Soft Starters

Yes youcan use soft starters that is much feasible, you can approach ABB soft start devices section to get more info.

recently i have used it for 200 to 500 hp motors at 480 v 3ph 60hz

in case of 950 kw motor we used 4.16 kv 3ph 60hz system this way we can reduce starting current.

hope this will help you approaching ABB you will get this device whic will siolv your problem of arcs at start

I am not sure about the soft starters feasible particularly with the motors serving minicipal water supply. If this motor is not frequent starting/operating, the electric bill saving is negligible.

soft starter is not an energy saving device.it helps in minimising in rush current during the starting of a motor.Even with a VFD energy saving is achived not because of VFD but in a square law torque equipment like fan or pump when speed is redused the power varies as cube root .Finally municipal pumps need not necessarily start and stop frequently.

Soft starters work fine for any kind of pump, but are especially suitable for municipal pumps because they will decrease the overall cost of ownership by reducing maintenance costs for the pump, piping and other equipment associated with it.

But they do not save energy in spite of the claims some people try to make. There are a FEW speicfic applications where an Nola Energy Saver circuit, or one of its spawn, will reduce a small portion of the losses in an unloaded system, but in general, unloaded motors are best turned off all together.

Your electric bill will reduce in terms of Maximum Demand charges. The soft starter will reduce the peek demand much better than the Star-Delta as well as reduce the stress on the electric motor winding by reducing the current surge at starts.

This is not universally true. Most power utilities use what is called a "sliding demand window" in which demand is read based on a sliding time window, usually 15, 20 or 30 minutes. Any specific short duration peak within that time frame is virtually meaningless, so only the actual connected load makes a difference. Accelerating in 1 second at 600% current has no more effect than accelerating in 30 seconds at 300% current, and vice versa.

This is a common myth used by sellers of soft starters to justify a purchase when they don't know how to quantify the real benefits. There are some very rare cases of small utilities using instantaneous demand metering, but those are so onerous as to be self-limiting; utilities that do this drive businesses away.

You are absolutely right about the impact on the bill.

What was required here was, I Tought, to describe the physics of the phenomena. Also, starting in Star/Delta does take few seconds depending on the size of the pump/motor and the timing set... which does contribute even if a little as you pointed, to the overall bill...It had to be pointed out and up to the OP to work it when explained...

Thanks Raef.

Brelvi,

JRaef has given you good advice. Regarding the power factor penalty, neither a Star/delta starter nor a Soft Start has any significant effect on this penalty. You can add power factor correcting capacitors to the main motors to do this. They can be added on the motor side of the starter (the overload settings would probably need to be lowered because of the lower net current), or with a separate contactor that is energized when each motor is running (more complex but no changes within the motor circuit). Make sure that your soft start can be used with power factor correcting capacitors.

--JMM

Sorry, but the Overload current setting does not need to be reset. It should be set as before according to the nameplate rating with, maybe a small margin. This has to do with the motor winding rating. The power factor correction only corrects the p.f. before the motor and not reduce the motor's impact on the p.f. It still consumes reactive power as designed, and this will be supplied by the capacitors instead of the main supply...

Sir,

I suggest you check further on this topic. Nearly all the reactive power consumed by the motor is supplied by the capacitor, as you note. Therefore, the vector sum of the amount of current drawn through the overload relay is reduced. For this reason, the setting of the overload relay will usually need to be lowered. This change is typically noted in the installation instructions for the capacitors.

With respect, John M.

John M.

You are right. I missed the point that the capacitors were connected directly on the motor and after the O/Load current device...

Thanks

Soft-starts do not save energy. They reduce the inrush current by, literally, starting the motor "softly", i.e. with reduced voltage for a short period so as to reduce the starting current.

Electricity bill savings will depend upon the tariff charged, which cannot be seen from here:

• If each kWh is paid for, then a soft-start will not reduce the bill.
• If the tariff is "peak demand", then soft-starts will pay for themselves in weeks.