PV Isolation Protection: Key Causes, Troubleshooting, and Preventative Measures (PV-ISO-PRO 01/02 Alarm)

Overview

PV plants often encounter minor yet impactful issues during rainy weather, which can affect their operational stability. This article will walk through the common causes, troubleshooting steps, and preventative measures for PV Isolation Protection issues, or "PV ISO-PR," that may arise due to environmental and installation-related factors. A recent case study highlights practical solutions to maintain reliable performance in these systems.

Case Overview

Recently, a PV plant reported an inverter alarm labeled "PV ISO-PR" on a cloudy day. Solis technical staff identified installation problems such as PV strings directly buried in the ground without PVC pipe protection and damaged DC cables. After replacing cables and adding PVC piping for protection, the system returned to normal. This case illustrates common causes and effective solutions for "PV ISO-PR" issues.

Understanding PV Isolation Protection (PV ISO-PR)

"PV ISO-PR" alerts typically indicate low insulation resistance between PV strings and ground, causing the inverter to disconnect from the grid and enter protection mode. This is essential for safety, preventing electric shock risks.

Alarm Codes and Meaning:

• PV ISO-PR01: Damage in the negative terminal of the PV string.
• PV ISO-PR02: Damage in the positive terminal of the PV string.

These alarms reflect an insulation resistance issue between PV+ or PV- terminals and ground, which needs urgent attention to ensure system safety and functionality.

Primary Causes of PV ISO-PR Alarms

PV ISO-PR alarms usually stem from one or more of the following:

1. Environmental Factors: Increased humidity, especially in rainy weather, lowers insulation resistance, increasing alarm frequency.
2. System Installation Factors: Poor grounding or damaged insulation in PV strings often triggers these alarms.
3. Inverter Settings: Protection thresholds may be too low for local environmental conditions, requiring adjustment.
   
   

   Note: Environmental and system factors account for more than 80% of PV ISO-PR cases, with increased vulnerability in wet or humid conditions.

Troubleshooting PV ISO-PR Alarms

1. Identify Environmental Influence

Determine if alarms occur during high-humidity conditions (mornings, evenings, cloudy/rainy weather). If so, automatic error recovery may indicate a temporary environmental issue. In cases where recovery does not occur, proceed with further analysis.

2. System Factors Analysis

• Method 1: Check Strings Individually
  Connect each PV string one by one and observe the inverter’s response. If the inverter does not show an error, the connected string is functioning properly. When an error appears, note whether it’s 01 or 02 to pinpoint whether the positive or negative terminal requires inspection.

• Method 2: Multi-Meter Testing
  Power off the inverter and disconnect all PV strings. Using a multi-meter set to DC, measure the DC voltage of each string to the ground. Connect the multi-meter's red lead to PV string positive or negative, with the black lead grounded. A stable voltage above 20V may indicate insulation problems.

• Method 3: Megohm-Meter Test for Insulation Resistance
  Use a megohm-meter to measure each string's insulation resistance. Connect the meter to the positive or negative terminals and ground. The resistance should be greater than 150KΩ; values below suggest poor insulation.

Steps for Resolving PV Isolation Issues

1. Inspect and Repair Damaged Cables
   Check all PV strings, especially those identified in previous tests, for damaged or exposed DC lines. Damaged cables should be replaced, and additional PVC pipe protection applied to avoid future issues.

2. Verify System Grounding
   Confirm the grounding quality of PV panels, supports, and inverters. Poor grounding can exacerbate insulation problems and make systems more susceptible to humidity-induced issues.

3. On-site troubleshooting plan:

   1. Read LCD alarm history on inverter

   2. Measure AC & DC IGBTs with inverters fully de-energized

      1. Contact Solis Support for inverter specific procedure

   3. Power off the inverter and disconnect all PV strings. Using a multi-meter set to DC, measure the DC voltage of each string to the ground. Connect the multi-meter's red lead to PV string positive or negative, with the black lead grounded. A stable voltage above 20V may indicate insulation problems. Check for any abnormal readings.

   4. Disconnect the inverter’s AC cables, use a multimeter in AC mode to measure the grid voltage, and check whether the grid voltage is abnormal.

Conclusion

The inverter plays a crucial role in energy conversion and system safety for PV plants. PV ISO-PR alarms highlight the importance of maintaining insulation resistance and addressing installation or environmental vulnerabilities. By regularly inspecting installations, particularly during the rainy season, and following these troubleshooting steps, O&M personnel can ensure uninterrupted, safe system operation.

For additional guidance or direct assistance with PV ISO-PR issues, visit the Solis technical support page.