VFD vs Soft Starter
VFD vs Soft Starter
(OP)
Did a little search and did not find anything that really answered my question so I figured I would try a post.
Looking at an application for agitators, they will be agitating a high solids slurry and there is a possibility that if we lost power the slurry would settle out and then we would have to start from a sanded condition. Motors are sized at about 200HP.
First option was a full voltage reversing starter, pros - high starting torque, cons could possibly shear the agitator shaft.
Soft Starter - don't know much about these, they would reduce the voltage at starting and decrease the starting current, have read that they are not good for high torque loads, any body with some information on this?
VFD - Again I don't have much experiance with these. Their cost is high, we don't need speed control so this feature would not be used, do they provided high torque for starting high torque loads?
Anybody that has possible dealt with a similar installation and could offer me some helpful info, or even is someone could point me to some good documentation on VFD vs Soft Starter documentation.
Thanks
Hank
Looking at an application for agitators, they will be agitating a high solids slurry and there is a possibility that if we lost power the slurry would settle out and then we would have to start from a sanded condition. Motors are sized at about 200HP.
First option was a full voltage reversing starter, pros - high starting torque, cons could possibly shear the agitator shaft.
Soft Starter - don't know much about these, they would reduce the voltage at starting and decrease the starting current, have read that they are not good for high torque loads, any body with some information on this?
VFD - Again I don't have much experiance with these. Their cost is high, we don't need speed control so this feature would not be used, do they provided high torque for starting high torque loads?
Anybody that has possible dealt with a similar installation and could offer me some helpful info, or even is someone could point me to some good documentation on VFD vs Soft Starter documentation.
Thanks
Hank





RE: VFD vs Soft Starter
What you want to look for is a soft starter that offers two selectable starting ramp profiles. Use one with as gentle of a start as you can under normal every day conditions, then program a harder start for a re-start after a problem. That way you can dial in the right amount of torque necessary to agitate the sand but without unnecessarily stressing the mechanical components.
RE: VFD vs Soft Starter
I'm not saying it's the right thing to do, but this application worked for out needs.
Cement Plant Electrician and
Instrumentation Technician
RE: VFD vs Soft Starter
RE: VFD vs Soft Starter
Mixers are not centrifuges. Generally, you need something between Locked Rotor Torque and Full Load Torque to get the material fluidized. Soft starters are an excellent choice for that, they are used extensively in that application (when, as I said earlier, there is no additional benefit from varying the speed).
Alternate means of fluidizing is also a good idea, but you will still need something to start the motor.
RE: VFD vs Soft Starter
RE: VFD vs Soft Starter
Regards
Alberto J. Hung C
Caracas Venezuela
RE: VFD vs Soft Starter
Regards
Roy
RE: VFD vs Soft Starter
This is not true of all soft-starters, just some that have low current limits.
RE: VFD vs Soft Starter
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If we learn from our mistakes I'm getting a great education!
RE: VFD vs Soft Starter
RE: VFD vs Soft Starter
Some manufacturers provide that information up front, some ignore it altogether. The ones who skirt the issue tend to have something to hide. There are a number of new soft starter designs out there which are being sold as "energy savers" and when you eventually dig through the marketing fluff, turn out to be rated so poorly that it's a wonder they can start anything. One very prominent one uses skimpy components that lead to it be rated for 200% current MAXIMUM for 30 seconds. That means it will have trouble starting almost any motor connected to a load, and only about once per hour (if you are lucky). Such a soft starter could NOT work in this scenario, it would shut itself down to protect its own components (hopefully).
RE: VFD vs Soft Starter
Sanded conditions are not really big problems if your process design already provided ways to do away with those conditions. We identified these problems during the design stage and the solution was to shut down the slurry tank, divert the operations to another backup tank. Our slurry is more sticky that, if after three tries of softstarting, and they can't make the agitator run, operators shift to the backup tank! NO shaft breaks, no agitator motor toasted, but we have to empty the "sticky mud" on the tank by other means!
I agree with jraef that the softstartes we have does its job most of the time- a few moments of overloads, i.e. drive the agitators even when some slurry are on top of its blades!