The maintenance of low-voltage distribution cabinets primarily ensures their normal and safe operation. A comprehensive annual inspection and maintenance of the low-voltage distribution cabinets is necessary. Maintenance should be completed with minimal power outage time, generally determined in advance of the owner's power outage schedule.
The content and steps of low-voltage distribution cabinet maintenance are as follows:
1. Maintenance should begin from the low-voltage side of the transformer. After de-energizing the distribution cabinet, clean the dust inside, check the busbar and downlead connections for good condition, check for overheating or discoloration at joints, check the cable heads and terminal blocks for secure fastening, check the grounding wire for corrosion, and check the terminal blocks for tightness. All secondary circuit connections should be reliable, and insulation should meet requirements.
2. When inspecting drawer-type switches, the drawer-type switch cabinet should move smoothly when pushed in or pulled out, and the mechanical interlocking should be reliable. Check that the automatic air switch operating mechanism on the drawer cabinet is in place and that the wiring screws are tight. Clean the contactor contact surface and surrounding area of dirt. Check the contactor contact for good contact. If poor contact is found, the contact surface can be slightly filed if necessary. If the contact is severely burned (the contact point is worn down to 1/3 of its original thickness), the contact should be replaced. Power indicators and indicator lights should be in good working order.
3. When overhauling the capacitor bank, first disconnect the main switch of the capacitor bank. Use a wire of at least 10mm² to discharge each capacitor to ground. Visually inspect the casing for damage and oil leakage. If the capacitor casing is swollen, address the issue promptly by replacing the discharge device, the wiring screws of the control circuit, and the grounding device. After reconnecting the circuit breaker, test the indicating and automatic compensation sections.
4. Overhauling circuit breakers in the receiving cabinet and interconnecting cabinet: First disconnect all loads, then use the handle to pull out the circuit breaker. Retighten the wiring screws and check if the spring force of the blades meets the specifications. Check for cracks or damage to the arc-extinguishing grid; manually test the mechanical interlocking for accurate opening and closing; check for good contact of the contacts; if necessary, file the contact surface; check for loose, deformed, or detached internal springs, washers, and screws.
Substation Maintenance
1. Before operation, follow these steps: disconnect the low-voltage side loads one by one, disconnect the high-voltage side circuit breaker, close the grounding switch, lock the high-voltage switchgear, and hang a "Do Not Close, People Working" sign on the switchgear handle. Then, short-circuit the busbars with a 10mm² or larger conductor and connect the grounding wire, tightening the busbar screws.
2. Maintenance operation steps: Clean the busbar contacts again and apply electrical compound grease. Tighten the screws with new spring washers. Check for any abnormalities in the insulators and spacing connections between busbars. Check the reliability of the current, voltage, and secondary winding terminal connections of the transformers.
3. Pre-energization Inspection and Testing: Remove all grounding wires and short-circuit wires. Check the work site for any tools left behind. After confirming everything is in order, close the isolating switch, disconnect the high-voltage side grounding switch, close the high-voltage side circuit breaker of the operating transformer, remove the warning signs, energize the transformer, then close the circuit breaker of the low-voltage side receiving cabinet to energize the busbar. Finally, close the relevant interconnection cabinets and the automatic air switches of each branch circuit.
Precautions
1. A dedicated person must supervise the maintenance process.
2. Voltage testing must be performed before work begins.
3. Maintenance personnel should be familiar with and able to operate the electrical and mechanical interlocks of the entire distribution cabinet.
4. During maintenance, it is essential to understand in detail which lines are powered by two lines.
5. When maintaining the busbar, residual charge in the lines should be fully discharged.
