Similarities And Differences Among Fuse, Circuit Breaker And Disconnector

Photovoltaic (PV) industry is experiencing a rapid development under the general trend of Carbon-Neutrality-oriented development, which however has led to increasingly problems around power plant safety as the higher-power modules are being widely used. PV system designs are going up in complexity as ever newer applications and situations for use are found. How to deploy the protection design of DC side has always been the concerns and disputation in the industry. Fundamentally, misunderstanding of fuse, circuit breaker and disconnector that are generally used for protection of PV system is the root cause.

Fuse, circuit breaker and disconnector, because of their similar functions (isolation, short-circuit protection etc.), are prone to confusion and misunderstanding in the industry. However in fact, they are totally different devices, as they are significantly different in principle of protection, standard requirement, scenario of application and protective effect! As for establishment of a distribution protection system, it is necessary to fully understand the requirements on production under scenarios of application, so that devices can be reasonably deployed based on their own features to give proper application to their functions, thereby improving the work safety and reliability of the station.

Fuse: referring to a current protector that consists of fuse element and cartridge. The fuse element will be blown out by the heat produced by itself when current outnumbers a limit for a certain time, and in this case circuit will be cut off so that the purpose of protection can be achieved.
Circuit breaker: referring to a mechanical switching device that is capable of switching on/off and carrying current and consists of a contact system, an arc quenching system, an actuator and a trip unit. It is used to cut off a circuit with a failure to achieve the purpose of protection. In case of a short circuit, the counter-force spring will be overcome by a magnetic field produced by a higher current, in this case the actuator will be driven by the trip unit to switch off immediately. In an over-load case, bimetallic strips will be deformed to a certain extent at a rising temperature due to increasing current, to trigger the actuator to switch off. The higher the current is, the shorter the time for this protective action will be.
Disconnector: to serve mainly as an isolator which can form an apparent break point between electrical apparatus being overhauled and the power supply, to guarantee work safety of overhaul. In the past, manually-operated disconnector is provided on DC side of string inverter. Along with the smart development of PV station, manually-operated disconnector is replaced by motor-operated disconnector.