Proving the Business Case for the Internet of Things

Arc-fault detection circuitry protects solar plants

Steve Rogerson
March 5, 2015
Tokyo-basedMitsubishi Electric has developed a DC arc-fault circuit protection technology for solar power plants that detects any DC arc fault, or high-temperature luminous electrical discharge between DC wiring, and isolates the faulty circuit in just 0.25 seconds. The technology enables plants both to prevent large decreases in power generation and quickly restore faulty circuits.
The technology detects the DC arc fault as well as identifies the faulty circuit by monitoring sources of high-frequency current and possible deviations from normal current and voltage characteristics in solar cells.
The quick detection of the DC arc fault prevents the spread of failure to circuits that are functioning normally. Continuous operation of healthy circuits and faster restoration of faulty circuits results in fewer decreases in electric power generation by individual solar cells and therefore the solar power plant overall.
The company has also announced its Arc Sweeper technology. DC, unlike AC, presents two difficulties when attempting to shut off the current to switches. First, the current direction is determined by magnetic polarity because current is interrupted by magnetic action. Secondly, larger magnets and a broader breaking area are necessary due to higher voltage used in circuits. Arc Sweeper improves the breaking capability by enhancing the magnetic blowout effect, so DC can be separated accurately and quickly regardless of current direction.
Following the occurrence of various fires at solar plants in North America due to DC arcs caused by malfunctioning circuit connections, the use of devices to detect DC arc has become increasingly mandatory according to UL standards in the USA. Also, the IEC is working to standardise DC arc countermeasures.
Conventional detectors require up to two seconds to detect a DC arc. As a result, all circuits, including healthy circuits, must be shut down, leading to drastic decreases in power generation and long intervals before the faulty circuit can be restored.