The lightning protection port of the inverter - LS generates electricity

According to the applied engineering practice, variable frequency drive (VFD) lightning strikes can be roughly divided into direct lightning, induced lightning and conducted lightning. But no matter what form it takes to reach the device, it can be summarized as a lightning surge from the following four parts, which is called a lightning protection port here, and is clarified by VFD.

The lightning protection port of the inverter - LS generates electricity

The lightning protection port of the inverter - LS generates electricity

1. Enclosure port

For example, we can treat any large or small VFD or system as a whole shell, such as transmission lines, signal relays, field instruments, systems, etc. , perhaps completely exposed to the environment and directly struck by lightning, resulting in damage to the equipment. According to the specification, the VFD or system will affect the normal operation when the equipment housing is subjected to 4kV lightning electrostatic discharge. For example, a sensor placed in an outdoor input VFD may be affected by lightning touch discharge; When the lightning cable of the building is discharged, the indoor VFD cabinet may be discharged by the space.

2. Signal line port

In the VFD control system, in order to complete the transmission of signals or information, it is necessary to have components connected to the outside world at all times, so these signal interfaces input from the outside world or output from the VFD may be affected by lightning surges. Because the surge of the external signal input to the VFD port of the cabinet often passes through long cables, a 10/700μs waveform is chosen. The specification specifies an inter-line surge voltage of 0.5 kV and a line-to-ground surge voltage of 1 kV. However, the surge effect on the signal transmission ports between the VFDs within the building is equivalent to the surge effect on the lines. The combination wave of 1, 2/50 (8/20) μs is selected, and the voltage constraint of line-to-ground surge remains unchanged. Once the constraints are exceeded, the signal port and the equipment behind the port may be damaged.

3. Power port

The power port is widely dispersed and can easily induce or conduct lightning surges. The power port of the VFD is from the switchboard to the VFD power input and from the VFD output. According to the specification, the interline surge voltage limit in the 1,2/50 (8/20) μs waveform is 0,5 kV and the line-to-ground surge voltage is 1 kV. However, the surge voltage here indicates that the operating voltage is 220V AC. If the operating voltage is low, it cannot be used as a standard. Small surges on the power line may not damage the device immediately, but at least it can have an impact on the service life.

4. Ground port

Although there is no specific standard for ground ports in the specification, the ground port of a VFD is actually important. In the event of a lightning strike, the ground port may be affected by the ground potential counterattack and the ground potential rise, or the ground resistance may be too large due to poor grounding and improper grounding, which will not meet the requirements of the reference potential, and damage the equipment. The ground port requires more than just a ground resistance/ground electrode (length, diameter, material, etc.). ), grounding mode, grounding grid setting, etc. It is also directly related to the electrical characteristics, operating frequency band, and operating environment of the equipment. At the same time, there is a possibility that the ground terminal will react to the DC operation power supply port VFD, damaging the unit circuit with DC as the operating voltage. To sum up, the lightning protection of VFD can be considered from four critical ports.

The lightning protection port of the inverter - LS generates electricity

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