What should I pay attention to when installing the power distribution cabinet?

The installation of power distribution cabinet is a key link in electrical construction, and it is necessary to strictly follow safety specifications and technical standards to ensure the stable operation of power system. The following are the core items that should be paid attention to during installation:First, preparation before installation

Evironmental inspection

Ensure that the installation location is dry and well ventilated, away from high temperature, humidity, dust and corrosive gas environment (such as caution near boiler room and bathroom).

Th ground shall be flat, and the height of foundation steel or bracket shall meet the design requirements, so as to avoid water soaking the cainet.

Check whether the positions and sizes of reserved holes and embedded parts in civil works match the distribution cabinet.

equipment inspection

Check whether the model, specification and quantity of the power distribution cabinet are consistent with the design drawings, and the accessories (such as door locks, instruments and switches) are complete and undamaged.

Check whether there is deformation and corrosion on the surface of the cabinet, the cabinet door can be opened and clFirst, the preparation work before debugging

Data and tool inspection

Confirm that the design drawings, equipment specifications, installation records and other information are complete, and be familiar with the circuit principle and equipment parameters.

Prepare debugging tools: multimeter, megger (insulation resistance tester), phase sequence table, clamp ammeter, oscilloscope (optional), screwdriver, wrench, etc.

Ensure that the commissioning personnel have electrician operation qualification and wear protective equipment such as insulating gloves and shoes.

Site safety confirmation

Clean up the sundries around the power distribution cabinet to ensure that the operation space is free of obstacles and well ventilated.

Disconnect all superior power supplies (such as transformers and main incoming switches), and hang "No Closing" warning signs on the power distribution cabinet to prevent power transmission by mistake.

Check whether the grounding of the cabinet is reliable, the PE line is firmly connected, and the grounding resistance value meets the design requirements (usually ≤4Ω).

Second, step-by-step debugging process

1. Insulation and grounding test

Insulation resistance test:

Use a 500V megohmmeter to measure the insulation resistance of each loop phase, phase ground (PE line) and phase zero (N line) respectively.

Standard: the insulation resistance of low-voltage system should be ≥0.5MΩ, and it should be ≥ 2mΩ in wet environment; If the resistance value is low, it is necessary to investigate the problems such as broken wires and damp elements.

Grounding continuity test:

Use multimeter to measure the continuity between the metal frame, door, guide rail and PE wire of the cabinet, and the resistance should be close to 0Ω to ensure no virtual connection or disconnection.

2. A loop check (main circuit)

Line connection confirmation:

Check whether the specification, phase sequence (yellow/green/red) and connection position of the primary loop wire are consistent with the drawings, and the terminal is firmly crimped without looseness.

Check whether the rated current and voltage of circuit breakers, disconnectors and contactors match the design load.

Component function test:

Manually open and close the circuit breaker and disconnector, and check whether the mechanical action is flexible and the contact is good (no ablation or oxidation).

Test the dual power switching device (if any): simulate the power failure of the main power supply, and check whether the standby power supply is automatically switched on and whether the switching time meets the requirements (for example, ≤1.5 seconds).

3. Secondary loop inspection (control circuit)

Line logic verification:

According to the control schematic diagram, use multimeter to measure the on-off of the wires of the secondary loop step by step, and confirm that the control lines and signal lines are connected correctly (such as buttons, indicator lights and relay coil loops).

Check whether the program settings of PLC, intelligent instrument, frequency converter and other equipment are consistent with the process requirements (such as start-stop logic and protection threshold).

Control function test:

Power the secondary circuit separately (keep the primary circuit powered off), and test the following functions:

Button operation: whether the start-stop button normally triggers the contactor action, and whether the indicator display is synchronized with the equipment state.

Protection function: simulate overload, short circuit, leakage and other faults, and test whether the circuit breaker and leakage protector can trip in time and whether the alarm device works normally.

Linkage control: for example, multiple devices are linked to start and stop, and the non-fire power supply is cut off with the fire fighting system, etc., to verify the consistency of signal transmission and action.

4. Simulated power-on test (without load)

Primary circuit power transmission:

Confirm that all outgoing switches are off, close the main incoming switch, and measure whether the incoming voltage is normal (three-phase 380V or single-phase 220V, with an error of ≤ 10%).

Use the phase sequence table to check whether the phase sequence of the three-phase power supply is correct (positive phase sequence: yellow → green → red) to avoid motor reverse rotation.

No-load operation inspection:

Close each branch switch in turn, and observe the operation of circuit breakers, contactors and other components under no-load condition:

Whether there is abnormal heating (contact temperature ≤70℃), vibration or abnormal sound.

Measure whether each phase current is balanced (no-load current should be close to 0A, with a deviation of ≤10%).

Whether the parameters such as voltage, current and power displayed by intelligent meters (such as multifunctional power meters) are consistent with reality.

5. Test run with load

Graded loading test:

Connect small load equipment (such as lighting and small motor) first, observe for 10~15 minutes, and check:

Whether the equipment is running stably and whether the current and voltage fluctuations are within the allowable range (such as voltage fluctuations ≤ 5%).

Whether there is heat at the connection of wires and terminals (detected by infrared thermometer, the temperature rise is ≤60K).

Gradually increase the load to the rated capacity, and test the running state under full load:

Record the current and temperature rise of each loop to ensure that it does not exceed the rated parameters of components (such as rated current of circuit breaker and current carrying capacity of conductor).

Verify the overload protection function: artificially set the overload current (such as 1.2 times the rated current), and check whether the circuit breaker trips within the specified time (such as the action time of thermal relay ≤20 minutes).

Linkage and intelligent function test (if any):

Test the remote monitoring function: check the real-time data (such as current and power factor) of the power distribution cabinet through the upper computer or mobile phone APP, and whether the remote control switch is sensitive and reliable.

Simulated emergency: If a circuit trips due to short circuit, check whether other circuits are operating normally and whether the standby power supply is put into operation according to the design logic.

Third, common problems and solutions

Problems, phenomena, possible causes and solutions

Low insulation resistance, damaged wires, damp components, water in the terminal to dry components, replacement of damaged wires, and sealing of wire inlet holes.

Short circuit, overload and misoperation of the leakage protector of the tripping circuit after the circuit breaker is closed. Use multimeter to check the short circuit point, check whether the load exceeds the limit, and recalibrate the leakage protector.

The indicator light is not on, the bulb is damaged, the control line is broken, and the power supply is not connected. Replace the bulb, measure the on-off of the control line, and check the power supply voltage.

The equipment reverses the phase sequence of the three-phase power supply and replaces any two-phase conductor, and reconfirms the phase sequence with the phase sequence table.

Abnormal heating of components, poor contact of contacts, insufficient cross-sectional area of wires, polishing contacts or replacing components, and increasing wire specifications.

Four, debugging records and acceptance

Fill in the debugging report

Record test data: insulation resistance value, voltage/current of each loop, component temperature rise, protection action time, etc.

Indicate the problems found and the treatment results, and the debugging personnel and supervision personnel shall sign for confirmation.

final acceptance of construction

Invite Party A, the supervisor and the design unit for joint acceptance, and check whether the installation process and functional indicators meet the specifications and design requirements.

Hand over the commissioning report, product certificate, circuit diagram and other materials to ensure that the files are complete.

Safety warning and delivery

Post the "energized" sign in the obvious position of the power distribution cabinet, and restore all safety protection devices (such as cabinet doors and protective covers).

Train the operators, and explain the operation process, emergency shutdown methods and daily maintenance points.