Electrical theory

[R.J.C.]

I've come across installs with de-rated neutrals getting hot recently. One fella I was working with insisted we could get away with a half sized neutral because all the (hundreds of) motors were 3 phase and therefore balanced even though every one of them had a VFD and the place was full of CF lamps spewing out harmonics eveywhere. Needless to say, things didn't go too well.

 

[i=p/u]

thats the only sum i know about motors tony, il read on on on and on, some day il be rewinding them and cleaning them

 

[Knobhead]

thats the only sum i know about motors tony, il read on on on and on, some day il be rewinding them and cleaning them

Rewinding is more or less a trade of it’s own. Got to admit it’s something I’d like to have a go at but with someone to stop me making a mess of it.

 

[i=p/u]

i be easy buns after first few

 

[Knobhead]

I've come across installs with de-rated neutrals getting hot recently. One fella I was working with insisted we could get away with a half sized neutral because all the (hundreds of) motors were 3 phase and therefore balanced even though every one of them had a VFD and the place was full of CF lamps spewing out harmonics eveywhere. Needless to say, things didn't go too well.

Over the years I must have put 100’s of 3½ core cables in. I wonder how they are fairing now?
I remember the first VSD panel we bought for a 25KW motor. It was the size of a wardrobe and cost a small fortune!
With the popularity of them now some cable companies can offer neutrals at 1.5 or 2 X phase conductor size to handle the harmonics. The trouble is then shifted to a very unhappy main transformer.

 

[malcolmsanford]

Might find you'll need one of these ..................perhaps not so big

 

[Knobhead]

It’s a long time since I’ve played with a mill motor like that Malc.

We had to get GEC in to replace one winding section. The guy was an absolute animal hammering and crow barring the coil in. Our manager showed up just as we finished putting the motor back together ready for it’s test run. He took me on one side and came out with “I hope you see how careful you need to be with the windings”. I burst out laughing!

 

[malcolmsanford]

Thought that was a mill motor tony, I was thinking more if i=p/u was going to rewind motors he might have need of that drying oven ...............

 

[Knobhead]

Years ago I saw a film by Crompton Motors. It showed the girls in the small motors winding shop, god they were fast. During the war they even delivered motors to peoples homes and they would wind them on the kitchen table.

Wouldn’t like to do rewinds, that smell sticks in your throat for days!

 

[amethyst]

heres a link to a page i justfound, with a lot of useful theory, proably more suited to those studying ONC/HNC ect, but useful none the less

Electrical Knowhow | Technical Publications | Schneider Electric UK?

cheers,
What is Electrical Theory And How does it affects in our society?I really need to clarify this matter in my mind of it really sounds so interesting.

 

[Knobhead]

I have the perfect (American) way to clear things in you’re mind.
Please sit in this chair, sorry the metal back is a bit uncomfortable and the back rests a bit damp. Once my charming assistants have strapped you in to place I will place this saline soaked natural sponge lined metal cap on you head.
I will then explain the impact of technology on you’re worthless and meaningless life.
Don’t worry about the voltmeters you will only feel the first 1200V for 3 seconds the other 600V for 12 seconds won’t bother you at all. But to make sure you fully understand its impact I will repeat the 1200V for 6 seconds and then 600V for a further 18 seconds.

Now where did I leave the salad garnish?

 

[aaslerecruit]

Some interesting material for study there John.