How to repair common faults in electrical contacts?

Repairing electrical contacts (especially the commonly used tulip contacts and their stationary contacts in medium and high-voltage switchgear) is a rigorous and professional task that must follow safety procedures. The following is a systematic guide to common fault repair.

Primary Principle: Safety First

Power Disconnection and Isolation: The equipment must be completely de-energized, moved to the maintenance position, and reliable grounding measures must be implemented.

Voltage Verification: Use a qualified voltage tester to verify that there is no voltage on both the incoming and outgoing lines.

Personal Protective Equipment: Wear qualified insulating gloves, insulating shoes, safety helmets, and other protective equipment.

Follow Procedures: Strictly adhere to your company's "Electrical Safety Work Procedures" and the maintenance guidelines for the specific equipment.

Qualification Requirements: This work should be performed by qualified professional maintenance personnel.

 

Common Fault Diagnosis and Repair Steps

Step 1: Fault Diagnosis and Inspection

Before and after disassembly, carefully inspect the following parts:

♦Overheating and Burning (Most Common Fault)

Symptoms: Contact surface is blackened or discolored (blue/purple indicates overheating, gray-white indicates severe burning), the silver plating is gone, and metal welding particles or pits appear.

Causes: Excessive contact resistance (e.g., insufficient pressure, oxidation of the contact surface, contamination), prolonged overload, short-circuit current surge.

Inspection Points:

Check if the contact fingers have lost their elasticity and can still make tight contact.

Check if the stationary contact surface is smooth and free of burn marks.

Check if the contact spring is overheated, annealed, or broken.

 

♦Poor Contact/Discharge

Symptoms: Discharge marks, electrical corrosion spots, localized overheating.

Causes: Contact pins not fully inserted or misaligned, presence of grease, dust, or chemical corrosive substances on the contact surface.

 

♦Mechanical Damage

Symptoms: Deformed or broken contact fingers; bent contact rod, damaged threads; loose connections in the contact arm.

Causes: Improper insertion/removal (misalignment), mechanical impact, long-term stress fatigue.

 

♦Severe Oxidation and Corrosion

Symptoms: Surface covered with a non-conductive black oxide film or green copper rust.

Causes: Humid environment, corrosive gases, prolonged high-temperature operation.

 

Step 2: Repair Methods and Procedures

Depending on the extent of the damage, choose either "repair" or "replace." Minor damage can be repaired, while severe damage requires replacement.

A. Cleaning and Decontamination

Tools: Anhydrous ethanol (alcohol), scouring pad or fine-grit sandpaper (e.g., 800 grit or higher), lint-free soft cloth.

Method:

Wipe the contact surface with a soft cloth dampened with alcohol to remove oil and dust.

For oxidized layers, gently polish along the original texture of the contact with a scouring pad or very fine sandpaper until the metallic luster is exposed. Avoid over-polishing, which can damage the silver plating!

Clean thoroughly again with alcohol to remove all debris.

Key point: After cleaning, immediately apply a thin, even layer of special electrical contact grease (conductive paste) to the contact surface. This prevents oxidation, reduces contact resistance, and improves heat dissipation.

 

B. Repairing Minor Burns and Pits

Tools: Fine file, oilstone.

Method: Carefully smooth down raised weld points and burrs with a fine file, then finely polish with an oilstone. Ensure the contact surface is flat. After completion, clean and apply electrical contact grease as before.

 

C. Checking and Restoring Contact Finger Pressure (Most Critical Step)

Tools: Vernier caliper, spring scale or dedicated contact finger pressure tester.

Method:

Check that each contact finger moves freely without jamming.

Measure the opening size of the contact fingers in the closed state; it should match the standard value.

Test the contact finger pressure: This is the core indicator. Use a spring scale to hook the middle of a single contact finger, slowly pull it to separate it from the stationary contact, and read the force at the moment of separation. The pressure values ​​of all contact fingers should be uniform and meet the manufacturer's technical requirements (usually between 20-70N per finger, depending on the model).

Handling insufficient pressure:

Replace the contact finger spring: This is the most fundamental and effective method. Remove the old spring and replace it with a new one (be sure to use original or equivalent high-quality spare parts).

Minor adjustment: For some structures, carefully use a tool to slightly bend the base of the contact finger to increase elasticity (exercise extreme caution to avoid breakage).

 

D. Check connection tightness

Check all bolted connections between the contacts and contact arms, and between the stationary contacts and busbars, ensuring they are tightened to the specified torque to prevent overheating due to looseness.

 

E. Replacement of parts (Replacement is mandatory in the following cases)

Cracks or fractures in the contact fingers.

Complete wear of the silver plating (the silver plating thickness is usually required to be ≥8μm, which can be checked with a thickness gauge).

Severe burning, deformation, or thread damage exceeding 1/3 of the stationary contact rod.

Cracks or significant deformation in the contact arm body.

Replacement principle: It is recommended to replace parts in pairs or as a complete set (e.g., replacing all contact finger assemblies, or simultaneously replacing the corresponding stationary contacts) to ensure matching contact performance.

 

Step 3: Assembly and Testing

Correct Assembly: Install in the reverse order of disassembly. Ensure the contact points are properly aligned with the stationary contacts, without any misalignment.

Lubrication: Apply an appropriate amount of low-temperature grease to the mechanical sliding parts such as guide rods and bearings.

Manual Simulation Test: Without power supply, manually or slowly operate the equipment, inserting and removing the contacts several times. Ensure the movement is smooth, without jamming, and that the insertion depth is correct.

Circuit Resistance Test (Mandatory):

Use a circuit resistance tester to measure the DC resistance of the entire conductive circuit (e.g., from the input end of the contact arm to the output end of the stationary contact).

The measured value should not exceed 1.2 times the factory value and should meet technical standards (usually in the micro-ohm range). This is the most direct evidence of the effectiveness of the repair.

Mechanical Characteristics Test (Optional but Important): Use a switch characteristic tester to check whether parameters such as opening and closing speed and synchronicity are normal, ensuring correct mechanical operation.

 

Summary and Prevention Recommendations

Prevention is better than repair: Regular infrared temperature measurement can detect overheating problems in contacts in advance.

Standardized operation: Ensure proper alignment when operating the switchgear to avoid pulling the switch under load.

Environmental control: Keep the switchgear clean and dry to prevent condensation and corrosion.

Establish records: Record test data from each maintenance inspection for trend analysis and predictive maintenance.

Remember, for critical high-voltage equipment, when you are unsure or the fault is serious, contacting the equipment manufacturer or a professional maintenance team is the safest and most economical option.

 

Shaanxi Huadian's contact surfaces utilize a special alloy formula and plating process, possessing excellent resistance to arc erosion and welding, ensuring reliable separation even after fault current interruption, thus guaranteeing operational safety. We are committed to supporting the stable and long-term operation of your power system with our superior contact and contact arm technology. For product brochures and technical inquiries, please contact us.

Email:pannie@hdswitchgear.com.

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