How are photovoltaic power stations operated and maintained?

Photovoltaic power plant

Photovoltaic (pv) power plant operations is short for photovoltaic power generation system operation maintenance, based on system safety, through preventive maintenance, periodic maintenance and regular equipment performance testing methods, scientific and reasonable to manage power plant, in order to ensure safe, stable and efficient operation of the entire power plant, so as to ensure the return of investors.
With the rapid development of global photovoltaic power generation industry, the construction quality and safety problems of photovoltaic power stations are frequent.
Problems such as design defects, equipment quality defects and non-standard construction have brought severe challenges to the operation and maintenance of photovoltaic power stations.

O&m requirements

During the operation of a photovoltaic power station, faults will occur on both the DC side and the AC side. The faults on the AC side, such as box transformer, cable and booster station equipment, can be observed from the real-time operation status monitoring background and are relatively easy to find. However, due to the large number of clusters on the DC side, the faults are not easy to be detected, and the failure frequency is high, which has a great impact on the power generation. At the same time, there is a certain space for improving the power generation in this part, which needs the attention of operation and maintenance personnel. It is found that the total fault frequency of DC side such as module, bus box and inverter accounts for 90% of the total fault proportion of photovoltaic power station operation, while the fault frequency of cable, box transformer, civil engineering and booster station accounts for a small proportion. Component problems such as component loosening, hot spot failure, glass breakage, junction box diode failure, etc., these problems are mainly related to their own quality in addition to the component loosening caused by the construction of untightened pressure block.

  • Component maintenance standards

(1) Cleaning and maintenance of components
Cleaning conditions: The PV square output is lower than 85% of the output in the initial state (at the end of the last cleaning).
Precautions for cleaning:
1) A soft and clean cloth can be used to wipe the photovoltaic module. Corrosive solvents or hard objects should not be used to wipe the photovoltaic module;

2) It is not appropriate to use the liquid cleaning module with a large temperature difference with the photovoltaic module;

3) It is not appropriate to clean the components in the case of hindering the personal safety of operation and maintenance personnel;

4) It is strictly prohibited to clean components under bad meteorological conditions;

5) It is not suitable to clean the components under the condition of too high temperature or too strong irradiation;

6) Special regional environment needs to make targeted cleaning plan.

(2) Regular inspection and maintenance of components
Check and repair items:
Module frame, glass, battery sheet, module surface, backplane, junction box, wire, nameplate, live warning mark on PV module frame and support structure, other defects, etc.

Photovoltaic building materials and photovoltaic components (such as double-glass components) should be regularly inspected, cleaned, serviced and maintained by professionals. If the following problems are found, the PV module should be adjusted or replaced immediately:
(1) There is glass breakage, backplane burning and obvious color change in the PV module;

(2) There is a bubble forming a connected channel between the photovoltaic module edge or any circuit;

(3) The terminal box of the photovoltaic module is deformed, twisted, cracked or burned, and the terminal cannot be properly connected.

(4) Dew, water intake and failure of insulating glass affect the sight line and thermal performance of photovoltaic curtain wall project;

(5) Glass cracking, including glass hot cracking and tempered glass self-explosive cracking;

⑥ Coated glass peeling, resulting in the loss of architectural beauty;

⑦ glass loosening, cracking, damage, etc.

(3) Regular testing of components
Disconnect the PV module from other electrical equipment before performing the insulation resistance test. For the system with square frame grounded, the photovoltaic array insulation resistance test can be performed in the following ways: a) first test the insulation resistance of the negative pole of the square array to ground, and then test the insulation resistance of the positive pole of the square array to ground; B) Test the insulation resistance of the photovoltaic square when the positive and negative poles are short-circuited to the ground. For the system with square frame not grounded, the following methods can be used to test: a) insulation test between the cable and the earth; B) Insulation test between the square cable and the frame of the assembly.
Test contents: insulation resistance, insulation strength, component I-V characteristics, component thermal characteristics.

(4) Regular inspection and maintenance of the array

Inspection and maintenance items: photovoltaic square array overall, stressed members, connecting members and connecting bolts, anti-corrosion layer of metal materials, prefabricated base, array bracket potential connection wire, grounding, and other defects.

