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The Misunderstandings Of UPS Power Supply Overvoltage Protection

2020-06-12

"Lightning protector" only for lightning protection

 

In the practical application of UPS power supply, users often encounter this situation: it is clear that there is no clear lightning, and there is no lightning phenomenon, but the built-in "lightning protector" of the UPS is damaged. The user said it was the UPS machine without any signs of lightning, but the built-in lightning protector of the UPS power supply that the user was running was broken, but the UPS was still working normally. In fact, when a lightning strike occurs in the distance, the lightning surge is transmitted to the equipment through the power grid or communication line. Although it is not necessary to damage the equipment immediately, it will also form a cumulative hazard to the interior of the equipment.

 

Cheap "lightning protector" also protects against lightning

 

Many users require the UPS power supply to be equipped with "lightning protector" at a lower price due to consideration of relevant regulations. Individual manufacturers simply install a small varistor in order to "satisfy" user requirements, also known as " There is lightning protection." In fact, a varistor with a small flow capacity can only have a certain overvoltage protection effect. If lightning protection is really needed, sufficient flow capacity equipment and related costs must be considered.

 

The role and cost of overvoltage protection measures have an important relationship with the choice of equipment and plans. Selecting a SPD device with a lower operating voltage and a larger flow capacity can reduce its residual voltage, but if the operating voltage is too low, the SPD equipment will fail frequently due to the instability of the power supply, and it will fail in advance. The larger the flow capacity, the higher the protection cost. Under normal circumstances, the first thing is not to consider lightning protection, but to protect the power supply from overvoltage.

 

One plan is to add the flow capacity of MOV, for example, choose 20D471, 25D471 or even 32D471 MOV equipment to increase the flow capacity to about 10kA to 25KA (8/20μs, once). In this way, it can not only accept the over-voltage energy discharge for a long time or period, but also keep the residual voltage on the line at a low level. However, this will greatly increase the protection cost (tens of times the addition).

 

Another plan is to add the operating voltage of MOV. For example, choose MOV equipment such as 14D561 or 14D621 to increase the operating voltage from 470V to 560V or 620V. In this way, without changing the flow capacity, it greatly reduces the MOV's action probability and depletion time without adding cost. However, this will increase the residual pressure on the line.

 

Finally, we are reminded that a reasonable overvoltage protection plan can not only accept long-term or periodic overvoltage energy discharge, but also keep the residual voltage on the line at a low level. So we must choose a good overvoltage protection plan for ourselves.

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