With the rapid development of solar photovoltaic (PV) power generation systems, HVDC designs are increasingly used in residential roofs, power plants and industrial/commercial projects. The fuse is a key part of circuit safety of PV systems. Its main function is to interrupt the circuit quickly in the event of overcurrent or short-circuit faults, so as to prevent equipment damage and safety incidents. However, some users mistakenly believe that standard AC fuses-which are cheaper-can be used as an alternative to special fuses for photovoltaic cells. In practice, this poses significant safety risks and can lead to protection failures, equipment damage and even fires.
So why not replace PV fuses with standard alternating current fuses? In this paper, the working principle, performance requirements and related standards will be analyzed in detail.
PV system usesDC
PV assembly produces direct current; the current stays DC throughout the circuit-from the assembly string and combination of chassis to the input level of the inverter.
Instead, standard AC fuses are designed for AC distribution systems based on the electrical characteristics of current (AC.
One of the main characteristics of AC is the changing direction of the current, which passes through "zero" several times per second. At 50Hz, for example, the current can exceed 100 times per second. When a circuit is fused, when the current passes through zero, the arc is extinguished naturally, so the arc extinguishing mechanism in an AC fuse is relatively simple.
By contrast, DC lacks a natural zero-point intersection and the current direction remains the same. During short circuit, the arc will persist, which requires the fuse to rely on a special arc extinguishing structure to quickly cut the current. Therefore, PV system requires a fuse
specially designed for DC applications.
DC arc is harder to extinguish than AC arc
This is the fundamental reason why standard AC fuses cannot replace photovoltaic fuses.
When the internal components of the fuse melt, a high-temperature arc forms between the two ends. During AC, the arc can be extinguished naturally as the current repeatedly drops to zero.
However, the arc still exists in the DC system, which can reach temperatures of several thousand degrees Celsius and continue to release a lot of heat. If the fuse does not have sufficient arc extinguishing capability, the following problems may arise:
The arc continues to burn, preventing the circuit from being truly interrupted.
Fuses implode or even explode;
Surrounding insulation materials burned;
Fire the combiner box or power distribution cabinet;
Equipment such as inverters and PV components is damaged.
Therefore, PV fuses are usually quenched with quartz sand, high strength ceramic shell, and the structure of the fuse element is optimized to ensure the rapid and safe extinguishing of DC arc.
Photovoltaic fuses have a high DC voltage ratings.
Common voltage levels for PV systems include:
600V DC
1000V DC
1500V DC
In contrast, the voltage ratings of a standard AC fuse is generally:
250V AC
400V AC
500V AC
690V AC
It is important to note that AC voltage rating isnot directly equivalent to DC voltage rating.
For example, an AC fuse with a rated current of 690V may withstand only about 250V to 400V of DC. If installed in a 1000V or 1500V PV system, the fuse may not provide protection, as the fuse cannot interrupt the high-voltage DC arc even if the fuse element itself melts.
Therefore, PV system requires a fuse specially designed for PV applications, and its DC voltage ratings should meet system requirements.
The protective characteristics of photovoltaic fuses are more suitable for solar energy systems.
Solar arrays have unique output characteristics.
For example:
Current fluctuates continuously with solar irradiance.
Output current varies between morning/evening, cloudy and sunny days;
When multiple strings are parallel, a backflow may occur;
Fault currents tend to last longer.
The time-flow characteristics of PV fuses are specifically designed for these operating conditions; they can withstand current fluctuations during normal operations while responding quickly in the event of failure.
Standard AC fuses are designed primarily for AC loads and do not work well in PV DC systems, leading to two potential problems:
Tripping (blowing) accidents during normal operation;
Delayed response or inability to operate during malfunction.
Both of these conditions can affect the steady operation of PV systems. PV fuzes in accordance with Specialized International Standards
Fuzes specially designed for photovoltaic applications must conform to international standards, such as:
IEC 60269-6 (Low-voltage fuses-Fuses protecting solar photovoltaic systems)
UL 248-19 (Standard for Photovoltaic Fuses)
These standards put forward strict requirements for DC breakability, temperature rise, durability, arc extinguishing performance and reliability.
In contrast, standard AC fuses are designed according to AC distribution standards and have not yet been validated by the operating environment of PV systems and therefore donot meet the safety requirements of PV system.
Risks of using standard AC fuses
Replacing photovoltaic fuses with standard AC fuses to reduce costs may lead to the following risks:
DC fault current cannot be interrupted;
Continued arc of electricity, leading to fuse damage;
High temperature burn inside the combination box;
Overcurrent stress of PV components and inverters;
Increased system downtime and maintenance costs;
Heavy and extremely large electrical fire hidden danger, endangers the person and property safety.
Considering the total investment in PV systems, the cost of fuses is negligible, but they play a crucial role in safety protection. Choosing the wrong product to save a small amount of procurement costs often leads to larger economic losses.
How to choose a PV Fuses correctly?
In order to ensure the safe and reliable operation of PV system, the following should be given priority in selection process:
Rated voltage: shall not be lower than the maximum DC voltage of the system (e.g., 1000V DC or 1500V DC).
Rated current: Based on short circuit current (Isc), number of parallel strands and design margins of the photovoltaic assembly.
Crushing capacity: The requirement of maximum potential fault current in the system must be met.
Accreditation criteria: Prioritize products that meet and are certified to IEC 60269-6, 248-19, and others.
Environmental Adaptability: Consider application environments such as high/low temperature, humidity, salt mist, etc., and choose products that are weather-resistant. Conclusion:
Although photovoltaic (PV) fuses look similar to standard AC fuses, there are fundamental differences in design principles, application environments and performance requirements. Because PV system operates under high voltage DC current, the requirements of DC arc fireextinguishing ability, fragmentation ability, rated voltage, etc are strict. Standard AC fuses donot meet these requirements, and the use of standard AC fuses not only does not provide effective protection, but also poses serious safety risks.
During the construction, operation and maintenance of PV power plants, special fuses for photovoltaic (PV) must be selected in accordance with relevant standards and according to the voltage, current and operation of the system. Only by using the correct protective device can the PV system operate safely and steadily for a long time.
Frequently Asked Questions
1.Photovoltaic fuses look the same as standard AC fuses. Is it interchangeable?
No. While some products may have similar physical dimensions, they have different internal structures, arc design and performance parameters; you can't interchange them simply because they look similar.
2.Why are DC systems harder to protect than AC systems?
The lack of a natural zero point of DC passing means that the arc formed during the failure will continue to burn; therefore, specialized DC protection elements with advanced arc extinguishing capability are required.
