High-frequency current noise

High-frequency noise on the DC current and voltage is the signature of a burning DC arc. The arc's length and voltage keep changing because hot material evaporates and magnetic forces push on the arc. Inverters with arc fault detection sense this noise from a series arc and shut down. On site this usually appears as an ARC Protect fault and a sudden stop in production. On some inverters you must clear the arc fault manually or reset the operation inhibition before the unit will restart. Arcs come and go, so they are hard to catch. Analysing the spectrum of the current and voltage waveforms is one way to detect them. A series arc can start where every solder bond of a cell has broken, the bypass diode cannot carry the current, and the system runs at high voltage. Such an arc can start a fire. Before restarting, look for burn marks along the affected string. An infrared image will show whether a spot is still hot or whether current has stopped flowing in that part of the circuit. Arc fault circuit interrupters installed on individual strings can protect the system from arc faults.

<!-- review notes

• sentence 2: support check: partial - Shutdown on series arc detection and an ARC Protect Fault figure are present, but 'sudden stop in production' is not stated.
• sentence 5: support check: partial - Passage says that if all solder bonds of a cell break, current is blocked and an arc can result if the bypass diode can't bypass it at high voltage, causing fire; it says 'can result', and 'every' bond and 'starts' are slightly stronger, though largely consistent.
• sentence 6: support check: partial - Passage says burn marks are visually identifiable and IR imaging shows whether the area is still hot or current has stopped, but it doesn't advise inspecting before restarting after an arc fault. -->