Photovoltaic power plants, closely connected to the lives and production of people, are raising high concerns across the industry regarding how to ensure the “safety” of photovoltaic power stations, especially in the case of retrofit distributed photovoltaic systems installed on building rooftops. Countries worldwide have made related regulations concerning the DC-side voltage, DC arc protection, and component-level rapid shutdown.
DC Series Arc Protection
Systems with a maximum DC system voltage greater than or equal to 120V should feature DC series arc protection. When a fault arc is detected, it should be capable of disconnecting the faulty photovoltaic array or shutting down the faulty arc location and issuing a visible alarm signal (local signal or remote monitoring signal).
Rapid Shutdown Device
The system should have a rapid shutdown function. Within 30 seconds of the activation of the rapid shutdown device, the voltage within a boundary extending 305mm from the edge of the photovoltaic array should decrease to below 120V, and the voltage outside this boundary should decrease to below 30V.
DC Arcing: The Main Culprit of Photovoltaic Safety Hazards
DC arcing is essentially a phenomenon of gas discharge, where the charged body changes from an insulating state to a conductive state in the surrounding medium, allowing electric energy to pass through. When a photovoltaic system experiences DC arcing, it can cause a rapid increase in conductor contact temperature, generating high temperatures of 3000-7000°C, leading to the destruction of components and equipment and even causing fires.
According to relevant statistics, over 80% of fire accidents in photovoltaic power stations are caused by DC-side faults. Additionally, rescuing accidents at photovoltaic power stations is extremely challenging. During a fire, conventional firefighting methods, such as fire hydrants, are ineffective. Chemical fire extinguishing agents can be used but have limited effectiveness, making it difficult to control the fire as it grows. If the photovoltaic power station includes energy storage devices, there’s also the risk of explosions.
Even if the inverter is shut down, the cables from the strings to the inverter still carry DC electricity, making firefighting work very dangerous, as firefighters cannot take timely rescue measures.
Component-Level Rapid Shutdown Function: Addressing “Firefighter Risk”
The rapid shutdown function is a requirement designed to directly and effectively eliminate the risk of electric shock for firefighters in the event of an emergency failure in the photovoltaic power station, specifically due to the presence of high DC voltage. ONCCY’s rapid shutdown device, equipped with component-level rapid shutdown functionality, uses component-level safety protection technology to manually and rapidly disconnect the connection between each photovoltaic module. Within 30 seconds, it instantaneously stops the operation of devices within a 305mm range of the photovoltaic array or reduces the system voltage to below 30V. This effectively eliminates the high DC voltage within the photovoltaic array, mitigating the “firefighter risk” in photovoltaic power stations.
ONCCY has been focusing on the significant issue of DC arcing faults in photovoltaic arrays for a long time. After years of dedicated research, ONCCY’s rapid shutdown syetem offers component-level arc protection, integrating automatic detection, protection, self/manual reset, warning, and precise location. In the event of a DC arcing fault, it rapidly shuts down and extinguishes the fault arc, ensuring the safety of life and property. ONCCY’s rapid shutdown device is the guardian of safety in photovoltaic systems!