Maintenance Guides 1 min read

A practical guide to switchgear maintenance: inspection of arc extinguishing chambers, measurement of transient resistance and testing of disconnector blocks

Technical analysis: Switchgear maintenance: arc chute inspection, contact resistance measurement, and trip unit testing

A practical guide to switchgear maintenance: inspection of arc extinguishing chambers, measurement of transient resistance and testing of disconnector blocks

1. Scope and purpose

This technical manual defines the standard maintenance procedure for air circuit breakers (ACB) and power switching devices with nominal currents from 630 A to 6300 A, used in industrial electrical installations of Ukrainian enterprises. The procedure covers the inspection and maintenance of arc extinguishing chambers, the measurement of the electrical resistance of the main direct current contacts, as well as the functional testing of microprocessor protection units (disconnectors).

The regulation is developed in accordance with the requirements of NPAOP 40.1.1-1.21 "Rules for the safe operation of electrical installations" (PBEE), standards EN 60947-2 (Low-voltage distribution and control equipment. Part 2. Automatic circuit breakers), ISO 45001 and internal regulations of UNITEC-D GmbH to ensure uninterrupted operation of industrial equipment.

Maintenance is performed during scheduled production shutdowns: annually for conditions with increased dust and humidity (mining and mineral processing plants, metallurgical plants) or once every 2 years for normal environmental conditions (engineering, food industry), as well as after tripping of the circuit breaker for a short-circuit current exceeding 50% of the nominal breaking capacity ($I_{cu}$).

2. Precautions and safety

ПОПЕРЕДЖЕННЯ! НЕБЕЗПЕКА УРАЖЕННЯ ЕЛЕКТРИЧНИМ СТРУМОМ ТА ДУГОВОГО СПАЛАХУ!
Перед початком будь-яких робіт виконайте повну процедуру блокування та маркування (LOTO): вимкніть вимикач, виведіть його в ремонтне положення (викатіть візок), заземліть вхідні та вихідні ошиновки за допомогою переносних заземлень відповідно до ДСТУ EN 50110-1. Використовуйте засоби індивідуального захисту (ЗІЗ): термостійкий одяг для захисту від дугового спалаху з мінімальним показником ATPV $\ge$ 12 ка/см², захисний шолом з лицьовим щитком (EN 166, клас захисту від електричної дуги), діелектричні рукавички класу 4 (до 36 кВ) згідно з EN 60903, та взуття з діелектричною підошвою.
ЗАБОРОНЕНО торкатися рухомих частин механізму під час взведення пружин. Переконайтеся, що запобіжні заходи виконані, а напруга на клемах дорівнює 0 В за допомогою перевіреного двополюсного індикатора напруги.

3. Necessary tools and materials

> > > > > > > > >
Name of tool / material Technical specification Quantity
Digital Microohmmeter (Micrometer)Range 0.1 μOhm – 10 Ohm, test current at least 100 A direct current 1 pc.
A set of insulated torque wrenchesSquare 1/4" and 1/2", force range 5-50 Nm and 20-200 Nm, IEC 60900 1 k-kt
Device for secondary current injection (Secondary Injection Test Set)For testing protection units (microprocessor trip units) with software 1 pc.
Set of isolated screwdriversSchlitz (SL) and Phillips (PH), class 1000V, IEC 60900 1 k-kt
Thermal sensor or thermal imagerRange -20°C to +350°C, matrix resolution at least 320x240 1 pc.
Stainless steel brush / brass brushSoft pile for cleaning contact surfaces 2 pcs.
Electrical contact cleanerQuick-drying aerosol without residue (isopropanol-based or specialized solvent) 2 cylinders
Specialized lubricant for electrical contactsTechnical contact lubricant (for example, based on synthetic oils with conductive or antioxidant additives) 1 jar
Lint-free napkinsIndustrial rolls for wiping 1 roll

4. Checklist of preliminary inspection

View element What to check Acceptance / rejection criterion Notes
Switch body The presence of cracks, chips, traces of soot or thermal effects on the insulating panels Acceptable: clean surface without damage. Deviations: the presence of cracks or black traces of current leakage - replacement of the part. Visual control in bright light
Connecting the busbar Tightening torque of bolted joints, absence of oxidation and discoloration of the metal Acceptable: clean connections, torque to spec. Deviations: darkening of the tires - tightening and cleaning. Use a torque wrench
Secondary circuits and connectors The integrity of the insulation of the wires, the reliability of fixing the control plugs Acceptable: tight fit of contacts, no scratches. Deviation: backlash in the connectors - tighten or replace the pin. Manual check
Operation counter (On/Off cycles) Indicators of the mechanical commutation counter Compare with the passport resource (usually 10,000 - 20,000 cycles). In case of excess, a capital inspection of the mechanism. Record the value in the maintenance log
Trolley locking mechanism Triggering of mechanical interlocks when trying to roll out an on switch Acceptable: Blocking severely prevents movement. Deviation: free movement — traction control. Inspection before rolling out

