Mike Dolt Enterprises
Mike Dolt Enterprises
User: Breaker19, Location: San Francisco Bay Area, CA, USA
Asked on: Monday, April 25, 2011 at 7:35 pm EDT
Answered on: Tuesday, May 14, 2024 at 4:37 am EDT
Question: Does anyone have any information on why it would be advantageous to install shielded feeder cable to the incoming AC section on a VFD lineup vs non-shielded? Or if braided straps would stop harmonics from polluting up the line. I can understand using it for the load side of the VFD but do not understand, fully, for the line side prior the filter, which already contains an isolation transformer.I just can't fathom the reasoning behind it, especially since 3c/750 w/g shld is around 80 dollars a foot. Then again I am not an engineer.Thanks in advance.
Advantages of Shielded Feeder Cable for VFD Line Side Reduced Harmonic Distortion
VFDs generate harmonic currents that can distort the voltage waveform on the line side, leading to voltage spikes and line disturbances. Shielded feeder cable provides a conductive pathway for these harmonic currents to bypass the voltage waveform, reducing distortion and improving power quality.
Improved Grounding
The shield provides a dedicated grounding path, reducing the risk of electrical noise and interference from other equipment on the same bus. This ensures proper grounding of the VFD and prevents potential safety hazards.
Protection against Electrical Noise
Shielded cable can block electromagnetic interference (EMI) from other sources, such as nearby motors, transformers, or other electronic devices, which can interfere with VFD operation.
Increased Reliability
The shielding can protect the cable from external damage and moisture, extending its lifespan and reducing the risk of breakdowns.
Role of Braided Straps
Braided straps are not typically used to eliminate harmonics on the line side of a VFD. They are primarily used on the motor side to provide a low-inductance path for harmonic currents generated by the VFD. On the line side, the isolation transformer already provides significant harmonic filtering.
Cost Considerations
While 3c/750 w/g shld cable is expensive, the benefits it provides in terms of power quality, reliability, and safety may justify the investment. It is important to weigh these benefits against the cost of the cable and other factors, such as the availability of other harmonic mitigation measures.
Usage Guidelines
It is recommended to use shielded feeder cable for the line side of VFDs with the following characteristics: High harmonic content on the line side Sensitive equipment or other devices sharing the same bus Concerns about grounding and electrical noise High reliability requirements Flag for review