The test of photovoltaic power generation system includes the test of photovoltaic array, the test of insulation resistance, the test of insulation withstand voltage, the test of ground resistance, and the performance test of controller.
1. PV array testing
In general, the specifications and models of the battery components in the square array string are the same, according to the technical parameters provided by the module manufacturer, find out the open-circuit voltage of a single module, multiply it by the number of series connections, which should be basically equal to the open-circuit voltage at both ends of the module string.
If there are several modules in series, the open-circuit voltage at both ends of the module string should be about an integer multiple of the above voltage. Measure the open-circuit voltage at both ends of the battery component string to see if it basically meets the above requirements. If the difference is too large, it is likely that the component is damaged, the polarity is reversed or the connection is not in good contact, etc. Check the open-circuit voltage and connection condition of the component one by one to find out the fault.
Measure the short-circuit current at both ends of the battery component string, it should be basically in line with the design requirements, if the difference is large, then there may be components with poor performance, should be replaced.
If the number of battery components in series is high, the open circuit voltage will reach 600~700V or even higher, so pay attention to safety when measuring.
After all the battery component strings are checked and passed, the battery component series parallel connection is checked. After confirming that the open-circuit voltage of all the battery component strings are basically the same, the parallel connection of each string can be carried out. After parallel connection, the voltage is basically unchanged, and the total short-circuit current should be roughly equal to the sum of the short-circuit currents of each component string. When measuring the short-circuit current, also pay attention to safety, the current is too large when the spark may jump, which can cause equipment or personal accidents.
If there are more than one sub-array, all in accordance with the above method to check and pass, before the output of each square positive and negative terminals into the sink or controller, and then measure the total working current and voltage parameters of the square array.
2. Insulation resistance test
In order to understand the insulation status of each part of the photovoltaic power generation system and determine whether it can be energized, insulation resistance testing is required. The insulation resistance test is generally conducted before the PV power generation system is ready to start operation after construction and installation, during the regular inspection and when a fault is identified during operation. The insulation resistance test mainly includes testing of the PV array, DC bus box, DC distribution cabinet, AC distribution cabinet and inverter system circuit.
As the PV array always has a higher voltage during the day, in the PV array circuit insulation resistance test, to prepare a switch that can withstand the PV array short-circuit current, first short-circuit the output of the PV array with a short-circuit switch, according to the need to choose 500V or 1000V insulation resistance meter (commonly known as megohmmeter or shake table), and then measure the insulation resistance between the output terminals of the PV array to ground The insulation resistance value should be not less than 10MΩ, the specific test method is shown in the figure below. When the PV array output terminal is equipped with lightning protector, the grounding wire of the lightning protector should be disconnected from the circuit before the test, and then restore the original state after the test.
The insulation resistance test method of the inverter circuit is shown in the figure below. Choose 500V or 000 insulation resistance meter for testing according to the rated working voltage of the inverter. The insulation resistance test of the inverter mainly includes the insulation resistance test of the input circuit and the insulation resistance test of the output circuit.
When testing the insulation resistance of the input and output circuits, first separate the battery components from the busbar, and short circuit all the input terminals of the DC input circuit and all the output terminals of the AC output circuit, then measure the insulation resistance between the input circuit and the ground and the insulation resistance between the output circuit and the ground respectively. The input and output insulation resistance value of the inverter should be not less than 2MQ.
The insulation resistance test method of DC sink box, DC distribution cabinet and AC distribution cabinet is basically the same as that of the inverter, and the insulation resistance of its input and output leads and box shell should be not less than 10MQ.
3. Test of insulation withstand voltage
For PV arrays and inverters, it is sometimes necessary to conduct insulation withstand voltage test according to the requirements to measure the insulation withstand voltage value of PV array circuit and inverter circuit. The conditions and methods of measurement are the same as the insulation resistance test above.
When conducting the insulation withstand voltage test of PV array circuit, the open circuit voltage of the standard PV array is used as the maximum use voltage, and 1.5 times of the maximum use voltage of DC voltage or 1 times of AC voltage is added to the PV array circuit, and the test time is about 10min to check whether there is insulation damage. The insulation withstand voltage test is generally performed by removing or disconnecting the lightning protection device from the circuit and then testing it.
When testing the insulation withstand voltage of the inverter circuit, the test voltage is the same as the test voltage of the PV array circuit, and the test time is also 10min, to check whether there is insulation damage in the inverter circuit.
4. Grounding resistance test
Grounding resistance is generally measured using a grounding resistance meter, which also includes a grounding electrode lead and two auxiliary electrodes. The grounding resistance test method is shown in the figure below. Test to make the grounding electrode and two auxiliary electrodes of the interval of about 20m each, and into a straight line arrangement. The grounding electrode is connected to the E terminal of the grounding resistance meter, and the auxiliary electrode is connected to the P terminal and C terminal of the resistance meter, and the grounding resistance value can be measured. Grounding resistance meter has hand-crank type, digital type, clamp type and so on several, detailed use can refer to the specific model of the instruction manual.
Grounding resistance test diagram
5. Controller performance test
For conditional occasions, it is best to conduct a comprehensive test of the controller's performance to verify whether it meets the specific requirements of the national standard GB/T19064-2003.
For general off-grid PV systems, the main function of the controller is to prevent the battery from overcharging and over-discharging. It is best to test the controller separately before connecting it to the PV system. A suitable DC regulated power supply can be used to provide a stable working voltage for the input of the controller, and adjust the voltage size to verify that the voltage when it is full disconnected, restored connected and low voltage disconnected meets the requirements. Some controllers have output voltage regulator function, you can change the input voltage in the appropriate range to measure whether the output remains stable. In addition to test the controller's maximum own power consumption to meet the requirements of not more than 1% of its rated operating current. If the controller also has intelligent control, equipment protection, data acquisition, status display, fault alarm and other functions, it can also be properly tested.
For small photovoltaic systems or to confirm that the controller has been factory-commissioned before passing, and in the transportation and installation process is not any damage, in the field can no longer carry out these tests.
