Common Problems Of Vacuum load switches

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 Vacuum load switches (typically referring to load switches with vacuum interrupter structures) have advantages such as compact structure, long service life, and low maintenance requirements. However, they may still encounter some common problems during operation. These problems can be mainly classified into three categories: mechanical and operating mechanism failures, abnormal electrical characteristics, and body defects.

The following are common fault phenomena, cause analyses, and handling suggestions:
1. Mechanical and operating mechanism failures
This is the most common type of failure, usually manifested as the switch being unable to operate normally for opening or closing.
Refusal to open/close (opening/closing failure)
Phenomenon: When remotely controlled or operated manually on-site, the switch cannot open or close.
Causes:
Electrical circuit: Disconnection in the opening/closing circuit, coil disconnection, low or lost operating power supply voltage.
Mechanical jamming: Jamming of the operating mechanism, deformation of the opening top rod, improper adjustment or poor contact of auxiliary contacts.
Abnormal energy storage: The spring operating mechanism fails to store energy fully or the energy storage motor malfunctions (such as the travel switch being improperly positioned or damaged).
Handling: Check the secondary circuit and power supply; measure the coil resistance; inspect the mechanism for any jamming, adjust or replace deformed parts; adjust the position of the travel switch.
Out-of-phase closing and opening and excessive bounce
Symptoms: The action times of the three-phase contacts are inconsistent (out-of-phase), or the contacts bounce during closing (a hidden fault that requires instrument detection).
Causes: Improper adjustment of the insulating pull rod length, insufficient pressure of the contact spring, wear or excessive clearance of the mechanism transmission components.
Treatment: Adjust the length of the three-phase insulating pull rods; check the pressure of the contact springs; improve assembly accuracy and reduce the clearance.
2. Electrical Characteristics and Insulation Faults
Heating or burning of contacts
Symptoms: Abnormal temperature rise at the connection point or contact, even burning.
Cause: Poor contact (such as insufficient contact pressure, oxidation of the contact surface), overload operation, or uneven current distribution due to three-phase asynchrony.
Treatment: Check and adjust the contact pressure and synchronization; measure the loop resistance; reduce the line load.
Operational overvoltage
Symptoms: When a switch opens or closes an inductive load (such as a motor or transformer), due to the rapid arc extinction, it may generate current interruption overvoltage or multiple restriking overvoltage, threatening the insulation of the equipment.
Cause: The strong arc quenching ability of the vacuum interrupter causes the current to be forcibly cut off before the natural zero crossing point (current interruption).
Treatment: Install overvoltage protection devices (such as zinc oxide arresters, RC absorbers) on the load side.
Flashover or breakage of insulators
Symptoms: Surface discharge or mechanical breakage of support insulators.
Cause: Dirty porcelain bottles, cracks, moisture, or external force impact.
Treatment: Power off and replace the insulators, and strengthen cleaning and inspection.
3. Defects of the Main Body and Arc-extinguishing Chamber
Reduced Vacuum Degree (Leakage)
Symptoms: The vacuum degree inside the arc-extinguishing chamber drops, leading to a decline in insulation performance. In severe cases, it may cause internal discharge or explosion.
Causes: Defects in the material or manufacturing process of the vacuum tube, aging or damage of the bellows, or external mechanical impact.
Treatment: Regularly conduct withstand voltage tests or vacuum degree detection; if the vacuum degree is substandard (e.g., lower than 6.6×10⁻² Pa), the vacuum arc-extinguishing chamber must be replaced immediately.
Fuse Failure (for Combined Electrical Apparatus)
Symptoms: The fuse element melts.
Causes: System short circuit, line overload, or improper selection of the fuse element.
Treatment: Determine the cause of the fuse blow (check for short circuits in the line) and eliminate the fault, then replace the fuse element with one that meets the specifications.
Daily Maintenance and Preventive Suggestions
Regular Inspection: Regularly measure the loop resistance, check the wear of the contacts, and perform mechanical characteristic tests (synchronization, bounce, travel).
Keep Clean: Maintain the insulator surface clean and dry to prevent condensation and pollution flashover.
Lubrication and Tightening: Regularly apply lubricating grease to the rotating and sliding parts of the operating mechanism and check if the fasteners are loose.
Condition Monitoring: For vacuum arc-extinguishing chambers with glass casings, observe the color of the internal metal components (they should be bright; if they appear red or dark, it may indicate a leak).

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