5. Step-by-step service procedure

  1. Dismantling and inspection of arc extinguishing chambers

    • Action: Unscrew the fixing screws and carefully remove the arc extinguishing chambers of each pole of the breaker. Inspect the deionization plates inside the chamber for burn-in, deformation, or significant metallic dust deposition.
    • Specific values: The gap between the plates must be uniform (the nominal value depends on the type of switch, on average 2.0–4.5 mm). Allowable local wear of the edges of the plates up to 15% of the initial thickness.
    • Visual indicators: Absence of melting of the insulation walls of the chamber, clean plates without a short circuit between them due to soot.
    • Typical mistakes: Do not install cameras in a wet state or with residues of abrasive cleaners. Do not use metal scrapers to clean ceramic walls.

  2. Cleaning and repair of arc extinguishing chambers

    • Action: Clean the interior cavity and plates of arc extinguishing chambers using an aerosol cleaner and lint-free wipes. In the presence of persistent soot, light sanding with fine-grained sandpaper (grit not coarser than P400) is allowed, after which blow with a dry, degreased guard under a pressure of no more than 2.0 bar.
    • Specific values: Compressed air pressure for purging: 1.5 – 2.0 bar. Drying temperature (if a thermal cabinet is used): no higher than +60°C.
    • Visual indicators: Complete absence of soot and carbon deposits on internal partitions.
    • Typical mistakes: Too high air pressure can damage the fragile ceramic partitions of the arc extinguishing chamber.

  3. Inspection of main contacts

    • Action: Move the switch to the "On" position by mechanical hand pulling (or using a test remote). Inspect the main and arc extinguishing contacts for erosion, pitting and the condition of the silver plating. Measure the residual travel of the contacts (contact failure).
    • Specific values: The minimum permissible thickness of the overlay made of precious metal (silver/cadmium oxide) on the main contacts: not less than 0.8 mm. Contact failure (contact pressure): 1.5 – 3.0 mm depending on the size of the switch.
    • Visual indicators: Uniform spot of contact over the entire contact plane (at least 80% of the surface area).
    • Typical mistakes: Do not try to level the deep sinks on the contacts with a file; this reduces the thickness of the silver layer and leads to rapid failure. If the wear is higher than normal, replace the contact group.

  4. Measurement of transient resistance of main contacts (microohmmeter)

    • Action: Connect the microohmmeter probes in a "four-wire" scheme (Kelvin connections) to the upper and lower lead bars of each pole of the switch with the contacts closed. Apply a measuring current of 100 A (or higher) and record the resistance value for each pole (phases A, B, C).
    • Specific Values: The contact resistance of one pole of the circuit breaker must meet the OEM factory specification (typically no more than 30-50 µOhms for 1600 A breakers and no more than 15 µOhms for 4000 A breakers). The difference between the phases should not exceed 10%.
    • Visual indicators: Stable digital value on the device display without jumps.
    • Typical errors: Poor contact of the microohmmeter probes with the oxidized bus gives inflated results. Before measuring, clean the connection points of the probes to a metallic sheen.

  5. Testing the microprocessor protection unit (disconnector)

    • Action: Connect a secondary current injection device to the test connectors of the trip unit (eg Schneider Electric Micrologic, ABB PR122/PR123, Siemens 7SJ/ETU, etc.). Run the software or test script to check operation by zone: overload protection ($L$ - Long time), short circuit protection with time delay ($S$ - Short time), instantaneous tripping ($I$ - Instantaneous), and ground fault protection ($G$ - Ground fault).
    • Specific values: The activation time must lie within the limits of the permissible current-time characteristic curves (TCC) with an error of no more than $\pm 10\%$. Check the voltage of the internal power supply and the condition of the backup lithium battery (battery voltage is at least 3.0 VDC).
    • Visual indicators: Clear opening of the power contacts of the switch within the specified time, the appearance of the corresponding error code or indication of operation on the display of the unit.
    • Typical errors: Always disconnect external control circuits before applying test signals to prevent false tripping in adjacent switchgear cells.