(5) Regular array testing
The PV array must meet the following requirements:
1) There should be no deformation, dislocation or loosening of the photovoltaic square array as a whole;

2) The planting bars or rear bolts used to fix the photovoltaic square shall not be loosened; The photovoltaic square array installed by the prefabricated base shall be placed smoothly and neatly, and the position shall not be moved;

3) The main stressed members, connecting members and connecting bolts of the photovoltaic phalanx should not be damaged or loosened, the weld should not be welded, the rust resistant coating of metal materials should be complete, and there should be no peeling and corrosion phenomenon;

4) There should be no other facilities between the supporting structures of the photovoltaic square array; No additional facilities that may affect the operation and safety of the PV system are allowed in the PV system area.
The mechanical strength of the array was tested, and 250N force was applied to the most unfavorable direction of the most unfavorable position of the photovoltaic array bracket and the photovoltaic module frame for 10 seconds. After five consecutive tests, the array could not be loosened, permanently deformed, cracked or damaged in other forms.

  • Major equipment inspection and maintenance

(1) Bus box
The operation and maintenance of the bus box shall comply with the following provisions:
1) The manifold box shall not have deformation, rust, water leakage and ash accumulation. The safety warning mark on the outer surface of the box shall be intact and free from damage. The waterproof lock on the box shall be flexible to open and close;

2) Each terminal in the bus box shall not be loose or corroded; 3) The specifications of HVDC fuses in the bus box should meet the design requirements;

4) The insulation resistance of the positive pole to the ground and the negative pole to the ground of the output bus shall be greater than 2mω;

5) The DC circuit breaker at the end of the DC output bus should be flexible and reliable;

6) The lightning protection device in the bus box should be effective.
Inspection and maintenance items include the structure of the bus box and the manufacturing quality of the cabinet itself, main circuit connections, secondary wires and electrical components installation. Test items include mechanical strength, insulation resistance, insulation strength measurement, display function, communication function, thermal characteristics of the bus box.

(2) AC power distribution cabinet
Ac power distribution cabinet maintenance must comply with the following requirements:
1) Before maintaining the AC power distribution cabinet, notify the start and end time of power outage in advance, and prepare the tools required for maintenance.

2) The following safety precautions should be paid attention to when maintaining the AC power distribution cabinet:
A) After the power failure, ensure that the power distribution cabinet is not charged for maintenance.

B) When maintaining the power distribution cabinet in sections, isolation devices should be installed at the junction of live and unlive power distribution cabinets.

C) When operating the AC side vacuum circuit breaker, wear insulation boots and gloves, and be supervised by special personnel.

D) Do not touch the capacitor cabinet before the capacitor discharge to the ground.

E) Before the power supply after the maintenance of the PDC, check whether there are any tools left in the PDC.

F) After the maintenance of the PDC, remove the safety device, disconnect the high-voltage side grounding switch, and close the vacuum circuit breaker. After observing that the transformer is put into operation correctly, supply power step by step to the low-voltage PDC.

G) Ensure that the metal frame of the PDC is properly connected with the foundation steel using galvanized bolts, and the anti-loose parts are complete.

H) In the power distribution cabinet, the identification devices indicating the number, name or operating position of the controlled equipment should be complete, and the number should be clear and neat.

I) Bus joint should be closely connected, should not be deformed, no trace of black discharge, insulation without loosening and damage, fastening connection bolts should not rust.

J) Push-pull of handcart and pull-out complete power distribution cabinet should be flexible and free of jamming and collision; The center line of moving contact and static contact should be consistent, and contact close.

K) Switch in the power distribution cabinet, the main contact should not be burned trace, the arc extinguishing cover should not be burned black or damaged, tighten the wiring screws, clean the dust in the cabinet.

L) Take the switches out of the cabinet of drawers and tighten the wiring terminals. Check the installation and wiring of the current transformer, ammeter, and watt-hour meter. Ensure that the handle operating mechanism is flexible and reliable. Tighten the inlet and outlet cables of the circuit breaker.

M) The heat dissipation of low-voltage electrical appliances should be good, the switching plate should be in good contact, and the signal lamp, button, light plate, electric bell, flashlight, accident electric clock and other actions and signal display should be accurate.

N) Check the insulation resistance values between cabinets, screens, tables, boxes, and plates and between lines and between lines to ground. The feed lines must be greater than or equal to
0.5 the MQ; The secondary loop must be greater than 1mω.

Inspection and maintenance items include the structure of the PDC and the manufacturing quality of the cabinet itself, main circuit connections, secondary lines and electrical components installation. The test items include insulation resistance, insulation strength measurement, display function, communication function, and PDC thermal characteristics.

