove it from the eight position insulator inside the connector. Water marks were found on the wire that exited from position D. After removing the connector shell, it was found that there was a breakdown phenomenon between the eight and D positions of the insulation inside the connector (Figure 1). Further disassembly of the connector revealed that there were pressure marks on the sealing rubber ring, which was analyzed to be due to improper assembly causing the rubber ring to be biased.

The failure mode of connector insulation burning is shown in Figure 2. The connector disassembly inspection and ground fault replication test showed that due to the inadequate assembly of the sealing rubber ring, the connector insulation was burnt out, resulting in rubber ring pressure deviation and sealing failure.

2. Cause analysis

2.1 Principle analysis

The principle of air conditioning grounding detection is shown in Figure 3. The air conditioning device uses an inverter to supply the outdoor condensing fan (C '. F) through the supply fan. At the same time, the vehicle sets a third side grounding detection circuit AC400V load detection for the single-phase. When the middle connector has a grounding fault, it reports a "main transformer third side grounding" fault.

The principle of grounding detection on the third side of high-voltage power supply is shown in Figure 4. When the load on the third side of the high-speed train unit and the positive and negative terminals of the main line are grounded, when the voltage in the third side grounding detection circuit (URT) of the transformer reaches 100V, the UR3 relay coil excites, and its normally open contact closes, causing the relay coil to excite. The URR3-1. URR3-2 relay coil excites, controlling the main circuit breaker of the vehicle to open, and reporting a "main transformer third side grounding" fault through the information control device.

2.2 Connector Structure Analysis

The air conditioning outdoor fan connector consists of a plug and a socket. The plug consists of a housing component Insulator components, cable sealing bodies, claws, pins, connecting nuts, and other components. The socket is composed of a square plate shell, a shell sealing ring, an insulator component, a cable sealing body, a socket component, and other components. According to the disassembly analysis of the connector, the compression pad is poorly sealed after compression, and there is water on the connector. The water on the connector plug and socket interface enter, causing a short circuit and grounding between the pins. Figure 5 shows the pathway of water ingress into the connector.

The comprehensive analysis of the reasons for the short circuit fault of connectors is that the size control of individual connectors is not strict, and the cumulative error exceeds the usage requirements, resulting in gasket deviation. During use, water intrusion leads to the grounding of the condensing fan power line U.

3. Preventive measures

(1) Checking the insulation performance of the online connector and adding putty protection at the connection can effectively prevent water from entering the interior.

(2) Optimize key dimensions and tolerances related to waterproofing performance to improve design sealing performance.

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

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

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