Saw tooth

[ptonsparky]

I was recording the current on a 15KVA 480 single phase xfmr. The current wave on the secondary side peaked with an image similar to a sawtooth. What type of load would I be looking for? I will find it eventually when we update the feeder. About 26 amps.

 

[brian john]

I was recording the current on a 15KVA 480 single phase xfmr. The current wave on the secondary side peaked with an image similar to a sawtooth. What type of load would I be looking for? I will find it eventually when we update the feeder. About 26 amps.

15 kva cannot be many thiings on it, some loads with switchmode power supplies, PC's ETC.....

 

[LarryFine]

The current wave on the secondary side peaked with an image similar to a sawtooth.

Ramp up and quick drop, or quick rise and ramp down? Over what time period per "tooth?"

 

[ptonsparky]

Very sharp rise above peak, sharp drop then back up to sine. 2 per cycle. Doesn't look like the PLC loads I have seen in the past. I picked up the equip today and will try to send a picture later.

 

[brian john]

Post a pic.

 

[ptonsparky]

Post a pic.

Saved trends of current readings , didn't manage to save the sine wave pict. Dang.

To be continued...

 

[gar]

100827-2107 EST

ptonsparky:

If it truly turns on with a very fast rise, and a somewhat slower fall, then it is probably a load with an SCR or equivalent device that is turned on at the leading edge of the current, is charging a capacitor, and turns off when the current thru the SCR drops to near zero. This is approximately when the supply voltage equals the capacitor voltage. This will be somewhat near the source voltage peak.

If it were simply a diode rectifier feeding a large capacitor with a resistive load that produced only a small amount of capacitor voltage ripple, then the leading edge would be slower and nearly like the trailing edge. Generally this looks a little like a short duration half sine wave perched on top of the other normal AC current from other resistive loads.

You are probably looking for some sort of electronic equipment.

.

 

[76nemo]

Is there some sort of problem, or are you just inquiring?

 

[hurk27]

UPS systems, forklift battery chargers, switch mode power supply? sounds like a AC to DC conversion that will peek then ramp down twice per cycle.

 

[ptonsparky]

Is there some sort of problem, or are you just inquiring?

No known problem, or at least one that stands out. We will be replacing an undergound feeder that comes from this xfmr to another building. Typical for older installs it just does not meet todays standards. Maybe not even when it was done. We were checking to make sure the transformer was not being overloaded (primary side fusing only) and happened to notice the "spike" at the top of the current sine wave and another equal to it 180 deg later. I have not looked at the primary side (doubt that it will show anything) but will when I get back from Dove hunting in a week or so. Dang trip to Wyoming is getting in the way of work.:grin:

As we disconnect things I will isolate the problem.

 

[ptonsparky]

Sine wave that, hopefully, is attached was the result of several different loads. The single load that changed it the most was a protien analyzer.

 

[ptonsparky]

Couldn't figure out how to send a better file.

No single load came close to the resultant current sine wave. We shut down loads until the wave form became similar to what I have seen with ballasts. The office computer and printer had no significant change.

 

[robbietan]

probably a loose connection somewhere, based on the waveform. during peak load, this is what happens