Star Delta Starter Power Consumption

~100KW. The star-delta starter reduces the current somewhat while starting, but has no influence on the long-time running current.

Your effective used power in your application/ efficiency factor of the motor.

Considered long runs with no frequent starts.

e.g. load in a mixing process with sticky thermoplasts will vary in time, while e.g. a universally loaded belt not.

I remember that for gum mixing we had up to 300% variation in load and this was monitored and used as a mixing parameter to define the process advance. The machine was a munition mixer adapted for bubble gum processing.

You appear to have voltage and current confused there.

Phase voltage will be 58% lower than line voltage when in star configuration, starting current, torque and input power will be reduced by about 67%.

As Tornado has stated, once the starter goes to delta mode (normally only a few seconds after initiating start procedure) then phase voltage will equal line voltage, and power will be as listed on the name plate.

I assume he talks about a (semiconductor based) starter. Not a manual or timed Star Delta Switch.

In this case the figures he gave could be the avg. setting he reads.

Your remark however, makes sense.

Based on your information the 100KW motor would consume 100KW x .58 = 58KW when in the STAR (WYE) configuration and 100KW in DELTA configuration.

This type of starter is sometimes referred to as a "reduced voltage" starter.

The purpose of this type of starter is to reduce inrush current therefore reducing starting torque requirements then allow full voltage to be applied once the motor has reached transfer point RPM or full speed.

This also reduces mechanical stress on the equipment drive and driven components allowing extended equipment service life.

I hope this information is helpful to you.

It's understandable that delta configuration motor consumes less power compared to star configuration in start-delta motor starter. I'm a bit confuse with motor where the star connection is made on the motor terminal, does the motor with star connection (DOL Starter) consumes less power(58% reduced from its nominal rating) compared to the motor having delta connection?. We were taught for DOL starter, the overload setting must be at least 100~110% of motor nominal capacity because the maximum current can flow would be 100% of motor nominal current, and from my experience, most of motors are connected in Star (DOL starter). But why in star-delta starter, the current is limit to 33% of motor nominal current in star configuration (during starting), why it's different from DOL starter (motor in start connection).

You don't appear to understand what has been said so far. Go back and read it....Less power will be consumed when starting in star than in delta.

Whilst a star connected motor will draw less current during starting, once it is up to speed and under full load then it will draw full load current. If the star connection is made at the motor terminals for DOL starting, then it will consume 67% less power during starting than it would in delta, but it also will provide 67% less starting torque.

Below is a chart for a 120kW 4 pole 50Hz 380v motor that may help you understand the figures.

When using a star delta starter, the overloads are often (but not always) inserted in the phase conductors between the motor and the delta contactor, so they are only carrying part of the load current. If connecting star via a DOL starter, then you would need to size the overloads for full load current as that is what the overloads will be carrying. A motor starting in star will draw the same starting current in DOL as it will via a star delta starter, and full load figures will be similar.

Very useful data. if this kind of readings are given for various kinds of starting methods it would be wonderful.

It may help you better to think of the motor fields as being "resistances in Ohms", rather than as being field coils with impedances as they really are.

This then turns it into an (slightly inaccurate) Ohm's Law Question/Answer!!

It is not correct to do so, but might serve as an easier way to learn better. Do remember that Impedances do not follow quite the same rules as resistance do.....but for the sake of simplicity here its is:-

In star connection, there are always two fields connected in series between any two phases. That is double the resistance (impedance) of a single field coil. Therefore halving the current for any set voltage.

In Delta, there is only one field between any two phases. Half the resistance (impedance) of the two coils in Star format. Therefore double the current will flow at the same set voltage!

I hope this helps a little. But do not forget, this is just a simple pointer, not the true facts of impedances in motors, do not let it mislead you later on!!!

I also agree with the semantics problem here, in that the STARTER only consumes coil power. The MOTOR consumes the kW for the load.

But there is another semantics error going on here as well. The motor only consumes the energy required by the LOAD, plus any losses associated in converting the electrical energy to mechanical (kinetic) energy. So just because you have a 100kW motor does NOT mean that it will consume 100kW! If the load only REQUIRES 28.36 kW, then the motor will consume 28.36kW plus a few added percent in losses such as heat, friction, wind age etc.

So with that in mind, there is a concept, promoted in some countries, that by using a Star-delta motor starting scheme, you can in theory save a small amount of energy by running a significantly UNDER LOADED motor in star, not letting it complete the transition to delta.

The concept is based on the fact that a small percentage of the small percentage of those losses in the motor are related to the voltage on the windings. So by lowering the effective voltage across the windings by reconnecting them in star, you reduce those losses. It's barely worth it, and extremely risky in terms of having the motor stall or overload, yet there are people continually promoting it. The energy savings amount to a fraction of a percent, unless it is a very old and very inefficient motor. But modern motors are now 90%+ efficient, some in that 100kW range will be 95% efficient. So only 5% of the energy is losses to begin with, then only 1/4 of that is related to voltage, and only 1/2 of that will be reduced by reducing voltage, and only by a small percent of change.

