Solution
Solutions for global temperature control systems
Photovoltaic equipment
subcategory： Solution
2024-09-12
1. Application background
· Reactors and transformers are often used in photovoltaic inverter systems to ensure the safe, stable and efficient operation of photovoltaic power generation systems and power grids by limiting current, improving voltage fluctuations, and adjusting voltage levels.
In particular, high-power reactors and transformers above 500W will generate a large amount of heat during operation, and overheating may cause equipment damage or even fire. Therefore, in order to ensure the safe and reliable operation of the equipment, the temperature switch is a small and efficient solution that can be used to monitor the temperature and take corresponding protective measures.
2. Protection principle
· Temperature switch is a mechanical passive component, mainly set in the control loop. When the circuit fails or the current exceeds the rated value, the abnormal heating of the circuit causes the temperature to rise. The temperature switch senses the external temperature change through the internal heat sensitive element bimetal. Once the temperature exceeds the set threshold, the two pieces will deform and disconnect Contact, cut off the circuit, so as to protect the whole machine.
When the heat sensitive element acts, the contact is disconnected, and the contact resistance changes instantly from less than 50mΩ to close to infinity, thus giving the control loop signal. After receiving the signal, the IC or MCU turns off the main loop current through MOS tube or other executive elements, thus playing the role of protecting the whole machine.
When the ambient temperature drops to the reset temperature of the temperature switch, the heat sensitive element returns to the initial state, the contact is closed again, and the resistance signal within 50mΩ is given to the circuit, and the actuator operates according to the program setting.
3. Installation position
In the application of photovoltaic inverter, the inductive devices such as DC reactor, sine wave filter reactor and grid connected transformer are the key heating components of the product. When designing the overheat protection function of the product, the temperature switch is often used to monitor the heating temperature of the reactor and the transformer coil, and the installation method is external or embedded.
External installation: the temperature switch should be close to the surface of the enameled wire and tied or bonded firmly with high temperature resistant materials.
Advantages: easy maintenance, easy observation, easy installation;
Disadvantages: appearance influence, affected by the external environment, protection performance slightly inferior.
Buried installation: timely induction coil temperature changes. It is necessary to consider the influence of the installation position and the embedded volume on the winding, and select the appropriate temperature switch model and installation position according to the design of the reactor and transformer products.
Advantages: beautiful appearance, good protection performance, strong protection;
Disadvantages: difficult maintenance, high installation cost, and difficult fault detection.
4. Selection factors
· Rated current and voltage: In the application of photovoltaic inverter, the temperature switch is often used in the control loop, and the current passing through is the signal current of milliampere level. Our temperature switch can meet the application requirements.
Protection temperature: often depends on the insulation level of the reactor or transformer, but also according to the design and installation location of different temperatures, usually choose more temperature points: 90/100/110/125/140/150 ℃.
· Contact switch form: it is divided into two types: normally closed and normally open. Normally closed is the initial state of contact closure, and the temperature protection contact is disconnected. It is always the opposite. Different switch forms are selected according to the design.
· Size and installation method: According to the product design of the reactor and transformer, combined with the size and installation space of the temperature switch, the appropriate installation method (external/embedded) is selected to ensure that the installation is convenient and does not affect the normal operation of the equipment.
Shell epoxy encapsulation product: the insulation layer of the temperature switch will be a little sharp after heat shrinkage, and the enameled wire with thinner paint layer will have the risk of cutting if it is assembled by force, causing short circuit or insufficient insulation withstand voltage. recommend use the shell epoxy encapsulated temperature switch, round and smooth, will not cause damage to the enameled wire.
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