As indicated above, contactors designed for connecting power factor correction capacitors must withstand high inrush current compared to the continuous current. Motor starting contactors must withstand moderate inrush current, but more importantly, they must break locked rotor current in the event that the motor stalls and the overload relay de-energizes the contactor. They may not be physically different, but they may have different ratings according to the duty. They may also may have different certifications indicating which code requirements they meet.

If you set the acceleration too fast, the motor will try to produce too much torque and draw too much current. With detailed information about the torque required to drive the fan and the fan't inertia, you could calculate what rate is ok, but it would probably be easier to watch the current with an ammeter as the fan operates. The VFD likely has protection features that will not let the drive accelerate at a rate that causes too much overload. If rapid acceleration causes a momentary overload that is within safe limits for occasional operation but the overload is repeated too frequently, the drive might shut down.

Something similar happens with deceleration. If the deceleration is too fast, the DC bus voltage could increase due to braking energy regenerated by the motor. The drive likely has protection features that will limit the actual deceleration rate to prevent the drive from shutting down due to overvoltage on the DC bus.

What is the altitude and ambient temperature of the VSD location? Does the VSD have an feature that automatically attempts to restart if the unit shuts down? If so, how many attempts are allowed? Is there a feature that is supposed to allow the VSD to start (or restart) a coasting motor?

There are many small VFDs that are designed for single phase input power and provide three phase output. In addition to the ones that are designed for single phase input, many others will operate successfully on single phase input if they are rated for about twice the HP of the connected motor. The exact derating required may be published in the drive manual or spec sheet. The best thing to do is to use one of these and replace the single phase motor with a three phase motor.

If replacing the motor is difficult, there are VFDs that will operate single phase motors but only if they are the permanent split capacitor or shaded-pole type of motor. See http://www.anaconsys...ext/opti_1.html.

Software that tied to a specific supplier's product may be useful if you are working with similar products. VSDs that are of the same general design are very similar in the harmonics they produce.

ABB USA has an MS Excel spreadsheet that allows input for various VSD characteristics. I can't seem to get a link directly to the location, but if you go to abb-drives.com and click "main menu" then "products" then "documentation" you should get a list of product documentation. There is a place to select a specific product, but the Harmonic Analyzer Tool seems to be listed under "-14 Software" section for all of the products. For each VSD connected to the source, you need to put in an entry for input converter type and percent internal impedance (%Z). If you mouse over the heading for the items, you get pop-up instructions for the entries required in the cells below.

Have you filed infringement notifications with the offending sites?

For an example of information required for a USA infringement notification see: http://www.youtube.com/t/dmca_policy.

I guess I will make some guesses:

I guess there is probably a rectifier and capacitive filter on the front end of your VFD and that you turn up the variac slowly to charge the capacitors without blowing them up destroying the rectifier and variac in the process.

I guess that when you apply full voltage by closing the CB, you have some mechanism that automatically limits the capacitor charging rate. I guess that mechanism may consistently allow a faster charge than you provide manually with the variac.

I guess something might happen with the faster charging or with the charge control mechanism that causes the output devices to fire in some uncontrolled way. I guess that may cause excessive current and activate the desat protection. I guess that the second time you close the CB, the capacitors may not have discharged completely and the problem doesn't occur upon recharging under that condition.

I guess that another possibility might be that there is a problem in the way the power supply for the control circuitry comes up when you apply power. I guess that could cause uncontrolled firing of the output devices as described above or an erroneous activation of the desat protection.

To calculate the total power factor for an entire plant, you must calculate or measure the plant’s total power and total RMS current (Irms) including the harmonic current content. Then you can calculate the total power factor from Total PF = Total Power/V x Irms x sqrt3 (assuming 3 phase).

For an accurate determination of Irms, you should determine the fundamental current (If) and each individual harmonic current for each individual load and then add the individual fundamental and harmonic currents to get totals for each, such as total fundamental (If), total 2nd harmonic (I2), total 3rd harmonic (I3) etc. The total RMS current for the plant is then Irms = sqrt(total If^2 + total I2^2 + total I3^2 + … total In^2).

If the loads have similar harmonic spectrums, I believe that you can just add together the total harmonic current (Ih) values for the individual loads to get a total Ih for the plant. For each distorted load, you can determine the total fundamental and harmonic currents from If = Irms/sqrt(1 + THD^2) and Ih = If x THD. To determine the total RMS current you add all the fundamental currents together and all the harmonic currents together and calculate the total RMS current from Irms = sqrt(If^2 + Ih^2). The currents of the loads without harmonic content are added as part of the total If.

You need to first verify what the utility measures and how they use it in their rate structure. Historically, utilities have had only equipment to measure displacement pf but many are now paying attention to distortion in one way or another.

If you know the displacement power factor and the total harmonic current distortion, you can calculate the total power factor from Total PF = Displacement PF/sqrt(1+THDi^2).

The history of Reliance on their web site (reliance.com/aboutre/aboutre_english.htm) indicates that the drives business was integrated with the Allen Bradley drives business and was not part of the power systems business.