PV Isolation Protection

Abstract
When the rainy weather is frequent, the PV plant will have many small problems. Therefore, the Solis Seminar will share with you some problems that are prone to PV plants during the rainy season, and with treatment methods.

Recently, a customer's on-site inverter alarmed "PV ISO-PR" on a cloudy day. The customer contacted Solis technical staff in time. Through on-site investigation, they found many installation problems such as: PV strings are directly buried in the ground without PVC pipe protection. , Many DC cables are damaged etc. Solis technical staff assisted the customer to replace the cable again, and recommended to do PVC pipe protection treatment for the string, and then the inverter worked normally.

In this Solis Seminar, we will use this case to introduce issues related to " PV ISO-PR ".

Ⅰ Failure phenomenon and cause
“PV ISO-PR "means PV Isolation Protection, which is a relatively frequent problem of the system, which is mainly manifested as: the inverter is disconnected from the grid and enters the protection mode. It’s screen displays the error message of "PV ISO-PR01/02".

Note：
1)The alarm code "PV ISO-PR01" indicates damage in the negative terminal of PV string connected to the inverter
2)The alarm code "PV ISO-PR02" indicates damage in the positive terminal of PV string connected to the inverter

Reason: This fault indicates that the inverter has detected that the PV+ or PV- insulation resistance to the ground is too low. According to safety regulations, the inverter must stop working and enter the protection mode to prevent the risk of electric shock.

The causes of "PV Isolation Protection" are mainly divided into three categories: external environmental factors (increased environmental humidity), system factors (poor system ground insulation), inverter factors (DC line insulation detection and protection threshold is too small). Among them, environmental and system factors account for more than 80%, especially in rainy weather, the system is more prone to this failure.

Ⅱ Failure analysis

1、Caused by environmental factors
Check the failure time of the inverter. If the error is reported in the morning, evening, cloudy or rainy, and the subsequent automatic recovery, it is a normal phenomenon. This is because at these times, the moisture in the air increases and the PV system's resistance to ground becomes lower, the inverter is easy to report PV insulation failure;

2、Caused by system factors
If the inverter reports an error and the fault cannot be automatically recovered, please do further investigate the problem point. The investigation content and method are as follows:
1）Check string one by one through the inverter. Method: connect the strings one by one, with the inverter's early warning function, if the inverter does not continue to report this errors after startup, it means that the string is well, if the inverter reports an error when the next one string connected, it means that this connected string does not meet the requirements. At the same time, pay attention to whether the error message is 01 or 02 in order to accurately locate the insulation fault point.

2）Check string through multi-meter.
Method: turn off the inverter, remove all PV strings, and use DC gear of multi-meter to measure the DC voltage of string to the ground. Multi-meter red test lead is connected to PV string positive or negative, and the black test lead is grounded.
Observe whether its DC voltage is reduced to less than 20V. If the voltage does not decrease, this string insulation is poor. It is necessary to check whether the DC line of this string is damaged.

3）Check string by megohm-meter。
Method: Use megohm-meter to measure the PV string’s insulation resistance of the positive or negative pole to the ground one by one. The impedance must be greater than 150KΩ. If it is less than this value, it means that the string has poor insulation.

Ⅲ Troubleshooting

1) Check the DC line of the faulty PV string, which confirmed in the previous step to find the final problem such as the skin is damaged or the cables are immersed in water, and deal with it in time.

2) Check whether the system grounding is good, including PV panel grounding, support grounding, and inverter grounding, etc.

3) The inverter setting threshold does not meet the on-site working conditions

After the necessary inspection and repair, if the system is in good situation, the isolation protection value could be revised according to local situation. The revising method is:

Advantage settings→special settings→IgZero_COPM.Set→Setting Riso.-Limit value

Note: The specific value depends on the on-site working conditions, please consult Solis engineers, or directly contact Solis engineers for on-site communication and resolution.www.solisinverters.com/aftersales.html

Conclusion
As the core part of the PV system, the inverter is responsible for energy conversion, fault detection & early warning, protection of personal & equipment safety. Therefore, if a system warning occurs, O&M personnel should to pay attention to it, investigate and solve the problem in time to make sure the normal operation of the PV system. Solis is the world's best string inverter and service team. If you have any technical and product questions about PV systems, welcome to visit us:www.solisinverters.com