Discuss star + delta connections HELP ME??? in the Commercial Electrical Advice area at ElectriciansForums.net



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Can someone please explain to me how a 3 phase star and delta connection works. I get the fact that the 3 phases are carrying a current and you can get 240 or 400V from them. I have star and delta diagrams in front of me but the ones i am looking at only have 3 lines/conductors whatever you want to call them coming from the red, blue and yellow phases. what i dont get is where does the current come from if I1 ,I2 + I3 are ALL carrying current away to a home or factory?? where is the input o?? it is probably really simple but my lecturer only spoke about it for 10mins last week and the class finished. its driving me nuts!!! please help ma heads bursting:confused:
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  • #2
Hows yer doin wllm, i think you are at a bit of crossed purposes with yourself, but no matter, star/delta is a term that is associated with motors and the there start up, you have a star delta contactor which when energised the motor will start in the star windings of the motor and then after a pre determined time switches over to the delta windings. hence star/delta.
What you are probably looking at is a 3ph/n cable in the street, and usually say no1 house would be on red"old colours" no2 house yellow, and no3 blue, in the old colours, thats when you see a phase gone down in a mains cable, not all the houses go off, every 3rd house would be off say, get it mate, if not say so, no prob.


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  • #3
hi there thanks for trying but ive obviously not explained myself correctly. i am trying to find out how a 3 phase 3 wire star connection and the "seperate" delta connection are wired up? i have the two seperate diagrams in front of me in different booklets. it says they are 2 different ways used for wiring 3 phase used for supplying domestic homes and factorys with power. in the star connection any phase and neutral gives you 230V etc. i hope we are both on the same page now, well im kinda on the page:). its just for instance in the star connection diagram i am looking at there is only one line leading away from each of the 3 branches of the star, if these are used to wire domestic homes and all 3 of the line currents are taking current away from the star to homes then where does the current supplying them come from??? if there was another line bringing current into the star it would make sense to me but there isnt. hope you can save the day


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  • #6
thanks.i see it now. i somehow got into my head the star and delta connections were made at your home or factory. now i see the line currents come from a transformer. my curse has been lifted.


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  • #7
Think you need to divorce star and delta connections from your thoughts about supplys.
Lines into homes will usually only come from one phase and N. and in commercial premises three phases and N. Star and delta have no relevance to a supply.
3Ph. Motor connections are made within either the motor or starter.
Single speed Motors are almost always wound with six wires terminating in the terminal box, typically to terminals marked u1,u2,v1,v2,w1,w2. a star connected motor is connected by linking the three terminals u2,v2,w2. with the three supply lives going to u1,v1,w1.
Delta connection is made by linking u1 to v2.- v1 to w2. and w1 to u2. with the 3Ph. supply going to the three links.
Reversing any 2 of the 3 input supply lines will reverse the motor.
Most modern small horsepower 3Ph. motors are wound to run on 380/440v connected star and 220/230v connected delta.
Some larger motors start in star and run in delta.:)


the high voltage side of the suipliers transformer will be configured in the delta arrangement. The low volt or 230/400volt consumer side of the transformer will be configured in the star arrangement. the cente point of the star being neutral. . . .

Andy Smith

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  • #9
supply trani delta || star ----------------------------L1 this is what u get as a consumer
star ----------------------------L2
star ----------------------------L3
mid ----------------------------N

as lurch has pointed out the supply transformer is delta on one side and star on the other. Most pictures do miss this fact out. the delta (or primary side of teh transformer) is on the end of the geni and the star (secondary side) is bit that we get at the end of the supply cable - simply put but with a few step down tranis inbetween
You could get anyone of the star phases or a combination of depending where you are :)


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  • #10
you do not have a facility to obtain a neutral in the delta configured transmission,that is why it is changed to star
at the consumers supply to configure a 230v spn supply.


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  • #12
Old thread haha


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  • #14
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