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What is a Solar Panel DC Isolator Switch? How to Choose this Isolator Switch?

  • news2023-04-10
  • news

PV DC Isolator Switch Application

 

        Isolator switch is a high-voltage switchgear, mainly used in high-voltage circuits. It is a switchgear without arc extinguishing device, mainly used to disconnect the circuit without load current, isolate the power supply, and have an obvious disconnection point in the open state to ensure the safe inspection and repair of other electrical equipment. It can reliably pass the normal load current and short-circuit fault current in the closed state. Because it has no special arc extinguishing device, it cannot cut off the load current and short-circuit current. Therefore, the isolation switch can only be operated when the circuit has been disconnected by the circuit breaker. It is strictly forbidden to operate with load to avoid serious equipment and personal accidents. Only voltage transformers, lightning arresters, no-load transformers with excitation current less than 2A, and no-load circuits with current no more than 5A can be directly operated with isolation switches. In electric power applications, circuit breakers and isolation switches are mostly used in combination, and the circuit breakers are used to switch and cut load (fault) current, and the isolator switch forms an obvious disconnection point.

        The solar panel dc isolator switch is an electrical safety device that can manually disconnect itself from the modules in the solar photovoltaic system. In photovoltaic applications, PV DC isolators are used to manually disconnect solar panels for maintenance, installation or repair. In installation, routine maintenance and emergency situations, the panel needs to be isolated from the AC side, so a manually operated isolation switch is placed between the panel and the inverter input. This type of switch is called a PV DC isolator switch because it provides DC isolation between the photovoltaic panel and the rest of the system. This is an indispensable safety switch, which is mandatory in every photovoltaic power generation system according to IEC 60364-7-712. Solar panel dc isolator switch is one of the most important components of photovoltaic system safety. Its reliability and stability are related to the stable power generation and profitability of the photovoltaic system, as well as the safe and reliable operation of the photovoltaic system. With the increase in photovoltaic installations, power generation has attracted much attention. However, electricity investors are increasingly worried about safety issues, which have frequently occurred in photovoltaic power plants in recent years.

        European countries such as Germany and the Netherlands require inverter manufacturers to configure built-in PV DC isolator switches, while countries such as the United Kingdom, India, and Australia require that photovoltaic systems must install external PV DC isolator switches. With the clarification of China’s photovoltaic policy, the number of photovoltaic installations has increased year by year, especially for distributed photovoltaic systems, and rooftop systems have become more and more popular.

        However, the so-called photovoltaic DC isolator switch on the market is an AC isolator switch or a modified wiring version, not a DC isolating switch with real arc extinguishing and high-power cut-off functions. These AC isolator switches are too lacking in arc extinguishing and power isolation from the load, which can easily lead to overheating, leakage and sparks, and even burn down the entire photovoltaic power station.

        Therefore, it is very important to choose a qualified solar panel dc isolator switch. BS 7671 stipulates that an isolation method must be provided on the DC side of the photovoltaic installation, which can be provided by an isolating switch classified in EN 60947-3.

        So, how to choose a suitable PV DC isolating switch for the photovoltaic system?

 

1. System Voltage Selection

        The rated working voltage of the DC isolating switch should be equal to or greater than the requirements of the system. Common ones meet UL508i 600V, IEC60947-3 1000V and 1500V. Usually the system voltage connected to the single-phase inverter is as high as 600V, and the three-phase string inverter or centralized inverter is as high as 1000V or 1500V.

 

2. The Number of Strings to be Isolated

        2 Pole – Single string, 4 Pole – Two string.

        For the built-in DC isolator switch, the number of MPPT of the inverter determines the pole of the DC isolator. Common string inverters have single MPPT, dual MPPT, and a small amount of triple MPPT. Generally speaking, inverters with a rated power of 1kW~3kW adopt a single MPPT design; the inverters with a rated power of 3kW~30kW adopt dual MPPT or a small amount of three MPPT.

        For the external DC isolator switch, you can choose 4 poles, 6 poles, 8 poles for multiple sets of solar panels or 2 poles for a set of solar panels according to different system designs.

 

3. Rated Current & Voltage of String of Panels

        The PV DC isolator switch should be selected according to the maximum voltage and current of the panel string. If the user knows the parameters of photovoltaic inverters, especially inverter manufacturers, in order to effectively save costs, they can choose according to the input DC voltage and current curve to ensure that they can be used in all weather conditions and temperatures.

        BS 7671 stipulates that isolating switches complying with EN 60947-3 are suitable for photovoltaic systems. The rated value of the isolator switch must consider the maximum voltage and current of the photovoltaic string to be isolated, and then adjust these parameters according to the safety factor specified by the current standard. This should be the minimum rating required for the isolator switch.

 

4. Environment and Installation

        The working environment temperature, protection level and fire protection level should be determined according to the environment. Generally a good PV DC isolator switch can be used safely at an ambient temperature of -40°C to 60°C. Generally, the protection level of the external DC isolating switch should reach IP65; the built-in DC isolator switch should ensure that the equipment reaches IP65. The fire rating of the housing box or main body shall comply with UL 94V-0, and the handle shall comply with UL 94V-2.

        Users can choose the appropriate mode according to actual needs. Generally, there are panel installation, base installation and single-hole installation.

Dongguan Slocable Photovoltaic Technology Co.,LTD.

Add:Guangda Manufacturing Hongmei Science and Technology Park, No. 9-2, Hongmei Section, Wangsha Road, Hongmei Town, Dongguan, Guangdong, China

TEL:0769-22010201

E-mail:pv@slocable.com.cn

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