transition starter from star to delta 3

[anitharts]

Hi everyone. I have a 132 kW motor with a star-delta starter. Full load amperage is 230A. I'm still confused about setting the timer relay. can you tell me how long it takes to switch the star connection to a delta motor to work safely? are there any standards regulate this issue?

 

[che12345]

I have the following opinion for your consideration.
"..I'm still confused about setting the timer relay. can you tell me how long it takes to switch the star connection to a delta motor to work safely? are there any standards regulate this issue?"
1. The standard can not determine the time. It depends on the load. However there are standards regarding the trip time of the thermal over-load (e.g. Class 10, 20, 30).
2. Suggestion: Set the the time delay to say 20s. Start the motor and observe the current. Start timing when it starts from a higher value to gradually down to and maintaining at a lower value. If the time from start to the time it starts to lever off takes say 10s. Reset the time delay to 10s + 2s = 12s. After say half an hour, start the motor again, it should be able to perform the expected SD starting.
Che Kuan Yau (Singapore)

 

[crshears]

Generally speaking, transition once line speed levels off and there is negligible further acceleration while in wye.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[LittleInch]

Go with what che said.

I would have said you're looking about the 10 to 15 second mark, but many variables.

Just remember to un load the motor as much as possible otherwise it will not start.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[waross]

I am with cr on this one.
It depends on the application.
Star-delta start may be used to start medium or high inertia loads.
It may be used for very low inertia loads when the utikity demands reduced current starting for motors above a certain size or to linit voltage dip in a plant on a soft supply.
Too much variation to suggest any fixed time.
Do a test start and note the acceleration time.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[che12345]

I would like to submit some additional information four your consideration.
1. It is correct to say that we expect the Speed to go up to say 75-80% during Star, before transfer to Delta. It is observed that the Speed is reflected on the Current. It is simple to observe the Current with a clamp-on meter or the ampere meter on the panel; than to take Speed measurement with a tachometer on the motor shaft.
2. It is preferred/suggested to connect L1 to U1 and V2; L2 to V1 and W2; L3 to W1 and U2 ; for CW rotation. There are other erroneous connections done for the past 75+ years, until being revised recently.
Che Kuan Yau (Singapore)

 

[crshears]

It is simple to observe the Current with a clamp-on meter or the ampere meter on the panel; than to take Speed measurement with a tachometer on the motor shaft.

True; but instead of complicating things by trying to use any kind of temporary tachometer, I'd simplify that and just listen to the sound of the machine, as you'll, unless hearing impaired, be able to discern when negligible further change is occurring. The result should be GE [good enough].

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[waross]

The difference between years of office theory and cr's years of experience actually doing it.
First choice. Sound
Second choice. Ammeter
Third choice. Tachometer? Overthinking it.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[jraef]

4th choice: jettison the 19th century technology of Star-Delta starting and install a Solid State Soft Starter...

No transition time to determine, no transition spike of torque and voltage, no guessing on the settings of overloads and short circuit protection, no rapid deterioration of contactors from incorrect settings, no incorrect reconnection by inexperienced electricians, etc. etc. etc.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[che12345]

"... I'd simplify just listen to the sound of the machine, as you'll, unless hearing impaired, be able to discern when negligible further change is occurring...".
1. True, but NOT always practical in the field. The machines is usually located some distance away from the the control station or the MCC, where the starting command is given; usually by push-button. Relating the sound to the speed is only possible at close proximity to the motor.
2. Observation of the current at the MCC starter panel amperemeter or with a clamp-on meter at the MCC instead of at the motor, is always practical.
Che Kuan Yau (Singapore)

 

[wayne440]

True, but NOT always practical in the field. The machines is usually located some distance away from the the control station or the MCC, where the starting command is given...

A helper and pair of 2-way radios can often make it practical.

 

[Parchie]

Delta changeover can be done when the speed of the motor goes above 90% of its synch speed. By that time, the starting current is just tapering but not near no-load values. Best for you to do acceleration time estimates and set your changeover time from the results of what you get in your estimates.

