Part 4: Equipment-level inspection and operation and maintenance SOP of PV side confluence and low-voltage distribution system of photovoltaic power station
This article corresponds to the panoramic topology diagram of the photovoltaic power station [Module 4: Convergence and Low-voltage Distribution System], which serves as the hub connecting the inverter and the boost box transformer/component array, covering string AC combiner box/AC distribution cabinet, centralized DC combiner box, intelligent string current collection module, aR-level fast fuse (Fuse), surge protector (SPD), MC4 interface temperature rise and DC cable arc prevention maintenance.
1. DC/AC combiner box cabinet protection and environmental anti-condensation SOP
The combiner box is installed in the outdoor environment of the photovoltaic array for a long time and is susceptible to rainwater immersion, high humidity condensation and dust poisoning.
(1) Mechanical protection and sealing inspection of the combiner box cabinet
Appearance and sealing strip inspection: Check that the shell of the combiner box (IP65 protection level) has no deformation, corrosion, leakage or cracking; check that the EPDM sealing strip of the cabinet door has not fallen off and hardened. Add anti-rust grease to maintain door locks and hinges.
Rain-proof eaves and anti-small animal nets: Check that the rain-proof eaves on the top of the cabinet are not collapsed or deformed; check that the cable threading holes at the bottom of the box are well sealed (fire-proof mud/fire-proof glue is not peeling off) to prevent small animals (such as snakes and rats) from crawling in and causing interphase short circuit accidents.
(2) Anti-condensation and insulation resistance test of the cabinet environment
Anti-condensation heater and temperature and humidity control: When the relative humidity in the cabinet is ≥ 75% RH, the anti-condensation heater must start automatically. Check that there is no water vapor condensation or green copper scale on the surface of the components in the cabinet.
Cabinet insulation resistance test: Under power outage, use a 1000V insulation megger to test the insulation resistance of the AC/DC bus to the metal shell and the ground. The insulation resistance must be ≥ 10.0 MΩ.
2. Intelligent string current collection, Voc/Isc testing and fuse (Fuse) maintenance SOP
(1) Calibration of intelligent string current acquisition module
Troubleshooting of string operating current deviation:
Use a DC clamp meter to actually measure the operating current of each string and compare it with the reading on the smart combiner box/inverter collection screen.
Standard: Under the same solar irradiance (> 600 W/m²), the operating current extreme deviation of each normal string in the same combiner box must be < 5.0%.
Current zero-point drift calibration: When the string has no current output (at night or in disconnected state), if the monitoring screen shows a small current, "Hall sensor zero-point drift calibration" must be performed in the background of the acquisition module.
(2) Actual measured SOP of string open circuit voltage (Voc) and short circuit current (Isc)
String open circuit voltage test:
Open the DC circuit breaker of the string and use a multimeter to measure the string open circuit voltage Voc. The deviation of the string open circuit voltage under the same square array must be < 2.0%.
If the measured Voc voltage is 1/3 or 1/2 less than the normal value, it means that the bypass diode of the component junction box inside the string is broken down and short-circuited, or there is a serious component crack accident.
(3) SOP for maintenance and replacement of aR-class string fast fuses (Fuse)
Fuse striker and status inspection: Check that the DC fuse base is tight; check that the red striker/status indicator on the top of the fuse has not popped out. Use a microohmmeter to test the contact resistance at both ends of the fuse. The impedance must be ≤ 0.1 mΩ.
熔断器替换 SOP：
Step 1: Open the DC main circuit breaker of the combiner box and turn off the input switch of the corresponding string to ensure that there is no load current in the circuit.
Step 2: Use a high-precision DC clamp meter to retest the string current to 0 A.
Step 3: Operation and maintenance personnel wear 1000V insulating gloves and use special insulating pullers to remove the burned fuse.
Step 4: Replace with a new original quick fuse with the same rated voltage (such as 1500V DC) and the same rated current (such as 25A ~ 32A), and fasten the base.
3. Surge Protector (SPD), MC4 interface and DC cable arc prevention SOP
(1) DC/AC surge protector (SPD) maintenance
Surge protector status window check: Check the status indication window on the SPD lightning protection module. If it displays green, it is normal; if it turns yellow or red, it means that the lightning protection module has been damaged by lightning pressure sensitivity, and the lightning protection core must be replaced immediately.
Remote signaling alarm contact test: Check the remote signaling alarm dry contact cable at the bottom of the SPD. When the lightning arrester fails during testing, the SCADA background must pop up the "Lightning Protector Failure Alarm" within < 1s.
(2) MC4 terminal and busbar connection tightening and infrared temperature measurement
Infrared thermal imaging temperature measurement: When the photovoltaic array is operating at full power (irradiance ≥ 700 W/m²), infrared temperature measurement is performed on the MC4 plug, DC circuit breaker terminals and busbar in the combiner box.
The operating temperature of the terminal block and MC4 interface must be < 60.0 ℃, and the operating temperature rise must be < 15.0 ℃. If the temperature of a terminal is > 75.0°C, the oxide layer must be polished without power and conductive paste applied.
Terminal tightening torque standards:
(3) SOP for laying DC cables along the bracket to prevent wear and arcing
There is no AC zero-crossing point on the DC side. Once the insulation of the high-voltage DC cable is damaged and the metal bracket is discharged, a continuous DC arc of several thousand degrees will be generated, which can easily cause a fire.
Laying and protection inspection: Check the laying of DC photovoltaic special cables (PV1-F / H1Z2Z2-K) along the brackets and bridges. Cables must be secured with weather-resistant and UV-resistant nylon ties with tie spacing < 1.5 meters apart.
Wear and tear inspection: Focus on checking whether the cable has sharp edges, wear and tear at the edges, corners and outlet of the metal bracket; check whether the cable joints are soaked in water troughs.
Photovoltaic power station PV side confluence and low voltage distribution system equipment level inspection and operation and maintenance sign-in form
Power station name: _______________________________ Inspection date: ____ month ____ day, 2026
Inspection area: DC/AC combiner box area Inspection person in charge: ____________________
Field equipment inspection and test data recording
2. Inspection defect registration and defect elimination dispatch
3. Inspection sign-in and review signature
Inspection Engineer (Signature): _______________ Supervision Engineer (Signature): _______________
Review (signature) of the shift leader: _______________ Sign-in and filing time: ____ hour on ____ month ____ day 2026