3 phase motor test

here we've got a motor and you can see that there's six ends of wire and each of those ins belongs to a winding okay so as we've seen we've got v1 w1 u1 u2 v2 w2 so but we've no idea which of these to form one complete winding so of course we need to find out we also need to check the resistance of the windings is pretty much the same to ensure that the motor is working properly and well-balanced and for that we need to use a low resistance own meter the important thing is before we start to make sure the the meter is accurate and that it's actually working correctly and of course very importantly we've zeroed the leads zero zero in the leads is something that needs to be taken pretty seriously because if we look at these crocodile clips we've got one piece which is this piece here which moves and we've got one piece here which is connected directly to the lead now if I'm zero zero in the leads what I'm actually doing is measuring the resistance of these leads and the connection of the crocodile clips if I connect it to the two moving parts obviously the joints here are going to offer a higher resistance so we're not zero the leads I'm probably going to zero them too much so we're not taking a reading of a resistance of a winding the resistance is going to come out less than an actual ease because I've taken off too much resistance for the leads so we're not zero the leads I need to make sure that I get the solid bits of the crocodile clips touching each other push the ends together as tightly as you can just to make sure you've got a good connection and if there's any dirt or anything inside the crocodile clips you push through that these are fairly new so I'm not going to have too much of a problem with this instrument we can see that these leads have got a resistance value of 0.3 7 over now if I just push the button this little symbol comes up in the bottom left-hand corner that tells me that the instrument is now zero and any measurement I take will be less the value of the leads okay so the next step for me really is to identify each end of the windings it really doesn't matter how I identify them I can call them whatever I like but I do need to find each end so first of all we'll say we're going to look for the end of winding W all I need to do is connect one end of the khakha dial clip tightly to one end of a winding and then between bit of luck or got it first time so between two ends so this the red and the green are the ends of W winding so we've got W 1 W 2 so and the resistance value is 1 point 8 5 ohms so I'll just mark these or even just for now twist them together so that I know which ones are which I can then move on and do the next winding so hopefully I'll be just as lucky again not this time so that's clearly those two aren't connected that one is and lo and behold I've got exactly the same reading again 1.85 which is telling me that that's a really good value okay that's a good reading they're both the same so I need to identify those two and make sure I don't get them lost so the easy way really is just to try and pull that out so twist it together and now I know that those ends go together that could be W that could be you and now I just need to identify that v is going to be the same resistance so same process make sure it's nice and tight touch it together 1.85 so this really is a good mode so the resistance of the windings are exactly the same and I can now proceed to connect it up and no full weld and it's going to work perfectly now I've connected the motor just six individual terminals to start with and really what I want to do just to be absolutely sure that I've not made a mistake is just check that I've got the correct things so on this terminal block this is w 2 this is w 1 so we know they should be together so if I'll join them together I should get a read in and they're together they all go on to V 1 and V 2 again take a reading close enough so I know I've got the right winding now 2 u 1 and u 2 are going close enough so I know I've got the right warning now what I need to do is connect the motor into star if I wanted to connect this motoring Delta I would need to run 6 wires up to a motor starter and inside the motor starter there's contactors that change from Delta 2 star which we'll look at in another video if we want to connect to motoring 2 star all I need to do is find three ends of the windings and join them together in the motor terminal block that's fairly easy because all I need to do is link or the v1 w1 u1 together or could you even use v2 w2 and you two together whichever way I'll do it it really doesn't matter so this motor nail is connected in star and for that to run all I would to run properly all all we need is to connect three phases l1 l2 l3 to those three terminals and it would run perfectly well the next thing I need to do of course to make sure the motor is serviceable is do an insulation resistance test because it's a motor and it's quite a big motor we want to check the quality of the insulation over a period of time really so just a a quick insulation resistance test really isn't suitable for a motor that's in continued use we need to do what's called a polarization test on the motor and for that we need to do a test for one minute and record the readings and a test for 10 minutes and record the readings and then do a small calculation by dividing the readings we've got after one minute into the readings we've got after 10 minutes so we'll do the test first and then we'll talk about what the readings represent a bit later okay so before I start the polarization test what I really need to do is just earth all of the windings simply to earth just to make sure they're completely discharged okay that's very very important once I've done that I connect the tester so connect it to a good earth push the button lock it so it tests for one minute so we can see now that's the reading after one minute we now need to wait a further 10 minutes to see what the reading would be after that and not explain what happens in a moment or two but first of all we'll white our 10 minutes and see what reading we get the first reading we got was 2.1 and then after 10 minutes we ended up with a reading of 7.2 what we need to do now is divide the reading that we got after 10 minutes by the reading that we got after 1 minute and the value needs to come out greater than 2 means the motor is serviceable if it's greater than 3 or even 4 or 5 it means the motor is in excellent condition the windings the varnish around the windings or whatever insulation Aries is in really good condition so well just do a quick calculation on the board just to find out what the values actually are and that's our polarization done when we carry out a polarization test really what we're testing is the insulation and the reason we need to do it over a period of time is because it takes a while for the insulation molecule molecules to polarize we look at this this would be say a winding in a motor when it's at rest with no current flowing through it we can see that if we pass current into this it can find paths through here fairly easily so after one minute the molecules of the insulation would be just randomly placed so the insulation it's got lots of paths for the for the current to flow through it takes a little bit of time for the molecules to polarize so that's what we need to do a test for 10 minutes because after 10 minutes the molecules will polarize and they're facing in the same direction and they offer more resistance for the current to pass through so that's what we need to do the test when we did the test the readings we got after 1 minute was 2.1 and after 10 minutes was 7.2 so I need to divide the 1-minute test into the 10 minute test and see what the value is value comes out at 3 point 4 2 anything above 2 the motor would be okay above 3 between 3 and 4 the motor would be in good condition and anything above 4 the motor would be an excellent condition and as you can see this is a good motor and all of the tests we've done show that to be correct as well you

Channel: chriskitcher

Views: 1,420,806

Rating: 4.7232575 out of 5

Keywords: 3 phase motor connections, 3 phase motor test

Id: FUjZwMMoltQ

Length: 10min 57sec (657 seconds)

Published: Mon Dec 14 2015