What is overvoltage protection? Causes of damage and explosion of overvoltage protectors

Overvoltage protection refers to the protection method of powering off or reducing the voltage of controlled equipment when the voltage exceeds the predetermined maximum value. It is a protective measure to avoid damaging electrical appliances when the voltage is too high. Lightning arresters, penetration protectors, and grounding devices are the most common overvoltage protection devices. Especially lightning arresters and overvoltage protectors are the most important. If damaged, it indicates that it cannot play a buffering role, which means that the pressure can exceed its bearing capacity, but under normal operation, the overvoltage protector will not move or cause accidents.

Overvoltage protectors are used to maintain equipment when the voltage is too high. The key is that when overvoltage is obtained in the circuit, the protector cuts off the ground and discharges voltage above the ground, which is generally used for lightning, equipment short circuit, or ground fault. Overvoltage refers to a fault voltage or abnormal voltage in a power supply system where the line voltage exceeds the rated value. Divided into lightning overvoltage and system overvoltage, the former naturally causes overvoltage in the power supply system due to lightning activities.

The analysis of the reasons for the damage and explosion of overvoltage protectors is as follows:

1. The rated current and continuous operating voltage selection values of the overvoltage protector are slightly lower

The general zinc oxide overvoltage protector (hereinafter referred to as seamless MOA) is actually a nonlinear resistance element (heating element) that has been connected to the power grid for many years because it does not have gap protection for operating voltage and internal overvoltage in the system. It is subjected to various voltages, leading to aging and thermal stability issues. Specifically, it has been observed that many small currents accumulate into large kinetic energy, exceeding a few large thermal kinetic energy (overvoltage impact), and MOA stands on the "first line of defense". Especially if it cannot withstand intermittent arc grounding overvoltage and harmonic overvoltage energy stress, it may become a grounding fault point or even explode.

2、 An overvoltage protector is an instantaneous energy absorption device that cannot withstand system overvoltage for a long time.

Its DC carrying characteristics are: when the voltage on the overvoltage protector is 0.8 times the rated current, the overvoltage protector can operate for a long time; When the voltage on the overvoltage protector is 0.8 times. When the voltage of the rated current is 1.0 times the rated current, it can work for 20 minutes; When the voltage on the overvoltage protector is 1 When doubled, the overvoltage protector can withstand 10 seconds; When the voltage on the overvoltage protector is twice the rated current At 15 times, the overvoltage protector can only withstand 0.1 seconds.

3、 The system may have experienced single-phase grounding or intermittent arc grounding.

The single-phase grounding fault rate of some high-voltage systems is very high. Single-phase grounding causes intermittent arc grounding conditions to generate resonance overvoltage, arc grounding overvoltage, long time, and high amplitude, which is unbearable for any overvoltage protector (lightning arrester), inevitably leading to thermal collapse and explosion of (zinc oxide resistor). If there are many single-phase grounding faults (especially arc grounding), each time it causes serious damage to the protector, the service life of the protector will be quickly shortened, greatly attenuated, and damaged in a very short period of time. Moreover, arc light Earth electrode is easy to cause interphase short circuit, which will inevitably cause equipment damage and failure.

4、 The effects of fading, aging, and turbidity

The reason for dampness is mainly related to the production and transportation of products, and the main factor is the lack of strict environmental regulations during the production process (normal working environments have strict requirements for temperature and humidity, especially gaps. Once the temperature and humidity do not meet the requirements, it is easy to explode, which is also one of the important reasons for the explosion of overvoltage protectors in power supply systems). There are two ways to regain moisture: one is due to poor sealing, which leads to moisture or water intrusion. The quality of the sealing gasket and assembly process are key; The second is caused by the resurgence of product components or the unqualified assembly workshop. External contamination may cause uneven surface voltage of the overvoltage protector, which may cause local heating of the overvoltage protector. This requires overvoltage phase to phase and phase to ground spacing to meet the needs of the system, and insulation materials such as overvoltage boxes, silicone sleeves, silicone cables, etc. are used The requirements are very high. Our company strictly adheres to the production environment conditions, strictly controls production according to the specified temperature and humidity, strictly bakes and dehumidifies key components, and avoids overvoltage protector failures or explosions caused by moisture regain. However, some manufacturers are limited to working environments, and due to management issues, the temperature and humidity of key components cannot meet production regulations. Human factors have buried accidents and even explosions during overvoltage protection operation.

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