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Member Since 29 Nov 2006
Offline Last Active Jan 11 2014 08:18 PM

Posts I've Made

In Topic: Kvar Contactor.

30 January 2007 - 10:42 PM

From http://library.abb.com -- Dated November 2004
UA..RA contactors for inrush currents exceeding 100 times the rated currents are now available up to 80 kvar. The UA..RA contactors are equipped with a special front mounted contact block which ensures the insertion of damping resistors in each phase, limiting the peak current at energization of capacitor banks. The contactors UA16..RA up to UA75..RA were released in June this year, and now the UA..RA range is completed by the addition of UA95..RA for 70 kvar and UA110..RA for 80 kvar.

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.

In Topic: Help, Big Problem With Vsd Installed

25 January 2007 - 02:46 AM

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.

In Topic: Help, Big Problem With Vsd Installed

23 January 2007 - 03:17 PM

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?

In Topic: Vfd On Single Phase Motor

16 January 2007 - 04:26 PM

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.

In Topic: Harmonics Calculations

16 January 2007 - 04:06 PM

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.