Incorrect phase sequence of a three phase compressor

[Ollectrical]

Hi there, I'm wondering if you gentlemen would so kind as to bless me with your wisdom.

Just to confirm, this is a question that I am attempting to answer as part of 304 of the 2365, so a point in the right direction with my answer would be mightily appreciated.

The exact question is "Explain the effect of incorrect phase sequence to the three phase compressor"

If I have a three phase compressor running with incorrect phase sequence, am I right in thinking the compressor would start working in the wrong direction, causing production to be going backwards, internally tripping shortly after startup? Or would it simply burnout, dependant on the type of compressor?


Many thanks in advance

 

[Pete999]

It would cause Electrically the motor to run the wrong way, however without knowing the nature of the production / use of the motor its hard to tell what the consequences would be, swap two of the phases over this should solve the problem theoretically.

 

[happysteve]

^^ wot Pete said

You're definitely on the right lines, Ollectrical. If you've not been given any more information (e.g. in the scenario described at the start of the task, or in the plans) then that's about the extent of what you can say.

A compressor might not be linked to the direction of production - but you're right in thinking it (the compressor itself) will go the wrong way (or try to!) and that at the very least it won't be doing what it's meant to do, and at the worst it might be damaged, and it might cause other things to be damaged too.

The aim of the questions is to allow you to show your knowledge of inspection and testing, and knowledge of the consequences of not correctly applying that knowledge in the field.

 

[GMES]

I suppose you could always say with it being a compressor that it would not build up pressure if the phase rotation was going in the wrong direction.

 

[Ollectrical]

Thank you very much for both of your responses, it's been such a great help. The only information supplied is "32A TP-N Compressor". I find the C&G questions to be so broadly written at times

If I were to test for correct phase sequence throughout an installation on a three phase system, am I correct in thinking the points that would require testing would be:

The origin of the supply
Main switches associated distribution boards
sub main distribution boards
three phase earth socket outlets
three phase neutral and earth socket outlets
three phase isolators
three phase motor starts
three phase machine supplies and switchgear

I have seen this on p465 of the C&G level 3 textbook, but can't help feeling like this is a great deal of areas to test, I take it this is required to ensure that the correct phase sequence has been used at every point of the installation associated with the compressor? I can't help but feel this is a great deal of areas requiring testing when the compressor is being supplied from a DB to a 32A switched fuse disconnector?

Any assistance would again be greatly appreciated

Many, Many Thanks

 

[Pete999]

The origin of the supply would be the best place to start, you could check everywhere, but if the compressor motor is running the wrong way swap the phase over at the motor connections, phase sequence should be correct throughout the distribution of the installation, as I mentioned earlier it's often at the end user were the sequence is around the wrong way, swap it there not at the DB.

 

[happysteve]

The origin of the supply would be the best place to start, you could check everywhere, but if the compressor motor is running the wrong way swap the phase over at the motor connections, phase sequence should be correct throughout the distribution of the installation, as I mentioned earlier it's often at the end user were the sequence is around the wrong way, swap it there not at the DB.

Ah, let me just stop you there, Pete.

What you're doing, is you're using your knowledge, skills, and above all many years of practical experience in the real world to try to answer a City & Guilds question.

Do you see where you went wrong?

It's all very well passing on excellent practical knowledge to the trainees, so that they know what to do in Real Life, but come on, that's not going to help them with their assignments now, is it?!?

Ollectrical: I can see you're getting the hang of this. Find the relevant page in the text book (or SmartScreen handouts). Cut and paste. Job done.

In all seriousness, though, you should use all the information they give you: question, scenario description (beginning of the assignment) and the plans. If the question relates specifically to the compressor, then (out of the list in the text book) you would select/modify slightly the relevant locations. If they are asking generically, you might tailor your answer to the three phase loads in the fictitious location given.

Keep at it - and I like your style, having a good pop at it first and asking for advice. Be aware though that others may be doing the same assignment, so if you end up with basically a model answer, then others could just be lazy and cut and paste the answers from here.

Although there are "one or two" college lecturers on here who I'm sure would notice if they were in their class. Just sayin'