Technical Transformation Solution for Power Module Failure of Vacuum Contactor KC2

1. Project Background and Problem Overview​
   The high-power air compressor is driven by a 10kV medium-voltage motor, and its starting cabinet was originally designed with an autotransformer step-down starting method. The starting process consists of two stages:

1. ​Starting Stage: Vacuum contactor KC1 first engages to short-circuit the autotransformer star point, allowing the motor to start at 7kV.
2. ​Running Stage: After the starting process is completed, KC1 disengages, and vacuum contactor KC2 engages to short-circuit the autotransformer and connect the 10kV main circuit, enabling the motor to operate at full voltage.

​Core Issue: During actual operation, the wide-voltage power supply module responsible for supplying power to the KC2 contactor coil frequently malfunctions. This module failure causes the contactor coil to lose power, resulting in abnormal disengagement of KC2 and unplanned downtime of production equipment, severely impacting production stability and efficiency.

The original wide-voltage power supply module is an enhanced rectification device with the following core features and requirements:

• ​Dynamic Output Voltage Switching: It must output 300V DC high voltage instantly upon AC input to drive the contactor engagement. After engagement, it must accurately switch to 12V DC low voltage within approximately 15ms to maintain the engaged state. If the switching time is too short, the contactor cannot engage reliably; if too long, it may burn out the fuse.
• ​Switching Trigger Mechanism: Triggering is based on output current detection. When a high current (indicating contactor engagement) is detected, it switches to 12V after 15ms; if no current is detected, it continues outputting 300V.

​II. Root Cause Analysis of the Failure​
​Direct Cause: On-site inspections revealed repeated fuse burnouts in the module. The core failure point was internal circuit aging, which prevented timely switching of the output voltage from 300V to 12V after contactor engagement. This resulted in sustained 300V high-voltage output, generating excessive current that ultimately burned out the fuse and rendered the module ineffective.

​Root Causes:

1. ​Poor Heat Dissipation Environment: The KC2 contactor and power supply module are installed inside the starting cabinet, which is enclosed with limited ventilation and heat dissipation.
2. ​Maintenance Design Flaw: For technical protection, the equipment manufacturer encapsulated the entire module, further hindering heat dissipation. The module must remain powered during operation, and in high-temperature environments, electronic components age rapidly, leading to performance degradation and eventual loss of normal switching functionality.

​III. Solution and Implementation​
​1. Core Transformation Approach​
Abandon the original module’s "dual-function" design (handling both high-voltage engagement and low-voltage holding), which is costly and prone to failure. Adopt a function-separation solution:

• ​Reuse Existing Components: Utilize the original wide-voltage power supply module’s ability to output 300V DC high voltage momentarily, specifically for driving contactor engagement.
• ​Add New Components: Introduce an independent, low-cost 12V DC regulated power supply module dedicated to maintaining contactor engagement after activation.
• ​Critical Control: The moment the contactor reliably engages, the control circuit automatically cuts off power to the original module, ensuring it operates only briefly. This prevents burnout caused by prolonged operation in high-voltage mode.

​2. Key Components and Functions of the Transformed System​

• ​Original Wide-Voltage Power Supply Module: Repurposed to provide only momentary 300V engagement voltage.
• ​New 12V DC Power Supply Module: Responsible for providing sustained 12V holding voltage, installed outside the starting cabinet in a well-ventilated area.
• ​Isolation Diodes (2 units)​: Isolate the 300V and 12V power sources to prevent mutual interference and backflow.
• ​Control Relay (KA1)​: Provides logical control signals to ensure sequential execution of the operation process.
• ​Anti-Bouncing Circuit: Serves as a safety redundancy design to prevent repeated "engagement-disengagement" cycling of the contactor under abnormal conditions.

​IV. Transformation Results​
This technical transformation has yielded significant economic and operational benefits:

1. ​Significant Cost Reduction: The addition of a new 12V power supply module (costing approximately RMB 100 per unit) replaced the original wide-voltage module (costing approximately RMB 5,000 per unit), drastically reducing maintenance costs per device and delivering a high return on investment.
2. ​Optimized Operating Environment: The new 12V module is installed outside the cabinet, greatly improving heat dissipation and enabling convenient online status monitoring and maintenance.
3. ​Extended Equipment Lifespan: The original module operates only briefly, significantly reducing wear and tear. The new module operates in an ideal environment, ensuring longevity. The overall solution markedly extends the service life of the KC2 power supply system.
4. ​High Flexibility: This solution can be implemented either as a repair measure after the original module fails or as a preventive technical upgrade before failure, offering flexibility regardless of the original module’s condition.
5. ​Proven Operational Stability: Practical operation has demonstrated the solution’s reliability and effectiveness. The first batch of transformed devices has operated stably for over two years without any downtime caused by KC2 power supply issues, fully validating the solution’s superiority.