(3) Inverter
The operation and maintenance of the inverter shall meet the following requirements:
1) The inverter structure and electrical connection should be kept intact, there should be no corrosion, ash accumulation and other phenomena, the heat dissipation environment should be good, the inverter operation should not have large vibration and abnormal noise.
2) The warning mark on the inverter should be intact without damage.
3) The function of starting and stopping the radiator fan of the module, reactor and transformer according to the temperature should be normal. The cooling fan should not have large vibration and abnormal noise when running. If there is any abnormal situation, the power should be checked.
4) Periodically disconnect the circuit breaker at the AC output side (network side) once, and the inverter should stop feeding power to the power grid immediately.
5) If the temperature of DC bus capacitor in inverter is too high or exceeds the service life, it should be replaced in time.
Inspection and maintenance items include inverter structure and manufacturing quality of the cabinet itself, main circuit connection, secondary wire and electrical components installation. Test items include performance indicators, protection functions, and other requirements.

(4) Transformer
Test and maintenance items: photovoltaic power plant main circuit boost transformer.
Test items: conversion efficiency test, other experiments.

(5) Energy storage equipment
The operation and maintenance of energy storage equipment shall meet the following requirements:
1) The temperature of the energy storage equipment room should be controlled at 5~25℃, and the ventilation measures should run well; When the temperature is low, appropriate insulation measures should be taken for the energy storage equipment.

2) When maintaining or replacing energy storage devices, tools (such as wrenches, etc.) must be equipped with insulating sleeves.

3) Over-charge and over-discharge should be avoided during the use of energy storage equipment.

4) No sundries shall be piled above and around the energy storage equipment.

5) The surface of energy storage equipment should be kept clean. If there is corrosion leakage, concave or bulging phenomenon, it should be treated in time and the reason should be found.

6) The connecting screws between the energy storage equipment monomers should be tightened.

7) In case of continuous overcast and rainy days, resulting in insufficient charging of energy storage equipment, the power supply time for load should be stopped or shortened.

8) The energy storage equipment should be charged in a balanced manner regularly, usually 2-3 times per quarter. If the voltage of a single battery in an energy storage device is abnormal, handle it in a timely manner.

9) Energy storage devices that have been out of service for more than 3 months should be recharged before being put into operation.

10) When replacing the battery, it is best to use the same brand, the same type of battery, to ensure the consistency of its voltage, capacity, charging and discharging characteristics, shape and size.

(6) Energy storage system controller
The operation and maintenance of the controller shall comply with the following provisions:

1) The Settings of overcharge voltage and overdischarge voltage of the controller should meet the design requirements.

2) The warning mark on the controller should be complete and clear.

3) The wiring terminals of the controller shall not be loose or corroded.

4) The specifications of HVDC fuses in the controller shall meet the design requirements.

5) The insulation resistance between the positive pole to the ground, the negative pole to the ground, and the positive and negative poles of the DC output bus should be greater than 2mω.

  • Main maintenance tools

Common tools: Tools required for disassembly and assembly of the equipment and components of the photovoltaic power station, and other tools that may be used in the operation and maintenance of the power station.
Test tools: multimeter, oscilloscope, current clamp, infrared thermal imager/temperature recorder, solar radiation sensor, IV curve test equipment, power quality analyzer, voltage tester, insulation resistance tester, ground resistance tester, contact current tester, square residual current monitoring function test equipment.
Protective tools: hard hat, insulation gloves, insulation shoes, safety sign, safety fence, fire extinguisher.
Spare parts: The photovoltaic power station operation and maintenance company shall equip the vulnerable and consumable parts during the operation of the photovoltaic power station, which shall be replaced in time when losses occur.

  • Power station inspection and troubleshooting
Power station inspection and troubleshooting
Power station inspection and troubleshooting

Equipment efficiency guarantee: the efficiency of the key equipment in the photovoltaic power station should meet the design requirements, and the efficiency of the key equipment should be monitored in real time and tested regularly. All data should be properly stored in written or electronic documents.
Equipment status: all key equipment in the photovoltaic power station should be in good running condition, and all key equipment should be checked regularly to reduce the failure rate.
Troubleshooting measures: Operation and maintenance service personnel shall troubleshoot the on-site faults within 7×24 hours. The fault should be handled clearly and recorded in writing, including the equipment where the fault occurred, the time when the fault occurred, the symptom, the method and way to solve the fault, the troubleshooter and the troubleshooter.

