Important Factors Affecting PV Plant Safety – Arc Faults

In recent years, with the widespread adoption of photovoltaic (PV) power generation, more and more rooftops have installed PV systems. However, both domestically and internationally, incidents of PV plant fires have occurred. Notably, 80% of these fires are caused by faults on the DC side, with arc sparks triggered by high DC voltage being the main culprit. Why are arc faults so impactful on the safety of PV plants? We can understand this from the following aspects.

1. High Probability to Cause PV Plant Fires

When a DC arc occurs, the triggering part will maintain stable combustion without extinguishing. The high temperatures generated by DC arcs can easily exceed 3000°C, which can destroy PV plant equipment and cause fires.

2. High Probability of Occurrence

In practical PV plants, solar modules are connected in series to form arrays, and the voltage of the entire string accumulates, generally reaching high voltages of 600V to 1000V. During long-term operation, issues such as loose connections, poor quality of contact parts, and aging of insulation parts over time can directly cause DC arc phenomena, breaking through the air and leading to fires. It is evident that with the increase in plant operation time, the probability of DC arcing also increases. Considering a 10MW distributed PV plant with over 80,000 electrical contact points, there is always the potential for DC arcing.

3. Detection Methods

Arcs generated in PV systems can be classified into normal arcs and abnormal arcs.

4. Relevant Measures

In developed countries such as the United States, Europe, Japan, and Australia, mandatory measures have been introduced to address high DC voltage issues in PV systems. PV plants must be equipped with arc monitoring devices.

The China National Building Material Test & Certification Group Co., Ltd. has implemented CTS 13001-2018, “Testing and Evaluation of Household Grid-connected PV Systems.” For household PV systems installed on rooftops, when the DC voltage exceeds 120V, an arc fault detection, alarm, and processing system must be used.

5. Related Programs

The main function of the FR-DCBS-AFC4C Arc Safety Protection Box is to detect whether there are arc faults in the PV string in real-time. If an arc fault is detected, an alarm signal will be immediately sent through local indicator lights and email, and the AC relay will be driven to disconnect the inverter. This stops the inverter from operating, ensuring that the DC circuit is in a no-current state, effectively preventing fire hazards caused by arcs. Additionally, users can remotely monitor the arc box’s arc alarms, relay status, and current levels through a mobile app.