harmonics on a delta system

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craig65

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I have the loads as balanced as I can on the delta side
A phase 43 B phase 39 and C phase 46.
On the Wye side A phase is 64 b phase is 110 c phase 86..
when you add them up the total are close +/- 1 amp.Everything I have been tought about transformers says if you have 50A on the low side you should have 25A on the high side. This not the case here
Could harmonics from the balasts have something to do with it?
 
beanland

beanland

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Location
Vancouver, WA
Power Factor, too

Power Factor, too

The currents you measure are magnitudes but in reality they also have phase angle. So, part of the issue may be power factor on the phases. Remember, two 20A currents, one purely leading and the other purely lagging add up to nothing.
 
richxtlc

richxtlc

Senior Member
Location
Tampa Florida
Did you read any current in the neutral. A quick graphic representation shows about 40 amps at 33 degrees in the neutral, I may be off a little.
Also are you using a true RMS meter to take these readings?
 
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craig65

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richxtlc said:
Did you read any current in the neutral. A quick graphic representation shows about 40 amps at 33 degrees in the neutral, I may be off a little.
Also are you using a true RMS meter to take these readings?
Click to expand...

There is no neutral, it's a 120/208 wye to 480v delta
the load is on the delta side.
Used a digital clamp on amp meter...not true RMS
 
richxtlc

richxtlc

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Location
Tampa Florida
Harmonics should not pass through the delta, the higher frequencies would circulate in the delta causing it to increase in temperature and possibly overheat.
Are the ballasts for the lighting balanced on each phase? I did some calculations without the neutral and with 43 amps on A-phase (line) the phase current in the delta would be 24.8 amps (43/sqrt3). with a step-up ratio of 4:1 (120/480) the phase and line currents in the wye would be 99.2 amps vise the 64 amps that you read. The same discrepancies exist with B- and C-phases.
Without using a true RMS meter you will not know if there are any harmonics in the secondary causing the discrepancies in the readings.
 
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craig65

Member
richxtlc said:
Harmonics should not pass through the delta, the higher frequencies would circulate in the delta causing it to increase in temperature and possibly overheat.
Are the ballasts for the lighting balanced on each phase? I did some calculations without the neutral and with 43 amps on A-phase (line) the phase current in the delta would be 24.8 amps (43/sqrt3). with a step-up ratio of 4:1 (120/480) the phase and line currents in the wye would be 99.2 amps vise the 64 amps that you read. The same discrepancies exist with B- and C-phases.
Without using a true RMS meter you will not know if there are any harmonics in the secondary causing the discrepancies in the readings.
Click to expand...

the Wye side of the transformer is the line side the delta side the load. The original problem was extreme overheating on the Wye side due to an unbalanced load on the delta side. The lighting load is now balanced as best we could as I mentioned earlier, what confuses me is the disproportionate readings phase to phase, but when you add them up the total load is within 1 amp on both sides.
:confused:
 
beanland

beanland

Senior Member
Location
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Overheating - Grounding Bank

Overheating - Grounding Bank

A grounded wye to delta transformer will act as a "ground transformer" or "zero sequence" source. You said the 208Y/120V is the source and the 480V delta is the load. If the voltages on the wye side are unbalanced due to loading on the 208Y/120V side, there will be current circulating in the delta (even with no load) that can cause the transformer to overheat.

Basically, the transformer tries to force the 208Y/120V system into balance by moving current from one 120V leg to another through the 480V delta. This could be the issue!
 
wirenut1980

wirenut1980

Senior Member
Location
Plainfield, IN
Look at the current unbalance on the delta side - 8.6%. Now compare to the current unbalance on the wye side - 27%.

I think this supports beanland's idea. The fact that the currents in the wye side are larger than they should be also supports this idea.What are some spot measurements of phase to phase voltage on the wye side?

Leaving the neutral ungrounded should rectify the problem.
 
beanland

beanland

Senior Member
Location
Vancouver, WA
Unground the neutral

Unground the neutral

I agree, the fix is to float (insulate and isolate) the 208Y/120V neutral. We do this all the time with transformers on the utility system.
 
brian john

brian john

Senior Member
Location
Leesburg, VA
craig65 said:
There is no neutral, it's a 120/208 wye to 480v delta
the load is on the delta side.
Used a digital clamp on amp meter...not true RMS
Click to expand...

You should be using a True RMS meter.

Complete the following

Line/primary/input at 208 VAC - A phase current, B phase current, C phase current
Load/secondary/output at 480 VAC - A phase current, B phase current, C phase current

Utilize a True RMS amp clamp
If possible the Crest Factor for each phase.
 
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Besoeker

Besoeker

Senior Member
Location
UK
richxtlc said:
Harmonics should not pass through the delta, the higher frequencies would circulate in the delta causing it to increase in temperature and possibly overheat.
Click to expand...
That's true for third and, I think, triple n in general. But not for the 6n+/-1 you would get from say from a VSD or other odd harmonics from non-linear loads.
 
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craig65

Member
wirenut1980 said:
Hmmm...I thought he meant no neutral on the delta side.
Click to expand...

ther is no neutral to the transformer from the panel on the Wye side.
there is a neutral in the Wye panel as it feeds some 110v time clocks and outlets.
All the lights are working now, but I still have the unbalanced loads across each phase on the Wye side, balanced on the delta side?????
 
sandsnow

sandsnow

Senior Member
Location
Southern California
craig65 said:
ther is no neutral to the transformer from the panel on the Wye side.
there is a neutral in the Wye panel as it feeds some 110v time clocks and outlets.
All the lights are working now, but I still have the unbalanced loads across each phase on the Wye side, balanced on the delta side?????
Click to expand...

Is this a delta wye transformer that is being back fed?

I have no idea if that makes a difference here. Maybe something to to consider?
 
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