3-phase compressor wiring

[mbreen23]

What's the difference between part-winding start and across the line? And why is there a less than one second time delay on the part winding start? Just looking to learn something today. Thanks

[coolwes]

Part wind start is to reduce the current inrush to the motor. It helps prevent dimming of lights etc. by reducing locked rotor amps. Power companies don't like heavy loads draging the voltage down.
A part wind motor is split into two sets of windings, each being half the total horsepower. For instance a 30 h.p. compressor will be wound as two 15 h.p. motors. At start-up you power one set of windings, then 1 second later power the other set. The time delay must be short to prevent overheating the first set of windings. A 15 h.p motor can't carry a 30 h.p. load very long. You see more part wind applications on lower voltages (208/230)because the amp draw is twice that of a 460/480 volt network.

[carriertech1]

Part wind start primarily is to keep starting amperage
to a reasonable amount of amperage. On large equipment your start amps can be 6-8 times you run load amps, which is extremely hard on the motor windings and will cause voltage drop on yor incoming voltage from your utility company. If there is no part wind start the amount of heat generated at start up will break down and damage winding insulator which will lead to a grounded or shorted motor. Part wind starter will pull in first conactor and start at 38% of capacity, second contactor will pull in and bring compressor motor to full load running amperage

[RichardL]

Originally posted by carriertech1

1- Part wind starter will pull in first conactor and start at 38% of capacity.

Sorry....but your Math is wrong on this one....
Part Winding start has a Inrush Line curreent of 65% of LRA on the initial start.

Wye-Delta Start gives a 33% Line current on inrush.

An Auto Transformer tapped @ 65% will give 42% of LRA on inrush.
Secondly, It is the Power Companies that mandate "Incremental start" on in certain areas on motors over a given horsepower. Not the manufacturers of compressors or their motors. As Carrier stated in their 17M steam driven compressors, "Slow starting of the compressor will result in premature bearing wear and early bearing failure due to the hydrodynamics of the lubricating oil"
At Westinghouse years back, we ran "Reversal Tests" on Bare shaft motors to ascertain the best insulating material & methods of secureing the "Surge Ring" on the wiring side of their motors.
100 HP motors were wired to Size 6 contactors with a 10 second Time delay to allow motor to reach full speed, It was then Reversed in direction @ full speed.
One motor that was "VPI" dipped(Dipped in a Vacuum with Alternating DC pulses to wiggle the windings)made over 8500 Full speed Reversals before letting go at the surge ring....Quite a light show there too....

[fingng]

So if I am understanding what you are saying, if I have a part winding start I will have two contactors starting the motor, right? What controls the sequencing of when these contactors close?

What I have done on all of the 3 phase motors that I have replaced is to tie 4 & 7, 5 & 8 and 6 & 9 motor leads together. This I assume is a full winding or across the line start configuration. Could I convert a motor like this to a part winding start, if I had the right start components?

Thanks, Scott

[RichardL]

What I have done on all of the 3 phase motors that I have replaced is to tie 4 & 7, 5 & 8 and 6 & 9 motor leads together. This I assume is a full winding or across the line start configuration. Could I convert a motor like this to a part winding start, if I had the right start components?

Whoaaaaaaa!!!

I am assuming that you then put Power to Leads #1,2&3.."Only".
If so, you have connected the motor for "High-Volts"...and "Across-The-Line" start...
The compressor motors wired like this can be connected "Part-Winding-Start" ONLY on the "Low-Volts" on the nameplate, such as 230/460.
Then.... the Line can be connected on #1,2&3.

For "Low-Volts" along with "Part-Winding-Start" Terminals #4,5,&6 are then tied together and power to 1,2&3 feeds one of the motors and after a brief period, the second contactor energizes thru a TDR(TimeDelay-Relay)and puts power on Terminls 7,8,& 9.
Now we have both compressor motors going. NEMA & the NEC have failed to specify "How Long" the time should be.
Therefore it is perfectly legal to simply bring in the second contactor thru a aux. contact on Contactor #1.
It still satisfies any requirement of "Incremental-Start"

[fingng]

Thanks for the reply Richard and yes, I only hooked power to leads 1,2 & 3. So is what you are saying is that you would never see a part winding start 460V motor? Most of our buildings are 460, 2 are 575 and 3 or 4 are 230. What is the advantage to a part winding start? Is it just lower inrush amperage? If you have sufficient electric service this really shouldn't be a problem. We have an air compressor with a 500 HP motor (460V) and it doesn't dim the lights when it is started, but when some settings on the soft start "somehow" got out of whack it would dim the lights in the whole building and screwed up all of the computers in the CNC machines when starting. According to one meter that we used, it was drawing over 2,000 amps when starting. We put all of the settings back where they were supposed to be and now you just push the button and voila nary a flicker of a light.

Thanks, Scott

[snipe70e]

Our main buss is 480 VAC all supply fan and compressors are part winding start. I have worked in other buildings with 480 VAC and part start windings.
Part winding start lower torque, and lower amps on start up.
Len

[joegrind]

Originally posted by fingng
Thanks for the reply Richard and yes, I only hooked power to leads 1,2 & 3. So is what you are saying is that you would never see a part winding start 460V motor? Most of our buildings are 460, 2 are 575 and 3 or 4 are 230. What is the advantage to a part winding start? Is it just lower inrush amperage? If you have sufficient electric service this really shouldn't be a problem. We have an air compressor with a 500 HP motor (460V) and it doesn't dim the lights when it is started, but when some settings on the soft start "somehow" got out of whack it would dim the lights in the whole building and screwed up all of the computers in the CNC machines when starting. According to one meter that we used, it was drawing over 2,000 amps when starting. We put all of the settings back where they were supposed to be and now you just push the button and voila nary a flicker of a light.

Thanks, Scott

[joegrind]

KEEP IN MIND THAT REDUCED CURRENT STARTING, IS USUALLY MANDATED BY THE UTILITY COMPANY.HERE, IN THE CAYMAN ISLANDS, ANYTHING OVER 20 HP MUST HAVE PART WINDING START. iF YOU CAN PROVE THE COMPS START UNLOADED, THE UTILITY WILL BE A LITTLE FLEXIBLE