What is DC Circuit Breaker?

    The DC circuit breaker refers to the circuit breaker used in the DC power distribution system, which can protect the electrical equipment running on DC power. It is generally suitable for solar photovoltaic power generation and power distribution systems, battery energy storage systems, and new energy vehicle DC charging systems. Slocable’s solar DC circuit breakers are designed to protect the cables located between each group of PV modules and PV inverters from overload and short-circuit DC circuits, and are installed in string PV protection enclosures at the end of each string of PV modules.

    The input power terminal of the DC circuit breaker is a system of direct current. General DC circuit breakers include DC MCB (DC miniature circuit breaker), DC MCCB (DC molded case circuit breaker) and type B RCD (residual current device).

DC Miniature Circuit Breaker (DC MCB)

    DC miniature circuit breakers are designed for DC circuit applications for overcurrent and short circuit protection in appliances or electrical equipment. DC mini circuit breakers are equipped with a special magnet that forces the arc into the arc slot and extinguishes the arc in a very short time.

    The DC circuit can be locked in the OFF position by means of a padlock device as a safety measure for dismantling the PV inverter. Since the fault current can flow in the opposite direction to the operating current, the DC circuit breaker can detect and prevent any bidirectional current flow. In any case, quick action in the field is required to clear the fault current.

    DC miniature circuit breakers are mainly used in DC system applications such as new energy, solar photovoltaic and solar battery energy storage systems. The voltage state of the DC mini circuit breaker is generally DC 12V-1500V.

    DC MCB and AC MCB have the same function, the main difference is the physical parameters of the product. Moreover, the usage scenarios of AC MCB and DC MCB are different.

    The AC circuit breaker is marked on the product as LOAD and LINE, and the DC circuit breaker symbol is marked on the product as positive (+), negative (-) signs and current direction.

What is the Function of DC Mini Circuit Breakers?

    The same thermal and magnetic protection principles as AC circuit breakers apply to DC miniature circuit breakers:

    Thermal protection trips the DC mini circuit breaker when the current exceeds the rated value. In this protection mechanism, the bimetallic contacts thermally expand and trip the circuit breaker. Thermal protection functions more quickly because more heat is generated to expand and open the electrical connection when the current is quite high. Thermal protection of DC circuit breakers prevents overload currents slightly higher than typical operating currents.

    Magnetic protection trips DC MCBs when strong fault currents are present, and the response is always instantaneous. As with AC circuit breakers, the rated breaking capacity of DC circuit breakers represents the most significant fault current that can be interrupted. For a DC mini breaker, the blocked current is constant, which means that the circuit breaker must further open the electrical contacts to interrupt the fault current. Magnetic protection of DC miniature circuit breakers protects against a wider range of short circuits and faults than overloads.

Why are DC Solar Circuit Breakers Important for PV Systems?

    Photovoltaic systems have the potential to be an efficient renewable energy mechanism. One or more solar panels can be used, or they can be combined using inverters and other electrical and mechanical components. PV systems must be maintained at all costs, and any minor incident can quickly escalate into a major problem for the entire system.

    Therefore, DC solar circuit breakers are an important part of photovoltaic systems, and thermal protection can help in current overload situations. Magnetic protection in solar DC circuit breakers can trip the solar circuit breaker when there are many fault currents. DC circuit breakers can interrupt fault currents even in the most extreme cases. Magnetic protection is critical in DC breakers as it protects against short circuits and other failures.

    Photovoltaic circuit breakers are critical in solar PV panel systems. The circuit of a solar panel is an expensive component of a photovoltaic system. Therefore, it is crucial to protect them with a solar PV circuit breaker. PV DC circuit breakers also protect circuits and circuit boards. It can convert solar radiation into direct current through solar panels, and photovoltaic installations require the use of PV circuit breakers.

    For electric vehicles, their batteries can be charged using an electric vehicle charging station. So these systems need DC MCBs to avoid accidents because they all need to use direct current, solar panels and electric cars work well together, and also don’t need to convert that direct current to alternating current, which can be easily controlled automatically using a DC circuit breaker system to respond quickly.

Another Type of DC Circuit Breaker – DC Molded Case Circuit Breaker (DC MCCB)

    DC molded case circuit breakers are ideal for energy storage, transportation and industrial DC circuits. Molded case circuit breakers are designed to meet the highest performance requirements, while a variety of accessories are available to suit different field specifications. Today’s DC MCCBs have expanded applications to include solar photovoltaics, electric vehicle charging stations, battery storage and UPS systems, and commercial and industrial DC power distribution.

    The DC MCCB has the same function as the AC MCCB, and has overload and short-circuit protection functions for high-current power distribution systems.

    They are also used in ungrounded battery-powered circuits for emergency backup and backup power. Available up to 150A, 750 VDC and up to 2000A, 600 VDC. For DC circuit breakers used in grounded photovoltaic systems in solar installations, application engineering and review ensure that protection requirements are met.

    DC Molded Case Circuit Breaker is a circuit control protection device for energy storage, transportation and industrial DC circuits. They can be applied to grounded or ungrounded systems, meeting the higher voltages and lower fault current levels of solar systems. Slocable manufactures high-voltage DC circuit breakers that provide superior performance and help keep costs down, Slocable’s MCCB DC breakers deliver up to 150-800A, 380V-800V DC and meet stringent quality standards.

Difference Between AC and DC Circuit Breaker

    The main difference between direct current and alternating current is that the output voltage of direct current is constant. In contrast, the voltage output in alternating current cycles several times per second, and the signal of alternating current is constantly changing its value every second. The circuit breaker arc will be extinguished at 0 V and the circuit will be protected from high current. But the signal of DC current is not alternating, it works in a constant state, and the voltage value changes only when the circuit trips or the circuit drops to a certain value.

    Otherwise, the DC circuit will provide a constant voltage value for one second per minute. Therefore, it is not recommended to use an AC circuit breaker in a DC state since there is no 0-volt point in the DC state.

Precautions When Buying Circuit Breakers

    Because the protection mechanisms for AC and DC currents are nearly identical, specific circuit breakers are designed to use both. However, it is critical to double-check that the power supply and circuit breaker are of the same type of current. If you place the wrong circuit breaker, the installation will not be adequately protected and an electrical accident may occur.

    Another important factor to consider is the current rating of the cables connecting the DC mini circuit breaker to the protected electrical equipment. Even if you set the DC breaker correctly, undersized cables can overheat, melt their insulation and cause electrical failure.

    DC circuit breakers are not as commonly used as AC circuit breakers, but are just as important. DC MCBs are a relatively new technology, as most household appliances run on alternating current. Solar DC circuit breakers play a key role in the electrical protection of high-cost energy-saving technologies such as LED lights, photovoltaic solar panels, and electric vehicles. As these technologies reach a wide range of consumers, solar circuit breakers will have a larger market. On the other hand, DC circuit breakers are a well-established and well-known technology in commerce, and they play an important role in protecting high-precision machinery and arc welding.

    When an electrical system requires the use of a direct current circuit breaker, it is often recommended to retain the services of expert engineers and technicians to ensure that you can select and install the appropriate smart DC circuit breaker.