Dry type Transformers
Dry type Transformers
(OP)
I have a question that I have posted at other forums but have gotten no useful answers. I am an electrical Meterman by trade. Occasionally we go to test a meter that is on a building under construction and generally the service is 277\480 4 wire wye with a stepdown dry type transformer that is loaded but generally only a construction load. Sometimes when I'm talking phase angles with my Arbiter, and tonging the load and taking a rev check on the meter my loads don't always match sometimes the rev of the meter and the measured values are half what they should be. Some times I get really weird phase andgles that correct when there is a heavy load applied. I don't know what the heck this is? Is it harmonics, is it a phase shift due to a lightly loaded transformer, is there some other phenomenon at work here like alchemy or the other black arts? Help
--peetey
--peetey






RE: Dry type Transformers
A little clarification might spark an idea:
1) Exactly which Arbiter model are you using?
2) At how low of loading are you seeing your problem? 10% of transformer rating? 5%? Other?
Let us know,
Old Dave
RE: Dry type Transformers
RE: Dry type Transformers
I can't answer your question, but something I noted on the 918B-datasheet:
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"The Model 918B measures phase angle and frequency using zero crossings. The calculated parameters are based on linear models, assuming low distortion. Because of this, measurement errors for harmonic-rich signals may exceed these specifications"
Ralph
RE: Dry type Transformers
RE: Dry type Transformers
Maybe harmonics are not the problem, but if there are harmonics present, you'll find some incorrect meausurements. Are there any harmonic sources feeding from the transformer? (Power supplies, PC's etc.)
Regards
Ralph
RE: Dry type Transformers
peetey, any way you can get your mitts on a 929/930/931 and see if there is indeed a harmonic problem at the site? It’s not that hard to check clip-on CTs for accuracy before you use them in the field with a 931.
It’s certainly not unreasonable check your 918 side-by-side in the shop and in the field with a more sophisticated instrument if you have one available.
RE: Dry type Transformers
--peetey