Star Delta Time Setting

Measure the inertia. How long does it take the motor and load to spin up-to-speed in star?

The maximum starting time is 15 seconds

^{"The maximum starting time is 15 seconds"}

What a completely useless answer. Based on what?

It is my belief that this is a forum for engineers and as such I expect us to be civil in the way we respond to one another. The golden rule of life is that you do unto others as you would want them to do to you.

The star-delta starting method is one of the reduced voltage starting methods, in which the voltage applied to the windings is some fraction of the line voltage, but at the expense of greatly reduced starting torque ( which is proportional to the square of the voltage applied. There's no fixed starting time setting, the determning factor is to allow a steady speed to be attained before the windings are connected in delta for motor operation. Motor acceleration should proceed as far as possible before the transistion is made so as to minimize the transient current peaks during changeover to the delta mode.

The 15second maximum given is just a guide so as to avoid tripping of the overload relay, and is universally acceptable . If you don't know, ask. Nobody knows it all.

Many years ago a Wadkin circular saw was started using a manual star-delta starter. The huge inertia of the saw blade invoked a starting procedure that involved getting the device up to speed in Star, and then flipping over into Delta at full speed before any timber was introduced to the blade. The start time was around 10 sec.

Any electrical-timer-based starter substitute would simply have mimicked the manual start procedure.

(For guidance purposes only, as each individual case needs to be determined on its own merits, as the inertia, among other factors, will determine the run-up time...)

Hello Guest,

In addition to the requirements of PWSlack post above, it depends on the capacity of your High tension Supply system, supply transformer, mains cable and cable from switchboard to the motor.

If your electrical supply is a marginal one, you would be better to use an electronic soft starter, or a VFD (Variable Frequency Drive), which can cope with a poor supply better than the star-delta system.

Kind Regards....

I would recommend to use solid state starter. Wye Delta starter generates voltage transient during the transition of wye to delta when using convetional which is open transition WYE DELTA Starter. Closed transition is recommende but the the enclosure is bulky and you need a vetilation to mitigate the heat desipated by the resistor during wye to delta transition.

I agree with sparkstation

I have worked with a lot of large motor loads in rock crushing locations and have found soft starts or VFD's to work great. When you figure the cost of a star delta install compared to an SCR controled soft start(added wiring-contactors-enclosures-ect) a soft start is the way to go, less moving parts-programable start times smaller foot print = ease of maintance. Also there not that $$

I agree that a soft start would be the best way to go. But if you have star-delta equipment now and just want to set it up properly you should get a current meter and measure the line current into the starter on one phase when starting. When the starter is first energized the current will jump to an initial value and then fade back to a lower level as the motor accelerates. When the transition is made to delta the current will jump again to a higher level. Then it will fall to the running current level when operating speed is reached. You want to adjust the transition time so that the peak current when going into delta is the same as the peak current when initially starting in star. If the delta current is higher then lengthen the time. If it's lower then shorten the time. If you reach maximum time and the current going into delta is still higher than the initial current then shorten the time until the peak delta current is just slightly higher than the peak delta current when the transition time is set to maximum. If the mechanical load varies from start to start then the adjustment procedure should be done with the greatest mechanical load.

If a current meter is not available you can simply adjust the time so that the motor just stops accelerating in star before transitioning to delta. Transitioning to Delta is better too late than too soon, but just right is best.

Take your time and let the motor cool somewhat between starts.

Don

That would work, but what I don't understand is this equipment all ready in place or is it a new install or are you changing HP. If your just changing out motor for motor all you should need to to is maybe a little tweeking with your start-run timer. If it's new or your increasing HP and need to pull new conductors why not go with delta and a soft start and save your self the need for the extra set of motor leads,cotactors,overloads and timing relays ect?

Let me know

DW

While I completely agree that soft starters are a much better way to go than star-delta, the reason so many people use star-delta is simply because it is cheapest. In spite of the extra contactors, extra cables etc. that you mention, it always comes out slightly cheaper to use star-delta and a lot of people only care about doing things cheap, not doing things the best way. Unfortunate, but true.

Re: how to set the timing;
I also agree that the current measurement mentioned above is best, but most of the time people just observe when the load stops accelerating in star and use that as the timing point. If you transition too soon, the resultant current spike can be EVEN LARGER than had you started across the line. If you transition too late, you can needlessly overheat the motor and run the risk of tripping the overload relay. But as was mentioned, better too late than too early.

It is a working machine.Wherein , the spindle now waits for 5 seconds before it starts moving and does the heavy drilling.

The agenda of this discussion whether can we start and run the motor directly in DELTA or reduce the time even less to 2 seconds?

Hello again Guest,

You do not explain the Motor Make/Type/year of manufacture.

Nor have you advised the supply voltage: 400V, 440V, 600V, 1100V, 3.3kV etc.

Nor do you explain the inertia of the various gears, belts pulleys etc associated with the motor, before you commence the heavy drilling.

Nor do you explain re your cabling, electrical supply mains etc.

If the motor is older than 40 years, it may not take easily to start in delta.

I would check the running and peak currents of the motor, in star start/delta run, then check again on delta start.

You can use a digital clip-on meter with current readings of peak/running, and take notes, advise here please.

If your motor peak current on delta start is more than 10X the running current, you do risk motor burnout, depending on how many motor starts per hour.

If you are using the motor on a large drilling machine, most of the good ones allow the motor to run all the time, and have a clutch to allow power to run the drill mechanism.

If you are not intending starting the motor very often, then it is best in your situation, to use a star/delta starter - bearing in mind we do not know the electric supply and cabling capacity.

Further useful feedback is always appreciated.

Kind Regards....