In a comprehensive lightning protection project, a surge protector (SPD) and an overcurrent protector are often installed at the same time. The two must be used together to protect the safety of electrical circuits.
According to relevant regulations, in order to ensure the normal operation of the low-voltage power distribution system, over-current protectors such as low-voltage circuit breakers, fuses, and air switches matched in series at the front end of the surge protector. In practical applications, there is often a mismatch between the surge protector (SPD) and the overcurrent protector. The overcurrent protector acts in advance, causing a power outage. This is mainly because when the lightning overvoltage first invades, the low-voltage circuit breaker has been activated. Although the first lightning overvoltage has been effectively discharged, the device will lose this level of protection and be damaged during subsequent intrusion. The subsequent current of the surge protector causes the action of the main circuit breaker, which affects the line power supply. Especially when the degree of deterioration of the surge protector is relatively high and the leakage current is relatively large, a sudden rise in temperature will cause a fire. This shows that the use of surge protectors and overcurrent protectors is very important.
2. Working principle of surge protector and overcurrent protector
Surge protector (SPD), also known as surge protector, lightning protector and lightning arrester, is a commonly used lightning protection device in low-voltage power distribution systems. It is usually connected in parallel or series to the line to discharge the wave The role of surge and protection circuit. According to the different working principles, it is divided into switch-type surge protector, voltage-limiting surge protector and combined surge protector.
An overcurrent protector is commonly an air switch, which is a switch that trips as long as there is a short circuit to form a loop. Fuse is a kind of electrical appliance with simple structure, convenient use and low price that plays a protective role. It is connected in series in the protected circuit. When the current of the line or electrical equipment exceeds the specified value for a long enough time, the heat generated by itself Fuses one or several specially designed and corresponding parts, disconnects the circuit of the person it is connected to and cuts off the power supply, thus playing a protective role. Overcurrent protectors are widely used in high and low voltage power distribution systems and control systems as well as electrical equipment. As protectors against short circuits and overcurrents, they are one of the most commonly used protection devices.
3. Surge protector and overcurrent protector should be reasonably matched
Based on the working principle of the surge protector and overcurrent protector, in order to ensure the safety of the power supply of the line, the surge protector and overcurrent protector should be reasonably selected, and the parameters must be matched with each other to ensure reliable Selectively cut off the circuit, that is, the protective device closest to the fault point is required to act, and the superior protective device does not act, so that the range of the circuit being cut is minimized, to avoid power interruption or equipment damage caused by the over-current protector malfunction.
In order to prevent the failure of the surge protector, a thermal fuse overcurrent protector is installed at the front end of the surge protector. The fuse current value of the front-end overcurrent protector and the fuse current value of the overcurrent protector on the main circuit should not be less than 1: 1.6141.