Installation of VFD.

Easy to install, near to plug and play by minor adjustment to default parameters; it has Accel. and Decel ramps to smoothly run high inertial loads.

When you buy it, make sure you read and understand the manual. If you're eager and restless, go straight to the Typical application/installation and then review the parameters description.

VFDs are easy to install, very beneficial and highly safer. When you just purchase the VFD, you normally need to adjust some parameters to suit your requirements because it will come with factory set parameters. If you're installing the VFD in very critical operations however, I would recommend that you keep a spare around so that you don't compromise the safety and productivity of your plant. I have worked with a good number of VFD brands including: Schneider Electric, ABB, WEG, Siemens and many others all of which are different physically but do the same thing.

Eng. Aaron

Remember that VSD don't include a main contactor, therefore for safety reasons it's mandatory to install a contactor (or motorized breaker if the power exceeds the ratings of large contactors, i.e. corresponding to currents of above approx. 2000 A) or a manually operated switch (in no automatic/remote operated disconnection is required).

In some very special cases an output contactor is required too but usually the motor is wired directly.

So-called Safe Torque Off options do not remove safely voltage at motor terminals but can prevent motion of the motor (excepted a limited angle motion with permanent magnet motors). Pay attention to the required safety level (up to SIL 3 / PL e, rarely above). STO options basically safely disable the powering of the IGBT gate drivers (modulation is impossible).

Current VFD's are plug and play once you've determined application -HP,Voltage ,KW etc.... Bosch ,GE,are common OEM VFD's there are others but I can't remember. The hi inertia component of your question isn't clear to me - I am Not an Engineer but a 40 year journeyman Mechanical/HVAC/Energy Management professional who has sold and installed many VFD's for many applications.

Installation is easier than a motor starter. Power into the line terminals and power out of the output terminals. Get them correct or you will get a rather loud bang on application of power and the magic smoke will come out. Be sure to ground the unit and if other instruments are near by, you will want a true VFD cable with shielding for noise protection.

The only catch is if programming is necessary. Many come ready to go, but some.... There are no 2 that program the same. I think I've programmed every type available and the similarities are definitely not there. Lower cost units pretty much come on ready for you to hit start, unless you want remote control via a PLC or such. The more expensive ones will kick you into a start up routine that will ask for motor statistics such as HP, FLA, voltage and such. The start up routines pretty much direct you what to do. Programming for remote control by other devices is where it gets tricky. If you must do this, read the manuals - most have a quick start and a full manual and they don't always have everything covered in just one manual. The expensive models with all the bells and whistles are by the larger vendors and have great support available if you call them.Fortunately, all the bells and whistles are very seldom needed, unless your motor is not VFD ready. (most are today and the literature on them will mention this) Older motors need some help with torque curves to function with a VFD. That is programming you will need help on.

Referring to the original poster's question, where required, a VFD can supply the nominal current at a low voltage and low frequency when starting the motor. Compared to a softstarter, a VFD-fed motor can deliver a higher starting torque.

High inertia low friction loads can be started by sofstarters or VFD, it's not only about the inertia but about the required torque (how much torque and how long the start duration) and the admissible maximum starting time. For example some large pumps can be started against closed valves, with high inertia flywheels or large impellers their start can take 20 seconds or even longer. It's important to not overload thermically the motor during the start phase.

As I mentioned it in some other topic, there are cases where a softstarter cannot be used due to torque requirements, in such cases it can be necessary to use a VFD even if after the start the motor runs only at 50 (or 60 Hz) (not talking about DOL of course which can be an option if some conditions are met, but DOL stresses the motor, the load including the whole transmission and also the grid).

I'd recommend to use VFD from major manufacturers but make sure they're not some private-branded Asian crap. Also within a company it can be a good idea to internally standardize drives whenever possible as it's easier to handle a family of drives from one manufacturer than having to use a zillion different softwares because everytime another manufacturer (or drive family) was chosen. For advanced drives there can be over thousand pages of documentation so it's not something you want to read for each motor because each drive is totally different. :)