  • Maintain arresters and cables

(1) Grounding and lightning protection system
Points to note include:
1) The connection between the photovoltaic grounding system and the reinforcing bars of the building structure should be reliable.
2) The photovoltaic module, bracket, cable metal armor and roof metal grounding grid should be connected reliably.
3) The grounding resistance of the ground wire shared by the photovoltaic square array and the lightning protection system shall comply with relevant regulations.
4) The function of the overvoltage protection device between the monitoring, control system, power regulation equipment and the lightning protection system of the photovoltaic square array should be effective, and its grounding resistance should comply with the relevant regulations.
5) Photovoltaic phalanx lightning protection device should be effective, and before the arrival of the thunderstorm season, after the thunderstorm check in time.
Test and maintenance items:
① Lightning arrester and lead off installation.
② Appearance state of lightning arrester and lead line. (3) the lightning arrester and the lead line are connected.
(4) Design and state of surge protector inside each key equipment.
⑤ All ground cables should be intact.
The grounding resistance meets the design requirements.
Test items:
① Lightning protection devices for key equipment of the power station should be installed before and after the thunderstorm season.
(2) Test the resistance to the ground. (3) Corrosion status of lightning protection device.

(2) Cable
The following items should be paid attention to when maintaining wires and cables:

1) The cable should not be operated under overload, and the lead cover of the cable should not expand or crack.

2) The cable should be well sealed at the inlet and outlet of the equipment. There should be no hole with a diameter greater than 10mm. Otherwise, the cable should be sealed with fireproof mud.

3) Where the pressure and tension of the cable on the equipment shell are too large, the cable support point should be intact.

4) There should be no perforation, crack and significant uneven at the mouth of cable protection steel pipe, and the inner wall should be smooth; Metal cable pipe should not be serious corrosion; There should be no burrs, hard objects and garbage. If there are burrs, file them down and wrap them with a cable jacket and tie them tightly
5) The accumulation and garbage in the outdoor cable well should be cleaned up in time; If the cable cover is damaged, handle it.

6) When checking the indoor cable trench, it is necessary to prevent cable damage; Ensure that the support is grounded and the heat dissipation in the trench is good.

7) The mark piles along the directly buried cable lines should be intact; No excavation of the ground near the path; Ensure that no heavy objects, building materials and temporary facilities are stacked on the ground along the path, and no corrosive substances are discharged; Ensure that the outdoor cable protection facilities are intact.

8) Ensure that the cover of cable trench or cable well is intact; There should be no water or debris in the channel; Ensure that the groove bracket should be firm, there is no corrosion, loose phenomenon; Armored cable skin and armor should not be seriously corroded.

9) If multiple cables are laid side by side, the current distribution and the temperature of the cable skin should be checked to prevent the cable from burning out the connection point due to poor contact.

10) Ensure that the cable terminal is well grounded, the insulation sleeve is intact, clean, no flashover discharge trace, and the cable color is obvious.

11) metal cable bridge and its support and the introduction or introduction of metal cable conduit must be grounded (PE) or zero (PEN) reliable, the bridge and bridge between the application of grounding wire reliable connection.

12) The fire closure at the bridge through the wall should be tight without falling off.

13) Ensure that the bolts between the bridge and the support and the bolts of the bridge connecting plate are fixed in good condition.

14) There should be no water on the bridge.
Testing and maintenance items include: ① cable selection and laying; ② load operation of cable; ③ Cable layout installation; (4) Cable environment; ⑤ cable grounding insulation; ⑥ Cable running status.
The test items include: (1) cable voltage drop; ② insulation resistance; ③ Insulation strength.

  • Requirements for power station data acquisition and processing center

(1) The contents of the environmental monitoring system include:
① Monitor the temperature and humidity in the equipment room.
(2) Monitor the UPS running status.

(2) Specific requirements for a secure and stable network environment:
①LAN: dual-link fiber switching.
②WAN: firewall ten intrusion detection equipment + network gate constitutes the security precautions of the outer network.

(3) Uninterrupted requirements for 7×24 hours fault monitoring and emergency treatment:
The UPS ensures uninterrupted power supply for 7 x 24 hours.
②7×24 hours of personnel on duty.
③ Redundancy design principle ensures uninterrupted 7 x 24 hours of device links

(4) Requirements for safe data storage:
① The data storage architecture consists of database server + disk

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