What are the common faults of load switches?

As an on-site maintenance technician, I frequently deal with electrical, mechanical, and insulation faults in load switches. The following outlines fault manifestations, causes, and solutions:

I. Electrical Fault Handling
(1) Contact Heating

Contact heating is mainly caused by poor contact, insufficient pressure, or three-phase asynchrony. When the contact resistance exceeds 1.5 times the initial value, the temperature rise will exceed the standard in a 40℃ environment. For example, the FW4-10 switch only has an electrical life of 5 times when breaking an 800A current.

Solutions:

• Clean silver contacts with 25%-28% ammonia water, then apply neutral Vaseline.

• Adjust main contact pressure to ≥150N.

• Calibrate opening/closing synchronism to ≤3.3ms/≤5ms.

(2) Fuse Blowing

Fuse blowing results from short circuits, overloads, or improper selection (e.g., RN1-10 fuses rated 2-5000A). Replace fuses after identifying the cause, and ensure the load switch can handle currents within the "transfer current" range.

(3) Abnormal Arcing

Arcing issues stem from failed arc extinguishers or degraded contact materials. Regularly inspect the arc chamber and cylinder seals in pneumatic switches, and avoid frequent high-current operations per GB/T 3804.

II. Mechanical Fault Handling
(1) Operating Mechanism Jamming

Jamming occurs due to component aging, insufficient lubrication, etc. Detect jamming via motor current analysis, then:

• Check connecting rod torque (M10 bolt 8.8 grade → 20±2N·m).

• Apply molybdenum disulfide grease (drop point ≥300℃).

• Replace fatigued springs and adjust the spindle angle/crank arm.

(2) Contact Wear

Wear is caused by frequent operations and arcing. Replace CuW80 contacts if wear exceeds 3mm. Monitor wear regularly and maintain synchronism (opening ≤3.3ms, closing ≤5ms) to balance three-phase currents.

(3) Interlock Failure

Interlock failure, often from mechanical wear, poses safety risks. Regularly inspect interlock structures and test functions, replacing components as needed.

III. Insulation Fault Handling
(1) Insulation Moisture

Moisture ingress occurs in high-humidity environments (e.g., coastal areas). Use EPDM seals and:

• Dry and apply nano moisture-proof coatings.

• Replace insulation parts or oil (ensure breakdown voltage ≥25kV for oil-immersed switches).

(2) Insulation Aging

Aging accelerates at high temperatures (10℃ rise shortens life by 50%-70%). Monitor via tanδ, insulation resistance, and partial discharge (PD ≤10pC). Replace aged parts and use CT scans for epoxy components.

(3) Insulation Resistance Drop

Test with a 2500V megohmmeter (≥1000MΩ). Investigate drops via oil analysis and replace/repair faulty parts.