Hi With a part wound semi comp with 50/50 windings does it matter which winding is supplied first.
Regards Bernard
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Hi With a part wound semi comp with 50/50 windings does it matter which winding is supplied first.
Regards Bernard
hi bernardQuote:
Originally Posted by bernard
not being a qualified electrician or motor winder, my first thought is you are on about three phase where L1 L2 L3 must go to there corrisponding terminals on the compressor, hope this is of some help:confused:
I'm sure you mean "part winding start". In this application your three phase motor contains windings that can be wired in a few different configurations. For part winding start it does not matter which winding you use for starting, however, please insure that the windings are phased the same.
Chill
Hi This as I thought however was advised differently the other day.
Has anyone come across 60/40 and what other variations is there and why.
Regards Bernard
Hi,Bitzer have part windings 60/40 and in practice I didnt have problem with starting of this compresor.The main problem on compressor start is can the first 60% of electrical power rotate the mass of rotor.The answer is yes.On Copeland is 50/50 but the mass of rotor is significal lower then on Bitzer so ther are no preoblem.
If Bitzer firs starts with 40% the compressor windings would burn out in time becose of great load on startings.
The answer for first question is 50/50 part winding dont need sequence for start.It is inrelevant wich kontactor starts first.
Best regards,
Renato
Quote:
Originally Posted by bernard
In a word - No.
Both windings should be identical, and wound on the stator so that they operate as a single motor when connected in parallel. In a three phase motor of this type, there is no ?start? or ?run? winding. This is a method of direct-on-line starting for induction motors that is popular in the USA and avoids the complexities and costs of star/delta.
The control circuit will have two contactors, one for each winding, and a short delay timer, about half a second, that delays the energising of the second contactor. The intention is to reduce the starting inrush current by spreading the time.
However, the control circuits will have been marked to show each ?half? and most compressor terminal plates will have six terminals divided into two lots of three, marked A & B or 1 & 2 as appropriate, so that the two parallel circuits are segregated.
What is crucial, if you disturb the supply wiring, is that you get the 3 phase supply to each half-winding arranged in the same order and that the compressor rotates in the correct direction. The two windings arranged in opposite rotations will result in a mighty bang and much lamentation.
WHATEVER YOU DO, DON'T MIX UP THE CONNECTIONS!
I have never come across a 60 / 40 arrangement - there doesn't seem any point to my thinking, but there may well be some out there.
The only other alternative start method for a medium sized induction motor is true star / delta. Soft start and resistance / timing are different issues.
Good luck
.
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Hi Thanks for the replys this site is GREAT
Bernard
Bernard,
By coincidence, USIceman has posted a link yesterday to an American web site that has an explanation of part wind starts.
Worth a look.
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I remember going to a site with 20 carriers on a roof top that the electricans had wired up, on my arrival they told me there were 6 compressors faulty! Further checking showed that all 6 cables to the compressors were in red with no identification at all, and they were crossed! what a job and a half to sort through that one.
This is a new one for me also. The only thing I can think of is the the motor load has some different starting torque requirements. Possibly the speed/torque curves for the compressor are such that the motor requires this. Therefore, the motor capability must be equivalent to match the speed/torque requirements of the compressor.Quote:
Originally Posted by Argus
Renato RR said a similar statement. It is usually dependent on the mass at rest being accelerated to a certain speed within a specific time.
So apparently, the Bitzer compressors have some requirement for the 60% winding being first to generate sufficient torque to start the compressor.