Analysis of a defective PV inverter: Testing-as-a-Service

The project

A customer in the photovoltaic sector contacted AUTFORCE after a fire broke out in an inverter when the DC switches of a PV system were switched off. The inverter then failed completely, with the display and controls no longer responding. AUTFORCE was commissioned to conduct a comprehensive investigation to determine the cause of the incident and prevent similar damage in the future.

Since there was no standardized test method for this specific fault scenario, AUTFORCE developed a customized test setup as part of its Testing-as-a-Service offering. The aim was to technically reconstruct the course of the fire, understand the causal chain leading to the fire, and, on this basis, propose specific measures to prevent faults.

Keyfacts

• Project objective: Root cause analysis of fire damage in a PV inverter
• AUTFORCE service: Testing-as-a-Service: Setup, simulation, and error analysis
• Focus: Behavior of the DC switch and the PV connection board during shutdown
• Result: Recreating a stable electric arc under realistic conditions
• Benefit: Identification of technical improvement measures to prevent future damage

Analysis of the defective inverter

To determine the cause of the fire, the defective inverter was examined together with an undamaged comparison device. Upon opening, it was found that the fire had started in the area of the connection board. The switch itself was hardly affected. This indicates that the cause could be an electrical process that occurred during shutdown.

We then developed a test setup to recreate this moment in the laboratory.
To do this, the connection board was connected to an external power source and gradually exposed to different conditions.

• No flashover occurred at normal room temperature.
• After the circuit board had cooled down to around 8 degrees Celsius, the temperature difference caused a fine layer of condensation to form on the surface. Under these conditions, an electrical flash-over occurred between the contact and the housing, destroying the circuit board.

Result of the analysis

When the system is switched off, a voltage spike occurs which, when combined with moisture, can trigger an electric arc. The surge protection designed to prevent this was installed in an unfavorable location in this case.
This finding provided the decisive clue to the cause of the fire and formed the basis for specific proposals to improve safety and reliability.