Contents
What is the dc bus on a VFD?
Dc bus: The second primary section of a VFD’s main power circuit, chiefly comprised of capacitors that store power rectified by the converter.
How do you check dc bus voltage in VFD?
The dc bus voltage is relative to the peak voltage of the mains input. What to look for: dc bus voltage is ~1.414 x the rms line voltage (e.g., for a 480V ac drive, the dc bus should be ~678V dc. A dc voltage value that is too low can cause the drive to trip.
What causes a ground fault on a VFD?
The most common causes of drive ground faults are motor cables shorted to ground, or motor windings shorted to ground. The capacitive reactances of the drive, cable and motor are rarely identical, and this means that, when supplied by a VFD, voltage levels in the cables can build up through the process of resonance.
How far can a VFD be from a motor?
Solutions Minimize Conductor Length. To reduce the likelihood of possible excessive voltage overshoot at the motor terminals, the lead length distance between the motor and VFD should be less than 150 feet. It is also a good idea to lower the carrier frequency of the VFD to what is audibly acceptable.
When should VFD cable be used?
When are VFD Cables needed? Whenever you are installing a VFD drive system, VFD cables should be strongly considered for use between the inverter and the motor. Standard power cable is not designed to handle the high frequency components of the drive’s inverter output.
What is the DC bus voltage for a variable frequency drive?
Variable Frequency Drives: Viewing the DC Bus. Normally the dc bus voltage in a VFD is 1.414 times the ac RMS line voltage. So for a 480-V unit we’re looking at 678 V on the dc bus, requiring the high-voltage differential probe set.
Is the DC BUS capacitor at ground potential?
Neither end of the DC bus capacitor [DC+ or DC-] is at ground potential. For medium to large drives, there will be two capacitors in series with the center point grounded. Many bench type oscilloscopes have the probe ground clip and the AC input ground connected.
Is it bad to ground a DC negative bus?
Grounding the dc negative bus is a really bad idea. If your substation is solidly grounded (as opposed to HRT, or ungrounded), you’ll probably just hear a loud bang at some point. If not, the bang may be in a seemingly unrelated piece of electrical equipment fed from the same sub.
How does the VFD monitor the DC BUS?
The VFD control circuit continuously monitor the magnitude and quality of DC bus voltage (DC link voltage or reservoir voltage) and triggers appropriate protective functions when the thresholds are crossed.