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?

 

[waross]

Transfer at the greatest possible speed. That is when acceleration stops.
Detectable by ear or by current monitoring.

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

 

[Parchie]

@waross,
That's a better way of saying it.
But, like manually synchronizing a generator unit, you would turn the CB switch knob just when you see the synchro hand nears the 12 o' clock position, not after.

 

[crshears]

But, like manually synchronizing a generator unit, you would turn the CB switch knob just when you see the synchro hand nears the 12 o' clock position, not after.

???

Motor type hasn't been specified in OP, but I neither thought of nor saw any use of a synchroscope in SD motor starting.

CR

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

 

[Parchie]

@cr,
Please take note of the use of the word "like". That means, it is not the thing, it is just "like" in plain English.

 

[crshears]

Gotcha.

CR

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

 

[waross]

The consequence of a late closing of a generator breaker are much more severe.
It may result in mechanical damage and currents in excess of normal fault currents.

Late transition of a star-delta starter results in some extra heating which may be acceptable, especially for a single start.

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

 

[Parchie]

We did have lots of damaged contactors that were traced to wrong setup of transition timing. The worst situation was when the arc chutes themselves helped in the destruction, the chutes accumulated previous debris, the contact arc sustained when switching happened.

 

[waross]

If the gear is setup so that the delta configuration leads the wye configuration rather than lagging it, the performance will be affected. Mechanicalshock and electrical transients.


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

 

[che12345]

@ Mr Parchie (Electrical)7 Jun 24 03:15
"..We did have lots of damaged contactors that were traced to wrong setup of transition timing..."
Please advise what is/are the root/main cause. Following are some example.
a) transition time is based on Current?
b) transition time is base on Sound?
c) transition time is too short, while the motor is speeding up say around 50-60% rated speed, while the current is still at high level.
d) transition time is too long, after reaching say 90% rated speed, while the current has gone down?
e) transition time is too short, motor speed remains at say 50-60% rated speed; while the current remains at high level? [This is the case that the motor is undersize]
f) start/delta transition timer reset time is too short (<50ms) that causes short circuit on the contactor during transition?
g) no mechanical inter-lock between the Star and the Delta contactor?
h) others...
2. Please advise how to set the transition time.
Che Kuan Yau (Singapore)

 

[che12345]

"...If the gear is setup so that the delta configuration leads the wye configuration rather than lagging it, the performance will be affected. Mechanicalshock and electrical transients".
I have the following opinion.
1. The gear/contactors set up does NOT determines the delta configuration leads the wye configuration rather than lagging it.... It is the wiring connection from the starter to the motor windings.
2. In Europe/IEC world, LV motors having 6 wires terminated on terminal block, where connection in Star, Delta or Star/Delta is possible at the field.
2.1 In US world, NEMA motors usually having 3 leads, where start/delta configuration at the field is IMPOSSIBLE. There are other formations on the market.
3. In Europe/IEC world, all major starter manufacturers had revised their wiring connection some 25+ years ago, after proven that the erroneous "standard" SD connection for the past 100+ years !. This is NOT so in the US world.
4. The revised Delta connection for CW rotation per IEC is L1-U1-V2; L2-V1-W2; L3-W1-U2 . There are other possible connections.
Che Kuan Yau (Singapore)

 

[Parchie]

@che,
The only way you can be sure the motor is very near it's rated speed is to do a motor acceleration time simulation. There are softwares that offer to do those. But you can calculate yourself using the well-extablished motor equations.

 

[che12345]

@ Parchie (Electrical)9 Jun 24 22:25
"..The only way you can be sure the motor is very near it's rated speed is to do a motor acceleration time simulation. There are softwares that offer to do those. But you can calculate yourself using the well-extablished motor equations".
I have the following opinion.
1. Use a tachometer take measurement on the motor shaft. It cost very little but achieve very high accuracy.
2. Computer software produce "theoretical values" (not the actual running value at the field). The software and correct data needed to set up is usually cost prohibitive. Unless you are a big timer, regularly involved in commissioning big motors, or where cost is of no consideration.
Che Kuan Yau (Singapore)

 

[waross]

I have to wonder how many of our posters have actually started a large motor.
The old compensators we used to use for high inertia motors depended on the the operator going by the sound of the motor to make the manual transition from auto-transformer to DOL.
They did have a current operated safety solenoid.
On the side of the compensator was an iron handle about three feet long.
To start the motor the handle was quickly and firmly pulled back.
That started the motor on the auto-transformer.
When the motor had accelerated enough, the handle was rapidly pushed forward (actually, slammed forward) to change the connections from auto-transformer to DOL.
If the current had not dropped enough the blocking solenoid stopped the travel half way.
That would jar your arm up to your shoulder.
The operators quickly learned to properly judge the proper speed for transition.
Why did we slam the handle back and forth?
The copper contacts were operated directly by the action of the handle mechanism.
The faster the motion the less arcing.
Eventually, an electrician would spend most of a Sunday shift stripping down the compensator and filling the copper contacts to remove the pitting and arc craters.
After a couple of rebuilds, they contact set would be completely replaced.
The faster you slammed the handle, the longer you could go between rebuilds.


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

 

[LionelHutz]

But you can calculate yourself using the well-extablished motor equations.

The equations I've seen are rather poor and not accurate.

 

[che12345]

@ Mr Parchie (Electrical)9 Jun 24 22:25
1. I am still looking forward to your learned advice on the questions I had raised on 7th instant, on your long bad experience "We did have lots of damaged contactors that were traced to wrong setup of transition timing...".
2. Your kind learned experiences on the root cause would certainly be appreciated and be beneficial to all the readers.
Che Kuan Yau (Singapore)