Why does VFD cable data sheet show Inductance, Capacitance?

In summary, a VFD uses PWM to generate an approximate sine wave. The frequency components in a square wave are much higher, and the rise time of the square wave can be in the realm of 3 to 9 kv/us. This wave, and the energy it represents, needs to be managed by considering the characteristic of the cable, length and the limitations of the motor.
  • #1
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Can someone point me to an understanding of why VFD rated cable include Inductance and Capacitance?
For example, Belden cable 29504 shows impedance, inductance, capacitance between conductors, capacitance between conductor and sheild, and DC resistance.
Is there a VFD motor calculation that is normally used with those values?
 
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  • #2
As you probably know a VFD operates by changing frequency. Since the cable has an inherent capacitance and inductance the impedance of the cable will vary with frequency. Also the amount of capacitance and inductance will also induce some phase shift, which I'm not sure matters as far as variable speed is concerned. Another thing to consider is that the VFD's use transistors switching at high frequency (kHz range) to generate the AC waveform. This high frequency component will also encounter an impedance dependent on capacitance and inductance.
 
  • #3
Thank you unix101os,
I was hoping someone might be familiar with ringing voltage or other examples of calculating possible problems.
I spoke with some of the silvered hairs at work and they were able to tell me about the time when vfds become popular in their areas, and the problems they had, but they were not familiar with specific formulas or circuit examples to predict problems other then voltage loss and to always use vfd rated cables
 
  • #4
Mostly some from the Switching done to create the PWM waveform. A typical VFD is using PWM to use pulse of the full DC voltage in the drive to generate an approximate sine wave. But each pulse is a Voltage Square wave, each pulse travels along the cable to the motor, where the impedance changes dramatically,

As a traveling wave hits the motor - a large voltage spike can be created, the most common detrimental effect being damage to the insulation on the winding of the motor, but EMI / noise, is also a concern.

While the Switching Frequency may be 2 to 6 kHz in a common motor drive, the frequency components in a square wave are much higher, and the rise time of the square wave can be in the realm of 3 to 9 kv / uS - this wave, and the energy it represents, needs to be managed by considering the characteristic of the cable, length and the limitations of the motor.

http://www.belden.com/docs/upload/vfd_choosing_wp.pdf

E-> Sorry hit enter too quick...
 
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Related to Why does VFD cable data sheet show Inductance, Capacitance?

1. Why is inductance listed on the VFD cable data sheet?

Inductance is listed on the VFD cable data sheet because it is an important characteristic that affects the performance of the cable. VFD cables are used to carry high frequency signals, and inductance measures the ability of the cable to resist changes in current. This is especially important in VFD applications because any changes in current can cause interference and affect the performance of the motor or other connected equipment.

2. What is the significance of capacitance in VFD cables?

Capacitance is listed on the VFD cable data sheet because it measures the cable's ability to store electrical energy. In VFD applications, high frequency signals can cause capacitance to build up in the cable, which can lead to voltage spikes and other issues. By knowing the capacitance of the cable, engineers can select the appropriate cable for their specific application and prevent potential problems.

3. How do inductance and capacitance affect the overall performance of VFD cables?

Inductance and capacitance are both important factors in the performance of VFD cables. Inductance affects the cable's ability to resist changes in current, while capacitance measures the cable's ability to store electrical energy. Both of these characteristics can impact the quality of the signal being transmitted through the cable, which can ultimately affect the performance of the motor or other equipment connected to the VFD cable.

4. What is the ideal range for inductance and capacitance in VFD cables?

The ideal range for inductance and capacitance in VFD cables depends on the specific application and the requirements of the equipment being used. Generally, lower inductance and capacitance values are preferred as they indicate better performance and less potential for interference. However, it is important to consult the VFD cable data sheet and the equipment manufacturer's specifications to determine the ideal range for a particular application.

5. How can I use the inductance and capacitance values on the VFD cable data sheet to select the right cable for my application?

To select the right VFD cable for your application, you should first determine the inductance and capacitance requirements based on the equipment being used. Then, compare these requirements to the values listed on the VFD cable data sheet. It is important to choose a cable with inductance and capacitance values that fall within the recommended range for your application to ensure optimal performance and minimize potential issues with interference.

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