3ph delta star switch, delta tripping fuse

[T0RN4D0]

Hi, im new here. Looks like a pretty active forum so i'm hoping someone can help me maybe.

Here's my problem. Neighbor just bought a used circular saw with a 10kW 3ph motor on it and asked me to rewire it, because the cable from the started switch to the motor box was all messed up.

Anyways, the delta star switching is done by a simple 16pole switch. First time around i marked all the connections and just duplicated them with the new wire. It worked in star, but the fuse tripped when i switched to delta. I then searched for the switch schematics, took everything apart and wired it according to that scheme. Still, same thing. He only had a 16A fuse, so we changed it to a 25A, didn't help.

I marked where i wired everything and tripple checked it, i think its right. I think i have a problem with phase sequence somewhere, but i'm not sure where and which wires to change.

Any ideas what could be wrong, and which wires i should change to make it work? The input phase sequence (L1, L2, L3) doesn't matter, or does it in this case?

 

[THE DUKE]

Have a look here Motor Starting - Star Delta

 

[T0RN4D0]

I went through that, and everything else i could find related to my problem.
Solved it today. Took everything apart, rewired, checked _everything_, the more i looked at it, the more i was sure everything was OK.

Then it hit me, and i let it run in star for about 15 seconds before switching to delta, and it worked. There was nothing wrong with the wiring in the first place, we just switched it too early every time.

 

[Darkwood]

Im a tad confused 10kw isn't a regular size are you sure irts not 10HP?
I assume you 16pole switch is not pole but Amp?
What is the fusing device used? Is it a mcb (60898)?

If its tripping on changeover from star to delta then it could be a few things but from what you have described i suspect you fusing device is tripping on the changeover spike from star to delta because it is undersized... to give you an idea

- A mcb for a 11kw motor either DOL or star/delta would need to be 63amp (B or C) or a 25amp(d) to ensure the mcb wont trip, this applies to a standard induction motor with a normal start up duty... next size down rated mcb's may hold but tripping may occur occasionally.

This is on the assumption that you have wired it correctly and the motor is ok.

Have you tested the motor prior to energising?


Of course upgrading any fusing device means you may have to calculate if the supply cable, volts drop, zs values all comply before energising the motor but of course you will know this anyway. To note your local regulations need to be complied to and we can't give assistance on here as we are based around the British Standards of BS7671 (amd2).

 

[Darkwood]

Incoming phase sequence will only change the rotation of the motor which could be dangerous as the blade may unscrew and fly off - always be cautious to power saw up first time - either be ready on the stop button or remove the blade until certain.


What are you a student in?

You're undertaking work here you shouldn't be without a qualified Electrician / Engineer to guide you and certainly shouldn't be trying to do this off a forum ... how will you test the supply etc meets disconnection times under fault conditions etc etc this should not be attempted as a DIY project..... im not sure how health and safety work in Slovenia bt you wouldn't be allowed to do this over here without a qualified competent person over seeing you .... i doubt this is the case as you are asking us the questions.

 

[Darkwood]

Any chance of an update ?

 

[onions1066]

Check post #3 darkwood

 

[Darkwood]

How did that sneak in there lol totally missed it... 15seconds sounds very lengthy i suspect it will only have needed a small adjustment but its not unheard off. I have larger systems with run up times half that he's just stated.

 

[T0RN4D0]

Hi, thanks for the replies. I'm not sure what responses you see and when because i'm new and my posts have to be authorized by the mods.

Im sure its 10kW. It may not be common but that doesn't mean they don't exist. (Or the plate is false). I'd attach a picture but i'm not sure i can. And the switch has 16 connections, and i messed up, it's an 8 pole switch. Still struggling with the terms.

The fusing device is a MCB, 3x25A, C rated. Looks like it really should be D rated to cope with the starting surge. It works, but you have to wait for a good 10 seconds before flipping to delta. Seems "a bit" long for a small load, but it works. I don't think there's anything wrong with it and i get over 400V on the motor clamps.

I'm in middle school for energetics.

 

[Darkwood]

It just seems excessive run up time.. is the saw blade driven through gears and or V-belts or coupled direct... also what pole is the motor (speed).