Energy Saving - 30hp Motor

First of all mention type of application where you are using this 30 HP motor. Type of application some idea about energy saving

Please mention motor full nameplate

VFD is the best choice

2nd best choice is Soft Starter

...and please describe the type of electricity tariff payable at that location.

You must also consider the characteristics of the load--does it require a high starting torque? Describe the load for us. Has the motor been chosen (NEMA type) to match the starting torque requirements of the load?

Do you need to vary the speed? If not, a VFD is (usually) not required.

Starting current, best to worst (of your three stated choices), which also translates to cost from highest to lowest:

1. VFD, because in most cases if you do not need to accelerate the load too quickly, you can limit the starting current to 100% of the motor FLA
2. Soft starter, because the starting current can be limited to 200% current (under ideal circumstances and light loading) but is infinitely adjustable in the field to optimize the current vs time vs motor thermal damage curve. In other words if it will start, the solid state soft starter can be adjusted to make it start in the best way possible.
3. Star-Delta, offers no advantages other than a perceived reduction in peak current (not really true in many cases) but is simply the lowest cost option if you do not care about anything else. It does expose the mechanical components to significant risk of torque shock damage, and it usually creates undesirable consequences on the electrical grid. I avoid them at all cost.

Energy savings are strictly a function of the connected load and the process involved. There is no "magic box" that is going to save energy unless it is first being wasred somewhere. Most of the advertisements that you see making claims of energy savings with magic boxes are complete scams designed solely to separate you from your money. There are a few legitimate claims however:

1. Some loads can be optimized to reduce losses using VFDs where there is some other form of process flow restriction involving fluid or air. A VFD can modulate the motor speed in lieu of the flow restriction, thus it can eliminate the losses associated with those restriction devices.
2. In a very few applications, a soft starter that has the Nola Energy Saver feature might possibly save a tiny amount of energy, but only if, for some reason, it is necessary to run your motor in an unloaded state for long periods. The general rule of thumb on that is more than 50% unloaded for more than 50% of the operating time. Anything less and the savings will be negligible. It is worth noting however that most applications like that can save a lot more energy just by figuring out why the motor must run at all if it is so unloaded. There is no better energy saver than the Off button, and sometimes using a slow stepless acceleration such as you get with a soft starter can facilitate more frequent Off cycles.
3. Star-Delta offers no possibility of energy savings.
   

Dear Mr.JRaef,

I have one observation in your posting.

The vfd - starting torque is relatively less than the star-delta starting. If due to some reason, starting against load may pose problem. There was a suggestion to start on star-delta mode, and switvh over to vfd mode, after normal working is reahced. But the elec.inspn authority objected for the dual star-delta starter connection with vfd.

Pl. let us know your views on this.

DHAYANANDHAN.S