Because the torque of the motor is also severely reduced, the LOAD on the motor must be less than 33% before you can even BEGIN to think of using this. Then consider that the savings are of the energy USED, not the potential energy capacity. So let's use the example above, I have a 100kW motor that for some reason is only consuming 28.36kW, and the motor is 95% efficient. That means my losses in that motor are 5% of 28.36 or 1.418kW. Of those, only 25% are related to the voltage, so 0.355kW, and of that, the reduction is by the voltage change, so 57.7% of that is only 0.2kW. 200watts.

Excellent point!

I think what is driving this is that the promoters are taking the total KW load of all motors in a plant then doing the math to show the apparent energy savings cost without stating all the facts and the real cost of implementation.

At one of our plants we consume roughly 160MWH per 24 hour day of which roughly 68% is from motors. The argument presented by the sales rep was/is a .2% power savings on 160 x .68 = 108.8MWH equates to at least $54,400 per day x 30 days per month = $1,630,000 x 12 = $19,584,000 in power cost savings per year.

However he did not account for; installation costs, equipment purchase cost, and the added cost of maintenance.

After carefully considering installation and maintenance costs as well as the rather small difference in equipment purchase cost we opted for VFD drives for all locations where "soft" starting is needed rather than installing any reduced voltage starters.

Doing so allows very finite tuning and maximization of energy savings while minimizing maintenance costs.

We still do have some reduced voltage starters on some of our older equipment such as fans however as we update and replace the equipment with new high efficiency motors we will also migrate those to VFD units.

"At one of our plants we consume roughly 160MWH per 24 hour day of which roughly 68% is from motors. The argument presented by the sales rep was/is a .2% power savings on 160 x .68 = 108.8MWH equates to at least $54,400 per day x 30 days per month = $1,630,000 x 12 = $19,584,000 in power cost savings per year."

Wow..and I thought electricity was expensive here in Australia.

By my calculations, that 0.2% savings on 108.8MWh equates to 217.6kWh per day or 6,528 kWh per month. To save $1,630,000 per month, you must be paying almost $250/kWh.

OOPS! Good catch.

Sorry all, I left some critically important information out of the equation when I posted it.

FYI: Our actual power cost is $25 -$68 per MW depending on what time of year it is and how much supplemental power we are generating at our facilities. Occasionally our cost approaches the $138 figure for outside provided emergency power from the grid.

The total savings number should be roughly $1,958,400 per year per plant multiplied by the quantity of plants this size in the continental USA which is 10.

The numbers from the sales rep is nowhere near accurate and very skewed which is why the decision was made to perform our own in-house power study and cost analysis prior to making any decisions.

I suspect that the same scenario is present in most cases such as this wherein the sales reps and consultants are spinning their equipment and/or ideas.

Always do your own analysis as a benchmark for your studies. What I didn't see in this thread was any discussion about the effect on your demand charges. Depending upon the exact timing of your starting load sequence there may be additional money to be saved. Same thing if you have to pay a poor pf penalty. Of course if yours is a "set it and forget" process it shouldn't matter much, but if you do any kind of repetitive start-stop sequencing it may.

You are on-target as usual.

We do experience some demand charges that depend on the power provider requirements but we try to minimize the cost as much as possible.

On every application wherein there are multiples of equipment connected to a common discharge header or mimicking processes that I have been responsible for upgrading, new purchasing, and installation I have included a programmable master sequence controller for scheduling and controlling equipment start-stop as well as mechanical loading to maximizing energy savings and equalize equipment wear.

So far I have not had any problem justifying the cost with a five year 100% payback on investment capital.

I have used several reputable consultants to review my documentation and respond with suggestions, corrections, and/or additions or to submit their recommendations for new equipment and/or process changes with very good success.

OT for using incorrect units.

The best way to reduce power consumption is to switch it off when the rotation is not needed.

Sales rep for what SHOCKHISCAN, Wye Delta starters or some sort of magic box energy saver scam? Sounds like to took the proper approach though.

There seems to be no end to the number of "spinners" out there pedaling their wares and ideas.

Some are so ridiculous that even I can see right through them at the first presentation meeting.

One of the most recent is a pump vendor that has successfully convinced management to change all of our deep well submersible pumps from MV 2300/4160V over to 480V.

The submersible motors range in size from 150HP up to 450HP.

I cannot get the managers in that area to realize the physical increase in pump motor diameter for a given HP size alone will prevent us from being able to install the units into the well casing. (The vendor rep has management convinced his pumps can pump at the required flow with less HP required.)

