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PV System Fuse 2017-12-07 17:06:55

Photovoltaic power plants are generally installed in the wilderness, or roof, components must be installed in the open air, the natural environment is bad, inevitably encounter natural disasters, typhoons, snowstorms, dust and other natural disasters can damage equipment, mice and other small animals bite Bad equipment, cable is also hard to be cut by thieves. The safety of the power station is very important, whether it is distributed small power plant, or centralized large-scale ground power plant, have a certain risk, it must be in the photovoltaic system equipment, are equipped with special security devices, such as fuses and Mine, usually obscure, the key to come forward, always keep the power station safe.


Fuse is based on the current exceeds the specified value after a certain time, with its own heat generated by the melt melt, so that the principle of breaking the circuit made of a current protector. Fuses are widely used in low-voltage distribution systems and control systems and electrical equipment, as short-circuit and over-current protection, is one of the most common protection devices. Photovoltaic power station fuses are divided into DC fuses and AC fuses.


The DC side of the PV plant is connected in parallel to the DC converter box (centralized inverter scheme) or the group of string inverter (group of string inverter) according to the different PV inverter scheme. Of the DC bus. When a number of PV strings are connected in parallel, such as a string of short-circuit faults, other strings on the DC bus and the grid will provide short-circuit current to the short-circuit point. Such as the lack of appropriate protective measures, will lead to photovoltaic components, coupled with the cable and other equipment burned. At the same time, it may cause burning of the attachment near the equipment. At present, there are many similar roof PV fire accidents in China, so it is necessary to install protective devices in parallel circuits of each string to enhance the safety of photovoltaic power plants.


Current DC fuses are used in converters, inverters, for overcurrent protection. Mainstream inverter manufacturers also will fuse as the basic components of DC protection. At the same time, fuse manufacturers such as Bussman, Littelfuse, also introduced a special DC fuse for photovoltaic.


With the photovoltaic industry, the increasing demand for DC fuses, how to correctly use DC fuse for effective protection, users and manufacturers should be seriously concerned about the issue, the choice of DC fuses, can not simply copy the AC fuse Electrical specifications and structural dimensions, because there are many different technical specifications and design concepts between the two, whether it is safe and reliable to break the fault current and no comprehensive accident considerations.


1) Since the DC current does not have zero current of the current, it can only rely on the arc in the quartz sand packing forced cooling, The reasonable design and welding method, the purity and particle size of quartz sand, the melting point of high and low, curing and other factors, have decided on the DC arc forced out of the effectiveness and role.


2) At the same rated voltage, the arc arc produced by the DC arc is more than 2 times the AC arc energy. To ensure that each arc can be confined within a controllable distance and quickly extinguished, no segment Arc directly connected in series into a huge energy pool, resulting in continuous arcing time is too long fuse burst accident, DC fuse body is generally longer than the AC fuse, or in normal use when the size can not see Differences, when the fault current occurs will have serious consequences.


3) According to the international fuse technology organization recommended data, DC voltage for each additional 150V, fuse body length that should be increased by 10mm, by analogy DC voltage of 1000V, the pipe length should be 70mm.


4) When the fuse is used in the DC circuit, the complex effect of the inductance and capacitance energy must be taken into account. Therefore, the time constant L / R is an important parameter that can not be neglected. It should be based on the short circuit fault current generation and decay rate of the specific line system. Accurate assessment, not arbitrarily selected or small can be selected. As the DC fuse time constant L / R size determines the breaking of arc energy and breaking time and allowable voltage, so the thickness and length of the pipe must be reasonable and safe choice.


AC Fuse: In the output of the off-grid inverter, or the input of the internal inverter of the centralized inverter, install the AC fuse to prevent the load from overcurrent or short circuit.

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