Short circuit currents appearing in variable speed drive systems
The knowledge of short circuit current level in variable speed drive systems is crucial for the design of system components as well as for the system protection. Inadequate dimensioning, unsuitable protection concept or wrong parameterization may lead to fatal consequences:
- Hazard situations (personal safety)
- Material damages
- Loss of production
- Consequential damages
Variable speed drive system has certain complexity and shall not be underestimated. The level of short circuit current depends on several factors such as:
- Fault location
- VFD hardware design
- VFD protection philosophy
- System parameters
- Characteristics of protection elements
- Selection of suitable sensors
- External factors
1. Fault location
The fault can appear in various sections of the electric drive system. Correspondingly, the fault level in each section is generally different. And not only the level – also the waveform of the short circuit current is not everywhere the same.
Figure 1 shows the typical fault locations within the drive system that shall be considered. Depending on specific configuration some cases can be excluded (e.g. no harmonic filter).
2. VFD hardware design
The hardware design of the VFD impacts the short circuit level in multiple ways. The most important ones are:
3. VFD protection philosophy
Next is the VFD protection philosophy. It is critical to determine how quickly does the protection system react, what does the reaction look like and if certain faults can actually be detected or not.
4. System parameters
Among the system parameters affecting the short circuit level belong:
More on short circuit currents in VSDS
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References
[1] How to choose a medium voltage VFD: Protection concept, https://mb-drive-services.com/choosing-mv-vfd-protection/
[2] Medium voltage AC drives, https://new.abb.com/drives/medium-voltage-ac-drives
1 Comment
How to calculate the short circuit current in a correct way? - MB Drive Services · June 14, 2022 at 6:09 am
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