  6. Lubrication of mechanical units and assembly

    • Action: Apply a thin layer of the recommended lubricant to the pivot joints of the moving mechanism, cam shafts and gears of the platoon spring mechanism. Check the tightening torques of all internal power screws. Install the arc extinguishing chambers in place and securely fasten them with screws.
    • Specific values: Tightening torque of arc extinguishing chamber mounting bolts: 8 - 10 Nm (according to the manufacturer's instructions). Tightening torque of main tire bolts (thread M10): 45-50 Nm; thread M12: 75 – 85 Nm (strength class 8.8).
    • Visual indicators: Absence of excess lubricant (which can collect dust), reliable mechanical fixation of all elements.
    • Typical mistakes: Excessive lubrication of the locking mechanism can lead to dust collection and jamming of moving parts in dusty production conditions.

6. Post-repair inspection checklist

Trial / Test Expected result Actual result Status (Passed / Failed)
Mechanical tests 5 cycles of manual and remote on/off without jamming [ ] Passed   [ ] Failed
Measurement of insulation resistance Insulation resistance of the main circuits relative to the ground and between poles $\ge 1000$ MΩ (megaohmmeter 2500 V) [ ] Passed   [ ] Failed
Check transient resistance The values on each pole correspond to the factory norm ( $\le$ nominal threshold) [ ] Passed   [ ] Failed
Uncoupling block test Correct operation according to the curves $L$, $S$, $I$, $G$ within the specified error limits [ ] Passed   [ ] Failed
Checking alarms and locks Correct signals in SCADA/DCS, activation of mechanical blocks of the cart [ ] Passed   [ ] Failed

7. Troubleshooting Guide

Symptom Probable cause Corrective action
Increased transient resistance of the pole (more than 50% of the original) Oxidation of contact surfaces, loosening of bolted connections or wear of contacts Clean the contacts, check the tire tightening torque (45–85 Nm). In case of significant wear, replace the contact group.
The spring mechanism does not wind up (the motor cracks or stops) Gear gear wear, damage to the limit switch of the motor drive Check the gearbox mechanism, replace worn gears or limit switch. Check the motor power supply voltage (norial $\pm 10\%$).
The protection unit issues a battery error or resets when the power fails Discharged or damaged internal lithium battery of the release Replace the lithium battery of the backup power supply of the release unit with a similar one according to the specification.
The switch does not lock in the on position (instantly snaps back) Malfunction of the locking mechanism, jamming of the switching electromagnet or the presence of a false alarm signal from the release Check the condition of the locking pawls of the mechanism, check the status of the block contacts and the absence of commands to disconnect from the relay protection.
Local overheating of bus terminals during loading (detected by a thermal imager) Weak contact at the point of connection of the power busbars to the switch De-energize the cell, disassemble the connections, clean the contact surfaces to a metallic shine, connect with the tightening torque according to the specification.

8. Recommended maintenance schedule

Task Frequency Estimated duration Qualification level
External inspection, television monitoring of tires, inspection of indicators Every month 0.5 hours Duty electrician (Group III)
Inspection of arc extinguishing chambers, cleaning, measurement of transient resistance Annually (or every 2000 operating hours) 3-4 hours Repair Engineer (Group IV)
Complete testing of the secondary current injection protection unit Once every 2 years 2 hours Specialist in relay protection
Overhaul of the mechanism, replacement of contact groups and worn nodes Every 5 years (or after 5000 switches) 8–12 hours Lead engineer / Service team

9. Directory of spare parts

For ACB with a nominal current of 1600A / 2500A / 4000A
Description of the part Typical specification Category UNITEC
Arc extinguishing chamber assemblySwitching devices and arc extinguishing devices
Main and arc extinguishing contacts (set per pole) Silver replacement pads or complete contact groups for industrial switches Contact groups and components
Spring platoon motor drive Operating voltage 220 V AC / 24 V DC, gearbox assembly Electric drives and motor mechanisms
Microprocessor unit of the uncoupler Basic or selective protection (LSI / LSIG types) Electronic protection units and controllers
Secondary plugs and control connectors Multi-pin block connectors (eg 24-pin, 32-pin) Connectors and switching cables

To select original or compatible spare parts for your switchgear, go to our electronic catalog UNITEC-D.

10. Links

  • DSTU EN 60947-2:2015 — Low-voltage distribution and control equipment. Part 2. Automatic switches.
  • NPAOP 40.1.1-1.21-98 — Rules for the safe operation of electrical installations (PBEE).
  • DSTU EN 50110-1:2016 — Operation of electrical installations.
  • EN 60364 — Low-voltage electrical installations.
  • Technical documentation and operating instructions of the leading OEM manufacturers of power equipment (Schneider Electric, ABB, Siemens, Eaton).

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