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

1. Housing port

For example, we can regard any large or small VFD or system as a whole shell, such as transmission lines, signal relays, field instruments, systems, etc. , may be completely exposed to the environment and be directly struck by lightning, resulting in equipment damage. According to the standard, the VFD or system will affect the normal operation when the equipment casing is subjected to 4kv lightning electrostatic discharge. For example, a sensor placed in an outdoor input VFD may be affected by lightning contact discharge; when a building’s lightning conductor discharges, an indoor VFD cabinet may be discharged by the space.

2. Signal line port

In the VFD control system, in order to achieve the transmission of signals or information, there must always be components connected to the outside world, so these signal interfaces input from the outside or output from the VFD may be affected by lightning surges. Since the surge of the external signal input at the VFD port of the cabinet often passes through a long cable, a 10/700μs waveform is used. The standard specifies a line-to-line surge voltage of 0,5kV and a line-to-ground surge voltage of 1kv. However, the surge effect on the signal transmission port between VFDs in the building is equivalent to the surge effect on the line. Using 1, 2/50 (8/20) μs combined wave, the voltage limit of line and line-to-ground surge remains unchanged. Once the limit is exceeded, the signal port and the equipment behind the port may be damaged.

Lightning Protection Port of the VFD

3. Power port

The power ports are widely distributed, and it is easy to 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 standard, the line-to-line surge voltage limit in 1, 2/50 (8/20) μs waveform is 0, 5kv, and the line-to-ground surge voltage is 1kv. However, the surge voltage here means that the working voltage is 220v AC. If the working voltage is low, it cannot be used as a standard. A small surge shock on the power line may not damage the device immediately, but at least it will have an impact on the service life.

4. Ground port

Although the specification of the grounding port is not specifically mentioned in the standard, the grounding port of the VFD is actually very important. When lightning strikes, the grounding port may be affected by ground potential counterattack and ground potential rise, or the grounding resistance is too large due to poor grounding and improper grounding, which cannot meet the requirements of the reference potential and damage the equipment. The grounding port not only requires grounding resistance/grounding electrode (length, diameter, material, etc.), grounding method, grounding grid setting, etc. , It is also directly related to the electrical characteristics of the equipment, the working frequency band, and the working environment. At the same time, it is possible that the ground terminal will react to the VFD of the DC working power port, and damage the unit circuit with DC as the working voltage. To sum up, VFD lightning protection can be considered from four key ports.

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

1. Housing port

For example, we can regard any large or small VFD or system as a whole shell, such as transmission lines, signal relays, field instruments, systems, etc. , may be completely exposed to the environment and be directly struck by lightning, resulting in equipment damage. According to the standard, the VFD or system will affect the normal operation when the equipment casing is subjected to 4kv lightning electrostatic discharge. For example, a sensor placed in an outdoor input VFD may be affected by lightning contact discharge; when a building’s lightning conductor discharges, an indoor VFD cabinet may be discharged by the space.

2. Signal line port

In the VFD control system, in order to achieve the transmission of signals or information, there must always be components connected to the outside world, so these signal interfaces input from the outside or output from the VFD may be affected by lightning surges. Since the surge of the external signal input at the VFD port of the cabinet often passes through a long cable, a 10/700μs waveform is used. The standard specifies a line-to-line surge voltage of 0,5kV and a line-to-ground surge voltage of 1kv. However, the surge effect on the signal transmission port between VFDs in the building is equivalent to the surge effect on the line. Using 1, 2/50 (8/20) μs combined wave, the voltage limit of line and line-to-ground surge remains unchanged. Once the limit is exceeded, the signal port and the equipment behind the port may be damaged.

Lightning Protection Port of the VFD

3. Power port

The power ports are widely distributed, and it is easy to 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 standard, the line-to-line surge voltage limit in 1, 2/50 (8/20) μs waveform is 0, 5kv, and the line-to-ground surge voltage is 1kv. However, the surge voltage here means that the working voltage is 220v AC. If the working voltage is low, it cannot be used as a standard. A small surge shock on the power line may not damage the device immediately, but at least it will have an impact on the service life.

4. Ground port

Although the specification of the grounding port is not specifically mentioned in the standard, the grounding port of the VFD is actually very important. When lightning strikes, the grounding port may be affected by ground potential counterattack and ground potential rise, or the grounding resistance is too large due to poor grounding and improper grounding, which cannot meet the requirements of the reference potential and damage the equipment. The grounding port not only requires grounding resistance/grounding electrode (length, diameter, material, etc.), grounding method, grounding grid setting, etc. , It is also directly related to the electrical characteristics of the equipment, the working frequency band, and the working environment. At the same time, it is possible that the ground terminal will react to the VFD of the DC working power port, and damage the unit circuit with DC as the working voltage. To sum up, VFD lightning protection can be considered from four key ports.

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