RMU circuit breakers maintenance cycle and key inspection items need to be determined according to the type of equipment, operating environment, industry standards, etc. Details are as follows:
I. Maintenance Cycle
Basic cycle
35kV and below: overhauled every 4 years.
Equipment 110 kV and above: overhaul every 3 years.
New equipment after operation: must complete the first overhaul within one year of operation, verify the state of the equipment, eliminate installation defects.
Cycle Adjustment Principles
Depending on the actual operation of the equipment (e.g. short-circuit capacity, number of operations, environmental corrosivity, etc.), the operation cycle may be extended or shortened as appropriate. Adjustments typically range from 50 to 200 per cent of the base period (i.e., 1~8 years or 1~6 years).
Technical assessment of adjustment needs. Equipment of 220kV and above also requires to be filed by provincial enterprises.
Temporary Overhaul Triggering Conditions
After the interruption of highcapacity short circuit current (if the busbar short-circuit capacity interruption more than 80% of the rated capacity of the circuit breaker, requires to be repaired after 3~5 interruptions). Serious defects that may affect safe operation (such as cracks in insulation, mechanism jamming, oil leakage, etc.) require immediate repair.
ii. Main Inspection Items
* Appearance and structural inspection
* Insulating Components: Inspect porcelain bushings and insulators for cracks, discharge marks or dirt accumulation; wash or replace if necessary.
:: Metal parts: Inspect for deformation or corrosion of housing, terminal block and flange sealing surfaces; check for loosening of fasteners (e.g. bolts).
* Chassis: Check the box's sealing performance to prevent rainwater and dust from entering and to ensure that the interior of the chassis is clean and dry.
:: Inspection of operational mechanisms
:: Mechanical Characteristics: test opening and closing times, speed and synchronicity (between phase breaks and three phases) to ensure compliance with manufacturer standards.
:: Energy storage Mechanisms: check that spring, hydraulic or pneumatic energy storage devices are working properly to ensure that the energy storage time is within specified limits.
:: Lubrication and abrasion: lubrication of moving friction parts (such as drive shafts and connecting rods); check for replacement of badly worn parts (such as contacts and buffers).
Electrical Performance Testing
Main circuit resistance: Measurement of resistance of the conductive circuit with a micro-ohmmeter. The initial difference of vacuum circuit breakers shall be less than 30% and that of circuit breakers in high-voltage switchgear shall be less than 20%.
Insulation resistance: Test the insulation resistance between grounding and two phases with a megohmmeter to ensure no less than 1000 Omega.
Low Voltage Operation Test: Measure the minimum operating voltage for closing and opening under rated operating voltage to verify the reliability of the mechanism.
SF6 Gas System (if applicable)
Pressure Check: Monitor the SF6 gas pressure pressure using density relay or pressure gauge to ensure that it is in the normal range (if gas is below the alarm value, supplement if required).
Leak Detection: use leak detector to check the leakage of pipe joints, valves, etc.. Annual leakage rate should be less than 1%.
Moisture Detection: The moisture content of the gas is regularly measured to prevent degradation of insulation (SF6 gas should be ≤300μL/L during operation).
Secondary Circuits and protection
Control Circuit: check whether the circuit is loose, ensure the auxiliary switch, micro-switch flexible, good contact. Signals and indicators: Verify that the opening and closing lights, traffic lights lights and indicators are correctly displayed and are consistent with the main control room lights.
Protective device: Verify the setting of overflow protection and instantaneous trip protection to ensure reliable operation.
Environmental Adaptability Check
Temperature and humidity: Check oil levels ((oil circuit breaker) and air pressure (SF6 circuit breaker) for sudden changes in temperature, load or temperature.
Moisture Prevention and warm: In a humid environment, start the heater to prevent condensation inside the mechanism box from insulation degradation.
Corrosion Prevention: For outdoor equipment, check thatcorrosion protection measures (e.g. paint, zinc plating) are intact and can be reused if necessary.
