Harmonic Solution Idea

[jktwn]

We are having problems in the field with drive trips, fuses blowing,etc caused by high level 5th order harmonics on our lines. With over 1000 6 pulse vfds installed and little or no filtering on the drives, the voltage distortion is really bad.

The thought is to have half of the sites pole top power transformers rewired from delta-delta to delta-wye to create a sort of area wide 30 degree phase shift on 50% of the distribution load and hopefully cancel out that troublesome 5th.

Was wondering if anyone had tried this before and seen it work in practice.

 

[Skogsgurra]

Are your problems concentrated to the LV side or the (assuming) 4160 V side?

The 30 degrees phase shift will not do much to improve the LV side situation, but it will definitely be a good thing to do for 4160 V distorsion.

So, if you have the problem on the 4160 V side - just do it. But if problems are on the LV side, find other solution.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[jktwn]

Problem is on the distribution (12.5KV) lines. All of the individual 480V vfds are working together to corrupt the grid PQ.
Any new drives added automatically are subjected to the harmonics.

 

[Skogsgurra]

OK. Then your 30 degrees idea will work very well.

It is being done with larger drives by using double secondary windings with 30 degrees phase difference (one Y and one D winding). Sometimes even with four 15 degrees shifted windings.

As I said, just do it!

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[Skogsgurra]

I need to add one thing; it is often good to have one of the windings in delta. That is because the triplens need a delta winding to 'circulate' in. So, make sure you either have D/D or Y/D. Y/Y will produce lots of third, ninth voltage harmonics.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[stevenal]

So if you rewire a 480 delta winding to wye, you'll have 831.

 

[waross]

You may have to purchase new transformers with 277V secondary windings to get 480V wye.
A previous discussions:
Harmonics and VFDs
thread237-205555

Alternately you may be able to do some phase shifting on parts of the 12.5KV lines.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Skogsgurra]

Oh, Bill! That thread...

Threadful, I would say

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.