Preparation before maintenance

1. Collect information

Inquire with the operator about the situation of the distribution cabinet malfunction, including the time and symptoms of the malfunction (such as whether there is smoke, odor, abnormal sound, indicator light status, etc.).

Check the operation records of the distribution cabinet to understand its recent load situation, whether there have been frequent trips, and other information.

2. Preparation of safety measures

Maintenance personnel must wear personal protective equipment such as insulated gloves and insulated shoes.

Prepare necessary maintenance tools such as multimeters, megohmmeters, soldering irons, screwdrivers, wrenches, etc., and ensure that the insulation performance of the tools is good.

Hang warning signs such as “under maintenance, no closing” on the operating handles, switches, and other parts of the distribution cabinet to prevent others from making mistakes.

3. Cut off the power supply

Strictly follow the operating procedures to cut off the main power supply and related branch power supply of the distribution cabinet. It can be achieved by operating devices such as circuit breakers and isolation switches. For distribution cabinets with energy storage devices, such as capacitor banks, they also need to be discharged to ensure the safety of maintenance personnel.

Troubleshooting

1. Appearance inspection

Carefully observe the cabinet of the distribution cabinet to see if there are any signs of burning, deformation, or corrosion. Check if the cabinet door can be closed and sealed properly, and if the door lock is intact.

Inspect the wiring inside the distribution cabinet, check for any damage, aging, or discoloration of the wires, and ensure that the connection points of the wires (such as terminal blocks, plugs, sockets, etc.) are not loose or oxidized.

Check the appearance of various electrical components (such as circuit breakers, contactors, relays, fuses, etc.) for burning, deformation, contact wear, and other conditions.

2. Component function inspection

Use a multimeter to check the continuity of the fuse. For blown fuses, it is necessary to further investigate the cause of their melting, which may be overload, short circuit, etc.

Check whether the operating mechanism of the circuit breaker is flexible and whether the manual closing and opening are normal. An insulation resistance meter can be used to check the insulation resistance of the circuit breaker to determine whether its insulation performance is good.

For contactors and relays, check whether the resistance value of their coils is within the normal range (obtain the standard resistance value by referring to the component manual), and check the contact condition of their contacts for adhesion or poor contact. The elasticity and tightness of the contact can be checked by manually pressing the contact points.

3. Circuit inspection

According to the electrical schematic, check if the circuit connections inside the distribution cabinet are correct. A segmented inspection method can be used to gradually check the voltage and current of each branch starting from the power supply end.

Use a megohmmeter to check the insulation resistance of the circuit, including phase to phase insulation resistance and relative to ground insulation resistance. The insulation resistance of a general low-voltage distribution cabinet should not be lower than 0.5M Ω. If the insulation resistance is too low, there may be a risk of leakage, and further investigation is needed to identify the damaged part of the insulation.

Fault repair

1. Replace damaged components

For electrical components that have been confirmed to be damaged, such as fuses, circuit breakers, contactors, etc., replace them according to the specifications and models of the components. When replacing components, pay attention to the correct wiring method to ensure that the components are installed firmly.

For damaged wires, it is necessary to cut off the damaged parts and reconnect new wires. When connecting, it is necessary to ensure that the joint is firm and insulated, and materials such as insulation tape or heat shrink tubing can be used.

2. Repair circuit connections

If loose circuit connections are found, use a screwdriver or other tool to tighten the screws on the wiring terminals. For the oxidized connection part, sandpaper or other tools can be used to polish off the oxide layer and then reconnect it.

For circuit damage caused by short circuits or other reasons, in addition to replacing damaged components, it is also necessary to check whether the surrounding circuits are affected, and if necessary, repair or adjust the relevant circuits.

Post repair testing

insulation test

Perform insulation resistance testing on the repaired distribution cabinet again using a megohmmeter to ensure that the phase to phase insulation resistance and relative to ground insulation resistance meet safety requirements.

power-on test

Perform a no-load power on test while ensuring good insulation. Close the main power switch, observe whether the indicator lights in the distribution cabinet are lit up normally, whether the voltmeter, ammeter and other instruments are indicating, and check for any abnormal sounds or odors.

After the no-load test is normal, gradually connect the load, increase the load according to a certain proportion, observe the operation of the distribution cabinet under different load conditions, check whether the electrical components can work normally, and whether the circuit can operate stably.

Cleaning and Recording

clean up the scene

After the repair is completed, clean up the debris inside the distribution cabinet and organize the tools and remaining materials. Check if the cabinet door of the distribution cabinet is closed properly and remove the warning sign.

Record the repair situation

Record in detail the fault symptoms, maintenance process, and replaced components of the distribution cabinet. These records are very helpful for future maintenance and fault analysis.