Dc Surge Protector Selection And Uc Value: Solving Customer Concerns

Recently, a customer inquired about the selection of DC surge protectors and questioned the requirement that the Uc (maximum continuous operating voltage) of the surge protector be 130Vdc. They believe that if the circuit system voltage is 120Vdc and the operating voltage of the back-end equipment is between 100Vdc-150Vdc, should the Uc of the surge protector be selected as 130Vdc to avoid exceeding the operating voltage range?

We selected a surge protector with a Uc of 200Vdc for this customer, which confused and worried the customer. The customer was worried that if an overvoltage between 150Vdc-200Vdc was generated in the system, would the surge protector fail to operate, causing the equipment to be damaged?

In order to answer the customer's concerns, we first need to understand the meaning of the Uc value of the surge protector. Uc represents the "maximum continuous operating voltage" of the surge protector, which means that the surge protector can work for a long time at this voltage, and this voltage will not affect the performance of the surge protector itself.

Next, we need to make it clear: when the circuit voltage exceeds Uc, will the surge protector be activated? The answer is no. The SPD will only be activated when it reaches the starting voltage, that is, the "varistor voltage" of the internal varistor. According to the "GBT 21431 Technical Specifications for Testing Lightning Protection Devices for Buildings"

For a surge protector with a Uc of 200Vdc, the surge protector will only be activated quickly when the voltage on the circuit exceeds 240Vdc. Therefore, when a surge voltage of 180Vdc appears in the circuit, a surge protector with a Uc of 200Vdc will definitely not be activated.

So, when the surge voltage exceeds the impulse withstand voltage Uw of the equipment, will the equipment be burned out? The answer is no! Because the surge voltage exists in the circuit for a very short time, only a few nanoseconds. Just like when the human body is briefly exposed to the mains, the body will only feel a momentary sting, and continuous electric shock will cause harm to the body. The same is true for equipment. The surge voltage disappears faster than the equipment reacts, so it will not cause damage to the equipment.

Only when the surge voltage reaches the device's impulse withstand voltage Uw, the device will be broken down and damaged. Fortunately, the Up value of the surge protector is always lower than the Uw value of the device. For excessively high surge voltages, the surge protector will limit it below the Up value, thereby continuously protecting the back-end equipment from electrical breakdown and damage. Therefore, when the UC value of the surge protector is greater than the operating voltage of the device, it will not cause lightning protection failure.

In summary, choosing a suitable surge protector Uc value can not only reduce costs and extend the service life of the surge protector, but also effectively protect the back-end equipment from damage by surge voltage. If you have more questions about the selection of DC surge protectors or need more information, please consult the engineers of Hangzhou Yizao. We will provide you with professional answers and selection suggestions.