I also cannot get them to understand the huge cost associated with installing a rather large step down transformer with new switchgear at every site which will drive the installation cost out the roof.

The poor maintenance crew will suddenly have to handle the weight of motor cables from several hundred feet in length up to 2,500 feet in length which will be almost four times as heavy and cost at least twice as much as the MV cables currently being used.

My direct report has given up so he told me to back down and let the vendor drive the bus off the cliff. (This one is going to hurt and most likely cause someone to lose their job before it is over so I am in "CYA all the way" mode which I thoroughly detest.)

Easy to do, show them pictures of the current motors, cabling, and switch gear compared to what they want to buy, then ask them which ones they'd rather work on/ pay for. Make sure you have their favorite donuts available during your pitch (with apologies to Dilbert). Also bring a few feet of the different cables, hopefully even though can figure out that more copper equals higher cost.

I had not thought about the "donut factor". Maybe it will work since nothing else seems to.

Wow... Most likely the spin doctoring was because that particular vendor does not offer MV ESPs, am I right? I've seen that before.

The flip side of that was a project I just proposed for 480V VFDs on some 250HP ESPs where a vendor came in and tried to convince the user that going with 4160V would save them 90% of the energy costs, because the current would go down 90%! The bean counters got all excited about that one, but it didn't get past the first EE. I only heard about it because they started chuckling when I asked how their meeting with that vendor went.

Incidentally, they were using 480V because they do not have any MV qualified technicians on staff, which is a valid consideration in my book. I put in some MV pumps and soft starters on a different project a few years ago and during the commissioning stage when I was training the workers on troubleshooting, they left the room, saying they were not qualified to work on MV, so it was a waste of their time. So the district sent them to MV training, got them certified, then they all came back and demanded a raise.

The vendor does not even know what an ESP or VFD is.

They are a local pump company that does not have any engineering staff and only deals with pump, pump motors, and pump accessories sales & service.

They are using one of their pump supplier sales representatives to do the spinning.

For some reason our management has the opinion that any vendor is extremely more competent than any company employee could ever be.

That has always been my experience too....

• For some reason our management has the opinion that any vendor is extremely more competent than any company employee could ever be.
  

I call it the "Pro from Dover" syndrome (taken from the MASH book and movie, although the movie left out the back story of where that came from).

Here's my version of it:

Anybody from more than 150 miles away is better suited for a job than anyone local, and the further they come, the better they are at whatever it is.

Management, management management!!!!

Politically motivated and haven't got a clue......

Now where did I see that some years ago?

Thats exactly why Sun Microsystems went down (the company I previously worked for before retirement!).

Luckily for me, I got a great package and I was retired when they were still financially viable, just because I started asking all the right questions, but naturally wrong for stupid management of course......it would have been easy to fix IF management had properly understood how the technical world functions, they never do....

It still killed the company within 3 years.....then Oracle simply took them over......out of the frying pan into the fire I feel!! In Europe we called Oracle "'Orrible!"

Rant over!!

Do you know about "The Peter Principle!"?, if not you should!

It sort of helped my head at the time understanding why.....I believe there is a book as well, but I never read that...

See here:- Peter_Principle

Yes I am very familiar with the Peter Principle and it is alive and doing well here in my little world.

I have many times been called into an upper manager's office to explain why I want to spend a substantial amount of funding on a critical facility that the person thinks "we don't even own!"

I understand ignorance but apathy just doesn't compute.

The reason for their ignorance is because they do not get out into the field nor do they do any research to find out exactly what they are responsible for.

Power=VxIxPF. During starting pf is low.

By connecting a power analyser to the motor feeder V,I,pf,W,waveform etc could be recorded accurately during starting and running in star and in delta as well as during transition from star to delta. It is worthy publishing by anyone possessing a unit in a workshop where motors,pumps etc are tested.

And there was I, believing that a motor's power consumption was to the greater extent determined by the mechanical load on it. Silly me!

After deep study of star delta starter and motor connected in star/delta, my confusion has been resolved, Star/delta starter and motor wiring in star/delta connection are different, The power consumption remains the same for both motor connected in star or delta. If we have 10A motors with same specification, both motors will consume same line current either in delta or star motor connection terminal, but phase current in delta connection terminal lesser than phase current in star connected terminal. This concept applies to start/delta motor starter where the FLA from main main breaker up to star delta contactor. The current flows from starter to the motor is 58% from FLA current.

Glad to have been of help.

If the motor's load is such that a motor of <...100KW...> is needed, then it makes no sense to supply it at the lower voltage produced by a <...Star Delta Starter...> operating only in star; the motor may run into overload and stall.

The <...power consumption...> is largely determined by the characteristics of the load. As the load torque goes up, the motor current will increase in order to sustain rotation.

Next thread, please.