Common Faults Of Disconnect Switches

Disconnecting switches are the most widely used and frequently operated primary equipment in power systems. Since they lack arc-extinguishing capabilities, their main functions are power isolation, switching operations, and handling small currents. Therefore, their faults are mostly related to mechanical structure, conductivity, and insulation condition.

Common Fault Types Analysis

1. Overheating of Contacts and Connections

Symptoms: Infrared thermometer shows abnormally high temperature; contacts or terminals discolor; in severe cases, melting occurs, even leading to fire.

 

Main Causes:
Poor Contact: Insufficient contact pressure; spring fatigue or breakage; uneven or misaligned contact surfaces between contact fingers and contacts; long-term operation leads to oxidation of the contact surface, forming silver sulfide/copper film, increasing resistance.

Improper Installation: Screws not tightened, loose connection.

Overload Operation: Current exceeding the rated value for an extended period.

Vicious Cycle: Overheating exacerbates oxidation, further increasing resistance and temperature.

 

2. Operational Malfunction (Refusal to Operate or Incomplete Opening/Closing)

Symptoms: During electric or manual operation, the switch cannot open or close normally, or the travel is insufficient.

 

Main Causes:

Mechanical Jamming:

Corrosion: Long-term exposure of outdoor switches leads to corrosion of transmission components.

Foreign Objects: Small animals, dust, ice, etc., enter the switch.

Deformation: Mechanical parts deform due to stress or aging.

Poor Lubrication: Lack of maintenance over a long period causes grease to dry out or deteriorate.

 

Electrical Faults (for Electric Operating Mechanisms):

Motor burnout, control circuit disconnection, relay failure, power supply problems, etc.

Electrical interlocks (such as "five-proof" interlocks) not disengaged, resulting in inoperability.

 

Improper Installation and Adjustment: Inaccurate limit switch position, improper mechanism adjustment.

 

3. Insulator (Porcelain Bottle) Faults

Symptoms: Insulator flashover, creepage, breakage.

 

Main Causes:

Pollution Flashover: Industrial dust, salt, bird droppings, and other contaminants form a conductive layer in humid weather, leading to surface discharge.

Mechanical Stress: Uneven stress during operation or external impact.

Aging and cracking: Porcelain insulators develop internal cracks due to long-term electrical, thermal, and mechanical stress, eventually leading to breakdown or breakage.

Product quality: The insulator itself has defects.

 

4. Corrosion and Loose Components

Symptoms: Severe corrosion of metal components; loose or detached screws, washers, etc.

 

Main Causes:
Environmental Factors: Long-term exposure to moisture, rain, and salt spray corrosion of outdoor switches.

Material Issues: Inadequate anti-corrosion treatment.

Insufficient Maintenance: Long-term lack of rust removal, tightening, and other maintenance work.

 

5. Abnormal Sounds and Discharges

Symptoms: A "buzzing" discharge sound is emitted during operation, or abnormal metal friction or impact sounds are heard during operation.

 

Main Causes:
Contact Discharge: Poor contact of contacts, generating sparks and discharge sounds when current passes through.

Looseness: Loose components vibrate under electromagnetic or wind-induced forces, producing sounds.

Insulation Surface Discharge: Dirt or cracks on the insulator surface cause localized discharge.

 

6. Deformation of Support Components or Frame

Symptoms: The switch is tilted overall, and the contact centerline is offset.

 

Main Causes:
Foundation Settlement: Unstable installation foundation leads to uneven stress.

External force damage: such as the enormous electrodynamic impact generated by short-circuit current.

Material fatigue: long-term exposure to mechanical stress.

 

Most faults of disconnecting switches are "mechanical" and "thermal" in nature. Preventive maintenance is far more important than post-fault repair. When serious signs of a disconnecting switch fault are detected, a power outage should be requested immediately. Forced operation with a fault is strictly prohibited, as this could lead to serious accidents such as grounding short circuits or equipment explosions.