 

[waross]

Generally speaking, transition once line speed levels off and there is negligible further acceleration while in wye.

At that point, the current will also level off.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[che12345]

"...No transition time to determine, no transition spike of torque and voltage, no guessing on the settings of overloads and short circuit protection, no rapid deterioration of contactors from incorrect settings, no incorrect reconnection by inexperienced electricians, etc. etc. etc".
I have the following opinion.
1. No transition time to determine. NOT true. It is necessary to set the Ramp-up time. Problem/damage may result for a 132kW, if the ramp-up time is erroneously set at say 5s or 30s.
2. No short circuit protection. NOT true. A proper breaker or high speed fuse per the manufacturer recommendation MUST be used in order to protect the SCR etc...
3. Soft starters are generally about 1.5 x the price of a SD assembly.
4. Most in-house technicians are NOT knowledgeable to repair a Soft starter.
5. A SD contactor assembly may last for 30+ years, double full for a Soft starter.
Summary: Soft starter has it advantages and disadvantages.
Che Kuan Yau (Singapore)

 

[crshears]

4th choice: jettison the 19th century technology of Star-Delta starting and install a Solid State Soft Starter...

No transition time to determine, no transition spike of torque and voltage, no guessing on the settings of overloads and short circuit protection, no rapid deterioration of contactors from incorrect settings, no incorrect reconnection by inexperienced electricians, etc. etc. etc.

Fair points, jraef, but many of these can be avoided and prevented without too much trouble, i.e. having electricians color code all wiring before disassembly so as to minimize the likelihood of incorrect reconnection.

Also, there are remote and not readily accessible locations where servicing of newer equipment can be problematic, and going with the simpler and field repairable without specialized expertise and/or customer support is worth considering.

 

[LionelHutz]

Current is the best way to set the transition time. Set to transition as the current drops to around FLA. Otherwise, go by acceleration sound.

5. A SD contactor assembly may last for 30+ years, double full for a Soft starter.

We just had a customer asking if they should update their working soft-starters from 1994 last week.

 

[che12345]

@ Mr LionelHutz
Thank you for your learned statement "Current is the best way to set the transition time. Set to transition as the current drops to around FLA. Otherwise, go by acceleration sound."
I would like to add the following.
For SD transition time
a) we are monitoring the Speed. Transfer when Speed is up to say >75%. The scientific/accurate measurement is by Tachometer, but cumbersome.
b) empirically it is observed that the Speed is reflected on the Current. As an alternative, Current measurement which is easily done instead of cumbersome Speed by tachometer.
c) Speed has NO relationship with the Sound level, which is dependent on the loudness and pitch. It is NOT acceptable scientifically to related the sound level to the speed, in this context . It is true to an experienced person would be able to "gauge" the speed based on the sound. It is unscientific.
Che Kuan Yau (Singapore)

 

[LionelHutz]

a) we are monitoring the Speed.

No, that's not how reality works. I'd bet way less than 1% of wye-delta starter installations have ever monitored motor speed. Few monitor current. Most just go by the motor sound, or just guess at a time setting.

There is a difference in sound between a motor accelerating and a motor running steady state.

 

[crshears]

Speed has NO relationship with the Sound level, which is dependent on the loudness and pitch. It is NOT acceptable scientifically to related the sound level to the speed, in this context . It is true to an experienced person would be able to "gauge" the speed based on the sound. It is unscientific.

"Unscientific?" Really?

Respectfully, I submit that the working human ear, when teamed with a working human brain, is perfectly capable of detecting whether there is any discernible delta f over time.

If this were not so, music would have to be declared both unscientific and non-mathematical.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[LionelHutz]

Transfer when Speed is up to say >75%.

This is wrong too, Transferring at 75% speed would draw high enough currents and cause such a surge that it's hardly worth using the wye-delta starter. The current at 75% speed is typically 75-90% of LRA so transitioning at such a low speed will cause most of the same inrush current and it's associated effects on the power system as just starting across the line would.

You want to transfer in the 90-95% speed range when the current has dropped close to or below FLA.