Phase Rotation??
- Thread starter Gastel
- Start date
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"AC Theory 3 phase"
You'll get lots like this http://www.elect.mrt.ac.lk/EE201_3phase_sym_comp.pdf
"AC Theory 3 phase"
You'll get lots like this http://www.elect.mrt.ac.lk/EE201_3phase_sym_comp.pdf
Cheers Taylor, Ive googled it but I was looking for a simple explanation from an experienced sparky,I have an interview for a permit to work next week & one of the questions is on phase rotation, I'm just looking to memorize a simple answer, any help would be appreciated.
H
holmslaw
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Take a pill holm, its the simplified wording im looking for not the overall understanding, ive already sat 5 exams & 3 practicals to get to this point...i'm a gas engineer who's being put thru an intense course which allows me to work on electric meters, cheers for the concern though 
H
holmslaw
..
the generator spins one way and makes 3 phase..
to get the motors to spin the same way the 3 phases have to be the same way..
to get it to go backwards, the 3 phases have to go backwards..
to get the motors to spin the same way the 3 phases have to be the same way..
to get it to go backwards, the 3 phases have to go backwards..
H
holmslaw
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H
holmslaw
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I will try to explain.
If the phases are connected brown to U1, black to U2, and grey to U3 the motor will rotate in one direction swapping any two so for example brown to U1, Black to U3, and grey to U2 will reverse the direction.
We use a phase rotation meter which is a very slow revving motor so we can see which direction the phases are rotating.
However using the meter can land one with a problem as they seem to be rare items and often electricians don't check the sockets they install.
We had a problem with concrete placing booms in Sizewell 'B' Power Station and it can easy spread throughout a site. One cable was laid wrong way around so the at that time red, yellow, blue did not match and twisting the cores in a cable joint would not be small enough for the shells to fit. So the phases were reversed. This was not a problem to start with as next joint swapped them back. However it was shortened removing second joint.
Called out to a boom not working the electrician simply swapped the two phases but not at the WMDU but at the plug. Once moved again the next electrician selected a different plug or socket so the problem started to spread throughout the site.
By putting a plug on the phase rotation meter we were able to quickly survey the whole site and correct all extension leads and find problem WMDU and change the phases there too.
Pumps just don't work backwards but of course some plant can completely destroy it's self if run in reverse so very careful control is required. This is especially important when paralleling two generators.
Connecting Brown to Black, Black to Grey and Grey to Brown would still produce correct rotation so keeping phases correct colour is not same as getting rotation correct.
There are some areas of Liverpool which have the phases swapped even today after they were connected incorrectly during WWII and each firm swapped back at their premises so first one has to work out the normal and not jump in and set Brown, Black, and Grey as it may be wrong for area.
Since I do have a phase rotation meter I always test and if reversed I always advise the client of the fact.
If the phases are connected brown to U1, black to U2, and grey to U3 the motor will rotate in one direction swapping any two so for example brown to U1, Black to U3, and grey to U2 will reverse the direction.
We use a phase rotation meter which is a very slow revving motor so we can see which direction the phases are rotating.
However using the meter can land one with a problem as they seem to be rare items and often electricians don't check the sockets they install.
We had a problem with concrete placing booms in Sizewell 'B' Power Station and it can easy spread throughout a site. One cable was laid wrong way around so the at that time red, yellow, blue did not match and twisting the cores in a cable joint would not be small enough for the shells to fit. So the phases were reversed. This was not a problem to start with as next joint swapped them back. However it was shortened removing second joint.
Called out to a boom not working the electrician simply swapped the two phases but not at the WMDU but at the plug. Once moved again the next electrician selected a different plug or socket so the problem started to spread throughout the site.
By putting a plug on the phase rotation meter we were able to quickly survey the whole site and correct all extension leads and find problem WMDU and change the phases there too.
Pumps just don't work backwards but of course some plant can completely destroy it's self if run in reverse so very careful control is required. This is especially important when paralleling two generators.
Connecting Brown to Black, Black to Grey and Grey to Brown would still produce correct rotation so keeping phases correct colour is not same as getting rotation correct.
There are some areas of Liverpool which have the phases swapped even today after they were connected incorrectly during WWII and each firm swapped back at their premises so first one has to work out the normal and not jump in and set Brown, Black, and Grey as it may be wrong for area.
Since I do have a phase rotation meter I always test and if reversed I always advise the client of the fact.
Why don't you ask your training body for some more training so you can simply explain phase rotation your self?
We have done, got the interview this week though so thought I get a heads up using the net first for more info, we have been given books but I explained to the tutor there is no mention of phase rotation in them hence why I'm on here, I appreciate this is simple stuff for the leccys out there but I aint a leccy!!
H
holmslaw
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I am very vocal on this forum with regards to people who attack posters for asking questions.
However, in this case, you are attempting to gain a job working with something you do not understand, and you have stated you don't wish to understand it, merely find a sentence you can memorise and use to blag your interviewer.
I'd also be fascinated to hear which electrical theory books you've been studying that don't mention phase rotation.
However, in this case, you are attempting to gain a job working with something you do not understand, and you have stated you don't wish to understand it, merely find a sentence you can memorise and use to blag your interviewer.
I'd also be fascinated to hear which electrical theory books you've been studying that don't mention phase rotation.
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